Quantum light sources are becoming an increasingly popular alternative to pulsed lasers for spectroscopy, microscopy, and sensing. The inherent quantum correlations of entangled photons present unique advantages in spectroscopy, enabling high signal-to-noise ratios, low excitation fluxes, and time-resolved measurements without requiring a pulsed laser. Entangled photon sources for spectroscopic measurements typically consist of bulk crystals or ion-diffused waveguides. Integrated platforms such as thin-film lithium niobate have potential for highly efficient, tailored, and compact entangled photon sources through periodically poled nanophotonic waveguides. The advantageous nonlinear optical properties of lithium niobate coupled with the nanophotonic thin film platform allows for frequency conversion, quantum state generation, state manipulation, and sample interaction all on a single compact chip, demonstrating thin-film lithium niobate's potential for compact and portable integrated spectrometers.
\r\n\r\nHere, we present our work in frequency conversion and sample interactions in thin-film lithium niobate. Most of the previous demonstrations of nanophotonic lithium niobate waveguides have focused on infrared wavelengths for applications in quantum communication and computing, leaving the shorter wavelengths that are of interest for spectroscopy still a largely unexplored space. In this work, frequency conversion in thin-film lithium niobate is investigated from ultraviolet through telecom wavelengths. Periodically poled lithium niobate nanophotonic waveguides are fabricated for second harmonic generation in the ultraviolet-A region and entangled photon generation at visible and near-infrared wavelengths. Using a violet continuous wave laser, a waveguide with a fluorescent dye-doped polymer cladding layer is investigated for sample interactions. Finally, preliminary work in entangled photon triplet generation down to telecom wavelengths is explored. This work represents a step towards compact, on-chip spectrometers and sensors through lithium niobate photonic integrated circuits.
" }, { "name": "Lei, Mi", "degree": "PhD", "year": "2024", "title": "Many-Body Cavity Quantum Electrodynamics and Spin Dynamics with an Ensemble of Rare-Earth Ions", "advisor": "Faraon, Andrei", "url": "https://resolver.caltech.edu/CaltechTHESIS:04102024-171434556", "creators": [ { "name": { "family": "Lei", "given": "Mi" }, "id": "Lei-Mi", "orcid": "0009-0001-5484-7982", "display_name": "Lei, Mi" } ], "advisors": [ { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "advisor", "display_name": "Faraon, Andrei" } ], "committee": [ { "name": { "family": "Endres", "given": "Manuel A." }, "id": "Endres-M", "orcid": "0000-0002-4461-224X", "role": "chair", "display_name": "Endres, Manuel A." }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "member", "display_name": "Faraon, Andrei" }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "orcid": "0000-0002-1581-9209", "role": "member", "display_name": "Painter, Oskar J." }, { "name": { "family": "Refael", "given": "Gil" }, "id": "Refael-G", "orcid": "0009-0007-4566-8441", "role": "member", "display_name": "Refael, Gil" }, { "name": { "family": "Yao", "given": "Norman Y." }, "id": "Yao-Norman-Y", "orcid": "0000-0003-0194-7266", "role": "member", "display_name": "Yao, Norman Y." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/gx1e-en28", "abstract": "Studying and controlling light-matter and matter-matter interactions is a central theme in quantum physics and provides the foundation for quantum applications. Rare-earth ions (REIs) doped in solids are promising candidates for engineering scalable quantum technologies, such as quantum memories and quantum transducers, and for exploring emerging fundamental phenomena. This is because REIs have highly stable optical and spin transitions at cryogenic temperatures, and as a solid-state platform, they are compatible for integrating with quantum devices using well-established semiconductor manufacturing techniques.
\r\n\r\nThis thesis is centered on nanophotonic devices coupling to an ensemble of REIs. To explore the light-matter interaction, we build a light-matter interface by coupling an inhomogeneously broadened ensemble of ytterbium-171 doped in yttrium orthovanadate to a nanophotonic cavity with high cooperativity. In this many-body cavity quantum electrodynamics (cavity QED) system, we observe the appearance of a narrow transparency window in the cavity reflection spectrum under optical driving (collectively induced transparency, CIT). This phenomenon results from the destructive interference between pairs of two-level emitters across the inhomogeneous line and the saturation of resonant ions. Furthermore, coherent excitation of the system within this transparency window enables us to observe highly nonlinear optical emission, spanning from fast superradiance to slow subradiance. To study matter-matter interactions, we shift the focus to the strongly interacting spins. These spins feature clock transitions and pure spin exchange interactions, leading to comparable magnitudes of interaction strength and on-site disorder. We characterize and control the many-body dynamics via Hamiltonian engineering and population initialization. Furthermore, we observe the emergence of robust subharmonic oscillations under Floquet driving, providing evidence for the presence of a discrete time crystal.
\r\n\r\nThe discoveries in many-body cavity QED enable new mechanisms for achieving slow light and frequency referencing, and they provide potential for superradiant lasers. Meanwhile, our studies on spin dynamics showcase REIs as a promising platform for the study of many-body physics, with potential applications in quantum sensing and quantum simulations. In general, our findings deepen the understanding for a disordered quantum system and offer valuable insights for development of quantum applications.
" }, { "name": "Ruskuc, Andrei", "degree": "PhD", "year": "2024", "title": "Single Rare-Earth Ions in Solid-State Hosts: A Platform for Quantum Networks", "advisor": "Faraon, Andrei", "url": "https://resolver.caltech.edu/CaltechTHESIS:10202023-123922325", "creators": [ { "name": { "family": "Ruskuc", "given": "Andrei" }, "id": "Ruskuc-Andrei", "orcid": "0000-0001-7684-7409", "display_name": "Ruskuc, Andrei" } ], "advisors": [ { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "advisor", "display_name": "Faraon, Andrei" } ], "committee": [ { "name": { "family": "Endres", "given": "Manuel A." }, "id": "Endres-M", "orcid": "0000-0002-4461-224X", "role": "chair", "display_name": "Endres, Manuel A." }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "member", "display_name": "Faraon, Andrei" }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "orcid": "0000-0002-1581-9209", "role": "member", "display_name": "Painter, Oskar J." }, { "name": { "family": "Hutzler", "given": "Nicholas R." }, "id": "Hutzler-N-R", "orcid": "0000-0002-5203-3635", "role": "member", "display_name": "Hutzler, Nicholas R." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/ecn2-pp53", "abstract": "Solid-state defects have emerged as leading candidates for quantum network nodes due to their compatibility with scalable device engineering and local nuclear spins for quantum processing. Rare-earth ions in crystalline hosts are particularly attractive due to their long optical and spin coherence times at cryogenic temperatures. However, until recently, detection and utilization of single rare-earth ions in quantum technologies has been hindered by their inherently weak optical transitions. In this thesis I present progress towards realizing a novel quantum network node architecture using single \u00b97\u00b9Yb\u00b3\u207a ions in YVO\u2084, coupled to a nanophotonic cavity.
\r\n\r\nFirst, we demonstrate coherent operation of single \u00b97\u00b9Yb\u00b3\u207a ions as optically addressed qubits. To do this, we leverage first order insensitivity of optical and spin transitions to electric and magnetic fields, thereby protecting the qubits from environmental noise. We demonstrate initialization, high fidelity control and readout of a hyperfine spin qubit with long quantum storage times. We also characterize the optical transitions and find a lifetime-limited echo coherence, thereby enabling a coherent spin-photon interface.
\r\n\r\nNext, we focus on realizing an auxiliary quantum register. The high-fidelity spin control of our \u00b97\u00b9Yb\u00b3\u207a qubit is leveraged to access local nuclear spins. These spins comprise a dense ensemble which serves as a deterministic quantum resource. We utilize Hamiltonian engineering to generate tailored interactions, enabling polarization, coherent control and preparation of many-body nuclear spin states. Finally, we implement a spin-wave based memory protocol and demonstrate storage and retrieval of quantum states.
\r\n\r\nMoving beyond a single quantum node, in the final section of this thesis we will realize a small-scale quantum network using this platform. As a first step we demonstrate time-resolved quantum interference between photons emitted by ions in two separate devices. Then, we demonstrate a novel heralded entanglement protocol which incorporates optical dynamical decoupling and frequency erasure via precise photon detection. This protocol counteracts both static and dynamic inhomogeneity in the ions\u2019 optical transition frequencies, thereby enabling entanglement generation between any pair of qubits in a scalable fashion.
\r\n\r\nThese results showcase single rare-earth ions as a promising platform for the future quantum internet.
" }, { "name": "Zheng, Tianzhe", "degree": "PhD", "year": "2024", "title": "Reconfigurable Metasurfaces in Nanoelectromechanical and Silicon-Organic Systems", "advisor": "Faraon, Andrei", "url": "https://resolver.caltech.edu/CaltechTHESIS:03062024-043923772", "creators": [ { "name": { "family": "Zheng", "given": "Tianzhe" }, "id": "Zheng-Tianzhe", "orcid": "0000-0001-7058-5196", "display_name": "Zheng, Tianzhe" } ], "advisors": [ { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "advisor", "display_name": "Faraon, Andrei" } ], "committee": [ { "name": { "family": "Vahala", "given": "Kerry" }, "id": "Vahaha-K", "orcid": "0000-0003-1783-1380", "role": "chair", "display_name": "Vahala, Kerry" }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "member", "display_name": "Faraon, Andrei" }, { "name": { "family": "Marandi", "given": "Alireza" }, "id": "Marandi-A", "orcid": "0000-0002-0470-0050", "role": "member", "display_name": "Marandi, Alireza" }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "orcid": "0000-0002-2160-9064", "role": "member", "display_name": "Scherer, Axel" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/2kmq-da15", "abstract": "Over the past decade, metasurfaces, a technology referring to 2D or 3D engineered nanostructures, has demonstrated itself as a groundbreaking solution for creating compact and multifunctional optical devices. Moreover, the integration of metasurfaces with various modulation techniques enables compact yet high-performance active optical systems. In this thesis I explore various optical modes in engineered nanostructures and apply different design techniques to improve the amplitude and phase response of free-space modulators.
\r\n\r\nIn Chapter 1 and 2, we first briefly introduce the concept of reconfigurable metasurfaces and its state of art. Then we introduce several nanophotonic concepts that will be used frequently in later projects and discuss the potential directions to improve modulator's performance.
\r\n\r\nIn Chapter 3, we find that the dual-mode resonant metasurfaces could improve the phase response in the nanoelectromechanical system(NEMS). The interaction between the quasi-bond state in the continuum and guided mode resonance boosts the phase response up to 144 degrees.
\r\n\r\nIn Chapter 4, the design target is to utilize the high-Q mode to decrease the driving voltage of the NEMS system to CMOS level. Motivated by the low-index confinement property of the slot mode, the device achieves over 10% reflection amplitude modulation with only 1.5V in the experiment. In addition, by adding a bottom gold mirror, 1.8\u03c0 phase response is numerically observed. Based on the success of this device, we propose a design that could achieve subwavelength wavefront control. As a example, we show a 3-pixel optical beam deflector with 75% diffraction efficiency.
\r\n\r\nIn Chapter 5, we extend the use of the slot mode into silicon-organic hybrid devices. The utilization of the slot mode achieves efficient electro-optic tuning under 17V in free space with a MHz modulation speed. We also explored various methods to enhance its phase response and discuss its feasibility. The spatial phase modulation design is also proposed with a 12-period supercell pixel. The beam deflector achieves 70% diffraction efficiency numerically.
\r\n\r\nIn Chapter 6, we bring this dissertation to a close and outline potential directions for future research.
\r\n\r\nThis thesis provides a foundation for the development of high-resolution and power-efficient one-dimensional spatial light modulators and showcases the potential of reconfigurable metasurfaces.
" }, { "name": "Biswas, Souvik", "degree": "PhD", "year": "2023", "title": "Electro-Optic Excitations in van der Waals Materials for Active Nanophotonics", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:04032023-062047194", "creators": [ { "name": { "family": "Biswas", "given": "Souvik" }, "id": "Biswas-Souvik", "orcid": "0000-0002-8021-7271", "display_name": "Biswas, Souvik" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Nadj-Perge", "given": "Stevan" }, "id": "Nadj-Perge-S", "orcid": "0000-0002-2394-9070", "role": "chair", "display_name": "Nadj-Perge, Stevan" }, { "name": { "family": "Hsieh", "given": "David" }, "id": "Hsieh-David", "orcid": "0000-0002-0812-955X", "role": "member", "display_name": "Hsieh, David" }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "member", "display_name": "Faraon, Andrei" }, { "name": { "family": "da Jornada", "given": "Felipe H." }, "id": "da-Jornada-FElipe-H", "orcid": "0000-0001-6712-7151", "role": "member", "display_name": "da Jornada, Felipe H." }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "member", "display_name": "Atwater, Harry Albert" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/tz4z-ed06", "abstract": "van der Waals materials are emerging due to their unique properties such as atomic thickness, diverse quasiparticle optical resonances, and no requirement for lattice matching. While there is a vast variety of materials, semiconductors hold a special place for opto-electronic and linear/non-linear optical studies. Black phosphorus (BP), a 2D quantum-well with direct bandgap and puckered crystal structure, is a compelling platform for this research direction. In this thesis, we investigate fundamental optical excitations in novel low-dimensional quantum materials to achieve strong light-matter interaction and integrate with nanophotonic motifs for low-footprint, reconfigurable optical technology, focusing primarily on black phosphorus and transition metal dichalcogenides.
\r\n\r\nThe thesis begins with the 'thin film limit' of van der Waals materials, between 5 and 20 nm thickness range. Chapters 2 and 3 explore how few-layer black phosphorus hosts interband and intraband optical excitations that can be strongly modified with gate-controlled doping and electric field, displaying epsilon near zero and hyperbolic behavior in the mid and far-infrared. In atomic thickness, strongly bound excitonic quasiparticles dominate the optical response. In Chapter 4, we investigate electrically tunable excitons in tri-layer black phosphorus, demonstrating a reconfigurable birefringent material that, when coupled with a Fabry-Perot cavity, enables the realization of a versatile and broadband polarization modulator. In Chapter 5, we examine the ultimate limit of a monolayer, studying MoTe2 via photoluminescence measurements and first-principles GW+BSE calculations, highlighting the Rydberg series associated with the exciton and its gate-tunability to understand strong electron-exciton interactions. In Chapter 6, we show how such excitons in monolayer black phosphorus can be strongly quantum confined at natural edges of exfoliated flakes, leading to highly temporally coherent emission. This emission is gate-tunable and understood via transmission electron microscopy and first-principles GW+BSE calculations of phosphorene nanoribbons to be originating from atomic reconstructions of the edge coupled with strain and screening effects.
\r\n\r\nOverall, our work highlights the potential of van der Waals materials for various electro-optical excitations and their applications in active nanophotonics.\r\n
" }, { "name": "Kim, Eun Jong", "degree": "PhD", "year": "2022", "title": "Waveguide Quantum Electrodynamics in Superconducting Circuits", "advisor": "Painter, Oskar J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:02122022-205429202", "creators": [ { "name": { "family": "Kim", "given": "Eun Jong" }, "id": "Kim-Eun-Jong", "orcid": "0000-0003-4879-8819", "display_name": "Kim, Eun Jong" } ], "advisors": [ { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "orcid": "0000-0002-1581-9209", "role": "advisor", "display_name": "Painter, Oskar J." } ], "committee": [ { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "chair", "display_name": "Faraon, Andrei" }, { "name": { "family": "Brandao", "given": "Fernando" }, "id": "Brand\u00e3o-F-G-S-L", "orcid": "0000-0003-3866-9378", "role": "member", "display_name": "Brandao, Fernando" }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "orcid": "0000-0002-1581-9209", "role": "member", "display_name": "Painter, Oskar J." }, { "name": { "family": "Preskill", "given": "John P." }, "id": "Preskill-J", "orcid": "0000-0002-2421-4762", "role": "member", "display_name": "Preskill, John P." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/bscv-b073", "abstract": "Achieving an efficient interface of light and matter has been a principal goal in the field of quantum optics. A burgeoning paradigm in the study of light-matter interface is waveguide quantum electrodynamics (QED), where quantum emitters are coupled to a common one-dimensional waveguide channel. In this scenario, cooperative effects among quantum emitters emerge as a result of real and virtual exchange of photons, giving rise to new ways of controlling matter.
\r\n\r\nSuperconducting quantum circuits offer an exciting platform to study quantum optics in the microwave domain with artificial quantum emitters interfaced to engineered photonic structures on chip. Beyond revisiting the experiments performed in atom-based platforms, superconducting circuits enable exploration of novel regimes in quantum optics that are otherwise prohibitively challenging to achieve. Moreover, the unprecedented level of control over individual quantum degrees of freedom and good scalability of the system provided by state-of-the-art circuit QED toolbox set a promising direction towards the study of quantum many-body phenomena.
\r\n\r\nIn this thesis, I discuss waveguide QED experiments performed in superconducting quantum circuits where transmon qubits are coupled to engineered microwave waveguides. Employing the high flexibility and controllability of superconducting quantum circuits, we realize and explore various schemes for generating waveguide-mediated interactions between superconducting qubits. We also demonstrate an intermediate-scale quantum processor based on a dispersive waveguide QED system involving ten superconducting qubits, exploring quantum many-body dynamics in a highly controllable fashion. The work described in the thesis marks an important step towards the construction of scalable architectures for quantum simulation of many-body models and realization of efficient coupling schemes for quantum computation.
" }, { "name": "Kim, Yonghwi", "degree": "PhD", "year": "2022", "title": "Light Modulation with Vanadium Dioxide-Based Optical Devices", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:06232021-050358035", "creators": [ { "name": { "family": "Kim", "given": "Yonghwi" }, "id": "Kim-Yonghwi", "orcid": "0000-0002-6652-7994", "display_name": "Kim, Yonghwi" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "chair", "display_name": "Faraon, Andrei" }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "member", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "member", "display_name": "Scherer, Axel" }, { "name": { "family": "Marandi", "given": "Alireza" }, "id": "Marandi-A", "orcid": "0000-0002-0470-0050", "role": "member", "display_name": "Marandi, Alireza" } ], "option_major": [ "eleceng" ], "doi": "10.7907/pkxj-9584", "abstract": "This thesis focuses on active material-based tunable optical devices. In particular, I have been working on tunable optical devices based on vanadium dioxide (VO2), which can produce tunable optical responses, such as amplitude, phase, thermal emission, and quantum emission. The modulations of light are achieved by coupling the phase-transition material with the precisely designed resonant structures or by placing it close to quantum emitters. This thesis presents three research streams, which aim at experimentally demonstrating the dynamically tunable optical responses using VO2. First, we propose and experimentally demonstrate an electrically tunable VO2-based reflectarray metasurface that exhibits largely tunable optical responses in the near-infrared region. We incorporate VO2 directly into the plasmonic resonator, which undergoes a phase transition triggered by Joule heating. The induced plasmonic resonance modulation is accompanied by a large and continuous modulation in optical responses, such as amplitude, resonance wavelength, and phase. Second, we propose and demonstrate an active tuning of thermal emission from VO2-based metasurfaces. We introduce a thin VO2 film as an absorbing layer on top of a metal reflector. This layer is coupled with a dielectric resonator, with a dielectric spacer placed between them. Upon undergoing a phase transition triggered by heating, the induced absorption tuning of the VO2 layer is accompanied by modulation in the absorption spectra of the coupled structure. We experimentally show narrowband absorption spectra, which can be tuned by controlling the VO2 temperature. Finally, we experimentally demonstrate the axial position of quantum emitters in a multilayered hexagonal boron nitride (hBN) flake with nanoscale accuracy, which is enabled through the modification of a photonic density of states by introducing VO2. Furthermore, we observe a sharp distance-dependent photoluminescence response by modulating the optical environment of an emitter placed close to the hBN/VO2 interface.
" }, { "name": "Rochman, Jake Herschel Lebi", "degree": "PhD", "year": "2022", "title": "Microwave-to-Optical Transduction Using Rare-Earth Ions", "advisor": "Faraon, Andrei", "url": "https://resolver.caltech.edu/CaltechTHESIS:05152022-181826611", "creators": [ { "name": { "family": "Rochman", "given": "Jake Herschel Lebi" }, "id": "Rochman-Jake-Herschel-Lebi", "orcid": "0000-0002-8475-3389", "display_name": "Rochman, Jake Herschel Lebi" } ], "advisors": [ { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "advisor", "display_name": "Faraon, Andrei" } ], "committee": [ { "name": { "family": "Marandi", "given": "Alireza" }, "id": "Marandi-A", "orcid": "0000-0002-0470-0050", "role": "chair", "display_name": "Marandi, Alireza" }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "orcid": "0000-0002-1581-9209", "role": "member", "display_name": "Painter, Oskar J." }, { "name": { "family": "Mirhosseini", "given": "Mohammad" }, "id": "Mirhosseini-M", "orcid": "0000-0002-9084-6880", "role": "member", "display_name": "Mirhosseini, Mohammad" }, { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "orcid": "0000-0001-8216-4815", "role": "member", "display_name": "Schwab, Keith C." }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "member", "display_name": "Faraon, Andrei" } ], "option_major": [ "eleceng" ], "doi": "10.7907/4h2f-wj87", "abstract": "Superconducting qubits that operate at microwave frequencies are one of the most promising platforms for quantum information processing. However, connecting distant processors with microwave photons is challenging since microwave photons suffer from thermal noise and large propagation losses in room temperature components.
\r\n\r\nConversely, optical photons within the telecommunications band are known to have extremely low loss in optical fiber and the thermal noise is minuscule at room temperature. In order to interface superconducting qubits with room temperature optical photons, a quantum transducer is required that can convert photons between microwave and optical frequencies.
\r\n\r\nThis thesis describes the development of a microwave-to-optical transducer using an ensemble of erbium ions, doped within a yttrium orthovanadate crystal, that are simultaneously coupled to a superconducting microwave resonator and a photonic crystal optical resonator. The erbium ions have spin transitions that couple to the microwave resonator and optical transitions at telecom wavelengths that couple to the optical resonator.
" }, { "name": "Kafaie Shirmanesh, Ghazaleh", "degree": "PhD", "year": "2021", "title": "Electro-Optically Tunable Metasurfaces for a Comprehensive Control of Properties of Light", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:09172020-190836007", "creators": [ { "name": { "family": "Kafaie Shirmanesh", "given": "Ghazaleh" }, "id": "Kafaie-Shirmanesh-Ghazaleh", "orcid": "0000-0003-1666-3215", "display_name": "Kafaie Shirmanesh, Ghazaleh" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "orcid": "0000-0003-1783-1380", "role": "chair", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "member", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "member", "display_name": "Scherer, Axel" }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "member", "display_name": "Faraon, Andrei" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/m554-as73", "abstract": "The ability to control electromagnetic wavefront is a central key in optics. Conventional optical components rely on the gradual accumulation of the phase of light as it passes through an optical medium. However, since the accumulated phase is limited by the permittivity of naturally existing materials, such a mechanism often results in bulky devices that are much thicker than the operating wavelength.
\r\n\r\nDuring the last several years, metasurfaces (quasi-2D nanophotonic structures) have attracted a great deal of attention owing to their promise to manipulate constitutive properties of electromagnetic waves such as amplitude, phase, and polarization. Metasurfaces are ultrathin arrays of subwavelength resonators, called meta-atoms, where each meta-atom imposes a predefined change on the properties of the scattered light. By precisely designing the optical response of these meta-atoms to an incident wave, metasurfaces can introduce abrupt changes to the properties of the transmitted, reflected, or scattered light, and hence, can flexibly shape the out-going wavefront at a subwavelength scale. This enables metasurfaces to replace conventional bulky optical components such as prisms or lenses by their flat, low-profile analogs. Furthermore, a single metasurface can perform optical functions typically attained by using a combination of multiple bulky optical elements, offering tremendous opportunities for flat optics.
\r\n\r\nThe optical response of a metasurface is typically dictated by the geometrical parameters of the subwavelength scatterers. As a result, most of the reported metasurfaces have been passive, namely have functions that are entirely fixed at the time of fabrication. By making the metasurfaces reconfigurable in their phase, amplitude, and polarization response, one can achieve real-time control of optical functions, and indeed, achieve multi-functional characteristics after fabrication. Dynamical control of the properties of the scattered light is possible by using external stimuli such as electrical biasing, optical pumping, heating, or elastic strain that can give rise to changes in the dielectric function or physical dimensions of the metasurface elements.
\r\n\r\nIn this dissertation, we present the opportunities and challenges towards achieving reconfigurable metasurfaces. We introduce a paradigm of active metasurfaces for real-time control of the wavefront of light at a subwavelength scale by investigating different modulation mechanisms and possible metasurface designs and material platforms that let us effectively employ the desired modulation mechanism. We will present multiple electro-optically tunable metasurface platforms. These electronically-tunable schemes are of great interest owing to their robustness, high energy-efficiency, and reproducibility. We will also show the design and experimental demonstration of active metasurfaces for which the tunable optical response can be tailored in a pixel-by-pixel configuration.
\r\n\r\nThe ability to individually control the optical response of metasurface elements has made active optical metasurfaces to be progressively ubiquitous by enabling a wide range of optical functions such as dynamic holography, light fidelity (Li-Fi), focusing, and beam steering. As a result, reconfigurable metasurfaces can hold an extraordinary promise for optical component miniaturization and on-chip photonic integration. Such compact and high-performance devices with reduced size, weight, and power (SWaP) can be used in future free-space optical communications or light detection and ranging (LiDAR) systems.
" }, { "name": "Kwon, Hyounghan", "degree": "PhD", "year": "2021", "title": "Dielectric Metasurfaces for Integrated Imaging Devices and Active Optical Elements", "advisor": "Faraon, Andrei", "url": "https://resolver.caltech.edu/CaltechTHESIS:05112021-170331252", "creators": [ { "name": { "family": "Kwon", "given": "Hyounghan" }, "id": "Hyounghan-Kwon", "orcid": "0000-0002-9257-687X", "display_name": "Kwon, Hyounghan" } ], "advisors": [ { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "advisor", "display_name": "Faraon, Andrei" } ], "committee": [ { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "orcid": "0000-0001-8791-0354", "role": "chair", "display_name": "Yang, Changhuei" }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "member", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Marandi", "given": "Alireza" }, "id": "Marandi-A", "orcid": "0000-0002-0470-0050", "role": "member", "display_name": "Marandi, Alireza" }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "member", "display_name": "Faraon, Andrei" } ], "option_major": [ "eleceng" ], "doi": "10.7907/j08n-0q77", "abstract": "Optical dielectric metasurfaces have shown great advances in the last two decades and become promising candidates for next-generation free-space optical elements. In addition to their compatibility with scalable semiconductor fabrication technology, metasurfaces have provided new and efficient ways to manipulate diverse characteristics of light. In this thesis, we demonstrate the potential of dielectric metastructures in the realization of compact imaging devices, reconfigurable optical elements, and multi-layer inverse-designed metasurfaces. With the metasurfaces\u2019 extreme capability to simultaneously control phase and polarization, we first showcase their potential toward optical field imaging applications. In this regard, we demonstrate a system of dielectric metasurfaces and designed random metasurfaces for single-shot phase gradient microscopes and computational complex field imaging system, respectively. Then, we propose nano-electromechanically tunable resonant dielectric metasurfaces as a general platform for active metasurfaces. For example, we demonstrate two different types of the phase and amplitude modulators. While one utilizes resonant eigenmodes in the lattice such as leaky guided mode resonances and bound-states in the continuum modes, the other is based on the high-Q Mie resonances in the dielectric nanostructures where symmetry is broken. In addition to the modulation of the phase and amplitude, we also show tuning of strong chiroptical responses in dielectric chiral metasurfaces. Next, we experimentally demonstrate inverse-designed multi-layer metasurfaces. Not only do they provide increased degree of freedom in the design space, but also overcome limits of conventional design methods of the metasurfaces. Finally, we summarize the presented works and conclude this thesis with a brief outlook on what aspects of the metasurfaces can be important for their real-world applications in the future and what challenges and opportunities remain.
" }, { "name": "Narasimhan, Vinayak", "degree": "PhD", "year": "2021", "title": "Bioinspired Nanostructures for Biomedical Applications", "advisor": "Choo, Hyuck; Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechTHESIS:07242020-111050846", "creators": [ { "name": { "family": "Narasimhan", "given": "Vinayak" }, "id": "Narasimhan-Vinayak", "orcid": "0000-0003-4165-402X", "display_name": "Narasimhan, Vinayak" } ], "advisors": [ { "name": { "family": "Choo", "given": "Hyuck" }, "id": "Choo-Hyuck", "orcid": "0000-0002-8903-7939", "role": "advisor", "display_name": "Choo, Hyuck" }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "co-advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Choo", "given": "Hyuck" }, "id": "Choo-Hyuck", "orcid": "0000-0002-8903-7939", "role": "member", "display_name": "Choo, Hyuck" }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "orcid": "0000-0002-2160-9064", "role": "member", "display_name": "Scherer, Axel" }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "orcid": "0000-0003-3003-7042", "role": "member", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "Siddique", "given": "Radwanul Hasan" }, "id": "Siddique-Radwanul-Hasan", "orcid": "0000-0001-7494-5857", "role": "member", "display_name": "Siddique, Radwanul Hasan" } ], "option_major": [ "medeng" ], "doi": "10.7907/atnt-8p46", "abstract": "Nature boasts a myriad examples of coloration achieved purely through the physical interaction of light with nano-scale features also known as biophotonic nanostructures. From reptiles to insects, birds to flora, structural coloration has been achieved through a variety of fascinating nano-architectures that leverage different physics. Beyond structural coloration, these nanostructures are often truly multifunctional. For instance, biophotonic nanostructures can also serve as self-cleaning and bactericidal surfaces, gas and thermal sensors, waveguides and beam splitters. With the growing need for robust and compact biomedical devices, the requirement to embed multiple functionalities towards sensing, monitoring, diagnostics and therapeutics within a diminutive device footprint becomes crucial. In this regard, inspiration from the multifunctionality of biophotonic nanostructures can prove to be greatly beneficial for medical applications. Consequently, this work attempts to showcase various examples of the utilization of nanostructures inspired from biophotonic nanostructures for biomedical applications under various overlapping themes such as ophthalmic sensors, bioinspired optics and plasmonic biosensing.
\r\n\r\nThis thesis is summarized in two parts. The first part (Chapters 2--4) introduces a proof-of-concept optical intraocular pressure (IOP) sensor implant and various challenges faced during its in vivo implementation. In Chapter 3, nanostructures inspired by light-trapping epidermal micro-/nanostructures on flower petals are proposed and embedded onto the sensor platform to improve its in vivo optical signal-to-noise ratio and biocompatibility. Chapter 4 covers nanostructures inspired by biophotonic nanostructures on longtail glasswing butterfly wings that improve the in vivo angle of acceptance and biocompatibility of the sensor.
\r\n\r\nThe second part (Chapters 5 and 6) presents the use of bioinspired nanostructures in plasmonic biosensors. Chapter 5 discusses an on-chip platform consisting of bioinspired plasmonic nanostructures to detect various nucleic acid sequences of relevance in the pathogenesis of HIV-1 via plasmon-enhanced fluorescence. Chapter 6 describes the employment of bioinspired quasi-ordered nanostructuring on flexible substrates for broadband surface-enhanced Raman spectroscopy (SERS). Here, SERS-based biosensing enabled by quasi-ordering is used to detect uric acid -- a biomarker of various pathologies in human tears.
" }, { "name": "Yu, Weilai", "degree": "PhD", "year": "2021", "title": "Stability of Photo-Electrochemical Interface for Solar Fuels", "advisor": "Lewis, Nathan Saul", "url": "https://resolver.caltech.edu/CaltechTHESIS:03172021-221106133", "creators": [ { "name": { "family": "Yu", "given": "Weilai" }, "id": "Yu-Weilai", "orcid": "0000-0002-9420-0702", "display_name": "Yu, Weilai" } ], "advisors": [ { "name": { "family": "Lewis", "given": "Nathan Saul" }, "id": "Lewis-N-S", "orcid": "0000-0001-5245-0538", "role": "advisor", "display_name": "Lewis, Nathan Saul" } ], "committee": [ { "name": { "family": "Gray", "given": "Harry B." }, "id": "Gray-H-B", "orcid": "0000-0002-7937-7876", "role": "chair", "display_name": "Gray, Harry B." }, { "name": { "family": "Lewis", "given": "Nathan Saul" }, "id": "Lewis-N-S", "orcid": "0000-0001-5245-0538", "role": "member", "display_name": "Lewis, Nathan Saul" }, { "name": { "family": "See", "given": "Kimberly" }, "id": "See-Kimberly", "orcid": "0000-0002-0133-9693", "role": "member", "display_name": "See, Kimberly" }, { "name": { "family": "Okumura", "given": "Mitchio" }, "id": "Okumura-M", "orcid": "0000-0001-6874-1137", "role": "member", "display_name": "Okumura, Mitchio" } ], "option_major": [ "chemistry" ], "doi": "10.7907/2z16-d005", "abstract": "Photoelectrochemical (PEC) water splitting is a promising approach to convert renewable solar energy to clean hydrogen (H2) fuels in one simple step. Although \u2162-\u2164 semiconductors are attractive candidates as light-absorbers in tandem solar-fuel devices, their long-term stability for the hydrogen-evolution reaction (HER) in either acidic or alkaline aqueous electrolytes needs to be established. Chapter 2-5 of this thesis first aims at revealing the underlying corrosion chemistry for a variety of \u2162-\u2164 semiconductors specifically under the HER conditions, offering a rational understanding towards the stability of semiconductor photoelectrode.
\r\n \r\nIn Chapter 2, we start from p-InP and reveal its susceptibility to cathodic photocorrosion forming metallic In0, which however can be completely mitigated by the presence of Pt catalyst due to kinetic stabilization. We also show that the resulting PEC performance of p-InP/Pt electrodes is sensitive to the changes in surface stoichiometry, whereas an InOx-rich surface developed in KOH caused a substantial degradation in the current density-potential (J-E) behavior. In Chapter 3, we discovered that a non-stoichiometric and As0-rich surface of p-GaAs, resulting from a galvanic corrosion by Pt, led to mid-gap surface states as well as a complete loss in photoactivity. In Chapter 4-5, we demonstrate similar kinetic stabilization applied to both p-InGaP2/Pt and pn+-InGaP2/Pt photocathodes for the HER at both pH 0 and pH 14. Additionally, we found that the corrosion of underlying GaAs substrates for the pn+-InGaP2/Pt photocathodes at positive potentials caused damage of structural integrity as well as instability in electrode performance. Altogether these works underscore the mutual dependence of the physical and electrochemical stability of semiconductor photoelectrodes during the HER, which also need to be considered separately. Moreover, both catalytic kinetics and surface stoichiometry are crucial factors for defining long-term corrosion chemistry for semiconductor photoelectrode.
\r\n \r\nIn Chapter 6-7, we further explore solar fuels beyond H2, namely electrochemical N2-to-NH3 conversion. We first establish a new analytical method to isotopically quantify the concentrations of 15NH3 in aqueous solutions with a high sensitivity and a low limit-of-detection of <1 \u03bcM. Further we applied this advanced method to rigorously verify the electrocatalytic activity of a CoMo electrode for reducing N2(g) to NH3. We show that the additional ammonia detected in electrolyte was instead attributed to the corrosion of N impurities present in the CoMo electrode under cathodic bias, thus giving false positive results. These works emphasize the importance of both rigorous product analysis and experiment design in further catalyst development.
" }, { "name": "Zhang, Zhewei", "degree": "PhD", "year": "2021", "title": "Hybrid Si/III-V Lasers for Next-generation Coherent Optical Communication", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechTHESIS:02222021-054057067", "creators": [ { "name": { "family": "Zhang", "given": "Zhewei" }, "id": "Zhang-Zhewei", "orcid": "0000-0002-1211-7957", "display_name": "Zhang, Zhewei" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "orcid": "0000-0003-1783-1380", "role": "chair", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "member", "display_name": "Faraon, Andrei" }, { "name": { "family": "Marandi", "given": "Alireza" }, "id": "Marandi-A", "orcid": "0000-0002-0470-0050", "role": "member", "display_name": "Marandi, Alireza" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/y85t-nj39", "abstract": "The most important application of semiconductor lasers is, without doubt, optical communication, the backbone of the information age. In the past few decades, incoherent optical communication with conventional semiconductor lasers, the III-V distributed feedback (DFB) lasers, has successfully fulfilled the global demand for the data rate. However, in order to support the rapidly growing Internet traffic of the 21st century, the transition from incoherent to coherent optical communication is inevitable, requiring new types of lasers, as the conventional III-V DFB lasers lack the phase coherence needed to serve as the light sources in coherent optical communication. The existent alternatives with high phase coherence are external cavity lasers (ECLs) and fiber lasers, whose high price and bulky size effectively thwart the upgrade of the current communication networks. This is the main motivation for us to develop high-coherence semiconductor lasers.
\r\n\r\nTo achieve the goal, we shall rethink and redesign semiconductor lasers. Advanced modern fabrication technology helps us to turn bold ideas into reality. Not only do we build semiconductor lasers on hybrid platforms, but also engineer elaborately the optical mode to enhance the lasers\u2019 phase coherence. The newly developed semiconductor lasers, hybrid Si/III-V lasers, are the core of the entire thesis. Their design principles, fabrication process, properties and performance in the coherent optical communication system will be presented and discussed. The experimental results show the Si/III-V lasers' superiority to their conventional counterparts.
\r\n\r\nAside from possessing high phase coherence, the Si/III-V lasers have great potential to be the light sources on the integrated photonic platforms. The fundamental obstacle thwarting photonic integration is optical feedback, to which the conventional semiconductor lasers are very sensitive. Without the protection provided by optical isolators, which unfortunately cannot be fabricated on chip, the performance of the conventional III-V DFB lasers could get significantly degraded by optical feedback. The Si/III-V lasers, with their built-in high-Q resonators, are very robust against optical feedback and can function properly in the isolator-free coherent optical communication systems. Thus, the cost of future optical networks can be further reduced by monolithically integrating passive photonic devices such as modulators and demodulators with the Si/III-V lasers.
\r\n\r\nFinally, all the studies centered on laser coherence trigger us to think deeply about the underlying relation between different means of characterizing laser coherence. A rigorous mathematical relation, the Central Relation, has been derived here, which not only unveils the fundamental relation between laser lineshape and frequency noise power spectral density (PSD) but also provides new methods of frequency noise controlling like optical filtering.
" }, { "name": "Craiciu, Ioana", "degree": "PhD", "year": "2020", "title": "Quantum Storage of Light Using Nanophotonic Resonators Coupled to Erbium Ion Ensembles", "advisor": "Faraon, Andrei", "url": "https://resolver.caltech.edu/CaltechTHESIS:06012020-134801698", "creators": [ { "name": { "family": "Craiciu", "given": "Ioana" }, "id": "Craiciu-Ioana", "orcid": "0000-0002-8670-0715", "display_name": "Craiciu, Ioana" } ], "advisors": [ { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "advisor", "display_name": "Faraon, Andrei" } ], "committee": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "orcid": "0000-0003-1783-1380", "role": "chair", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "member", "display_name": "Faraon, Andrei" }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "orcid": "0000-0002-1581-9209", "role": "member", "display_name": "Painter, Oskar J." }, { "name": { "family": "Endres", "given": "Manuel A." }, "id": "Endres-M", "orcid": "0000-0002-4461-224X", "role": "member", "display_name": "Endres, Manuel A." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/yn6n-7x40", "abstract": "This thesis presents on-chip quantum storage of telecommunication wavelength light using nanophotonic resonators coupled to erbium ions. Storage of light in an optical quantum memory has applications in quantum information and quantum communication. For example, long distance quantum communication using quantum repeater protocols is enabled by quantum memories. Efficient and broadband quantum memories can be made from resonators coupled to ensembles of atoms. Like other rare earth ions, erbium is appealing for quantum applications due to its long optical and hyperfine coherence times in the solid state at low temperatures. However, erbium is unique among rare earth ions in having an optical transition in the telecommunication C band (1540 nm), making it particularly appealing for quantum communication applications. In this work, we use nano-scale resonators coupled to erbium-167 ions in yttrium orthosilicate crystals (167Er 3+:Y2SiO5).
\r\n\r\nWe demonstrate quantum storage in two types of resonators. In a nanobeam photonic crystal resonator milled directly in 167Er 3+:Y2SiO5, we show storage of weak coherent states using the atomic frequency comb protocol. The storage fidelity for single photon states is estimated to be at least 93.7% ± 2.4% using decoy state analysis, Storage of up to 10 μs and multimode storage are demonstrated. Using a hybrid amorphous silicon 167Er 3+:Y2SiO5 resonator and on-chip electrodes, we demonstrate a multifunctional memory using the atomic frequency comb protocol with DC Stark shift control. In addition dynamic control of memory time, Stark shift control allows modifications to the frequency and bandwidth of stored light. We show tuning of the output pulse by ± 20 MHz relative to the input pulse, and broadening of the pulse bandwidth by more than a factor of three. The storage efficiency in both devices was limited to < 1%.
\r\n\r\nOn the way to these results, we describe 167Er 3+:Y2SiO5 spectroscopy measurements including optical coherence times and hyperfine lifetimes below 1 K, and we estimate the linear DC stark shift along two crystal directions. The design and fabrication of the on-chip resonators is presented. We discuss the limitations to storage time and efficiency, including superhyperfine coupling and resonator parameters, and we outline a path forward for improving the storage efficiency in these types of devices.
" }, { "name": "Ng, Ryan Cecil", "degree": "PhD", "year": "2020", "title": "Nanophotonic Phenomena in Dielectric Photonic Crystals", "advisor": "Greer, Julia R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:02122020-151048251", "creators": [ { "name": { "family": "Ng", "given": "Ryan Cecil" }, "id": "Ng-Ryan-Cecil", "orcid": "0000-0002-0527-9130", "display_name": "Ng, Ryan Cecil" } ], "advisors": [ { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "advisor", "display_name": "Greer, Julia R." } ], "committee": [ { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "role": "chair", "display_name": "Faraon, Andrei" }, { "name": { "family": "Shapiro", "given": "Mikhail G." }, "id": "Shapiro-M-G", "role": "member", "display_name": "Shapiro, Mikhail G." }, { "name": { "family": "Brady", "given": "John F." }, "id": "Brady-J-F", "role": "member", "display_name": "Brady, John F." }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." } ], "option_major": [ "chemeng" ], "doi": "10.7907/ZP30-F550", "abstract": "Photonic crystals are periodic optical nanostructures with varying dielectric constant that allow light flow to be controlled and manipulated much in a similar way to electrons within a semiconductor crystal. These nanostructures tend to have a spatially varying refractive index on the order of the wavelength of light to be manipulated. 1D and 2D photonic crystals have already garnered significant attention in the realm of thin-film optics, while 3D photonic crystals have been thus far limited in application, due to difficulties in fabrication and a lack of available materials for fabrication.
\r\n\r\nIn this work, we first explore 1D and 2D photonic crystals based on the concept of a guided mode resonance, which manifests as a narrow near-unity resonance in reflection or transmission that arise from the coupling of an incident wave into a leaky waveguide mode via a grating vector that is subsequently re-radiated. Such a resonance is well-suited for multi- and hyper- spectral filtering applications in the infrared. We designed a platform consisting of amorphous Si arrays embedded in SiO2 in simulation and experiment for application as narrow stopband filters. We present the tunability of the spectral characteristics of the resonance in these arrays through variation of array geometric parameters in simulation and experiment. Guided mode resonance designs often consider only the case of an infinite array, where the leaky waveguide mode can propagate laterally for hundreds of periods, allowing for this mode to eventually scatter out of the array giving rise to the characteristic narrow near-unity rapid spectral variations of a GMR. With an insufficient number of periods, the quality factor and thus the optical filtering performance is greatly diminished. Thus, we further extend our analysis to compact periodic arrays of finite size, which are required for high spatial resolution snapshot imaging, and introduce array designs that operate under finite size limitations in the near-infrared.
\r\n\r\nWe then transition to 3D photonic crystals, exploring the use of an additive manufacturing process to directly fabricate nanocrystalline rutile TiO2 with ~100 nm resolution. Though TiO2 was chosen as the model material, the key to this work is that a similar process can be used to print many different materials, enabling future applications of 3D photonic crystals. The focus here is the additive manufacturing of high index materials such as TiO2, and its potential for photonic applications is demonstrated by characterizing the optical band gap of 3D PhC TiO2 structures printed with this method. We present a system where the ability to print high refractive index 3D photonic crystals would be useful, by studying 3D polymer-germanium core-shell structures that should exhibit all-angle negative refraction in the mid-infrared regime.
" }, { "name": "Ren, Hengjiang", "degree": "PhD", "year": "2020", "title": "Cavity Optomechanics for Hybrid Quantum Systems", "advisor": "Painter, Oskar J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06082020-144243454", "creators": [ { "name": { "family": "Ren", "given": "Hengjiang" }, "id": "Ren-Hengjiang", "orcid": "0000-0002-5612-8287", "display_name": "Ren, Hengjiang" } ], "advisors": [ { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "orcid": "0000-0002-1581-9209", "role": "advisor", "display_name": "Painter, Oskar J." } ], "committee": [ { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "chair", "display_name": "Faraon, Andrei" }, { "name": { "family": "Marandi", "given": "Alireza" }, "id": "Marandi-A", "orcid": "0000-0002-0470-0050", "role": "member", "display_name": "Marandi, Alireza" }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "orcid": "0000-0002-1581-9209", "role": "member", "display_name": "Painter, Oskar J." }, { "name": { "family": "Wang", "given": "Lihong" }, "id": "Wang-Lihong", "orcid": "0000-0001-9783-4383", "role": "member", "display_name": "Wang, Lihong" } ], "option_major": [ "eleceng" ], "doi": "10.7907/vr67-w986", "abstract": "Recent advances in optomechanical systems have led to a series of scientific and technical advances. In addition, they have demonstrated macroscopic quantum phenomena, including probabilistic preparation of quantum states, squeezed light, and coherent transduction between photons with different energies. There are advantages in using phonons within a quantum information network. Within the solid state, all optical and electronic phenomena strongly depend on the local distortions of the crystal lattice, i.e. mechanical phonons, hence could connect dissimilar degrees of freedom such as superconducting qubits operating at gigahertz frequencies with atomic/optical states. Also, unlike photons, phonons do not radiate into free space. Energy damping of phonon can occur through radiation into bulk structure which support the mechanical resonator, through impurities and defects in the material, and due to the inherent anharmonic motion of atoms within solid-state materials.
\r\n\r\nIn this thesis, we explore the limits of acoustic damping and coherence of a microwave-frequency acoustic nanocavity with a phononic crystal shield that possesses a wide bandgap for all polarizations of acoustic waves. The nanocavity is formed from an optomechanical crystal (OMC) nanobeam resonator. It supports an acoustic breathing mode at ~ 5 GHz and a co-localized telecom optical resonant mode which allows us to excite and readout mechanical motion using radiation pressure from a pulsed laser source. This minimally invasive pulsed measurement technique avoids a slew of parasitic damping effects - typically associated with electrode materials and mechanical contact, or probe fields for continuous readout - and allows for the sensitive measurement of motion at the single phonon level. The results of acoustic ringdown measurements at millikelvin temperatures show that damping due to radiation is effectively suppressed by the phononic shield, with breathing mode quality factors reaching mechanical quality factor Q = 4.9 x 1010, corresponding to an unprecedented frequency-Q product of f-Q = 2.6 x 1020 and an effective phonon propagation length of several kilometers. Measurement of the frequency jitter of the acoustic resonance is also performed, indicating telegraph-like noise corresponding to a coherence time of ~ 130 \u00b5s. The observed breathing mode behavior can be explained by TLS interactions when taking into account the highly modified density of phonon states in the shielded OMC cavity, which are most likely present in the amorphous etch-damaged region of the silicon surface. In particular, we find that damping due to nearly resonant TLS is suppressed due to the bandgap of the phononic shield, and that relaxation damping from non-resonant TLS can explain the magnitude, low temperature dependence of the breathing mode damping, and lack of saturation of the damping with both temperature and acoustic amplitude.
\r\n\r\nThe extremely small motional mass and narrow linewidth of the OMC cavity make it ideal for precision mass sensing and in exploring limits to alternative quantum collapse models.
\r\n\r\nOur mechanical modes exist in the same frequency range as common superconducting qubits, suggesting a possibility for creating a hybrid quantum architecture consisting of acoustic and superconducting quantum circuits, where the small scale, reduced cross-talk, and ultralong coherence time of quantum acoustic devices may provide significant improvements in connectivity and performance of current quantum hardware. A proposal of mechanical quantum memory based on ultra-high-Q mechanical model and piezo-electrical coupling is also discussed in this work. \r\nOne remaining roadblock, which significantly compromises the utility of OMCs integration with superconducting circuits, is the very weak, yet non-negligible parasitic optical absorption, which is thought to occur due to surface defect states, and together with inefficient thermalization can yield significant heating of the hypersonic mechanical mode of the device at ultralow temperatures, where microwave systems can be reliably operated as quantum devices. In 1D OMC experiments, the quantum cooperativity (Ceff), which corresponds to the standard photon-phonon cooperativity divided by the Bose factor of the thermal bath and is the most relevant figure-of-merit for operation of optomechanical systems at ultralow temperatures, was lower than unity for all but a microsecond around the time an optical pulse is applied. This limits quantum optomechanical experiments to schemes with short pulses. Increased Ceff can be achieved with improved thermalization, for example, by employing a two-dimensional (2D) OMC cavity.
\r\n\r\nIn this thesis, we demonstrate an improved silicon quasi-2D OMC with an over 50-fold improvement in back-action per photon over previous reports. We are able to measure the dynamics of the internal cavity acoustic modes of both 1D nanobeam and quasi-2D OMCs. Quasi-2D OMC shows much lower bath occupancy compared to 1D structures. Most importantly, quasi-2D OMCs demonstrated a Ceff greater than unity under steady-state optical pumping, a crucial threshold for realizing a variety of optomechanical applications. For example, bi-directional transduction or amplification of continuous quantum signals require the optomechanical device to be operated in a continuous mode. An analysis of piezo-optomechanical bi-directional microwave to optics transducer is also presented in this thesis.
" }, { "name": "Arbabi, Ehsan", "degree": "PhD", "year": "2019", "title": "Metasurfaces: Beyond Diffractive and Refractive Optics", "advisor": "Faraon, Andrei", "url": "https://resolver.caltech.edu/CaltechTHESIS:04222019-151834122", "creators": [ { "name": { "family": "Arbabi", "given": "Ehsan" }, "id": "Arbabi-Ehsan", "orcid": "0000-0002-5328-3863", "display_name": "Arbabi, Ehsan" } ], "advisors": [ { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "role": "advisor", "display_name": "Faraon, Andrei" } ], "committee": [ { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "role": "chair", "display_name": "Hajimiri, Ali" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" }, { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "member", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "role": "member", "display_name": "Faraon, Andrei" } ], "option_major": [ "eleceng" ], "doi": "10.7907/EQEY-KZ52", "abstract": "Optical metasurfaces are a category of thin diffractive optical elements, fabricated using the standard micro- and nano-fabrication techniques. They provide new ways of controlling the flow of light based on various properties such as polarization, wavelength, and propagation direction. In addition, their compatibility with standard micro-fabrication techniques and compact form factor allows for the development of several novel platforms for the design and implementation of various complicated optical elements and systems. In this thesis, I first give a short overview and a brief history of the works on optical metasurfaces. Then I discuss the capabilities of metasurfaces in controlling the polarization and phase of light, and showcase their potential applications through the cases of polarimetric imaging and vectorial holography. Then, a discussion of the chromatic dispersion in optical metasurfaces is given, followed by three methods that can be utilized to design metasurfaces working at multiple discrete wavelengths. As a potential application of such metasurfaces, I present results of using them as objective lenses in two-photon microscopy. In addition, I discuss how metasurfaces enable the at-will control of chromatic dispersion in diffractive optical elements, demonstrate metasurfaces with controlled dispersion, and provide a discussion of their limitations. Integration of multiple metasurfaces into metasystems allows for implementation of complicated optical functions such as imaging and spectrometry. In this regard, I present several examples of how such metasystems can be designed, fabricated, and utilized to provide wide field of view imaging and projection, microelectromechanically tunable lenses, optical spectrometers, and retroreflectors. I conclude with an outlook on where metasurfaces can be most useful, and what limitations should be overcome before they can find wide-spread application.
" }, { "name": "Brouillet, Jeremy Jean", "degree": "PhD", "year": "2019", "title": "Graphene-Mediated Light-Matter Interaction", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:06022019-011156429", "creators": [ { "name": { "family": "Brouillet", "given": "Jeremy Jean" }, "id": "Brouillet-Jeremy-Jean", "orcid": "0000-0001-6664-5643", "display_name": "Brouillet, Jeremy Jean" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "chair", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Rossman", "given": "George Robert" }, "id": "Rossman-G-R", "role": "member", "display_name": "Rossman, George Robert" }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "role": "member", "display_name": "Faraon, Andrei" }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "member", "display_name": "Atwater, Harry Albert" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/VRFE-ZY57", "abstract": "Advances in 2D materials have opened a wealth of possibilities for the control of emission and propagation of light on length scales much smaller than the wavelength of light. Graphene, with highly-confined electrostatically tunable plasmons, provides a strong platform for explore a number of avenues.
\r\n\r\nWe show that graphene that can increase the luminescence of erbium by 80%, can induce population inversion in a three-level system, speed up the response time by over an order of magnitude, and has modulation depth of up to 14 dB for luminescence.
\r\n\r\nWe experimentally demonstrated a tunable epsilon-near-zero metamaterial with a elliptic-to-hyperbolic transition. The device had been theorized for many years and we provide the first experimental realization.
\r\n\r\nWe explore the properties of an isotropic tunable 2D heterostructure composed of black phosphorus, hexagonal boron nitride, and graphene. These symmetry-breaking materials create an effective permittivity that is biaxially anistropic and tunable. This material supports tunable beam steering based on propagation of energy along the hyperbolic dispersion lines.
" }, { "name": "Fleischman, Dagny", "degree": "PhD", "year": "2019", "title": "Nanophotonic Structures: Fundamentals and Applications in Narrowband Transmission Color Filtering", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:12032018-173954965", "creators": [ { "name": { "family": "Fleischman", "given": "Dagny" }, "id": "Fleischman-Dagny", "orcid": "0000-0003-2913-657X", "display_name": "Fleischman, Dagny" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "chair", "display_name": "Greer, Julia R." }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "member", "display_name": "Scherer, Axel" }, { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "role": "member", "display_name": "Schwab, Keith C." }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "member", "display_name": "Atwater, Harry Albert" } ], "option_major": [ "matsci" ], "doi": "10.7907/RA1G-GS84", "abstract": "The optical properties of materials can be manipulated by structures roughly the size of the wavelength of light of interest. For visible wavelengths, many different types of structures sized on the order of 10s-100s of nanometers have been used to engineer materials to produce a targeted optical response. Multilayer stacks of nanoscale metal and dielectric films are a widely explored geometry that has been used to make composite materials with effective optical properties that vary significantly from their constituent films. In this thesis, carefully designed multilayer stacks were used to induce artificial magnetism in non-magnetic materials, opening new directions for tailoring wave propagation in optical media. By perforating these multilayer structures with an array of sub-wavelength slits, these nanophotonic structures were shown to be able to function as narrowband transmission color filters. Using numerical optimization methods, these narrowband filterswere further refined and simplified to only require a single thin film sandwiched between two mirrors to achieve this high resolution spectral filtering. Novel methods were used to fabricate these ultracompact narrowband transmission color filters, which were shown to possess extremely narrow transmission resonances that can be controllably pushed across the visible and near IR parts of the spectrum. These mirrored color filters have footprints as small as 400 nm, well below the size of state-of-the-art CMOS pixels, inviting the possibility for integrating multi- and hyperspectral imaging capabilities into small portable electronic devices.
" }, { "name": "Giwa, Adenike Monsurat", "degree": "PhD", "year": "2019", "title": "Microstructure and Small-Scale Deformation of Al\u2080.\u2087CoCrFeNi High-Entropy Alloy", "advisor": "Greer, Julia R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06252018-172548450", "creators": [ { "name": { "family": "Giwa", "given": "Adenike Monsurat" }, "id": "Giwa-Adenike-Monsurat", "orcid": "0000-0002-1229-7505", "display_name": "Giwa, Adenike Monsurat" } ], "advisors": [ { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "advisor", "display_name": "Greer, Julia R." } ], "committee": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "chair", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Faber", "given": "Katherine T." }, "id": "Faber-K-T", "role": "member", "display_name": "Faber, Katherine T." }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "member", "display_name": "Goddard, William A., III" } ], "option_major": [ "matsci" ], "doi": "10.7907/PSWX-RY20", "abstract": "Novel engineering materials are continuously being designed for structural applications, particularly for improved mechanical properties such as high strength, enhanced ductility, and great thermal stability. High entropy alloys (HEAs) as an emerging material can be distinguished from other metal systems as a five-or-more-component alloy in which the constituents are in equiatomic or near equiatomic proportions, thereby maximizing the configurational entropy.
\r\n\r\nThis thesis is focused on understanding the microstructure of an aluminum-containing HEA in relation to its small-scale mechanical properties. Physical phenomena such as size-effect, slip sizes, temperature effect, crystallographic orientation effect, influence of interface, and small perturbations in atom motions are studied.
\r\n\r\nUniaxial compression experiments were conducted on nanopillars fabricated from the individual phases (i.e. Face Centered Cubic (FCC) and Body Cubic Centered (BCC) present in the Al0.7CoCrFeNi HEA. We observed the presence of a size-effect in both phases, with smaller pillars having substantially greater strengths compared with bulk and with larger sized samples. The size-effect power law exponent m in \u03c4y \u03b1 D-m for the BCC phase was \u2212 0.28, which is lower than that of most pure BCC metals, and the FCC phase had m = \u2212 0.66, which is equivalent to most pure FCC metals. These results are discussed in the framework of nano-scale plasticity and the intrinsic lattice resistance through the interplay of the internal (microstructural) and external (dimensional) size effects.
\r\n\r\nIn addition to higher stresses observed at cryogenic temperature in both phases, the microstructural analysis of the deformed pillar via Transmission Electron Microscopy (TEM) showed that FCC pillars undergo deformation by planar-slip dislocation activities even at temperatures of 40 K. Bulk FCC HEAs have been studied to deform via twinning mechanism at low temperatures. The BCC phase, however, confirms dislocation\u2013driven plasticity and twinning at 40 K. These results are explained from the intrinsic nature of the dislocation structure of both phases at low temperatures.
\r\n\r\nThe effect of an 'interphase' in micron-sized HEA pillars was studied from different orientation configurations of the BCC | FCC phases. Slip transmission across the phases was observed in high symmetry orientation combination of both phases. Configurations having a mixture of both low and high symmetry orientations vary in deformation mechanisms. We explain these findings in relation to crystal orientation effect of the combining half pillars, competing plastic mechanisms, dislocation \u2013 boundary interactions and how these findings correlate with their mechanical response.
\r\n\r\nAlso, we conducted dynamic mechanical analysis on the FCC and BCC HEA nanopillars to reveal their damping properties. Higher storage modulus and damping factor values were observed in FCC and BCC the nanopillars. Storage Moduli in the nano-sized HEAs are a factor of 2 greater than both bulk BCC and FCC HEA counterparts. The difference is due to greater surface contribution of the external atoms in the small-sized HEAs.
" }, { "name": "Kamali, Seyedeh Mahsa", "degree": "PhD", "year": "2019", "title": "Dielectric Metasurfaces from Fundamentals to Applications", "advisor": "Faraon, Andrei", "url": "https://resolver.caltech.edu/CaltechTHESIS:05112019-120905666", "creators": [ { "name": { "family": "Kamali", "given": "Seyedeh Mahsa" }, "id": "Kamali-Seyedeh-Mahsa", "orcid": "0000-0002-6968-811X", "display_name": "Kamali, Seyedeh Mahsa" } ], "advisors": [ { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "role": "advisor", "display_name": "Faraon, Andrei" } ], "committee": [ { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "role": "chair", "display_name": "Emami, Azita" }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "role": "member", "display_name": "Faraon, Andrei" }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "member", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Wang", "given": "Lihong" }, "id": "Wang-Lihong", "role": "member", "display_name": "Wang, Lihong" }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "role": "member", "display_name": "Minnich, Austin J." } ], "option_major": [ "eleceng" ], "doi": "10.7907/TPN1-XA53", "abstract": "In the past few decades, the advancements in nanotechnology have significantly altered many fields of science and technology, especially electronics and integrated photonics. Free-space optics, on the other hand, has remained mostly unaffected, and even today \"optics\" reminds us of carefully shaped and polished pieces of various types of glasses and crystals lumped into lenses and beam shapers. Several of these devices are then combined into more complicated optical systems like microscopes and pulse shapers that are expensive, bulky, sensitive to various environmental factors, and require several alignment steps. This thesis contains my work on designing and utilizing structures engineered at the nano-scale, which are called metasurfaces, to implement compact optical elements and systems with capabilities beyond those of conventional refractive and diffractive optics. My contributions to this field are two-fold: I have developed and contributed to the development of new concepts that take metasurfaces beyond conventional difractive optics in various aspects, in addition to paradigm changing platforms for optical element and system design. Here, I first give an overview and a brief history about optical metasurfaces. Next I discuss the unprecedented capabilities of metasurfaces in controlling light based on its degrees of freedom like illumination angle and polarization. Then, I will focus on various novel metasurface platforms of conformal and tunable metasurfaces, 3D metasurface beam shapers, and integrated metasurfaces. I conclude with an outlook on future potentials and challenges that need to be overcome for realizing their wide-spread applications." }, { "name": "Kettenbeil, Christian", "degree": "PhD", "year": "2019", "title": "Dynamic Strength of Silica Glasses at High Pressures and Strain Rates", "advisor": "Ravichandran, Guruswami", "url": "https://resolver.caltech.edu/CaltechTHESIS:02202019-104738145", "creators": [ { "name": { "family": "Kettenbeil", "given": "Christian" }, "id": "Kettenbeil-Christian", "orcid": "0000-0003-0301-3678", "display_name": "Kettenbeil, Christian" } ], "advisors": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "advisor", "display_name": "Ravichandran, Guruswami" } ], "committee": [ { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "orcid": "0000-0003-0559-0794", "role": "chair", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Mello", "given": "Michael" }, "id": "Mello-Michael", "orcid": "0000-0003-2129-9235", "role": "member", "display_name": "Mello, Michael" }, { "name": { "family": "Clifton", "given": "Rodney J." }, "id": "Clifton-Rodney-J", "role": "member", "display_name": "Clifton, Rodney J." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" } ], "option_major": [ "space" ], "doi": "10.7907/RZJW-MX30", "abstract": "Understanding the behavior of silica glasses at high pressures and strain rates is of great importance for geological processes and highly relevant to many technological applications including high-powered laser-matter interactions in optical elements and impact/blast damage in defense systems. Materials typically experience large inelastic deformations at high pressures, which are strongly affected by strength-related phenomena such as work hardening, damage and thermal softening. The pressure-shear plate impact experiment (PSPI) provides detailed information on the pressure and strain rate dependent strength properties of materials subjected to uniaxial compression. However, its range of attainable pressures has so far been limited and the assumptions required for its analysis become invalid at pressures beyond the Hugoniot elastic limit of the anvil materials. In this dissertation, a high-pressure PSPI (HP-PSPI) technique is developed that greatly extends the range of attainable experimental conditions by achieving higher terminal projectile velocities in a powder gun setup. A novel fiber-optic heterodyne transverse velocimeter (HTV) is developed to enable the use of robust frequency-based data reduction techniques, which reduce the effect of signal noise and light coupling losses. A forward analysis method, based on finite element simulations, is employed to match the experimentally observed material response during HP-PSPI experiments on soda-lime glass samples while considering the inelastic deformation of the utilized tungsten carbide anvils. Symmetric HP-PSPI experiments on tungsten carbide revealed a loss of strength at normal stresses exceeding 25 GPa, which hint at active damage or softening mechanisms under nominally uniaxial strain compression. A pressure-dependent strain softening model transitions soda-lime glass from an intact strength of 2.8 GPa, below strains of 10-30%, to a failed granular state following extensive inelastic shear deformation, which accurately predicts the measured response over a wide range of stresses (9-21 GPa) and strain rates (3\u2022105-2\u2022107s-1). Extending the range of previously attainable pressures and strain rates in PSPI experiments, combined with more robust diagnostics and analysis tools, will greatly benefit our understanding of material strength in extreme environments and enables the investigation of material behavior in a currently unexplored range of pressures and strain rates.
" }, { "name": "Kim, Laura", "degree": "PhD", "year": "2019", "title": "Novel Light Emitting Mechanisms Originating from Graphene Plasmons Near and Far from Equilibrium", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:05062019-203520662", "creators": [ { "name": { "family": "Kim", "given": "Laura" }, "id": "Kim-Laura", "orcid": "0000-0002-9745-3668", "display_name": "Kim, Laura" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "orcid": "0000-0001-8216-4815", "role": "chair", "display_name": "Schwab, Keith C." }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "member", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Johnson", "given": "William L." }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William L." }, { "name": { "family": "Nadj-Perge", "given": "Stevan" }, "id": "Nadj-Perge-S", "orcid": "0000-0002-2394-9070", "role": "member", "display_name": "Nadj-Perge, Stevan" } ], "option_major": [ "matsci" ], "doi": "10.7907/1CDC-HV37", "abstract": "Graphene supports surface plasmons bound to an atomically thin layer of carbon, characterized by tunable propagation characteristics and distinctly strong spatial confinement of the electromagnetic energy. Such collective excitations in graphene enable the strong interactions of massless Dirac fermions with light. In this work, I explore fundamental properties and applications of graphene plasmons both near and far from equilibrium. I discuss the ability of graphene plasmons to interact with its local environment in various forms of mid-infrared, optically active excitations, demonstrated by tunable graphene plasmon dispersions and an emergence of a new mode via addition of a monoatomic dielectric layer. Furthermore, the viability of graphene for optics-based applications and large-scale integration is epitomized by the experimental demonstration of perfect tunable absorption in a large-area chemically grown graphene by using a noble-metal-graphene metasurfaces. Using these properties of graphene plasmons, electronically tunable thermal radiation is demonstrated. Finally, I present theoretical predictions and experimental validations of nonequilibrium graphene plasmon excitations via ultrafast optical excitation, originating from a previously unobserved decay channel: hot plasmons generated from optically excited carriers. These studies reveal novel infrared light emitting processes, both spontaneous and stimulated, and provide a platform for achieving ultrafast, ultrabright mid-infrared light sources.
" }, { "name": "Kindem, Jonathan Miners", "degree": "PhD", "year": "2019", "title": "Quantum Nanophotonics with Ytterbium in Yttrium Orthovanadate", "advisor": "Faraon, Andrei", "url": "https://resolver.caltech.edu/CaltechTHESIS:03132019-062905529", "creators": [ { "name": { "family": "Kindem", "given": "Jonathan Miners" }, "id": "Kindem-Jonathan-Miners", "orcid": "0000-0002-7737-9368", "display_name": "Kindem, Jonathan Miners" } ], "advisors": [ { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "role": "advisor", "display_name": "Faraon, Andrei" } ], "committee": [ { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "chair", "display_name": "Painter, Oskar J." }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Hutzler", "given": "Nicholas R." }, "id": "Hutzler-N-R", "role": "member", "display_name": "Hutzler, Nicholas R." }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "role": "member", "display_name": "Faraon, Andrei" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/Q40T-8907", "abstract": "Quantum light-matter interfaces that can reversibly map quantum information between photons and atoms are essential for building future quantum networks. Crystals doped with rare-earth ions (REIs) are an attractive solid-state platform for such light-matter interfaces due to their exceptional optical and spin coherence properties at cryogenic temperatures. Building scalable REI-based technology has proven to be challenging due to the inherently weak coupling of REIs with light. This thesis explores the integration of REIs with nanophotonic resonators to overcome this weak light-matter interaction and enable efficient, scalable quantum light-matter interfaces. Specifically, this work focuses on the development of quantum nanophotonics with ytterbium in yttrium orthovanadate.
\r\n \r\nThis thesis begins with an introduction to a nanophotonic platform based on photonic crystal cavities fabricated directly in rare-earth host materials and highlights the initial successes of this platform with neodymium-doped materials. This motivates an examination of the optical and spin coherence properties of 171Yb:YVO4, a REI material that was previously unexplored for quantum technology applications. This material is found to have strong optical transitions compared to other REI-doped materials, a simple energy level structure, and long optical and spin coherence lifetimes.
\r\n\r\nThe focus then turns to the detection and coherent manipulation of single ytterbium ions coupled to nanophotonic cavities. The Purcell-enhancement in these cavities enables efficient optical detection and spin initialization of individual ytterbium ions. We identify ions corresponding to different isotopes of ytterbium and show that the coupling of electron and nuclear spin in ytterbium-171 at zero-field gives rise to strong electron-spin-like transitions that are first-order insensitive to magnetic field fluctuations. This allows for coherent microwave control and the observation of long spin coherence lifetimes at temperatures up to 1 K. We then make use of the optical selection rules and energy structure of 171Yb:YVO4 to demonstrate high-fidelity single-shot optical readout of the spin state. These results establish nanophotonic devices in 171Yb:YVO4 as a promising platform for solid-state quantum light-matter interfaces.
" }, { "name": "Korth, William Zachary", "degree": "PhD", "year": "2019", "title": "Mitigating Noise in Interferometric Gravitational Wave Detectors", "advisor": "Adhikari, Rana", "url": "https://resolver.caltech.edu/CaltechTHESIS:05292019-020613259", "creators": [ { "name": { "family": "Korth", "given": "William Zachary" }, "id": "Korth-William-Zachary", "orcid": "0000-0002-4422-1070", "display_name": "Korth, William Zachary" } ], "advisors": [ { "name": { "family": "Adhikari", "given": "Rana" }, "id": "Adhikari-R", "orcid": "0000-0002-5731-5076", "role": "advisor", "display_name": "Adhikari, Rana" } ], "committee": [ { "name": { "family": "Weinstein", "given": "Alan Jay" }, "id": "Weinstein-Alan-J-Physics", "orcid": "0000-0002-0928-6784", "role": "chair", "display_name": "Weinstein, Alan Jay" }, { "name": { "family": "Adhikari", "given": "Rana" }, "id": "Adhikari-R", "orcid": "0000-0002-5731-5076", "role": "member", "display_name": "Adhikari, Rana" }, { "name": { "family": "Chen", "given": "Yanbei" }, "id": "Chen-Yanbei", "orcid": "0000-0002-9730-9463", "role": "member", "display_name": "Chen, Yanbei" }, { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "orcid": "0000-0001-8216-4815", "role": "member", "display_name": "Schwab, Keith C." } ], "option_major": [ "physics" ], "doi": "10.7907/4H7V-W213", "abstract": "Gravitational waves, first predicted by Einstein in 1916, eluded detection for nearly a century. These faint ripples in the fabric of spacetime, with typical strain amplitudes at the Earth on the order of |h| \u223c 10\u221222, carry secrets of the universe untold by electromagnetic radiation. Following decades of research and development, a network of terrestrial interferometric detectors succeeded in measuring the passing of a gravitational wave (GW150914) for the first time in 2015. Individual detectors within this network are currently said to be operating in a \u201csecond-generation\u201d configuration; over the next decade, planned upgrades will take these detectors beyond this into a new generation. This thesis concerns the characterization and reduction of noise in one of these second-generation detectors, Advanced LIGO, as well as efforts underway to improve its sensitivity in the coming years.
\r\n\r\nThe first part of this thesis is a detailed overview of gravitational waves, the history of gravitational wave detection, and a reasonably thorough description of the Advanced LIGO detector. Particular attention is paid to a pedagogical motivation of the optical configuration of Advanced LIGO with reference to its forebears. This part ends with an overview of the sources of noise limiting the sensitivity of Advanced LIGO, and an exposition of plans to reduce their influence in the future.
\r\n\r\nThe second part describes the development of a laser gyroscope for use in tilt sensing in Advanced LIGO, starting with a motivation of the work based on limitations in the area of seismic noise sensing and cancellation.
\r\n\r\nThe third part recounts the design, fabrication, testing, installation and commissioning of an important component of the Advanced LIGO detector: the output mode cleaner (OMC).
\r\n\r\nThe fourth part outlines a proposed scheme for reduction of quantum noise in gravitational wave detectors and other experiments. In particular, this scheme allows for the operation of a so-called \u201coptical spring\u201d cavity in such a way as to be largely immune from the deleterious effects of quantum radiation pressure noise.
\r\n\r\nThe fifth and final part describes progress towards a direct measurement of thermal noise in thin silicon ribbons, which is pertinent to the design of suspensions in future cryogenic gravitational wave detectors.
\r\n\r\nThis thesis has the internal LIGO document number P1900035.
" }, { "name": "Kou, Junlong", "degree": "PhD", "year": "2019", "title": "Tailoring Thermal Radiation from Near Field to Far Field", "advisor": "Minnich, Austin J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05302019-214849044", "creators": [ { "name": { "family": "Kou", "given": "Junlong" }, "id": "Kou-Junlong", "orcid": "0000-0002-0481-5149", "display_name": "Kou, Junlong" } ], "advisors": [ { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "orcid": "0000-0002-9671-9540", "role": "advisor", "display_name": "Minnich, Austin J." } ], "committee": [ { "name": { "family": "Wang", "given": "Lihong" }, "id": "Wang-Lihong", "orcid": "0000-0001-9783-4383", "role": "chair", "display_name": "Wang, Lihong" }, { "name": { "family": "Marandi", "given": "Alireza" }, "id": "Marandi-A", "orcid": "0000-0002-0470-0050", "role": "member", "display_name": "Marandi, Alireza" }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "orcid": "0000-0002-9671-9540", "role": "member", "display_name": "Minnich, Austin J." }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "orcid": "0000-0002-2160-9064", "role": "member", "display_name": "Scherer, Axel" } ], "option_major": [ "eleceng" ], "doi": "10.7907/MCZC-7E85", "abstract": "Control of heat flow in both near and far field through thermal radiation is of fundamental interest for applications in thermal management and energy conversion.
\r\n\r\nOne challenge is how we can realize high contrast control of heat flow with high temporal frequencies and without moving parts. We try to resolve this problem and propose two schemes in the near field: one based on electrical tuning of silicon and the other based on optical pumping of doped silicon slabs. Both methods rely on the change of free carriers, leading to tuning of the plasma frequency, resulting in modulation of near-field thermal radiation. Calculations based on fluctuational electrodynamics show that the electric method gives 10% tuning range. On the other hand, heat transfer coefficient between two silicon films can be tuned from near zero to 600 Wm-2K-1 with a gap distance of 100 nm at room temperature with the optical pumping method.
\r\n\r\nIn the far field, we predict and demonstrate two spectrally selective absorbers based on semiconductors, by utilizing their band gap properties and dedicated photonic structure design. The germanium photonic crystals have around 95% absorption from 500 nm to 1000 \u00b5m and over 0.9 over the entire visible and near infrared spectrum. The effective absorptivity is as high as 0.91. The black silicon achieves 100% absorption for light with wavelength under 1 \u00b5m. The effective absorptivity is as high as 0.96. Field test shows that black silicon is able to maintain at 130 degrees Celcius under unconcentrated condition.
\r\n\r\nAnother interesting topic is to achieve over 100 Wm-2 electricity-free cooling power density with simple fabrication method by passive radiative cooling under direction sunlight. We theoretically predicted three schemes for achieving this goal and experimentally demonstrate that a polymer-coated fused silica mirror, as a near-ideal black-body in the mid-infrared and near-ideal reflector in the solar spectrum, achieves radiative cooling below ambient air temperature under direct sunlight (8.2 \u00b0C) and at night (8.4 \u00b0C). Its performance exceeds that of a multi-layer thin film stack fabricated using vacuum deposition methods by nearly 3 \u00b0C. Furthermore, we estimate the cooler has an average net cooling power of about 127 Wm-2 during daytime at ambient temperature, more than twice that reported previously, even considering the significant influence of external conduction and convection. Our work demonstrates that abundant materials and straight-forward fabrication can be used to achieve daytime radiative cooling, advancing applications such as dry cooling of thermal power plants.
" }, { "name": "MacCabe, Gregory Scott", "degree": "PhD", "year": "2019", "title": "Phonon Dynamics and Damping in Three-Dimensional Acoustic Bandgap Cavity-Optomechanical Resonators", "advisor": "Painter, Oskar J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:03082019-114637094", "creators": [ { "name": { "family": "MacCabe", "given": "Gregory Scott" }, "id": "MacCabe-Gregory-Scott", "orcid": "0000-0003-2369-1580", "display_name": "MacCabe, Gregory Scott" } ], "advisors": [ { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "orcid": "0000-0002-1581-9209", "role": "advisor", "display_name": "Painter, Oskar J." } ], "committee": [ { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "orcid": "0000-0002-1581-9209", "role": "chair", "display_name": "Painter, Oskar J." }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "member", "display_name": "Faraon, Andrei" }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "orcid": "0000-0002-9671-9540", "role": "member", "display_name": "Minnich, Austin J." }, { "name": { "family": "Endres", "given": "Manuel A." }, "id": "Endres-M", "orcid": "0000-0002-4461-224X", "role": "member", "display_name": "Endres, Manuel A." } ], "option_major": [ "physics" ], "doi": "10.7907/7R9W-EV53", "abstract": "Mechanical resonators are used in a wide variety of technical applications, from precision time keeping and sensing, to the delay and filtering of microwave signals in mobile communication systems. Critical to many of these applications is the ability of a mechanical object to store vibrational energy at a well defined frequency of oscillation and with minimal damping. Energy damping can occur through acoustic radiation into the resonator support structure, or through impurities and defects in the resonator material, and is highly dependent on the temperature of operation due to the inherent anharmonic motion of atoms within solid-state materials. Here, we present optical measurements down to milliKelvin temperatures of the acoustic mode properties of a crystalline silicon nanobeam cavity incorporating a three-dimensional phononic bandgap support structure for acoustic confinement. Utilizing pulsed laser light to excite a co-localized optical mode of the optomechanical crystal (OMC) device, we are able to measure the dynamics of the internal cavity acoustic modes which are coupled to the light field via radiation pressure. These measurements represent an almost ideal scenario in which the ringdown occurs free of any additional mechanical or probe field contact, and where elastic scattering or radiation of the acoustic field does not lead to energy damping due to the full bandgap shield. The resulting ringdown measurements for the fundamental 5 GHz acoustic mode of the cavity show an exponential increase in phonon lifetime versus phononic shield period number, which at a bath temperature of 35 milliKelvin saturates above six periods to a value as long as 1.5 seconds. This ultra-long lifetime, corresponding to an effective phonon propagation length of several kilometers, is found at the lowest temperatures to be consistent with damping from non-resonant tunneling states whose energy lies below the acoustic shield phononic bandgap, and which are most likely present in the amorphous etch-damaged region of the silicon surface. Other, more rapid forms of damping such as resonant tunneling state damping or three-phonon scattering are suppressed due to the phononic bandgap shield and the reduced density of phonon states in the effectively one-dimensional nanobeam geometry. Prospects for newapplications of ultra-coherent nanoscale mechanical resonators include tests of various collapse models of quantum mechanics, or, if appropriately integrated with microwave superconducting quantum circuits, as miniature quantum memory or processing units with potentially many-orders of magnitude longer coherence time than their electromagnetic counterparts.
" }, { "name": "Mauser, Kelly Ann Weekley", "degree": "PhD", "year": "2019", "title": "Resonant Thermoelectric Nanophotonics: Applications in Spectral and Thermal Sensing", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:06062019-191307495", "creators": [ { "name": { "family": "Mauser", "given": "Kelly Ann Weekley" }, "id": "Mauser-Kelly-Ann-Weekley", "orcid": "0000-0001-9903-8559", "display_name": "Mauser, Kelly Ann Weekley" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "role": "chair", "display_name": "Schwab, Keith C." }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "member", "display_name": "Painter, Oskar J." }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "role": "member", "display_name": "Minnich, Austin J." }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "member", "display_name": "Atwater, Harry Albert" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/0HJF-X691", "abstract": "Plasmon excitation enables extreme light confinement at the nanoscale, localizing energy in subwavelength volumes and thus can enable increased absorption in photovoltaic or photoconductive detectors. Nonetheless, plasmon decay also results in energy transfer to the lattice as heat which is detrimental to photovoltaic detector performance. However, heat generation in resonant subwavelength nanostructures also represents an energy source for voltage generation, as we demonstrate in the first part of this thesis via design of resonant thermoelectric (TE) plasmonic absorbers for optical detection. Though TEs have been used to observe resonantly coupled surface plasmon polaritons in noble-metal thin films and microelectrodes, they have not been employed previously as resonant absorbers in functional TE nanophotonic structures.
\r\n\r\nWe demonstrate nanostructures composed of TE thermocouple junctions using established TE materials \u2013 chromel/alumel and bismuth telluride/antimony telluride \u2013 but patterned so as to support guided mode resonances with sharp absorption profiles, and which thus generate large thermal gradients upon optical excitation and localized heat generation in the TE material. Unlike previous TE absorbers, our structures feature tunable narrowband absorption and measured single junction responsivities 4 times higher than the most similar (albeit broadband) graphene structures, with potential for much higher responsivities in thermopile architectures. For bismuth telluride \u2013 antimony telluride single thermocouple structures, we measure a maximum responsivity of 38 V/W, referenced to incident illumination power. We also find that the small heat capacity of optically resonant TE nanowires enables a fast, 3 kHz temporal response, 10-100 times faster than conventional TE detectors. We show that TE nanophotonic structures are tunable from the visible to the MIR, with small structure sizes of 50 microns x 100 micons. Our nanophotonic TE structures are suspended on thin membranes to reduce substrate heat losses and improve thermal isolation between TE structures arranged in arrays suitable for imaging or spectroscopy. Whereas photoconductive and photovoltaic detectors are typically insensitive to sub-bandgap radiation, nanophotonic TEs can be designed to be sensitive to any specific wavelength dictated by nanoscale geometry, without bandgap wavelength cutoff limitations. From the point of view of imaging and spectroscopy, they enable integration of filter and photodetector functions into a single structure. Other thermoelectric nanophotonic motifs are also explored.
\r\n\r\nGenerating localized, high electric field intensity in nanophotonic and plasmonic devices has many applications, from enhancing chemical reaction rates, to thermal radiation steering, to chemical sensing, and to photovoltaics. Along with a strongly localized electric field comes a temperature rise in non-lossless photonic materials, which can affect reaction rate, photovoltaic efficiency, or other properties of the system. Measuring temperature rises in nanophotonic structures is difficult, and methods commonly employed suffer from various limitations, such as low spatial resolution (Fourier transform infrared microscopy), bulky and expensive setups (scanning thermal microscopy), intrusive methods that interfere with nanophotonic structures (Pt resistive thermometry), or the need for specialized materials (temperature dependent photoluminescence).
\r\n\r\nIn the second part of this thesis, we overcome these limitations with the first-ever demonstration of temperature measurements of nanophotonic structures by employing both room temperature noise thermometry and the thermoelectric effect under ambient conditions without external probes by utilizing the properties of the materials that make up the nanophotonic structure itself. We have previously estimated the \u0394 T in a nanophotonic device using the thermoelectric effect, but could not determine the absolute temperature of the system. In the application we will discuss, the absolute electron temperature of the nanophotonic material itself is measured. Because Johnson-Nyquist noise is material independent and is a fundamental measure of absolute temperature, there is theoretically no need for calibration as in the case of resistive thermometry. To measure the temperature rise of a nanophotonic resonant region remotely, the Seebeck coefficient of the material is first carefully measured using noise thermometry, then the thermoelectric voltage generated in the nanophotonic materials themselves is measured from electrical leads spanning the resonantly excited region. To accomplish this, we have developed a metrology technique capable of simultaneously measuring electrical noise at two locations on the nanophotonic structure as well as the electrical potential between the two points, under chopped laser illumination that heats the structure via nanophotonic absorption, thus providing drift-corrected light on/off temperature information.
" }, { "name": "Tertuliano, Ottman Aeman", "degree": "PhD", "year": "2019", "title": "Small-Scale Deformation and Fracture of Hard Biomaterials", "advisor": "Greer, Julia R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10162018-124906600", "creators": [ { "name": { "family": "Tertuliano", "given": "Ottman Aeman" }, "id": "Tertuliano-Ottman-Aeman", "orcid": "0000-0003-0524-3944", "display_name": "Tertuliano, Ottman Aeman" } ], "advisors": [ { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "advisor", "display_name": "Greer, Julia R." } ], "committee": [ { "name": { "family": "Faber", "given": "Katherine T." }, "id": "Faber-K-T", "role": "chair", "display_name": "Faber, Katherine T." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." } ], "option_major": [ "matsci" ], "doi": "10.7907/CAPE-5661", "abstract": "Structural materials engineering often aims to realize materials that are simultaneously strong, tough, and lightweight \u2014 a combination classically considered mutually exclusive. Natural composite materials such as bone exhibit a combination of these properties far exceeding that of their constituents, a feat generally credited to their hierarchical structure \u2014 all the way down the nanoscale. To date, a quantitative description of how this property combination arises in such microstructurally complex materials has remained elusive due to challenges in experimentally isolating and probing the salient deformation and toughening mechanisms at the micro and nanometer scales \u2014 length scales on the order the constituents of many natural composites.
\r\n\r\nIn this thesis, we first investigate the site-specific nanoscale structure of human bone using transmission electron microscopy. We show the presence of previously undiscovered disordered arrangement of collagen and mineral \u2014 alongside a well known ordered structure \u2014 within the trabecular architecture of bone. We perform micro- and nano-mechanical compression experiments to probe strength and deformation of each of these microstructures, revealing a size-dependent strength of bone attributed to the limited number of failure-initiating critical defects (e.g pores) in the small-scale samples relative to macro-scale tissue.
\r\n\r\nUnlike experiments for investigating strength at small-scales, fracture experiments are standardized for the macroscale. To address this, we developed an in situ SEM/nanoindenter methodology that enables 3-point bending fracture experiments with observation and measurement of crack growth and toughening behavior at nano and micrometer scales. Using this technique, we discuss the crack initiation and growth toughness arising primarily from the underlying fibril microstructure in bone. In the context of a crack growth resistance, we describe a transition in the toughening behavior of bone originating from different levels of hierarchy. Given its versatility, this experimental technique establishes a platform for understanding the coupling between structure and fracture behavior of micron-sized materials.
" }, { "name": "Xia, Xiaoxing", "degree": "PhD", "year": "2019", "title": "Adaptive and Reconfigurable Architected Materials Driven by Electrochemistry", "advisor": "Greer, Julia R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06012019-140706232", "creators": [ { "name": { "family": "Xia", "given": "Xiaoxing" }, "id": "Xia-Xiaoxing", "orcid": "0000-0003-1255-3289", "display_name": "Xia, Xiaoxing" } ], "advisors": [ { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "advisor", "display_name": "Greer, Julia R." } ], "committee": [ { "name": { "family": "Faber", "given": "Katherine T." }, "id": "Faber-K-T", "role": "chair", "display_name": "Faber, Katherine T." }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." }, { "name": { "family": "Johnson", "given": "William L." }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William L." }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "member", "display_name": "Daraio, Chiara" } ], "option_major": [ "matsci" ], "doi": "10.7907/Q092-P711", "abstract": "Architected materials are a new class of engineered materials with carefully controlled internal structures that give rise to properties that differ from or surpass those of their constituent materials. Recent advances in additive manufacturing provide an extraordinary opportunity to rationally design the structure and the chemical composition of architected materials across multiple length scales to optimize properties and functionalities for a variety of applications. These functional architected materials are capable of decoupling critical trade-offs, such as strength vs. density, to reach new regions of the material property space, and enabling exotic properties that rarely exist in classical materials such as negative refraction and negative thermal expansion.
\r\n\r\nThis thesis probes into the dynamic behaviors of architected materials undergoing electrochemical reactions and aims to provide an in-depth understanding of the underlying mechanisms as well as design principles generalizable for other functional architected material systems. We developed novel fabrication methods based on two-photon lithography and various physical and chemical post-processing techniques to create architected materials with multi-level design freedom including feature sizes, structural geometries, and material compositions, which resonates with the multi-faceted challenges in electrochemical systems. We demonstrated that architected materials provide a new platform to design battery electrodes that could accommodate the large volumetric changes associated with conversion-based electrode materials, while decoupling the longstanding trade-off between active material loading and transport kinetics in batteries. Furthermore, we presented a new class of electrochemically reconfigurable architected materials that could transform their structures in a programmable, reversible and non-volatile fashion, which provide new vistas for designing mechanical metamaterials with tunable phononic bandgaps and deployable micro-devices for biomedical applications.
\r\n\r\nThe multi-scale and multi-physics nature of these electrochemically driven architected materials prompted us to develop a toolset of (1) in situ SEM and optical microscopy to visualize the dynamic responses, (2) coupled chemo-mechanical finite element analysis to reconstruct detailed mechanical evolution as electrochemical reactions proceed, and (3) a statistical mechanics framework to capture the transient interactions between coupled mechanical instabilities. Using these tools, we investigated lithiation-induced cooperative beam buckling in tetragonal Si microlattices: from the deformation mechanisms of individual beams and the cooperative coupling between buckling directions of neighboring beams to the lithiation rate-dependent distribution of ordered buckling domains separated by distorted domain boundaries. Results indicate that local defects and stochastic energy fluctuations play a critical role in the dynamic response of architected materials in a way analogous to that during phase transformations of classical materials. These connections have profound implications on how we could understand and design architected materials by drawing inspiration from established theories in materials science.
\r\n" }, { "name": "Yalamanchili, Sisir", "degree": "PhD", "year": "2019", "title": "Light Management in Photovoltaics and Photoelectrochemical Cells using Tapered Micro and Nano Structures", "advisor": "Atwater, Harry Albert; Lewis, Nathan Saul", "url": "https://resolver.caltech.edu/CaltechTHESIS:12182018-111020369", "creators": [ { "name": { "family": "Yalamanchili", "given": "Sisir" }, "id": "Yalamanchili-Sisir", "display_name": "Yalamanchili, Sisir" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "advisor", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Lewis", "given": "Nathan Saul" }, "id": "Lewis-N-S", "role": "advisor", "display_name": "Lewis, Nathan Saul" } ], "committee": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "chair", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "member", "display_name": "Goddard, William A., III" }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Lewis", "given": "Nathan Saul" }, "id": "Lewis-N-S", "role": "member", "display_name": "Lewis, Nathan Saul" } ], "option_major": [ "matsci" ], "doi": "10.7907/RRYM-VK03", "abstract": "Enhancing the efficiency and reducing the cost of solar photovoltaic (PV) systems is critical for increasing their penetration into energy generation market. The intermittency of energy generation from such systems due to diurnal, seasonal, and weather-related variation of sunlight limits them to low capacity factors (typically ~ 25%). Therefore, despite the cost of electricity from solar PV systems being cost competitive, further reductions are necessary to incorporate storage and increase the fraction of solar energy in total energy generation. An integrated photoelectrochemical (PEC) system that can generate fuel directly from sunlight could potentially reduce the balance of systems cost that dominates current PV systems, and provide an alternative way for energy storage. PEC systems are currently in research stage.
\r\n\r\nIn this work conical and triangular micro-nano structures are utilized to explore optical solutions for maximizing the light absorption and therefore enhancing the efficiencies of both PV and PEC systems. Silicon (Si) based micro conical arrays demonstrate < 1 % Spectrum-and-Angle-Averaged reflection, and absorption nearing ray optic light trapping limit in a 20 \u00b5m effectively thick Si substrates. Si microcone based photocathodes prepared for performing hydrogen evolution reaction (HER) show that thick layers of light blocking Pt and Co-P catalysts can be incorporated with only a 6 % photocurrent loss. The light trapping properties of Si micro-cones are a result of efficient coupling of light to available waveguide modes in a conical geometry. Alternatively, TiO2 based dielectric nano-conical arrays are shown to couple the light to waveguide modes and transmit the light into a planar Si substrate despite covering 54 % of the planar front surface with a light blocking Ni catalyst as an alternative way of light trapping without texturing the light absorber.
\r\n\r\nTriangular silver (Ag) front contacts in place of conventional flat contacts over PV cells are shown as another alternative for reducing front contact reflection losses and enhancing the efficiency by ~ 1% in Si heterojunction solar cells. These structures are implemented using a polymer stamp prepared from a Si master with triangular groves, and by flowing Ag ink through them. A Si master fabrication method is shown for fabrication of multiple configurations of triangular Ag contacts which can potentially be applied to other PV and PEC systems to enhance their efficiency.
\r\n" }, { "name": "Bartels, Phillip Leon", "degree": "PhD", "year": "2018", "title": "Elucidating the Role of [4Fe4S] Clusters in DNA Replication and Repair Proteins", "advisor": "Barton, Jacqueline K.", "url": "https://resolver.caltech.edu/CaltechTHESIS:03012018-094939210", "creators": [ { "name": { "family": "Bartels", "given": "Phillip Leon" }, "id": "Bartels-Phillip-Leon", "orcid": "0000-0002-9688-6592", "display_name": "Bartels, Phillip Leon" } ], "advisors": [ { "name": { "family": "Barton", "given": "Jacqueline K." }, "id": "Barton-J-K", "role": "advisor", "display_name": "Barton, Jacqueline K." } ], "committee": [ { "name": { "family": "Gray", "given": "Harry B." }, "id": "Gray-H-B", "role": "chair", "display_name": "Gray, Harry B." }, { "name": { "family": "Barton", "given": "Jacqueline K." }, "id": "Barton-J-K", "role": "member", "display_name": "Barton, Jacqueline K." }, { "name": { "family": "Campbell", "given": "Judith L." }, "id": "Campbell-J-L", "role": "member", "display_name": "Campbell, Judith L." }, { "name": { "family": "Tirrell", "given": "David A." }, "id": "Tirrell-D-A", "role": "member", "display_name": "Tirrell, David A." } ], "option_major": [ "chemistry" ], "doi": "10.7907/Z9H1307G", "abstract": "[4Fe4S] clusters, redox cofactors, have been discovered in DNA processing enzymes ranging from bacterial base excision repair glycosylases to eukaryotic DNA polymerases. Bacterial repair proteins are activated toward redox activity when bound to DNA and can take advantage of DNA-mediated charge transport (DNA CT) to search the genome for lesions. DNA CT involves the rapid transport of charges through the \u03c0-stacked base pairs and is sharply attenuated in the presence of lesions, mismatches, or other stacking perturbations. Thus, [4Fe4S] repair proteins use this chemistry to rapidly redistribute to target lesions and communicate with one another over long distances.
\r\n\r\nThe general function of [4Fe4S] clusters in bacterial DNA repair has received much attention, but previous efforts have left several critical questions unanswered. First, while the redox potential of these proteins is affected by DNA binding, the relative importance of the negatively-charged DNA, the protein environment surrounding the cluster, and solvent has remained unclear. Second, the importance of [4Fe4S] clusters and DNA CT to human disease has never been directly addressed. The biological consequences of this chemistry are certainly a pressing issue, as numerous disease-relevant mutations in the human homologues of well-studied repair proteins have been recorded. Finally, the existence of [4Fe4S] clusters in eukaryotic DNA replication proteins in general, and in the B-family DNA polymerases in particular, was entirely unexpected. The function of the [4Fe4S] cluster in replication proteins was far from obvious, and the functional differences from repair proteins made them difficult to explain even in the context of CT signaling. Herein, these questions have been addressed using a combination of electrochemical, spectroscopic, and biochemical approaches.
\r\n\r\nFirst, we describe the use of pyrolytic graphite edge electrodes (PGE) and S K-edge X-ray absorption spectroscopy (XAS) to address the influence of protein environment, DNA, and solvation on the [4Fe4S] cluster redox potential in the bacterial base excision repair glycosylases endonuclease III (EndoIII) and MutY. The PGE surface is rough and favorable for protein binding; electron transfer can be further enhanced in the presence of carbon nanotubes. Electrochemical signals for EndoIII and MutY in the absence of DNA are large and reproducible, and a potential shift upon DNA binding is observed. With respect to studying proteins in the absence of DNA, the PGE electrode represents a significant advance over previously used highly-oriented pyrolytic graphite (HOPG), which is hydrophobic and difficult to prepare. To test the effect of protein environment on redox potential, a series of EndoIII point mutants were prepared in which the charge within 5 \u00c5 of the cluster was reversed or added in. None of these mutations induced a significant shift in redox potential relative to wild type, arguing that DNA electrostatics are the dominant factor in potential modulation. In parallel, XAS studies were performed on EndoIII and MutY in the presence and absence of DNA, and in the presence and absence of solvent. Ligating cysteinyl thiols and inorganic S atoms in the [4Fe4S] cluster absorb at different intensities in XAS depending on solvent environment and local electrostatics; these changes, in turn, directly correlate to redox potential. By XAS, DNA was found to induce a significant shift in absorbance, and thus potential; the removal of solvent had a smaller effect. Together, these studies provide new approaches for the study of DNA-binding [4Fe4S] proteins and reveal the critical role of DNA in tuning the redox potential.
\r\n\r\nSecond, we report on a novel mutation in human MUTYH identified from a colorectal cancer patient and confirmed to be pathological. MUTYH is responsible for repairing certain lesions induced by oxidative stress and is thus frequently implicated in cancer. This new variant, C306W, contains a mutation in one of the cysteines that ligates the [4Fe4S] cluster. Electrochemistry, activity and DNA binding assays, and spectroscopic analyses were performed for C306W alongside wild type MUTYH and two other disease-relevant mutants, Y179C and G396D, with an unaltered cluster environment. From this work, it is now clear that C306W can still bind a cluster, but it is susceptible to oxidative degradation to the [3Fe4S]+ state upon redox signaling in an aerobic environment. Consequently, enzymatic activity is very low, and DNA binding is poor. Overall, this represents the first complete characterization of the [4Fe4S] cluster in a human homologue of MutY, and the first demonstration of pathology resulting from a mutation that primarily affects the [4Fe4S] cluster.
\r\n\r\nMoving into DNA replication proteins, we report on the characterization of the [4Fe4S] cluster in yeast DNA polymerase (Pol) \u03b4, the eukaryotic lagging strand polymerase. Pol \u03b4 shows reversible electrochemical signals at a midpoint potential indistinguishable from EndoIII under the same conditions, and EPR spectroscopy confirms use of the [4Fe4S]3+/2+ couple. The electrochemical signal is attenuated on DNA containing an abasic site or a CA mismatch, confirming that Pol \u03b4 is capable of DNA-mediated signaling. Bulk electrolysis and photooxidation were used to oxidize Pol \u03b4 under anaerobic conditions, and activity assays were carried out using oxidized or untreated protein. Oxidation stalls replication activity, while electrochemical reduction of oxidized samples restores activity to untreated levels. These results thus reveal that cluster oxidation serves as a reversible switch regulating Pol \u03b4 activity, suggesting an in vivo role in responding to replication stress, especially oxidative stress. In an effort to address these possibilities, we have carried out preliminary efforts in the characterization of two potentially CT-deficient mutants, W1053A and Y1078A. Both mutants were found to be too structurally unstable to proceed with in vivo experiments, but they can serve to guide future efforts in this direction.
\r\n\r\nFinally, a strategy to examine charge transport through RPA-bound single-stranded DNA is reported. RPA is the eukaryotic single-stranded binding protein and forms a protective coat around vulnerable unwound DNA at replication forks. Given the importance of redox signaling in replication proteins, we aimed to use photooxidation experiments to determine if CT through RPA is a viable pathway; if so, this would open up a large set of long-range transfer pathways to [4Fe4S] proteins in replication. These efforts are ongoing, but the experimental strategy and initial efforts are discussed.
" }, { "name": "Chernow, Victoria Fay", "degree": "PhD", "year": "2018", "title": "Design, Fabrication, and Characterization of 3D Nanolattice Photonic Crystals for Bandgap and Refractive Index Engineering", "advisor": "Greer, Julia R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05112018-154344223", "creators": [ { "name": { "family": "Chernow", "given": "Victoria Fay" }, "id": "Chernow-Victoria-Fay", "orcid": "0000-0001-5405-1928", "display_name": "Chernow, Victoria Fay" } ], "advisors": [ { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "advisor", "display_name": "Greer, Julia R." } ], "committee": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "chair", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Rossman", "given": "George Robert" }, "id": "Rossman-G-R", "role": "member", "display_name": "Rossman, George Robert" }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "member", "display_name": "Painter, Oskar J." }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." } ], "option_major": [ "matsci" ], "doi": "10.7907/FK5P-FA29", "abstract": "Three-dimensional (3D) photonic crystals (PhCs) have been the focus of ever-increasing interest in the scientific community given their potential to impact areas spanning energy conversion to analyte sensing. These architected materials are defined by a refractive index that is spatially modulated with a period comparable to that of the electromagnetic wavelength. As a result, constructive and destructive interference due to multiple scattering gives rise to a band structure for photons which may contain gaps. Both bands and bandgaps can be engineered to specifically manipulate light propagation by 3D PhCs. In this work we explore the effect of lattice architecture, finite-size effects, and material constraints on stopband position and emergence of band dispersion phenomena like negative refraction. We show that uniaxial mechanical compression can be used to stably and reversibly tune stopband position in 3D polymer nanolattice PhCs with octahedron unit-cell geometry. We then explore how lattice architecture, namely the differences in 3D cubic space group and finite size effects impact experimentally observable stopbands, and assess the degree to which the stopband behavior of real PhCs can be adequately described by the photonic band structure for an infinite, ideal PhC. Finally, we discuss the design, fabrication, and characterization of a core-shell 3D nanolattice PhC which exhibits an effective negative refractive index in the mid-infrared range.
" }, { "name": "Dou, Nicholas Gang", "degree": "PhD", "year": "2018", "title": "Thermal Transport in Three-Dimensional Nanoarchitected Materials", "advisor": "Minnich, Austin J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06022018-070416991", "creators": [ { "name": { "family": "Dou", "given": "Nicholas Gang" }, "id": "Dou-Nicholas-Gang", "orcid": "0000-0001-8199-5588", "display_name": "Dou, Nicholas Gang" } ], "advisors": [ { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "role": "advisor", "display_name": "Minnich, Austin J." } ], "committee": [ { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "role": "chair", "display_name": "Blanquart, Guillaume" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." }, { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "role": "member", "display_name": "Hunt, Melany L." }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "role": "member", "display_name": "Minnich, Austin J." } ], "option_major": [ "mecheng" ], "doi": "10.7907/TPC8-VH59", "abstract": "Materials that simultaneously possess ultralow thermal conductivity, high stiffness, and damage tolerance are highly desirable for engineering applications. However, this combination of properties has never been demonstrated in a single material because thermal and mechanical properties are coupled in most fully dense and porous solids. A new class of lattice materials with nanoscale features, called nanolattices, can fill this void in the material property space by virtue of their architecture and nanoscale dimensions. Extensive work on nanolattice mechanical properties report their excellent stiffness-to-density ratio and recoverability from large compressive strains. In contrast, the framework for studying their thermal properties has not been established. Our work develops the computational and experimental tools necessary to study heat conduction in nanoarchitected materials and applies those tools to prove the viability of octet-truss nanolattices as multifunctional thermal insulators.
\r\n\r\nWe implement significant improvements to a phonon Monte Carlo method to solve the Boltzmann transport equation (BTE) in highly complex geometries like the octet-truss. No prior works solve the BTE in a domain as intricate as a nanolattice, so we create a geometry representation scheme that can model any arbitrary 3-D body. Our enhanced variance-reduced Monte Carlo code incorporates this scheme, allowing us to predict the thermal conductivity of nanolattices and analyze the phonon transport behavior in them. Results suggest that hollow-beam silicon nanolattices indeed reach ultralow thermal conductivities. Based on Monte Carlo and finite element simulations, we develop a predictive thermal conductivity model that accounts for both diffusive and radiative phonon transport in nanolattices.
\r\n\r\nWe also devise custom modifications to the 3\u03c9 method to experimentally measure the thermal conductivity of additively manufactured nanolattices. Since the serial fabrication process of nanolattices makes it costly to cover large areas, we design a specialized 3\u03c9 sample that minimizes the required structure size while maintaining good experimental sensitivity. We derive a new thermal model to account for conductive losses through the heater line in our novel sample geometry. 3\u03c9 measurements and compression tests of hollow-beam alumina nanolattices show that they combine ultralow thermal conductivity with excellent mechanical stiffness and resilience, which proves that nanolattices occupy a previously unreachable region in material property space. Our work provides motivation to further investigate and improve the thermal properties of architected materials.
\r\n" }, { "name": "Harfouche, Mark", "degree": "PhD", "year": "2018", "title": "The Coherence Collapse Regime of High-Coherence Si/III-V Lasers and the Use of Swept Frequency Semiconductor Lasers for Full Field 3D Imaging", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechTHESIS:10242017-104926655", "creators": [ { "name": { "family": "Harfouche", "given": "Mark" }, "id": "Harfouche-Mark", "orcid": "0000-0002-4657-4603", "display_name": "Harfouche, Mark" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "chair", "display_name": "Painter, Oskar J." }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "member", "display_name": "Scherer, Axel" }, { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "role": "member", "display_name": "Emami, Azita" }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "role": "member", "display_name": "Faraon, Andrei" } ], "option_major": [ "eleceng" ], "doi": "10.7907/Z9W66J07", "abstract": "The semiconductor laser is the linchpin of optical communication and is now also penetrating a wide spectrum of new applications such as biomedical sensing, coherent communication, metrology, and time keeping. These require a higher degree of temporal coherence than is available from the present generation. Recently, it has been proposed and shown that heterogeneously integrated lasers on silicon and InGaAsP can be used to design high coherence single mode lasers with a much narrower linewidth than their all InGaAsP counterparts. Unfortunately, these lasers suffer from large thermal impedances and their optical feedback characteristics have not yet been explored. In the first part of this thesis, we will explore how flip chip bonding can help decrease the thermal impedance of these lasers to improve their overall performance and show that these lasers can provide up to 20 dB of optical isolation compared to their all III-V counterparts.
\r\n\r\nIn the second part of this thesis, we will report on the use of commercially available semiconductor lasers, in conjunction with an optical modulator to obtain high-resolution tomographic images in one shot without any moving parts. The electronic control over the imaged depth of this novel tomographic imaging camera enables it to monitor arbitrary depth slices in rapid succession over a depth range limited only by the coherence length of the laser. Not only does this imaging modality acquire the transverse image intensity (x,y) distribution of the light reflected from a particular depth, but also the phase of the reflected light enabling imaging beyond the conventional depth of field of the lens. This has important implications in applications requiring high lateral resolution images where the shallow depth of field would often require mechanical scanning of the lens elements to change the imaged depth.
" }, { "name": "Horie, Yu", "degree": "PhD", "year": "2018", "title": "Controlling the Flow of Light Using High-Contrast Metastructures", "advisor": "Faraon, Andrei", "url": "https://resolver.caltech.edu/CaltechTHESIS:09202017-124555409", "creators": [ { "name": { "family": "Horie", "given": "Yu" }, "id": "Horie-Yu", "orcid": "0000-0001-7083-1270", "display_name": "Horie, Yu" } ], "advisors": [ { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "role": "advisor", "display_name": "Faraon, Andrei" } ], "committee": [ { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "role": "chair", "display_name": "Faraon, Andrei" }, { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "role": "member", "display_name": "Emami, Azita" }, { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "role": "member", "display_name": "Hajimiri, Ali" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "member", "display_name": "Yang, Changhuei" } ], "option_major": [ "eleceng" ], "doi": "10.7907/Z94X5604", "abstract": "A new class of planar optical components and devices has emerged using subwavelength metastructures with a strong contrast in refractive indices. High-contrast metastructures have shown promises to manipulate optical fields in an extraordinary way and to replace conventional bulky optical elements by their low-profile analogs, typically with subwavelength-scale features. We elucidate the underlying principle, how these seemingly low-profile geometries render unique optical responses, using the coupled-mode analysis in a multimode waveguide. Moreover, strong field localization in high-index structures allows us to interpret each single element in the metastructures as a low-quality-factor resonator (or a localized scatterer), permitting us to realize designer surface that shapes phase, amplitude, and polarization of light in free space, also known as an optical metasurface. The remainder of the thesis is devoted to explore novel applications in optics using high-contrast metastructures. One of the particularly interesting applications is to use them in an optical resonator. Specifically, we demonstrate to incorporate high-contrast subwavelength grating reflectors and dielectric metasufaces in a vertical Fabry\u2013Perot cavity, and show that we can flexibly tune the resonance frequency by the subwavelength patterning. With this technique, we envision the realization of compact, on-chip spectrometers when integrating them on a photodetector array. Secondly, we investigate the use of high-contrast subwavelength gratings in visible wavelengths. We perform the optimization of their geometries and demonstrate a set of RGB color filters, down to near a micrometer in the pixel size. This platform exhibits unique performances such as high efficiency, angular insensitivity, and color tunability by the design. A novel device concept is also explored, where a high-contrast subwavelength grating reflector is integrated on a silicon platform to constitute an active resonant antenna, enabling high-speed, phase-dominant modulation by means of thermo-optic effect of silicon. We demonstrate an array of such active antennas, yielding a beam deflection capability. This justifies the robustness of our device design, enabling a large-scale integration of high-speed, phase-dominant spatial light modulators. Finally, we introduce a disorder-engineered metasurface in the context of wavefront shaping. Recently, wavefront shaping with disordered media has demonstrated optical manipulation capabilities beyond those of conventional optics, but translating this class of technology into a practical use has remained challenging due to enormous amounts of information needed to be characterized as the input-output responses. As a paradigm shift, we propose the use of disorder-engineered metasurface in wavefront shaping, where the disorder is programmatically designed and makes the system characterization-free prior to use. With this approach, we demonstrate high numerical aperture focusing in an extended volume as well as wide-field fluorescence imaging with unprecedented performances.
" }, { "name": "Jones, William Maxwell", "degree": "PhD", "year": "2018", "title": "Nanoscale Field Emission Devices", "advisor": "Scherer, Axel", "url": "https://resolver.caltech.edu/CaltechTHESIS:12132017-132404589", "creators": [ { "name": { "family": "Jones", "given": "William Maxwell" }, "id": "Jones-William-Maxwell", "orcid": "0000-0002-8610-2176", "display_name": "Jones, William Maxwell" } ], "advisors": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "advisor", "display_name": "Scherer, Axel" } ], "committee": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "chair", "display_name": "Scherer, Axel" }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" }, { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "role": "member", "display_name": "Emami, Azita" }, { "name": { "family": "DeRose", "given": "Guy A." }, "id": "DeRose-Guy-A", "role": "member", "display_name": "DeRose, Guy A." }, { "name": { "family": "Neches", "given": "Philip M." }, "id": "Neches-Philip-M", "role": "member", "display_name": "Neches, Philip M." } ], "option_major": [ "eleceng" ], "doi": "10.7907/Z94B2ZHZ", "abstract": "This thesis outlines work done to produce in-plane nanoscale field emission devices. Field emission, the process of quantum tunneling electrons from a conductor into a vacuum, has been theorized as a device concept for almost as long as integrated circuits have existed. This is because the micro- and nanoscale dimensions of integrated circuits make field emission possible at modest voltages, and because the physics of field emission and conduction in a vacuum channel suggest that field emission devices can operate at extremely high frequencies and in harsh environments where CMOS devices face challenges. Yet despite many attempts to make practical field emission devices none have risen to the level of commercial products. These attempts were stymied by short lifetimes, high operating voltages, and the necessity for vacuum enclosure. In this thesis work, I outline how new fabrication technologies like high resolution electron beam lithography, atomic layer deposition, and refinement in reactive ion etching make lateral field emission devices with extremely short vacuum channels practical. The demonstrated devices can operate at near CMOS voltages and at atmospheric pressures, and are robust to emitting tip destruction. These devices are prime candidates for integration into demonstration circuits.
\r\n\r\nThe second part of this thesis outlines work done in an emerging field to combine field emission with plasmonics for practical devices. The tunneling process in field emission depends exponentially on the magnitude of the instantaneous electric field, either static or time-varying, at the emitting surface. While it has long been known that using extremely powerful pulsed lasers one can field emit electrons from a metallic surface, the combination of plasmonics into a field emitting device has the potential to dramatically lower the incident optical power needed to produce field emission. This could enable extremely fast opto-electronic devices. This thesis presents work in progress to realize a plasmonically enhanced field emission opto-electronic modulator that is designed to operate at 1550 nm and is integratable with existing silicon photonics platforms.
" }, { "name": "Kim, Dongwan", "degree": "PhD", "year": "2018", "title": "Frequency Noise Control of Heterogeneous Si/III-V Lasers ", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechTHESIS:10262017-003847721", "creators": [ { "name": { "family": "Kim", "given": "Dongwan" }, "id": "Kim-Dongwan", "orcid": "0000-0002-5661-2503", "display_name": "Kim, Dongwan" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "chair", "display_name": "Painter, Oskar J." }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "role": "member", "display_name": "Faraon, Andrei" }, { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "role": "member", "display_name": "Schwab, Keith C." }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/Z90Z71G6", "abstract": "Narrow-linewidth lasers have many applications including optical telecommunication, laser spectroscopy, atomic clocks, and light detection and ranging. Conventionally, narrow linewidth lasers have been realized in the form of fiber-based or solid-state lasers. These lasers are bulky and relatively expensive, limiting their usage as bench-top systems in laboratory environments. Historically, semiconductor lasers, also known as laser diodes, have served applications where size and cost are important factors, including fiber optic communications. The linewidth of the semiconductor lasers, however, has been limited to the MHz-level, due to high loss in laser cavities and small size.
\r\n\r\nRecently, reduction of the frequency fluctuations in the semiconductor lasers has been achieved, obtaining tens of kHz linewidth, using the heterogeneous Silicon/III-V platform with a new design strategy. In this design, the majority of the optical energy is stored in the low-loss high-Q silicon resonator away from the high-loss III-V active region, requiring the minimal gain from the active region to overcome the reduced modal loss.
\r\n\r\nThis work explores the new design strategy further, and demonstrates theoretically and experimentally that the strategy eliminates the frequency fluctuations arising from the amplitude-phase coupling by placing a relaxation resonance frequency at frequencies of a few hundred MHz. Consequently, it becomes possible to obtain a semiconductor laser device possessing sub-kHz quantum-limited linewidths at frequencies of a few GHz (the frequencies of interest in optical telecommunication).
\r\n\r\nIn addition to the frequency noise reduction, the strategy turns out to have the additional benefit of accomplishing a coherent and stable lasing operation, even under external reflections. Thus, the new design strategy has the potential to replace the costly, but currently indispensable external optical isolators, which have been traditionally used to maintain the consistent performance of semiconductor lasers in the presence of external reflection.
\r\n\r\nThis work paves the way for the design of narrow-linewidth and stable semiconductor lasers that can function without the use of the bulky and costly external components, such as external cavities or optical isolators.
" }, { "name": "Lloyd, John Vickery", "degree": "PhD", "year": "2018", "title": "Optoelectronic Design and Prototyping of Spectrum-Splitting Photovoltaics", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:05212018-185007265", "creators": [ { "name": { "family": "Lloyd", "given": "John Vickery" }, "id": "Lloyd-John-Vickery", "display_name": "Lloyd, John Vickery" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "chair", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "orcid": "0000-0002-9675-1508", "role": "member", "display_name": "Greer, Julia R." }, { "name": { "family": "Gray", "given": "Harry B." }, "id": "Gray-H-B", "orcid": "0000-0002-7937-7876", "role": "member", "display_name": "Gray, Harry B." }, { "name": { "family": "Bernardi", "given": "Marco" }, "id": "Bernardi-Marco", "orcid": "0000-0001-7289-9666", "role": "member", "display_name": "Bernardi, Marco" } ], "option_major": [ "matsci" ], "doi": "10.7907/G1CG-E962", "abstract": "Global energy production is dominated by the combustion of fossil fuels but in order to avoid the projected consequences of anthropogenic climate change it is necessary that humankind reduce the carbon intensity of its energy supply. Fortunately the sun supplies a ubiquitous flow of energy of with excellent thermodynamic quality to earth. Massive investment and manufacturing scale has driven the costs of photovoltaic systems to levels competitive with fossil fuel generation, and yet commercial photovoltaic systems convert power from the sun into electricity with less than 20% efficiency. In this thesis we consider the thermodynamic and practical limits to the power conversion efficiency of photovoltaic systems and seek to design systems that address the greatest sources of loss, namely the lack of sub-bandgap absorption and the thermalization of excited carriers. We present several designs of spectrum-splitting systems that utilize optical structures to allocate incident broadband solar radiation into narrower spectral bands which can be converted by multiple distinct photovoltaic cells at greater efficiency. Furthermore, we report on the design and fabrication of thin film III-V single-junction cells at bandgaps spanning the solar spectrum for incorporation within spectrum-splitting systems. These devices were fabricated by utilizing epitaxial lift-off processes from both GaAs and InP wafers as proof of scalability. We additionally report on the fabrication and characterization of series of a spectrum-splitting prototypes. This design featured seven distinct spectral bands with single-junction photovoltaic cells designed to convert them with highest possible efficiency, and the ultimate prototype exhibited an 84.5% spectrum splitting efficiency and 30.2% power conversion efficiency under a standard AM1.5D solar spectrum. We also report a technical pathway to raise the prototype efficiency to a record breaking 45.2%. Finally, we present an optical design of a spectrum-splitting module that is informed by a technoeconomic analysis which drastically reduces the complexity and cost relative to the fabricated prototype.
" }, { "name": "Maggi, Alessandro", "degree": "PhD", "year": "2018", "title": "Three-Dimensional Nano-Architected Materials as Platforms for Designing Effective Bone Implants", "advisor": "Greer, Julia R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:12242017-060345135", "creators": [ { "name": { "family": "Maggi", "given": "Alessandro" }, "id": "Maggi-Alessandro", "display_name": "Maggi, Alessandro" } ], "advisors": [ { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "advisor", "display_name": "Greer, Julia R." } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Shapiro", "given": "Mikhail G." }, "id": "Shapiro-M-G", "role": "member", "display_name": "Shapiro, Mikhail G." }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." } ], "option_major": [ "medeng" ], "doi": "10.7907/Z947482K", "abstract": "The growing world population coupled with longer human life expectancy warrants the need for better medical implant development. Recent advances in lithographic techniques have opened the door to a variety of approaches to tackle the aforementioned issue. However, several scientific hurdles must be overcome before patients can use fully synthetic and effective implants.
\r\n\r\nIdentifying the optimal material, porosity, and mechanical properties of the scaffold to induce cell functionality are key obstacles. Limitations in established fabrication techniques have hindered the ability to fully understand cell behavior on 3D substrates. 3D printing is limited to feature sizes that are at least one order of magnitude larger than a single cell (~10\u03bcm); electrospinning is able to yield features that are on the same scale as cells, but its stochastic nature leads to scaffolds with poor mechanical properties; salt leeching doesn\u2019t allow for control of pore size and distribution which have detrimental effects on nutrient diffusion and cell ingrowth, thereby thwarting the formation of functional tissue.
\r\n\r\nMuch effort has been made to create a suitable platform for regenerating a relatively less complex organ, such as bone, yet the inability to fully understand cell mechanics on 3D scaffolds has curbed the fabrication of effective bone implants.
\r\n\r\nThe first part of this thesis focuses on the suitability of nanoarchitected materials as 3D platforms for bone-tissue growth. We employed two-photon lithography to create polymeric and hydroxyapatite-coated 3D nanolattices to explore scaffold biocompatibility and material effects on osteoblast attachment and growth. Our experiments showed that the unit cell geometry, tetrakaidekahedron, and size, 25\u03bcm, were adequate for cell attachment and infiltration, which are hallmark signs of biocompatibility. Our study also corroborated previous findings that mammalian cells respond differently to different materials that they come in contact with. To isolate structural effects, we fabricated nanolattices coated with a uniform 20nm-thick outermost layer of TiO2. These nanolattices, which had fixed porosity and unit cell size (25\u03bcm) while they varied in structural stiffness (~2-9MPa) were used to explore the influence of scaffold properties on the viability of osteoblasts in a microenvironment similar to that of natural bone. Upon growing osteogenic cells on the nanolattices, significant cell attachment and presence of various calcium phosphate species, which are commonly found in natural bone, were observed. These findings suggest that 3-dimensional nano-architected materials can be used as effective scaffolds for bone cell growth and proliferation.
\r\n\r\nThe second part of the thesis investigates the effects of nanolattice structural stiffness and loading conditions on osteoblast behavior. We fabricated nanolattices with stiffness ranging from ~0.7MPa to 100MPa. Experiments done by seeding osteoblast-like cells on these nanolattices revealed that both stress fiber concentration and bioapatite deposition were higher on the most compliant nanolattice, (0.7 MPa) by ~20% and ~40% respectively. These results provide insights into cell behavior in 3D microenvironments which can lead to a better understanding of stress shielding at the cellular level. Preventing stress shielding by creating scaffolds with structural stiffness and porosity that enhances osteoblasts activity could lead to the creation of effective implants with improved mechanical stability which ultimately improves osteointegration.
\r\n\r\nIn addition to investigating static cell-scaffold interactions we took advantage of the nanolattices tunability to study the effects of dynamic loading on cell behavior. Bone adaptation is driven by dynamic, rather than static loading, however there is still wide controversy on whether stress, strain or loading frequency plays the most significant role in bone remodeling, which drives bone healing.
\r\n\r\nIn order to understand cell sensitivity to varying loads, displacements and frequencies, we fabricated hollow TiO2 nanolattices with stiffness ranging from ~0.7-35MPa which were populated with osteoblast-like cells and subjected to cyclic compression to either a constant stress or strain. After seeding SAOS-2 cells on the nanolattices for 12 days different dynamic loading conditions were tested: (1) cyclic uniaxial compressions to strains ranging from ~0.3-2% strain were carried out to investigate the effects of strain magnitude on cell behavior. (2) Cyclic uniaxial compressions to stresses spanning from ~0.02-1MPa were performed to explore the role of stress magnitude on the cells\u2019 stress fibers formation. (3) The nanolattices were cyclically loaded at different frequencies, ~0.1-3Hz, while maintaining stress and strain constant, which provided insights into how loading frequency affects osteoblasts behavior.
\r\n\r\nCell activity, which was measured by monitoring f-actin and vinculin fluorescence intensity, revealed increased fluorescence in those cells that were mechanically stimulated as opposed to those that were statically grown on the nanolattices regardless of loading condition. Cell response was most drastically affected by varying the loading frequency. A ~30% increase in f-actin fluorescence was observed in the cells grown on the nanolattices that were loaded at ~3Hz compared to those that were grown on the nanolattices that were cyclically compressed at ~0.1Hz.
\r\n\r\nThe last part of this thesis is focused on developing a three-dimensional architected capacitor that could be used as a strain gauge to further our understanding of cell mechanics in 3D. We took advantage of the mechanical tunability of the nanolattices to fabricate a 3D parallel-plate capacitor with a basal capacitance of ~280fF and able to sense forces as low as ~30\u03bcN. This work points to nano-architected materials as promising candidates for ideal platforms to investigate more realistic cellular conditions which can immensely benefit the field of tissue engineering.
" }, { "name": "Mateos Arrieta, Arturo Jos\u00e9", "degree": "PhD", "year": "2018", "title": "Tensile Failure and Fracture of Three-Dimensional Brittle Nanolattices", "advisor": "Greer, Julia R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06122018-094549478", "creators": [ { "name": { "family": "Mateos Arrieta", "given": "Arturo Jos\u00e9" }, "id": "Mateos-Arrieta-Arturo-Jos\u00e9", "orcid": "0000-0002-9306-3531", "display_name": "Mateos Arrieta, Arturo Jos\u00e9" } ], "advisors": [ { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "advisor", "display_name": "Greer, Julia R." } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Faber", "given": "Katherine T." }, "id": "Faber-K-T", "role": "member", "display_name": "Faber, Katherine T." }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "role": "member", "display_name": "Pellegrino, Sergio" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/AZXG-NB17", "abstract": "The emergence of a new class of cellular solids, i.e., nano- and micro-architected materials, poses the question of whether they can be characterized as a continuum solid. Extensive research has shown that these ultralight and strong structural metamaterials are particularly attractive for mechanically-demanding applications; yet their susceptibility to flaws, fracture behavior, and discrete-continuum duality remains relatively unexplored. In the course of this work, we report the fabrication and tensile-to-failure response of three-dimensional ceramic nanolattices, comprised of 50nm-thick alumina tubes that are arranged into periodic 5um-wide octet-truss unit cells, with and without pre-fabricated through-thickness center notches oriented at different angles to the loading direction. In-situ uniaxial tensile experiments revealed that for all notch orientations, failure always initiated at the notch root, as would be in a monolithic material, with the tube walls at nodal junctions fracturing first, followed by instantaneous crack propagation through the discrete lattice architecture along nodal planes orthogonal to the loading direction. Measured tensile strength of 27.4 MPa was highest for the unnotched samples and decreased systematically with the increase of notch orientation to its minimum of 7.2 MPa in the orthogonally-notched samples. We found the specific tensile strength of hollow-tube octet alumina nanolattices to be 4 times higher than what has been reported for architected and bulk materials at similar low densities. Three-dimensional finite element simulations closely reproduce the observed failure mechanism and trends in failure strength. A direct comparison is made between the experimental measurements, finite element simulations, and predictions of linear elastic fracture mechanics for a self-similar monolithic tensile samples made out of an ideally-brittle solid. Results are in good agreement with the scaling of failure strengths from classical mode I fracture criteria and suggest that trajectory of crack propagation can be adequately explained by considering the connectivity of the lattice architecture. These findings imply that the continuum nature of nano-architected materials offers predictability of failure stresses, which helps enable the development of advanced materials through informed architectural design." }, { "name": "O'Brien, Elizabeth", "degree": "PhD", "year": "2018", "title": "Redox Signaling in Eukaryotic DNA Replication and Repair", "advisor": "Barton, Jacqueline K.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06112018-200314076", "creators": [ { "name": { "family": "O'Brien", "given": "Elizabeth" }, "id": "O'Brien-Elizabeth", "orcid": "0000-0003-2889-1688", "display_name": "O'Brien, Elizabeth" } ], "advisors": [ { "name": { "family": "Barton", "given": "Jacqueline K." }, "id": "Barton-J-K", "role": "advisor", "display_name": "Barton, Jacqueline K." } ], "committee": [ { "name": { "family": "Gray", "given": "Harry B." }, "id": "Gray-H-B", "role": "chair", "display_name": "Gray, Harry B." }, { "name": { "family": "Rees", "given": "Douglas C." }, "id": "Rees-D-C", "role": "member", "display_name": "Rees, Douglas C." }, { "name": { "family": "Tirrell", "given": "David A." }, "id": "Tirrell-D-A", "role": "member", "display_name": "Tirrell, David A." }, { "name": { "family": "Barton", "given": "Jacqueline K." }, "id": "Barton-J-K", "role": "member", "display_name": "Barton, Jacqueline K." } ], "option_major": [ "chemistry" ], "doi": "10.7907/KGCP-SD98", "abstract": "DNA-mediated charge transport chemistry (DNA CT) offers an intriguing regulatory mechanism in biology, as it is long-range, rapid, and sensitive to mismatches and perturbations to base stacking. DNA-processing enzymes in all three domains of life moreover have been shown to contain [4Fe4S] clusters, commonly redox cofactors. Bacterial [4Fe4S] repair proteins have been shown to signal one another using long-range DNA-mediated charge transport (DNA CT), facilitating the redistribution to damaged genomic DNA in cells. The role of metabolically expensive, [4Fe4S] cluster cofactors in eukaryotic systems, however, was less clear than in prokaryotes.
\r\n\r\nHere we examine the chemical role of the [4Fe4S] cluster in eukaryotic DNA primase and the human base excision repair glycosylase, MUTYH. The primase cluster functions as a redox switch regulating DNA binding and redox signaling activity in humans and yeast. Yeast moreover require the primase redox switch for viability. Human MUTYH, a bifunctional glycosylase which repairs oxidative DNA lesions, performs DNA-mediated redox signaling, similarly to the bacterial homologue MutY. The MUTYH mutation which destabilizes the [4Fe4S] cluster during redox signaling, C306W, promotes degradation and loss of activity, associated with hereditary colorectal cancer.
\r\n\r\nTo assess the redox role of the human primase [4Fe4S] cluster, we perform anaerobic DNA electrochemistry on the [4Fe4S] domain of human primase (p58C), which independently binds DNA. On DNA-modified Au electrodes, we compare the redox activity of electrochemically oxidized and electrochemically reduced p58C. Oxidized [4Fe4S]3+ p58C is electrochemically active, and reduced [4Fe4S]2+ p58C state is redox-inert. This redox-driven switch is electrochemically reversible, and is mediated by a triad of conserved tyrosines between the DNA binding interface and [4Fe4S] cluster. Mutation of residues Y309, Y345, and Y347 to phenylalanine causes attenuation of redox switching on DNA. Single-atom mutations in the redox pathway moreover compromise initiation and truncation of primer synthesis but do not affect RNA polymerase activity. We find that primase truncation is gated by DNA CT in vitro; a single mismatch in the nascent primer abrogates truncation of primase products. As\r\nprimase is tethered to DNA polymerase \u03b1, a putative [4Fe4S] enzyme to which primase hands off the RNA-primed template, we propose that DNA-mediated signaling between primase and polymerase \u03b1 chemically regulates this handoff during the first steps of replication.
\r\n\r\nEukaryotic primase must bind both DNA and nucleotide triphosphates (NTPs) in order to convert to active form. Using DNA electrochemistry we show that p58C, and full-length DNA primase, display a robust, semi-reversible NTP-dependent signal on DNA, centered near 150mV vs. NHE. This signal is dependent on the tyrosine redox pathway. The presence of reversible redox activity at a physiological potential when primase is bound to DNA and NTPs suggests that reversible redox switching from the [4Fe4S]2+ to the [4Fe4S]3+ state is important for the activity of primase during replication.
\r\n\r\nThe cluster serves as a redox switch governing DNA binding in yeast primase, just as in human primase. Mutation of tyrosines 395 and 397 in yeast primase moreover, alters the same electron transfer chemistry as the mutation of their orthologues, Y345 and Y347, respectively, alters in human primase. Although these tyrosines are arranged differently in the yeast and human proteins, they perform the same reaction to affect the switch. The single-atom Y395F mutation causes some sensitivity to chemically induced oxidative stress in yeast, and single-residue mutation Y397L confers lethality in yeast cells. A constellation of tyrosines for protein-DNA electron transfer mediates the redox switch in eukaryotic primases, regulates the affinity for RNA-primed DNA template, and is required for primase function in vivo.
\r\n\r\nWe finally characterize a novel mutation in the [4Fe4S] human base excision repair protein, MUTYH, which destabilizes the cluster environment and has pathogenic consequences. The MUTYH C306W mutation alters one of the cysteines coordinating the cluster to tryptophan. This mutation moreover is associated with hereditary colorectal cancer and causes defective DNA binding and enzymatic activity. We perform DNA electrochemistry on WT MUTYH, as well as C306W and two cancer-associated mutants, Y197C and G396D, which have an unaltered cluster environment. MUTYH variants participate in redox signaling, but C306W is destabilized upon oxidation from the [4Fe4S]2+ to the [4Fe4S]3+ state during signaling on DNA, leading to degradation to a [3Fe4S]+ cluster and loss of DNA binding and activity. A [4Fe4S] human DNA repair enzyme performs redox signaling on DNA; dysregulation of this signaling activity is linked to tumorigenesis.
\r\n" }, { "name": "Sherrott, Michelle Caroline", "degree": "PhD", "year": "2018", "title": "Active Infrared Nanophotonics in van der Waals Materials", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:01262018-171457982", "creators": [ { "name": { "family": "Sherrott", "given": "Michelle Caroline" }, "id": "Sherrott-Michelle-Caroline", "orcid": "0000-0002-7503-9714", "display_name": "Sherrott, Michelle Caroline" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "chair", "display_name": "Greer, Julia R." }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "member", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Rossman", "given": "George Robert" }, "id": "Rossman-G-R", "role": "member", "display_name": "Rossman, George Robert" }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "role": "member", "display_name": "Minnich, Austin J." } ], "option_major": [ "matsci" ], "doi": "10.7907/Z9J964M8", "abstract": "Two-dimensional van der Waals materials have recently been introduced into the field of nanophotonics, creating opportunities to explore novel physics and realize first-of-their kind devices. By reducing the thickness of these materials, novel optical properties emerge due to the introduction of vertical quantum confinement. Unlike most materials, which suffer from a reduction in quality as they are thinned, layered van der Waals materials have naturally passivated surfaces that preserve their performance in monolayer form. Moreover, because the thickness of these materials is below typical charge carrier screening lengths, it is possible to actively control their optical properties with an external gate voltage. By combining these unique properties with the subwavelength control of light-matter interactions provided by nanophotonics, new device architectures can be realized.
\r\n\r\nIn this thesis, we explore van der Waals materials for active infrared nanophotonics, focusing on monolayer graphene and few-layer black phosphorus. Chapter 2 introduces gate-tunable graphene plasmons that interact strongly with their environment and can be combined with an external cavity to reach large absorption strengths in a single atomic layer. Chapter 3 builds on this, using graphene plasmons to control the spectral character and polarization state of thermal radiation. In Chapter 4, we complete the story of actively controlling infrared light using graphene-based structures, introducing graphene into a resonant gold structure to enable active control of phase. By combining these resonant structures together into a multi-pixel array, we realize an actively tunable meta-device for active beam steering in the infrared. In Chapters 5 and 6, we present few layer black phosphorus (BP) as a novel material for active infrared nanophotonics. We study the different electro-optic effects of the material from the visible to mid-infrared. We additionally examine the polarization-dependent response of few-layer BP, observing that we can tune its optical response from being highly anisotropic to nearly isotropic in plane. Finally, Chapter 7 comments on the challenges and opportunities for graphene- and BP-integrated nanophotonic structures and devices.
" }, { "name": "Yang, Kiyoul", "degree": "PhD", "year": "2018", "title": "Integrated Ultra-High-Q Nonlinear Photonic Platform for On-Chip Optoelectronic Systems", "advisor": "Vahala, Kerry J.", "url": "https://resolver.caltech.edu/CaltechThesis:10042017-102201104", "creators": [ { "name": { "family": "Yang", "given": "Kiyoul" }, "id": "Yang-Kiyoul", "orcid": "0000-0002-0587-3201", "display_name": "Yang, Kiyoul" } ], "advisors": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "advisor", "display_name": "Vahala, Kerry J." } ], "committee": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "chair", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "member", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "role": "member", "display_name": "Emami, Azita" }, { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "role": "member", "display_name": "Hajimiri, Ali" }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "member", "display_name": "Scherer, Axel" } ], "option_major": [ "eleceng" ], "doi": "10.7907/Z96T0JTQ", "abstract": "Silicon technology provided a concrete basis of the integrated microelectronics revolution, and it might usher disruptive advances in photonics again. An integrated photonic system can potentially revolutionize instrumentation, time standards, spectroscopy, and navigation. Driven by these applications, various high-Q platforms have emerged over the last decade. However, applications require to satisfy challenging combinations of ultra-high-Q (UHQ) cavity performance, monolithic integration, and nonlinear cavity designs: the monolithic integration of UHQ devices still remains elusive. In this thesis, an integrated UHQ microcavity is demonstrated for the first time. A silicon nitride waveguide is monolithically integrated with a silicon oxide cavity, and the integrated waveguide can provide nearly universal interface to other photonic devices. Significantly, this thesis discusses far beyond setting a new record for integrated Q factor: the integrated UHQ cavity provides functionality as soliton source with electronic-repetition-rates. Demonstration of low-pump-power soliton generation at 15 GHz was previously possible in only discrete devices but essentially required for integrated self-referenced comb, which can unlock new level of performance and scale in an optoelectronic system. In addition, nonlinear cavity design is another outstanding challenge towards a further development on the optoelectronic system, and will be discussed in this thesis. The dispersion-engineered platform can potentially tailor the spectral bandwidth of frequency comb, and extend the frequency comb to visible and ultraviolet band. Importantly, the design methods are directly transferable to the integrated platform." }, { "name": "Darbe, Sunita", "degree": "PhD", "year": "2017", "title": "Optics for High-Efficiency Full Spectrum Photovoltaics", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:01032017-032640614", "creators": [ { "name": { "family": "Darbe", "given": "Sunita" }, "id": "Darbe-Sunita", "orcid": "0000-0002-8099-1814", "display_name": "Darbe, Sunita" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "chair", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "role": "member", "display_name": "Faraon, Andrei" } ], "option_major": [ "matsci" ], "doi": "10.7907/Z96W9833", "abstract": "While the price of solar energy has dropped dramatically in the last few years, costs must be further reduced to reach wide-scale adoption. One strategy to decrease cost is to increase efficiency. Photovoltaic energy conversion is most efficient for a narrow frequency range. Lack of absorption of low energy photons and thermalization of high-energy photons leads lead to a loss of over 40% of incident solar power on a silicon cell. Current-matching and lattice-matching restrictions limit the efficiency of traditional monolithic multijunction solar cells. In order to avoid these limitations and realize ultrahigh efficiency (close to 50%), this thesis explores use of optical elements to split broadband sunlight into multiple spectral bands that can each be sent to physically separated solar cells tuned to best convert that band.
\r\n\r\nDesign of a holographic diffraction grating based spectrum-splitting system resulted in a simulated module efficiency of 37%, meeting the efficiency of state-of-the-art modules. One of four holographic grating stacks is experimentally characterized. Next, a design incorporating dichroic filters, seven subcells with bandgaps spanning the solar spectrum, and concentrators with efficiency potential exceeding 45% module efficiency is presented. While prototyping this design, we also used on-going cost-modeling to ensure that our design was on-track to be a high-volume technology with low lifetime energy cost.
\r\n\r\nFinally, high-contrast gratings are used as resonant, dielectric spectrally selective mirrors in a tandem luminescent solar concentrator and as alternatives to Bragg reflectors. Gratings can have omnidirectional, high reflectivity by appropriately offsetting grating resonances in nano-patterned subwavelength thickness high-refractive index material. Subwavelength feature sizes suppress diffraction, and the high-refractive index of the grating layer leads to relatively angle-insensitive reflectance. Gratings can be fabricated by nanoimprint lithography, making them a scalable and economical option for photovoltaic applications. Simulations show hemispherically average reflectivity near 90% possible from a single subwavelength thickness layer. These properties are well suited for a variety of applications including multiple spectrum-splitting device architectures.
" }, { "name": "Kim, Seyoon", "degree": "PhD", "year": "2017", "title": "Electronically Tunable Light Modulation with Graphene and Noble Metal Plasmonics", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:02152017-220505611", "creators": [ { "name": { "family": "Kim", "given": "Seyoon" }, "id": "Kim-Seyoon", "orcid": "0000-0002-8040-9521", "display_name": "Kim, Seyoon" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "chair", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "member", "display_name": "Scherer, Axel" }, { "name": { "family": "Choo", "given": "Hyuck" }, "id": "Choo-Hyuck", "role": "member", "display_name": "Choo, Hyuck" } ], "option_major": [ "eleceng" ], "doi": "10.7907/Z9ZW1HXJ", "abstract": "Graphene is a monolayer of carbon atoms constructing a two-dimensional honeycomb structure, and it has an excellent carrier mobility and a very high thermal conductivity. Remarkably, it has been experimentally demonstrated that a monolayer graphene exhibits an exotic optical properties. To be specific, the plasmonic dispersion relation of a transverse magnetic graphene plasmon is electronically tunable by adjusting carrier density in graphene with external gate bias, and graphene plasmonic nano cavities have been utilized to modulate mid-infrared light.
\r\n\r\nIn this thesis, we present how to efficiently modulate mid-infrared light by combining graphene plasmonic ribbons with noble metal plasmonic structures.
\r\n\r\nFirst, we propose and demonstrate electronically tunable resonant perfect absorption in graphene plasmonic metasurface enhanced by noble metal plasmonic effect, which results in modulating reflecting light. In this device, we improve coupling efficiency of free-space photons into graphene plasmons by reducing wavevector mismatching with a low permittivity substrate. In addition, the graphene plasmonic resonance is significantly enhanced by plasmonic light focusing effect of the coupled subwavelength metallic slit structure, which results in strongly fortifying resonance absorption in the graphene plasmonic metasurface. In the proposed device, theoretical calculation expects that perfect absorption in the graphene plasmonic metasurface is achievable with low graphene carrier mobility. We also present an analytical model based on surface admittance in order to fully understand how this enhancement occurs.
\r\n\r\nIn the second device, we propose and demonstrate a transmission type light modulator by combining graphene plasmonic ribbons with subwavelength metal slit arrays. In this device, extraordinary optical transmission resonance is coupled to graphene plasmonic ribbons to create electrostatic modulation of mid-infrared light. Absorption in graphene plasmonic ribbons situated inside metallic slits can efficiently block the coupling channel for resonant transmission, leading to a suppression of transmission. This phenomenon is also interpreted by anti-crossing between the graphene plasmonic resonance in the ribbons and the noble metal plasmonic resonance in the subwavelength metal slit arrays.
\r\n\r\nFinally, we devise a platform to demonstrate graphene plasmonic resonance energy transport along graphene plasmonic ribbons. In this device, two metal-insulator-metal waveguides are connected by a subwavelength metal slit, and graphene plasmonic ribbons are located inside this slit. Due to the large impedance mismatch at the junction, light coupling efficiency across the junction is poor. If the graphene plasmonic ribbons are tuned to support strong graphene plasmonic resonances, the light energy can be transferred via graphene plasmons along the ribbons, and it leads to significant improvement in the light coupling efficiency across the junction. In addition to enhanced light coupling efficiency, we also present how to totally suppress the transmission by inducing a Fano resonance between a non-resonant propagation mode across the junction and a resonant graphene plasmonic transport mode, which can be utilized to efficiently modulate light in a noble metal plasmonic waveguide with the graphene plasmon resonance energy transfer.
" }, { "name": "Lei, Chan U", "degree": "PhD", "year": "2017", "title": "Circuit Cavity Electromechanics in the Quantum Regime", "advisor": "Schwab, Keith C.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10182016-152744850", "creators": [ { "name": { "family": "Lei", "given": "Chan U" }, "id": "Lei-Chan-U", "orcid": "0000-0002-2790-2421", "display_name": "Lei, Chan U" } ], "advisors": [ { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "role": "advisor", "display_name": "Schwab, Keith C." } ], "committee": [ { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "role": "chair", "display_name": "Schwab, Keith C." }, { "name": { "family": "Chen", "given": "Yanbei" }, "id": "Chen-Yanbei", "role": "member", "display_name": "Chen, Yanbei" }, { "name": { "family": "Adhikari", "given": "Rana" }, "id": "Adhikari-R", "role": "member", "display_name": "Adhikari, Rana" }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "role": "member", "display_name": "Faraon, Andrei" } ], "option_major": [ "physics" ], "doi": "10.7907/Z93T9F6W", "abstract": "Generating nonclassical states of a macroscopic mechanical object has been a subject of considerable interest. It offers a route toward fundamental test of quantum mechanics in an unexplored regime. However, a macroscopic quantum state is very susceptible to decoherence due to the environment. One way to generate robust quantum states is quantum reservoir engineering. In this work, we utilize the reservoir engineering scheme to generate a steady quantum squeezed state of a micron-scale mechanical oscillator in an electromechanical system. Together with the backaction evading measurement technique, we demonstrate a quantum nondemolition measurement of the mechanical quadratures to characterize the quantum squeezed state. By measuring the quadrature variances of the mechanical motion, more than 3dB squeezing below the zero-point level has been achieved." }, { "name": "Liontas, Rachel", "degree": "PhD", "year": "2017", "title": "Controlling Deformability in Metallic Glass Nanopillars and Nanolattices", "advisor": "Greer, Julia R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:09132016-104159178", "creators": [ { "name": { "family": "Liontas", "given": "Rachel" }, "id": "Liontas-Rachel", "orcid": "0000-0001-9925-9466", "display_name": "Liontas, Rachel" } ], "advisors": [ { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "orcid": "0000-0002-9675-1508", "role": "advisor", "display_name": "Greer, Julia R." } ], "committee": [ { "name": { "family": "Brady", "given": "John F." }, "id": "Brady-J-F", "orcid": "0000-0001-5817-9128", "role": "chair", "display_name": "Brady, John F." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "orcid": "0000-0002-9675-1508", "role": "member", "display_name": "Greer, Julia R." }, { "name": { "family": "Arnold", "given": "Frances Hamilton" }, "id": "Arnold-F-H", "orcid": "0000-0002-4027-364X", "role": "member", "display_name": "Arnold, Frances Hamilton" } ], "option_major": [ "chemeng" ], "doi": "10.7907/Z9028PHX", "abstract": "Metallic glasses offer desirable mechanical properties, including high strength, hardness, and elasticity. In bulk, they suffer from catastrophic failure upon mechanical loads. However, ductility may emerge upon (1) reducing the characteristic dimension of the metallic glass to the nanoscale or (2) irradiating the metallic glass. These two methods of controlling metallic glass deformability are investigated through a host of mechanical experiments on metallic glass nanopillars and nanolattices before and after irradiation. The mechanical experiments are conducted inside a scanning electron microscope to allow simultaneous mechanical loading and visualization of nanoscale deformation behavior.
\r\n\r\nSuch experiments reveal that helium irradiation of electrodeposited Ni73P27 metallic glass tensile nanopillars increases plasticity by a factor of two with no sacrifice in strength. Other tensile experiments on Zr-Ni-Al metallic glass nanopillars in as-sputtered and annealed states reveal substantial ductility, highly dependent upon both the nanopillar size and processing conditions. Molecular dynamics simulations, transmission electron microscopy, and synchrotron x-ray diffraction are used to explain the observed mechanical behavior through changes in free volume and short-range order.
\r\n\r\nLarger nanolattice structures are fabricated to contain hollow beams of metallic glass, with beam wall thicknesses in the nanoscale size range that may allow proliferation of the beneficial \u201csmaller is more ductile\u201d size effect observed in metallic glass nanopillars. Compression experiments on Zr-Ni-Al metallic glass nanolattices reveal enhanced deformability as the nanolattice wall thickness is reduced and upon irradiation. This work points to metallic glass nanolattices as promising candidates for radiation-intensive applications and demonstrates that by fabricating the metallic glass in a nanolattice architecture the beneficial nanoscale size effect in deformability can be preserved.
\r\n" }, { "name": "McClung, Andrew Corby", "degree": "PhD", "year": "2017", "title": "Photonic Crystal Waveguides for Integration into an Atomic Physics Experiment", "advisor": "Kimble, H. Jeff", "url": "https://resolver.caltech.edu/CaltechTHESIS:06082017-134311664", "creators": [ { "name": { "family": "McClung", "given": "Andrew Corby" }, "id": "McClung-Andrew-Corby", "orcid": "0000-0001-6995-3289", "display_name": "McClung, Andrew Corby" } ], "advisors": [ { "name": { "family": "Kimble", "given": "H. Jeff" }, "id": "Kimble-H-J", "role": "advisor", "display_name": "Kimble, H. Jeff" } ], "committee": [ { "name": { "family": "Kimble", "given": "H. Jeff" }, "id": "Kimble-H-J", "role": "chair", "display_name": "Kimble, H. Jeff" }, { "name": { "family": "Alicea", "given": "Jason F." }, "id": "Alicea-J", "orcid": "0000-0001-9979-3423", "role": "member", "display_name": "Alicea, Jason F." }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "orcid": "0000-0002-1581-9209", "role": "member", "display_name": "Painter, Oskar J." }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "orcid": "0000-0003-1783-1380", "role": "member", "display_name": "Vahala, Kerry J." } ], "option_major": [ "physics" ], "doi": "10.7907/Z9154F3G", "abstract": "Strongly interacting systems of atoms and photons are an important resource in many active areas of research, including quantum information science, quantum simulation, and metrology. Frequently, the strength of these interactions is enhanced by using an optical resonator to confine light to a small volume. In recent years, there have been efforts to replace traditional Fabry\u2013P\u00e9rot resonators, formed from macroscopic mirrors, with micro- and nano-fabricated systems, leveraging techniques and infrastructure from semiconductor manufacture to scalably produce high-quality, small mode volume waveguides and resonators. Of particular interest are nano-fabricated photonic crystals, in which very fine control over modal and dispersion properties is possible. Here I describe our efforts to reliably produce photonic crystal waveguides with guided modes designed to trap and interrogate an array of ultracold cesium atoms. Specifically, I present models capturing band placement, modal structure, finite photonic crystal effects, and waveguide input and output coupling; I discuss the techniques we use to fabricate our photonic crystal waveguides; and I describe our characterization capabilities and the packaging and installation of the waveguides into the atomic physics system.
" }, { "name": "Miyazono, Evan Tsugio", "degree": "PhD", "year": "2017", "title": "Nanophotonic Resonators for Optical Quantum Memories based on Rare-Earth-Doped Materials", "advisor": "Faraon, Andrei", "url": "https://resolver.caltech.edu/CaltechTHESIS:03152017-114949088", "creators": [ { "name": { "family": "Miyazono", "given": "Evan Tsugio" }, "id": "Miyazono-Evan-Tsugio", "orcid": "0000-0003-2176-0335", "display_name": "Miyazono, Evan Tsugio" } ], "advisors": [ { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "role": "advisor", "display_name": "Faraon, Andrei" } ], "committee": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "chair", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "role": "member", "display_name": "Schwab, Keith C." }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "member", "display_name": "Scherer, Axel" }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "role": "member", "display_name": "Faraon, Andrei" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/Z98K773F", "abstract": "The growing interest in optical quantum systems has led to the exploration of multiple platforms. Though pioneering experiments were performed in trapped atom and trapped ion systems, solid state systems show promise of being scalable and robust. Rare earth dopants in crystalline hosts are an appealing option because they possess a rich spectrum of energy levels that result from a partially filled electron orbital. While level structure varies across the period, all elements possess crystal field splittings corresponding to near infra-red or optical frequencies, as well as Zeeman and often hyperfine levels separated by radio frequency and microwave frequencies. These levels demonstrate long excited-state lifetimes and coherence times and have been used in diverse applications, including demonstrating storage of a photonic state, converting of optical to microwave photons, and manipulating a single ion as a single qubit. The ions' weak interaction with their environment results in low coupling to optical fields, which had previously required measurements with macroscopically large ensembles of ions. Coupling the ions to an optical cavity enables the use of a smaller ensemble, which is required for the development of the aforementioned technologies in an on-chip scalable architecture.
\r\n\r\nThis thesis contains recent progress towards fabricating optical micro and nanocavities coupled to ensembles of erbium ions, mainly erbium in yttrium orthosilicate. In one design, focused ion beam milling was used to create a triangular nanobeam photonic crystal cavity in a bulk erbium-doped substrate. A second design leveraged the fabrication capabilities of silicon photonics, defining amorphous silicon ring resonators using electron beam lithography and dry etching. These devices coupled evanescently to erbium ions below the ring, in the bulk substrate. Simulation, design, fabrication, and characterization of both resonators are discussed. Coupling between the ions and the resonator is demonstrated for each, and capabilities offered by these devices are described. Preliminary work implementing coherent control of erbium ions is presented. Lastly, alternative substrates are evaluated for possible future solid-state erbium systems.
" }, { "name": "Ravichandran, Navaneetha Krishnan", "degree": "PhD", "year": "2017", "title": "Theoretical and Experimental Investigation of Phonon Boundary Scattering in Thin Silicon Membranes", "advisor": "Minnich, Austin J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:01172017-145551495", "creators": [ { "name": { "family": "Ravichandran", "given": "Navaneetha Krishnan" }, "id": "Ravichandran-Navaneetha-Krishnan", "display_name": "Ravichandran, Navaneetha Krishnan" } ], "advisors": [ { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "role": "advisor", "display_name": "Minnich, Austin J." } ], "committee": [ { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "role": "chair", "display_name": "Hunt, Melany L." }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "role": "member", "display_name": "Minnich, Austin J." }, { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "role": "member", "display_name": "Blanquart, Guillaume" }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "role": "member", "display_name": "Faraon, Andrei" } ], "option_major": [ "mecheng" ], "doi": "10.7907/Z9SJ1HK2", "abstract": "The thermal transport properties of thin semiconductor membranes play an important role in the performance of many technologies like micro-electronics and solid-state energy conversion. The dominant resistance to heat flow in thin membranes is offered by the scattering of thermal phonons at the membrane boundaries. In this dissertation, we examine the nature of microscopic phonon boundary scattering processes and their effect on the thermal conductivity of the thin membranes using a pump-probe experimental technique and computationally efficient solutions of the phonon Boltzmann transport equation (BTE).
\r\n\r\nFirst, we investigate the boundary scattering-limited thermal transport in nanostructures using an efficient variance-reduced Monte Carlo (MC) solution of the BTE to elucidate the impact of specular and diffuse phonon boundary scattering events on the thermal conductivity of the nanostructures. To directly measure the relative frequency of these two boundary scattering events, called the phonon specularity parameter, we design, implement and characterize a non-contact laser-based pump-probe experiment called the transient grating (TG) to perform phonon mode-dependent measurements of the specularity parameter in suspended free-standing thin silicon membranes. We describe the phenomenon of quasiballistic heat conduction, which enables the phonon mode-dependent measurements of the specularity parameter, and derive a transfer function based on the BTE with ab-initio phonon properties as inputs, to connect the specularity parameter with the experimentally measured thermal conductivity of the thin membranes.
\r\n\r\nFinally, we present the methodology adopted to invert the BTE transfer function to extract the phonon specularity parameter from the thermal conductivity measurements in the TG experiment, while rigorously accounting for the experimental uncertainties. We find that the observed magnitudes and trends of the thermal conductivity of the thin membranes cannot be explained by the 50-year old Ziman's model for the phonon specularity parameter and the Fuchs-Sondheimer theory of phonon boundary scattering. We also find that the partially specular boundary scattering picture of phonon boundary interactions works well for one of the membranes, enabling a direct measurement of the mode-dependent phonon specularity parameter for the first time in an experiment. We discuss the possibility of phonon mode conversion at the boundaries of a few membranes for which the partially specular phonon boundary scattering picture fails to explain the observed thermal conductivity trends. Considering the importance of understanding phonon boundary scattering to engineer and improve nanoscale device performance, we expect that the new experimental and computational tools developed in this work will advance a variety of nanoscale energy applications and further our understanding of nanoscale heat transport.
" }, { "name": "Sadek, Akram Sarwat", "degree": "PhD", "year": "2017", "title": "Wireless Nano and Molecular Scale Neural Interfacing", "advisor": "Scherer, Axel", "url": "https://resolver.caltech.edu/CaltechTHESIS:12162016-094948729", "creators": [ { "name": { "family": "Sadek", "given": "Akram Sarwat" }, "id": "Sadek-Akram-Sarwat", "display_name": "Sadek, Akram Sarwat" } ], "advisors": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "advisor", "display_name": "Scherer, Axel" } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Andersen", "given": "Richard A." }, "id": "Andersen-R-A", "role": "member", "display_name": "Andersen, Richard A." }, { "name": { "family": "Choo", "given": "Hyuck" }, "id": "Choo-Hyuck", "role": "member", "display_name": "Choo, Hyuck" }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "member", "display_name": "Scherer, Axel" } ], "option_major": [ "cns" ], "doi": "10.7907/Z9RJ4GG4", "abstract": "Nanoscale circuits and sensors built from silicon nanowires, carbon nanotubes and other devices will require methods for unobtrusive interconnection with the macroscopic world to fully realise their potential; the size of conventional wires precludes their integration into dense, miniature systems. The same wiring problem presents an obstacle in our attempts to understand the brain by means of massively deployed nanodevices, for multiplexed recording and stimulation in vivo. We report on a nanoelectromechanical system that ameliorates wiring constraints, enabling highly integrated sensors to be read in parallel through a single output. Its basis is an effect in piezoelectric nanomechanical resonators that allows sensitive, linear and real-time transduction of electrical potentials. We interface multiple signals through a mechanical Fourier transform using tuneable resonators of different frequency and extract the signals from the system optically. With this method we demonstrate the direct transduction of neuronal action potentials from an extracellular microelectrode. We further extend this approach to incorporate nanophotonics for an all-optical system, coupled via a single optical fibre. Here, the mechanical resonators are both driven and probed optically, but modulated locally by the voltage sensors via the piezoelectric effect. Such piezophotonic nanoelectromechanical systems may be integrated with nanophotonic resonators, allowing concordant multiplexing in both the radiofrequency and optical bandwidths. In principle, this would allow billions of sensor channels to be multiplexed on an optical fibre. With view to eventually integrating such technology into a neural probe, we develop fabrication methods for crafting wired silicon neural probes via photolithography and electron beam lithography. Finally, to complement recording, we propose novel ideas for wireless, multiplexed neural stimulation through the use of radiofrequency-sensitive molecular scale resonators." }, { "name": "Suh, Myoung-Gyun", "degree": "PhD", "year": "2017", "title": "Nonlinear Optics in Chip-based Microresonators and their Applications", "advisor": "Vahala, Kerry J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06012017-163114372", "creators": [ { "name": { "family": "Suh", "given": "Myoung-Gyun" }, "id": "Suh-Myoung-Gyun", "orcid": "0000-0002-9527-0585", "display_name": "Suh, Myoung-Gyun" } ], "advisors": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "advisor", "display_name": "Vahala, Kerry J." } ], "committee": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "chair", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "role": "member", "display_name": "Schwab, Keith C." }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "member", "display_name": "Painter, Oskar J." }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "role": "member", "display_name": "Faraon, Andrei" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/Z92F7KG8", "abstract": "Optical micro-resonators have been studied for decades as a platform to investigate optical physics, and to miniaturize bulky optical systems. In the last decade, optical frequency combs, which have revolutionized the precision measurement of time and frequency, have been demonstrated in optical micro-resonators via the combined effect of parametric oscillation and cascaded four-wave mixing. More recently, soliton mode-locking has made possible low-noise/reproducible generation of these miniature combs (microcombs). In this thesis, we demonstrated the generation of soliton microcombs from silica wedge disk micro-resonators and the characteristics of the soliton microcombs are described. We also applied soliton microcombs to dual-comb spectroscopy and distance measurement (LIDAR) for the first time. Also, ways to improve spectral resolution, signal-to-noise ratio, and spectral coverage are discussed. In addition to soliton microcombs, a novel spiral resonator is studied as a stable optical frequency reference. Combined with a frequency comb, this new type of chip-based reference cavity is also applied to generate stable microwaves via optical frequency division. Lastly, we generated a stimulated Brillouin laser (SBL) from the optical micro-resonator and its phonon-limited linewidth is studied. Application of the SBL for rotation measurement is also demonstrated. This thesis is organized into six chapters. Throughout the thesis, the implication and potential of my PhD work toward chip-based advanced optics system are discussed.
" }, { "name": "Yu, Su-Peng", "degree": "PhD", "year": "2017", "title": "Nano-Photonic Platform for Atom-Light Interaction", "advisor": "Kimble, H. Jeff", "url": "https://resolver.caltech.edu/CaltechTHESIS:06022017-134307910", "creators": [ { "name": { "family": "Yu", "given": "Su-Peng" }, "id": "Yu-Su-Peng", "orcid": "0000-0003-1348-7447", "display_name": "Yu, Su-Peng" } ], "advisors": [ { "name": { "family": "Kimble", "given": "H. Jeff" }, "id": "Kimble-H-J", "role": "advisor", "display_name": "Kimble, H. Jeff" } ], "committee": [ { "name": { "family": "Kimble", "given": "H. Jeff" }, "id": "Kimble-H-J", "role": "chair", "display_name": "Kimble, H. Jeff" }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "orcid": "0000-0002-1581-9209", "role": "member", "display_name": "Painter, Oskar J." }, { "name": { "family": "Chen", "given": "Xie" }, "id": "Chen-Xie", "orcid": "0000-0003-2215-2497", "role": "member", "display_name": "Chen, Xie" }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "member", "display_name": "Faraon, Andrei" } ], "option_major": [ "physics" ], "doi": "10.7907/Z9668B7F", "abstract": "Development of technology can allow access to new regimes in science and creation of new fields of research. The development of ultra-high finesse mirror technology enabled the development of the field of cavity quantum electrodynamics, and an abundance of wonderful physics experiments soon followed. The sophistication of the field of nano-fabrication and nano-photonics would allow unprecedented capability to mold the shape and flow of light, and provide a novel platform for efficient and hopefully integrable quantum systems. In this project, we hope to interface cold atoms, perhaps the most quintessential of quantum systems, to the engineering power of nano-photonics. We believe this field of study will not only lead to the demonstration of new physics in the quantum regime, but work toward building a network with quantum capabilities mediated by optical channels.
\r\n\r\nIn this project, we develop a nano-fabricated platform capable of interfacing nano-photonic devices with cold Cesium atoms in free-space. Nano-photonic waveguide devices are fabricated in a Silicon Nitride device layer on Silicon substrate. The fabrication is compatible with conventional semiconductor fabrication processes, and the chip design has been adapted to allow incorporation with free-space optics to support cold Cesium atom cloud around the waveguides. An ultra-high vacuum system that is compatible to the chip and its supporting structures was constructed to perform experiments.
\r\n\r\nWith our system, we were able to fabricate and characterize nano-photonic structures, including 1D photonic crystal waveguides, cavities, and 2D photonic crystal slabs. For the 1D photonic crystal waveguide devices, enhanced atom-light coupling between localized Cesium atoms in the vicinity of the devices, and also atom-atom interaction between Cesium atoms mediated by the guided mode of the photonic crystal waveguide, has been observed. The 2D photonic devices allow us many capabilities beyond that of the 1D waveguide. Demonstration of exotic optical properties including natural decay rate suppression and circular polarization engineering, should be within reach in the near future.
" }, { "name": "Blasius, Timothy Dobson", "degree": "PhD", "year": "2016", "title": "Optomechanical Inertial Sensors and Feedback Cooling", "advisor": "Painter, Oskar J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:01122016-170853872", "creators": [ { "name": { "family": "Blasius", "given": "Timothy Dobson" }, "id": "Blasius-Timothy-Dobson", "display_name": "Blasius, Timothy Dobson" } ], "advisors": [ { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "advisor", "display_name": "Painter, Oskar J." } ], "committee": [ { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "chair", "display_name": "Painter, Oskar J." }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "role": "member", "display_name": "Faraon, Andrei" }, { "name": { "family": "Adhikari", "given": "Rana" }, "id": "Adhikari-R", "role": "member", "display_name": "Adhikari, Rana" } ], "option_major": [ "physics" ], "doi": "10.7907/Z9NK3BZS", "abstract": "The optomechanical interaction is an extremely powerful tool with which to measure mechanical motion. The displacement resolution of chip-scale optomechanical systems has been measured on the order of 1⁄10th of a proton radius. So strong is this optomechanical interaction that it has recently been used to remove almost all thermal noise from a mechanical resonator and observe its quantum ground-state of motion starting from cryogenic temperatures.
\r\n\r\nIn this work, chapter 1 describes the basic physics of the canonical optomechanical system, optical measurement techniques, and how the optomechanical interaction affects the coupled mechanical resonator. In chapter 2, we describe our techniques for realizing this canonical optomechanical system in a chip-scale form factor.
\r\n\r\nIn chapter 3, we describe an experiment where we used radiation pressure feedback to cool a mesoscopic mechanical resonator near its quantum ground-state from room-temperature. We cooled the resonator from a room temperature phonon occupation of <n> = 6.5 million to an occupation of <n> = 66, which means the resonator is in its ground state approximately 2% of the time, while being coupled to a room-temperature thermal environment. At the time of this work, this is the closest a mesoscopic mechanical resonator has been to its ground-state of motion at room temperature, and this work begins to open the door to room-temperature quantum control of mechanical objects.
\r\n\r\nChapter 4 begins with the realization that the displacement resolutions achieved by optomechanical systems can surpass those of conventional MEMS sensors by an order of magnitude or more. This provides the motivation to develop and calibrate an optomechanical accelerometer with a resolution of approximately 10 micro-g/rt-Hz over a bandwidth of approximately 30 kHz. In chapter 5, we improve upon the performance and practicality of this sensor by greatly increasing the test mass size, investigating and reducing low-frequency noise, and incorporating more robust optical coupling techniques and capacitive wavelength tuning. Finally, in chapter 6 we present our progress towards developing another optomechanical inertial sensor - a gyroscope.
\r\n" }, { "name": "Chen, Christopher Tien", "degree": "PhD", "year": "2016", "title": "Heteroepitaxy of Group IV and Group III-V semiconductor alloys for photovoltaic applications", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:11062015-161003458", "creators": [ { "name": { "family": "Chen", "given": "Christopher Tien" }, "id": "Chen-Christopher-Tien", "orcid": "0000-0001-5848-961X", "display_name": "Chen, Christopher Tien" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "chair", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." }, { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "role": "member", "display_name": "Schwab, Keith C." } ], "option_major": [ "matsci" ], "doi": "10.7907/Z9KW5CX0", "abstract": "Photovoltaic energy conversion represents a economically viable technology for realizing collection of the largest energy resource known to the Earth -- the sun. Energy conversion efficiency is the most leveraging factor in the price of energy derived from this process. This thesis focuses on two routes for high efficiency, low cost devices: first, to use Group IV semiconductor alloy wire array bottom cells and epitaxially grown Group III-V compound semiconductor alloy top cells in a tandem configuration, and second, GaP growth on planar Si for heterojunction and tandem cell applications.
\r\n\r\nMetal catalyzed vapor-liquid-solid grown microwire arrays are an intriguing alternative for wafer-free Si and SiGe materials which can be removed as flexible membranes. Selected area Cu-catalyzed vapor-liquid solid growth of SiGe microwires is achieved using chlorosilane and chlorogermane precursors. The composition can be tuned up to 12% Ge with a simultaneous decrease in the growth rate from 7 to 1 \u03bcm/min-1. Significant changes to the morphology were observed, including tapering and faceting on the sidewalls and along the lengths of the wires. Characterization of axial and radial cross sections with transmission electron microscopy revealed no evidence of defects at facet corners and edges, and the tapering is shown to be due to in-situ removal of catalyst material during growth. X-ray diffraction and transmission electron microscopy reveal a Ge-rich crystal at the tip of the wires, strongly suggesting that the Ge incorporation is limited by the crystallization rate.
\r\n\r\nTandem Ga1-xInxP/Si microwire array solar cells are a route towards a high efficiency, low cost, flexible, wafer-free solar technology. Realizing tandem Group III-V compound semiconductor/Si wire array devices requires optimization of materials growth and device performance. GaP and Ga1-xInxP layers were grown heteroepitaxially with metalorganic chemical vapor deposition on Si microwire array substrates. The layer morphology and crystalline quality have been studied with scanning electron microscopy and transmission electron microscopy, and they provide a baseline for the growth and characterization of a full device stack. Ultimately, the complexity of the substrates and the prevalence of defects resulted in material without detectable photoluminescence, unsuitable for optoelectronic applications.
\r\n\r\nCoupled full-field optical and device physics simulations of a Ga0.51In0.49P/Si wire array tandem are used to predict device performance. A 500 nm thick, highly doped \"buffer\" layer between the bottom cell and tunnel junction is assumed to harbor a high density of lattice mismatch and heteroepitaxial defects. Under simulated AM1.5G illumination, the device structure explored in this work has a simulated efficiency of 23.84% with realistic top cell SRH lifetimes and surface recombination velocities. The relative insensitivity to surface recombination is likely due to optical generation further away from the free surfaces and interfaces of the device structure.
\r\n\r\nFinally, GaP has been grown free of antiphase domains on Si (112) oriented substrates using metalorganic chemical vapor deposition. Low temperature pulsed nucleation is followed by high temperature continuous growth, yielding smooth, specular thin films. Atomic force microscopy topography mapping showed very smooth surfaces (4-6 \u00c5 RMS roughness) with small depressions in the surface. Thin films (~ 50 nm) were pseudomorphic, as confirmed by high resolution x-ray diffraction reciprocal space mapping, and 200 nm thick films showed full relaxation. Transmission electron microscopy showed no evidence of antiphase domain formation, but there is a population of microtwin and stacking fault defects.
" }, { "name": "Emmer, Hal S.", "degree": "PhD", "year": "2016", "title": "Paths Towards High Efficiency Silicon Photovoltaics", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:04102016-142401400", "creators": [ { "name": { "family": "Emmer", "given": "Hal S." }, "id": "Emmer-Hal-S", "display_name": "Emmer, Hal S." } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "chair", "display_name": "Greer, Julia R." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "role": "member", "display_name": "Schwab, Keith C." }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "member", "display_name": "Atwater, Harry Albert" } ], "option_major": [ "matsci" ], "doi": "10.7907/Z9RV0KN6", "abstract": "While photovoltaics hold much promise as a sustainable electricity source, continued cost reduction is necessary to continue the current growth in deployment. A promising path to continuing to reduce total system cost is by increasing device efficiency. This thesis explores several silicon-based photovoltaic technologies with the potential to reach high power conversion efficiencies. Silicon microwire arrays, formed by joining millions of micron diameter wires together, were developed as a low cost, low efficiency solar technology. The feasibility of transitioning this to a high efficiency technology was explored. In order to achieve high efficiency, high quality silicon material must be used. Lifetimes and diffusion lengths in these wires were measured and the action of various surface passivation treatments studied. While long lifetimes were not achieved, strong inversion at the silicon / hydrofluoric acid interface was measured, which is important for understanding a common measurement used in solar materials characterization.
\r\n\r\nCryogenic deep reactive ion etching was then explored as a method for fabricating high quality wires and improved lifetimes were measured. As another way to reach high efficiency, growth of silicon-germanium alloy wires was explored as a substrate for a III-V on Si tandem device. Patterned arrays of wires with up to 12% germanium incorporation were grown. This alloy is more closely lattice matched to GaP than silicon and allows for improvements in III-V integration on silicon.
\r\n\r\nHeterojunctions of silicon are another promising path towards achieving high efficiency devices. The GaP/Si heterointerface and properties of GaP grown on silicon were studied. Additionally, a substrate removal process was developed which allows the formation of high quality free standing GaP films and has wide applications in the field of optics.
\r\n\r\nFinally, the effect of defects at the interface of the amorphous silicon heterojuction cell was studied. Excellent voltages, and thus efficiencies, are achievable with this system, but the voltage is very sensitive to growth conditions. We directly measured lateral transport lengths at the heterointerface on the order of tens to hundreds of microns, which allows carriers to travel towards any defects that are present and recombine. This measurement adds to the understanding of these types of high efficiency devices and may aid in future device design.
\r\n" }, { "name": "Hung, Peter Shek-Ho", "degree": "PhD", "year": "2016", "title": "Advanced Applications of Nanoelectromechanical Systems", "advisor": "Roukes, Michael Lee", "url": "https://resolver.caltech.edu/CaltechTHESIS:05272016-154210811", "creators": [ { "name": { "family": "Hung", "given": "Peter Shek-Ho" }, "id": "Hung-Peter-Shek-Ho", "orcid": "0000-0002-9034-5330", "display_name": "Hung, Peter Shek-Ho" } ], "advisors": [ { "name": { "family": "Roukes", "given": "Michael Lee" }, "id": "Roukes-M-L", "role": "advisor", "display_name": "Roukes, Michael Lee" } ], "committee": [ { "name": { "family": "Roukes", "given": "Michael Lee" }, "id": "Roukes-M-L", "role": "chair", "display_name": "Roukes, Michael Lee" }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "member", "display_name": "Painter, Oskar J." }, { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "role": "member", "display_name": "Schwab, Keith C." }, { "name": { "family": "Yeh", "given": "Nai-Chang" }, "id": "Yeh-Nai-Chang", "role": "member", "display_name": "Yeh, Nai-Chang" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/Z9J38QJ3", "abstract": "Nanoelectromechanical systems (NEMS) have advanced the technologies in a wide spectrum of fields, including nonlinear dynamics, sensors for force detection, mass spectrometry, inertial imaging, calorimetry, and charge sensing. Due to their low power consumption, fast response time, large dynamic range, high quality factor, and low mass, NEMS have achieved unprecedented measurement sensitivity. For optimized system functionalization and design, precise characterization of material properties at the nanoscale is essential. In this thesis, we will discuss three applications of NEMS: mechanical switches, using anharmonic nonlinearity to measure device and material properties, and mass spectrometry and inertial imaging.
\r\n\r\nThe first application of NEMS we discuss is NEMS switches, switches with physical moving parts. Conventional electronics, based largely on silicon transistors, is reaching a physical limit in both size and power consumption. Mechanical switches provide a promising solution to surpass this limit by forcing a jump between the on and off states. Graphene, which is a single sheet of carbon atoms arranged in a hexagonal structure, has high mechanical strength and strong planar bonding, making it an ideal candidate for nanoelectromechanical switches. In addition, graphene is conductive, which decreases resistive heating at the contact area, therefore reducing bonding issues and subsequently reducing degradation. We demonstrate using exfoliated graphene to fabricate suspended graphene NEMS switches with successful switching.
\r\n\r\nThe second application of NEMS we discuss in this thesis is the use of mechanical nonlinearity to measure device and material properties. While the nonlinear dynamics of NEMS have been used previously to investigate the longitudinal speed of sound of materials at nano- and micro-scales, we correct a previously attempted method that employs the anharmonicity of NEMS arising from deflection-dependent stress to interrogate the transport of RF acoustic phonons at nanometer scales. In contrast to existing approaches, this decouples intrinsic material properties, such as longitudinal speed of sound, from properties associated with linear dynamics, such as tension, of the structure. We demonstrate this approach through measurements of the longitudinal speed of sound in several NEMS devices composed of single crystal silicon along different crystal orientations. Good agreement with literature values is reported.
\r\n\r\nThe third application of NEMS we discuss is mass spectrometry and inertial imaging. Currently, only doubly clamped beams and cantilevers have been experimentally demonstrated for mass spectrometry. We extend the one-dimension model for mass spectrometry to a novel method for inertial imaging. We further extend the theory of mass spectrometry and inertial imaging to two dimensions by using a plate geometry. We show that the mode shape is critical in performing NEMS mass spectrometry and inertial imaging, and that the mode shapes in plates deviate from the ideal scenario with isotropic stress. We experiment with various non-ideal conditions to match non-ideal mode shape observed.
" }, { "name": "Meza, Lucas Rosendo", "degree": "PhD", "year": "2016", "title": "Design, Fabrication, and Mechanical Property Analysis of 3D Nanoarchitected Materials", "advisor": "Greer, Julia R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05232016-115645913", "creators": [ { "name": { "family": "Meza", "given": "Lucas Rosendo" }, "id": "Meza-Lucas-Rosendo", "orcid": "0000-0003-0250-2621", "display_name": "Meza, Lucas Rosendo" } ], "advisors": [ { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "advisor", "display_name": "Greer, Julia R." } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "role": "member", "display_name": "Kochmann, Dennis M." }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "role": "member", "display_name": "Pellegrino, Sergio" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." } ], "option_major": [ "mecheng" ], "doi": "10.7907/Z9154F1K", "abstract": "Recent developments in micro- and nanoscale 3D fabrication techniques have enabled the creation of materials with a controllable nanoarchitecture that can have structural features spanning 5 orders of magnitude from tens of nanometers to millimeters. These fabrication methods in conjunction with nanomaterial processing techniques permit a nearly unbounded design space through which new combinations of nanomaterials and architecture can be realized. In the course of this work, we designed, fabricated, and mechanically analyzed a wide range of nanoarchitected materials in the form of nanolattices made from polymer, composite, and hollow ceramic beams. Using a combination of two-photon lithography and atomic layer deposition, we fabricated samples with periodic and hierarchical architectures spanning densities over 4 orders of magnitude from \u03c1=0.3-300kg/m3 and with features as small as 5nm. Uniaxial compression and cyclic loading tests performed on different nanolattice topologies revealed a range of novel mechanical properties: the constituent nanoceramics used here have size-enhanced strengths that approach the theoretical limit of materials strength; hollow aluminum oxide (Al2O3) nanolattices exhibited ductile-like deformation and recovered nearly completely after compression to 50% strain when their wall thicknesses were reduced below 20nm due to the activation of shell buckling; hierarchical nanolattices exhibited enhanced recoverability and a near linear scaling of strength and stiffness with relative density, with E\u221d\u03c11.04 and \u03c3y\u221d\u03c11.17 for hollow Al2O3 samples; periodic rigid and non-rigid nanolattice topologies were tested and showed a nearly uniform scaling of strength and stiffness with relative density, marking a significant deviation from traditional theories on \u201cbending\u201d and \u201cstretching\u201d dominated cellular solids; and the mechanical behavior across all topologies was highly tunable and was observed to strongly correlate with the slenderness \u03bb and the wall thickness-to-radius ratio t/a of the beams. These results demonstrate the potential of nanoarchitected materials to create new highly tunable mechanical metamaterials with previously unattainable properties." }, { "name": "Montemayor, Lauren Christine", "degree": "PhD", "year": "2016", "title": "Fabrication, Characterization, And Deformation of 3D Structural Meta-Materials ", "advisor": "Greer, Julia R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:07132015-150843708", "creators": [ { "name": { "family": "Montemayor", "given": "Lauren Christine" }, "id": "Montemayor-Lauren-Christine", "display_name": "Montemayor, Lauren Christine" } ], "advisors": [ { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "orcid": "0000-0002-9675-1508", "role": "advisor", "display_name": "Greer, Julia R." } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "orcid": "0000-0001-5877-4824", "role": "member", "display_name": "Ortiz, Michael" }, { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "orcid": "0000-0002-9112-6615", "role": "member", "display_name": "Kochmann, Dennis M." }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "orcid": "0000-0002-9675-1508", "role": "member", "display_name": "Greer, Julia R." } ], "option_major": [ "space" ], "doi": "10.7907/Z9D21VH2", "abstract": "Current technological advances in fabrication methods have provided pathways to creating architected structural meta-materials similar to those found in natural organisms that are structurally robust and lightweight, such as diatoms. Structural meta-materials are materials with mechanical properties that are determined by material properties at various length scales, which range from the material microstructure (nm) to the macro-scale architecture (\u03bcm \u2013 mm). It is now possible to exploit material size effect, which emerge at the nanometer length scale, as well as structural effects to tune the material properties and failure mechanisms of small-scale cellular solids, such as nanolattices. \r\nThis work demonstrates the fabrication and mechanical properties of 3-dimensional hollow nanolattices in both tension and compression. Hollow gold nanolattices loaded in uniaxial compression demonstrate that strength and stiffness vary as a function of geometry and tube wall thickness. Structural effects were explored by increasing the unit cell angle from 30\u00b0 to 60\u00b0 while keeping all other parameters constant; material size effects were probed by varying the tube wall thickness, t, from 200nm to 635nm, at a constant relative density and grain size. In-situ uniaxial compression experiments reveal an order-of-magnitude increase in yield stress and modulus in nanolattices with greater lattice angles, and a 150% increase in the yield strength without a concomitant change in modulus in thicker-walled nanolattices for fixed lattice angles. These results imply that independent control of structural and material size effects enables tunability of mechanical properties of 3-dimensional architected meta-materials and highlight the importance of material, geometric, and microstructural effects in small-scale mechanics. \r\nThis work also explores the flaw tolerance of 3D hollow-tube alumina kagome nanolattices with and without pre-fabricated notches, both in experiment and simulation. Experiments demonstrate that the hollow kagome nanolattices in uniaxial tension always fail at the same load when the ratio of notch length (a) to sample width (w) is no greater than 1/3, with no correlation between failure occurring at or away from the notch. For notches with (a/w) > 1/3, the samples fail at lower peak loads and this is attributed to the increased compliance as fewer unit cells span the un-notched region. Finite element simulations of the kagome tension samples show that the failure is governed by tensile loading for (a/w) < 1/3 but as (a/w) increases, bending begins to play a significant role in the failure. This work explores the flaw sensitivity of hollow alumina kagome nanolattices in tension, using experiments and simulations, and demonstrates that the discrete-continuum duality of architected structural meta-materials gives rise to their flaw insensitivity even when made entirely of intrinsically brittle materials.\r\n" }, { "name": "Rios, Gustavo", "degree": "PhD", "year": "2016", "title": "Nanofabricated Neural Probe System for Dense 3-D Recordings of Brain Activity", "advisor": "Siapas, Athanassios G.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05172016-133516099", "creators": [ { "name": { "family": "Rios", "given": "Gustavo" }, "id": "Rios-Gustavo", "orcid": "0000-0003-1411-4933", "display_name": "Rios, Gustavo" } ], "advisors": [ { "name": { "family": "Siapas", "given": "Athanassios G." }, "id": "Siapas-A-G", "role": "advisor", "display_name": "Siapas, Athanassios G." } ], "committee": [ { "name": { "family": "Dickinson", "given": "Michael H." }, "id": "Dickinson-M-H", "role": "chair", "display_name": "Dickinson, Michael H." }, { "name": { "family": "Siapas", "given": "Athanassios G." }, "id": "Siapas-A-G", "role": "member", "display_name": "Siapas, Athanassios G." }, { "name": { "family": "Elowitz", "given": "Michael B." }, "id": "Elowitz-M-B", "role": "member", "display_name": "Elowitz, Michael B." }, { "name": { "family": "Lubenov", "given": "Evgueniy V." }, "id": "Lubenov-E-V", "role": "member", "display_name": "Lubenov, Evgueniy V." } ], "option_major": [ "bioeng" ], "doi": "10.7907/Z9BG2M0B", "abstract": "Computations in brain circuits involve the coordinated activation of large populations of neurons distributed across brain areas. However, monitoring neuronal activity in the brain of intact animals with high temporal and spatial resolution has remained a technological challenge. Here we address this challenge by developing dense, three-dimensional (3-D) electrode array system for electrophysiology. The front-end of the system is composed of nanofabricated neural probes with ultrathin shanks that are engineered to minimize tissue damage. The probes are connected via flexible cables to custom PCBs that multiplex the electrophysiological signals. This system architecture decouples the front-end both mechanically and thermally from the PCB which carries all active electronics for signal conditioning and multiplexing. This system was validated in vivo with hippocampal recordings from head-fixed mice. The culmination of these efforts was a 3-D array with 1024 sites packed within 0.6 mm3 of tissue that yielded the densest electrophysiological recordings to date." }, { "name": "Aitken, Zachary Howard", "degree": "PhD", "year": "2015", "title": "Effect of Microstructural Interfaces on the Mechanical Response of Crystalline Metallic Materials", "advisor": "Greer, Julia R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:04302015-143917971", "creators": [ { "name": { "family": "Aitken", "given": "Zachary Howard" }, "id": "Aitken-Zachary-Howard", "display_name": "Aitken, Zachary Howard" } ], "advisors": [ { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "advisor", "display_name": "Greer, Julia R." } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "member", "display_name": "Goddard, William A., III" }, { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "role": "member", "display_name": "Kochmann, Dennis M." }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." } ], "option_major": [ "mecheng" ], "doi": "10.7907/Z9C24TCP", "abstract": "Advances in nano-scale mechanical testing have brought about progress in the understanding of physical phenomena in materials and a measure of control in the fabrication of novel materials. In contrast to bulk materials that display size-invariant mechanical properties, sub-micron metallic samples show a critical dependence on sample size. The strength of nano-scale single crystalline metals is well-described by a power-law function, \u03c3\u03b1D-n, where D is a critical sample size and n is a experimentally-fit positive exponent. This relationship is attributed to source-driven plasticity and demonstrates a strengthening as the decreasing sample size begins to limit the size and number of dislocation sources. A full understanding of this size-dependence is complicated by the presence of microstructural features such as interfaces that can compete with the dominant dislocation-based deformation mechanisms. In this thesis, the effects of microstructural features such as grain boundaries and anisotropic crystallinity on nano-scale metals are investigated through uniaxial compression testing. We find that nano-sized Cu covered by a hard coating displays a Bauschinger effect and the emergence of this behavior can be explained through a simple dislocation-based analytic model. Al nano-pillars containing a single vertically-oriented coincident site lattice grain boundary are found to show similar deformation to single-crystalline nano-pillars with slip traces passing through the grain boundary. With increasing tilt angle of the grain boundary from the pillar axis, we observe a transition from dislocation-dominated deformation to grain boundary sliding. Crystallites are observed to shear along the grain boundary and molecular dynamics simulations reveal a mechanism of atomic migration that accommodates boundary sliding. We conclude with an analysis of the effects of inherent crystal anisotropy and alloying on the mechanical behavior of the Mg alloy, AZ31. Through comparison to pure Mg, we show that the size effect dominates the strength of samples below 10 \u03bcm, that differences in the size effect between hexagonal slip systems is due to the inherent crystal anisotropy, suggesting that the fundamental mechanism of the size effect in these slip systems is the same." }, { "name": "Cohen, Justin Daniel", "degree": "PhD", "year": "2015", "title": "Fiber-Optic Integration and Efficient Detection Schemes for Optomechanical Resonators", "advisor": "Painter, Oskar J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:03312015-144223105", "creators": [ { "name": { "family": "Cohen", "given": "Justin Daniel" }, "id": "Cohen-Justin-Daniel", "display_name": "Cohen, Justin Daniel" } ], "advisors": [ { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "advisor", "display_name": "Painter, Oskar J." } ], "committee": [ { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "chair", "display_name": "Painter, Oskar J." }, { "name": { "family": "Roukes", "given": "Michael Lee" }, "id": "Roukes-M-L", "role": "member", "display_name": "Roukes, Michael Lee" }, { "name": { "family": "Adhikari", "given": "Rana" }, "id": "Adhikari-R", "role": "member", "display_name": "Adhikari, Rana" }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "member", "display_name": "Scherer, Axel" }, { "name": { "family": "Shaw", "given": "Matthew D." }, "id": "Shaw-M-D", "role": "member", "display_name": "Shaw, Matthew D." } ], "option_major": [ "physics" ], "doi": "10.7907/Z95D8PSH", "abstract": "With the advent of the laser in the year 1960, the field of optics experienced a renaissance from what was considered to be a dull, solved subject to an active area of development, with applications and discoveries which are yet to be exhausted 55 years later. Light is now nearly ubiquitous not only in cutting-edge research in physics, chemistry, and biology, but also in modern technology and infrastructure. One quality of light, that of the imparted radiation pressure force upon reflection from an object, has attracted intense interest from researchers seeking to precisely monitor and control the motional degrees of freedom of an object using light. These optomechanical interactions have inspired myriad proposals, ranging from quantum memories and transducers in quantum information networks to precision metrology of classical forces. Alongside advances in micro- and nano-fabrication, the burgeoning field of optomechanics has yielded a class of highly engineered systems designed to produce strong interactions between light and motion.
\r\n\r\nOptomechanical crystals are one such system in which the patterning of periodic holes in thin dielectric films traps both light and sound waves to a micro-scale volume. These devices feature strong radiation pressure coupling between high-quality optical cavity modes and internal nanomechanical resonances. Whether for applications in the quantum or classical domain, the utility of optomechanical crystals hinges on the degree to which light radiating from the device, having interacted with mechanical motion, can be collected and detected in an experimental apparatus consisting of conventional optical components such as lenses and optical fibers. While several efficient methods of optical coupling exist to meet this task, most are unsuitable for the cryogenic or vacuum integration required for many applications. The first portion of this dissertation will detail the development of robust and efficient methods of optically coupling optomechanical resonators to optical fibers, with an emphasis on fabrication processes and optical characterization.
\r\n\r\nI will then proceed to describe a few experiments enabled by the fiber couplers. The first studies the performance of an optomechanical resonator as a precise sensor for continuous position measurement. The sensitivity of the measurement, limited by the detection efficiency of intracavity photons, is compared to the standard quantum limit imposed by the quantum properties of the laser probe light. The added noise of the measurement is seen to fall within a factor of 3 of the standard quantum limit, representing an order of magnitude improvement over previous experiments utilizing optomechanical crystals, and matching the performance of similar measurements in the microwave domain.
\r\n\r\nThe next experiment uses single photon counting to detect individual phonon emission and absorption events within the nanomechanical oscillator. The scattering of laser light from mechanical motion produces correlated photon-phonon pairs, and detection of the emitted photon corresponds to an effective phonon counting scheme. In the process of scattering, the coherence properties of the mechanical oscillation are mapped onto the reflected light. Intensity interferometry of the reflected light then allows measurement of the temporal coherence of the acoustic field. These correlations are measured for a range of experimental conditions, including the optomechanical amplification of the mechanics to a self-oscillation regime, and comparisons are drawn to a laser system for phonons. Finally, prospects for using phonon counting and intensity interferometry to produce non-classical mechanical states are detailed following recent proposals in literature.
" }, { "name": "Fakonas, James Spencer", "degree": "PhD", "year": "2015", "title": "Quantum Interference and Entanglement of Surface Plasmons", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:12052014-101005469", "creators": [ { "name": { "family": "Fakonas", "given": "James Spencer" }, "id": "Fakonas-James-Spencer", "display_name": "Fakonas, James Spencer" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "chair", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "role": "member", "display_name": "Faraon, Andrei" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/Z9MG7MD3", "abstract": "Surface plasma waves arise from the collective oscillations of billions of electrons at the surface of a metal in unison. The simplest way to quantize these waves is by direct analogy to electromagnetic fields in free space, with the surface plasmon, the quantum of the surface plasma wave, playing the same role as the photon. It follows that surface plasmons should exhibit all of the same quantum phenomena that photons do, including quantum interference and entanglement.
\r\n\r\nUnlike photons, however, surface plasmons suffer strong losses that arise from the scattering of free electrons from other electrons, phonons, and surfaces. Under some circumstances, these interactions might also cause \u201cpure dephasing,\u201d which entails a loss of coherence without absorption. Quantum descriptions of plasmons usually do not account for these effects explicitly, and sometimes ignore them altogether. In light of this extra microscopic complexity, it is necessary for experiments to test quantum models of surface plasmons.
\r\n\r\nIn this thesis, I describe two such tests that my collaborators and I performed. The first was a plasmonic version of the Hong-Ou-Mandel experiment, in which we observed two-particle quantum interference between plasmons with a visibility of 93 \u00b1 1%. This measurement confirms that surface plasmons faithfully reproduce this effect with the same visibility and mutual coherence time, to within measurement error, as in the photonic case.
\r\n\r\nThe second experiment demonstrated path entanglement between surface plasmons with a visibility of 95 \u00b1 2%, confirming that a path-entangled state can indeed survive without measurable decoherence. This measurement suggests that elastic scattering mechanisms of the type that might cause pure dephasing must have been weak enough not to significantly perturb the state of the metal under the experimental conditions we investigated.
\r\n\r\nThese two experiments add quantum interference and path entanglement to a growing list of quantum phenomena that surface plasmons appear to exhibit just as clearly as photons, confirming the predictions of the simplest quantum models.
" }, { "name": "Fountaine, Katherine Theresa", "degree": "PhD", "year": "2015", "title": "Mesoscale Optoelectronic Design of Wire-Based Photovoltaic and Photoelectrochemical Devices", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:05292015-151831184", "creators": [ { "name": { "family": "Fountaine", "given": "Katherine Theresa" }, "id": "Fountaine-Katherine-Theresa", "orcid": "0000-0002-0414-8227", "display_name": "Fountaine, Katherine Theresa" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "chair", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Brady", "given": "John F." }, "id": "Brady-J-F", "role": "member", "display_name": "Brady, John F." }, { "name": { "family": "Lewerenz", "given": "Hans Joachim" }, "id": "Lewerenz-H-J", "role": "member", "display_name": "Lewerenz, Hans Joachim" }, { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "role": "member", "display_name": "Flagan, Richard C." } ], "option_major": [ "chemeng" ], "doi": "10.7907/Z9P26W1K", "abstract": "The overarching theme of this thesis is mesoscale optical and optoelectronic design of photovoltaic and photoelectrochemical devices. In a photovoltaic device, light absorption and charge carrier transport are coupled together on the mesoscale, and in a photoelectrochemical device, light absorption, charge carrier transport, catalysis, and solution species transport are all coupled together on the mesoscale. The work discussed herein demonstrates that simulation-based mesoscale optical and optoelectronic modeling can lead to detailed understanding of the operation and performance of these complex mesostructured devices, serve as a powerful tool for device optimization, and efficiently guide device design and experimental fabrication efforts. In-depth studies of two mesoscale wire-based device designs illustrate these principles\u2014(i) an optoelectronic study of a tandem Si|WO3 microwire photoelectrochemical device, and (ii) an optical study of III-V nanowire arrays.
\r\n\r\nThe study of the monolithic, tandem, Si|WO3 microwire photoelectrochemical device begins with development and validation of an optoelectronic model with experiment. This study capitalizes on synergy between experiment and simulation to demonstrate the model\u2019s predictive power for extractable device voltage and light-limited current density. The developed model is then used to understand the limiting factors of the device and optimize its optoelectronic performance. The results of this work reveal that high fidelity modeling can facilitate unequivocal identification of limiting phenomena, such as parasitic absorption via excitation of a surface plasmon-polariton mode, and quick design optimization, achieving over a 300% enhancement in optoelectronic performance over a nominal design for this device architecture, which would be time-consuming and challenging to do via experiment.
\r\n\r\nThe work on III-V nanowire arrays also starts as a collaboration of experiment and simulation aimed at gaining understanding of unprecedented, experimentally observed absorption enhancements in sparse arrays of vertically-oriented GaAs nanowires. To explain this resonant absorption in periodic arrays of high index semiconductor nanowires, a unified framework that combines a leaky waveguide theory perspective and that of photonic crystals supporting Bloch modes is developed in the context of silicon, using both analytic theory and electromagnetic simulations. This detailed theoretical understanding is then applied to a simulation-based optimization of light absorption in sparse arrays of GaAs nanowires. Near-unity absorption in sparse, 5% fill fraction arrays is demonstrated via tapering of nanowires and multiple wire radii in a single array. Finally, experimental efforts are presented towards fabrication of the optimized array geometries. A hybrid self-catalyzed and selective area MOCVD growth method is used to establish morphology control of GaP nanowire arrays. Similarly, morphology and pattern control of nanowires is demonstrated with ICP-RIE of InP. Optical characterization of the InP nanowire arrays gives proof of principle that tapering and multiple wire radii can lead to near-unity absorption in sparse arrays of InP nanowires.
" }, { "name": "Goldberg, Mark David", "degree": "PhD", "year": "2015", "title": "Development of Microfluidic Devices with the Use of Nanotechnology to Aid in the Analysis of Biological Systems Including Membrane Protein Separation, Single Cell Analysis, and Genetic Markers", "advisor": "Scherer, Axel", "url": "https://resolver.caltech.edu/CaltechTHESIS:06022015-150554177", "creators": [ { "name": { "family": "Goldberg", "given": "Mark David" }, "id": "Goldberg-Mark-David", "display_name": "Goldberg, Mark David" } ], "advisors": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "advisor", "display_name": "Scherer, Axel" } ], "committee": [ { "name": { "family": "Davidson", "given": "Eric H." }, "id": "Davidson-E-H", "role": "chair", "display_name": "Davidson, Eric H." }, { "name": { "family": "Campbell", "given": "Judith L." }, "id": "Campbell-J-L", "role": "member", "display_name": "Campbell, Judith L." }, { "name": { "family": "Elowitz", "given": "Michael B." }, "id": "Elowitz-M-B", "role": "member", "display_name": "Elowitz, Michael B." }, { "name": { "family": "Kartalov", "given": "Emil P." }, "id": "Kartalov-E-P", "role": "member", "display_name": "Kartalov, Emil P." }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "member", "display_name": "Scherer, Axel" } ], "option_major": [ "biology" ], "doi": "10.7907/Z9P848V6", "abstract": "Computation technology has dramatically changed the world around us; you can hardly find an area where cell phones have not saturated the market, yet there is a significant lack of breakthroughs in the development to integrate the computer with biological environments. This is largely the result of the incompatibility of the materials used in both environments; biological environments and experiments tend to need aqueous environments. To help aid in these development chemists, engineers, physicists and biologists have begun to develop microfluidics to help bridge this divide. Unfortunately, the microfluidic devices required large external support equipment to run the device. This thesis presents a series of several microfluidic methods that can help integrate engineering and biology by exploiting nanotechnology to help push the field of microfluidics back to its intended purpose, small integrated biological and electrical devices. I demonstrate this goal by developing different methods and devices to (1) separate membrane bound proteins with the use of microfluidics, (2) use optical technology to make fiber optic cables into protein sensors, (3) generate new fluidic devices using semiconductor material to manipulate single cells, and (4) develop a new genetic microfluidic based diagnostic assay that works with current PCR methodology to provide faster and cheaper results. All of these methods and systems can be used as components to build a self-contained biomedical device. " }, { "name": "Gu, Xun Wendy", "degree": "PhD", "year": "2015", "title": "Strength, Deformation and Fracture in Metallic Nanostructures", "advisor": "Greer, Julia R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:02242015-173330087", "creators": [ { "name": { "family": "Gu", "given": "Xun Wendy" }, "id": "Gu-Xun-Wendy", "display_name": "Gu, Xun Wendy" } ], "advisors": [ { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "advisor", "display_name": "Greer, Julia R." } ], "committee": [ { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "chair", "display_name": "Greer, Julia R." }, { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "role": "member", "display_name": "Haile, Sossina M." }, { "name": { "family": "Wang", "given": "Zhen-Gang" }, "id": "Wang-Zhen-Gang", "role": "member", "display_name": "Wang, Zhen-Gang" }, { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "role": "member", "display_name": "Kochmann, Dennis M." } ], "option_major": [ "chemeng" ], "doi": "10.7907/Z91J97NV", "abstract": "An understanding of the mechanics of nanoscale metals and semiconductors is necessary for the safe and prolonged operation of nanostructured devices from transistors to nanowire- based solar cells to miniaturized electrodes. This is a fascinating but challenging pursuit because mechanical properties that are size-invariant in conventional materials, such as strength, ductility and fracture behavior, can depend critically on sample size when materials are reduced to sub- micron dimensions. In this thesis, the effect of nanoscale sample size, microstructure and structural geometry on mechanical strength, deformation and fracture are explored for several classes of solid materials. Nanocrystalline platinum nano-cylinders with diameters of 60 nm to 1 \u03bcm and 12 nm sized grains are fabricated and tested in compression. We find that nano-sized metals containing few grains weaken as sample diameter is reduced relative to grain size due to a change from deformation governed by internal grains to surface grain governed deformation. Fracture at the nanoscale is explored by performing in-situ SEM tension tests on nanocrystalline platinum and amorphous, metallic glass nano-cylinders containing purposely introduced structural flaws. It is found that failure location, mechanism and strength are determined by the stress concentration with the highest local stress whether this is at the structural flaw or a microstructural feature. Principles of nano-mechanics are used to design and test mechanically robust hierarchical nanostructures with structural and electrochemical applications. 2-photon lithography and electroplating are used to fabricate 3D solid Cu octet meso-lattices with micron- scale features that exhibit strength higher than that of bulk Cu. An in-situ SEM lithiation stage is developed and used to simultaneously examine morphological and electrochemical changes in Si-coated Cu meso-lattices that are of interest as high energy capacity electrodes for Li-ion batteries." }, { "name": "Norte, Richard Alexander", "degree": "PhD", "year": "2015", "title": "Nanofabrication for On-Chip Optical Levitation, Atom-Trapping, and Superconducting Quantum Circuits \r ", "advisor": "Painter, Oskar J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10292014-120111728", "creators": [ { "name": { "family": "Norte", "given": "Richard Alexander" }, "id": "Norte-Richard-Alexander", "display_name": "Norte, Richard Alexander" } ], "advisors": [ { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "advisor", "display_name": "Painter, Oskar J." } ], "committee": [ { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "chair", "display_name": "Faraon, Andrei" }, { "name": { "family": "Weinstein", "given": "Alan Jay" }, "id": "Weinstein-Alan-J-Physics", "orcid": "0000-0002-0928-6784", "role": "member", "display_name": "Weinstein, Alan Jay" }, { "name": { "family": "Libbrecht", "given": "Kenneth George" }, "id": "Libbrecht-K-G", "orcid": "0000-0002-8744-3298", "role": "member", "display_name": "Libbrecht, Kenneth George" }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "orcid": "0000-0002-1581-9209", "role": "member", "display_name": "Painter, Oskar J." } ], "option_major": [ "physics" ], "doi": "10.7907/Z9WS8R61", "abstract": "Researchers have spent decades refining and improving their methods for fabricating smaller, finer-tuned, higher-quality nanoscale optical elements with the goal of making more sensitive and accurate measurements of the world around them using optics. Quantum optics has been a well-established tool of choice in making these increasingly sensitive measurements which have repeatedly pushed the limits on the accuracy of measurement set forth by quantum mechanics. A recent development in quantum optics has been a creative integration of robust, high-quality, and well-established macroscopic experimental systems with highly-engineerable on-chip nanoscale oscillators fabricated in cleanrooms. However, merging large systems with nanoscale oscillators often require them to have extremely high aspect-ratios, which make them extremely delicate and difficult to fabricate with an \"experimentally reasonable\" repeatability, yield and high quality. In this work we give an overview of our research, which focused on microscopic oscillators which are coupled with macroscopic optical cavities towards the goal of cooling them to their motional ground state in room temperature environments. The quality factor of a mechanical resonator is an important figure of merit for various sensing applications and observing quantum behavior. We demonstrated a technique for pushing the quality factor of a micromechanical resonator beyond conventional material and fabrication limits by using an optical field to stiffen and trap a particular motional mode of a nanoscale oscillator. Optical forces increase the oscillation frequency by storing most of the mechanical energy in a nearly loss-less optical potential, thereby strongly diluting the effects of material dissipation. By placing a 130 nm thick SiO2 pendulum in an optical standing wave, we achieve an increase in the pendulum center-of-mass frequency from 6.2 to 145 kHz. The corresponding quality factor increases 50-fold from its intrinsic value to a final value of Qm = 5.8(1.1) x 105, representing more than an order of magnitude improvement over the conventional limits of SiO2 for a pendulum geometry. Our technique may enable new opportunities for mechanical sensing and facilitate observations of quantum behavior in this class of mechanical systems. We then give a detailed overview of the techniques used to produce high-aspect-ratio nanostructures with applications in a wide range of quantum optics experiments. The ability to fabricate such nanodevices with high precision opens the door to a vast array of experiments which integrate macroscopic optical setups with lithographically engineered nanodevices. Coupled with atom-trapping experiments in the Kimble Lab, we use these techniques to realize a new waveguide chip designed to address ultra-cold atoms along lithographically patterned nanobeams which have large atom-photon coupling and near 4\u03c0 Steradian optical access for cooling and trapping atoms. We describe a fully integrated and scalable design where cold atoms are spatially overlapped with the nanostring cavities in order to observe a resonant optical depth of d0 \u2248 0.15. The nanodevice illuminates new possibilities for integrating atoms into photonic circuits and engineering quantum states of atoms and light on a microscopic scale. We then describe our work with superconducting microwave resonators coupled to a phononic cavity towards the goal of building an integrated device for quantum-limited microwave-to-optical wavelength conversion. We give an overview of our characterizations of several types of substrates for fabricating a low-loss high-frequency electromechanical system. We describe our electromechanical system fabricated on a Si3N4 membrane which consists of a 12 GHz superconducting LC resonator coupled capacitively to the high frequency localized modes of a phononic nanobeam. Using our suspended membrane geometry we isolate our system from substrates with significant loss tangents, drastically reducing the parasitic capacitance of our superconducting circuit to \u2248 2.5$ fF. This opens up a number of possibilities in making a new class of low-loss high-frequency electromechanics with relatively large electromechanical coupling. We present our substrate studies, fabrication methods, and device characterization." }, { "name": "Vilenchik, Yaakov", "degree": "PhD", "year": "2015", "title": "Narrow-Linewidth Si/III-V Lasers: a Study of Laser Dynamics and Nonlinear Effects", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechTHESIS:06042015-232226135", "creators": [ { "name": { "family": "Vilenchik", "given": "Yaakov" }, "id": "Vilenchik-Yaakov", "display_name": "Vilenchik, Yaakov" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "chair", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "member", "display_name": "Painter, Oskar J." }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "role": "member", "display_name": "Faraon, Andrei" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/Z9513W57", "abstract": "Narrow-linewidth lasers play an important role in a wide variety of applications, from sensing and spectroscopy to optical communication and on-chip clocks. Current narrow-linewidth systems are usually implemented in doped fibers and are big, expensive, and power-hungry. Semiconductor lasers compete favorably in size, cost, and power consumption, but their linewidth is historically limited to the sub-MHz regime. However, it has been recently demonstrated that a new design paradigm, in which the optical energy is stored away from the active region in a composite high-Q resonator, has the potential to dramatically improve the coherence of the laser.
\r\n \r\nThis work explores this design paradigm, as applied on the hybrid Si/III-V platform. It demonstrates a record sub-KHz white-noise-floor linewidth. It further shows, both theoretically and experimentally, that this strategy practically eliminates Henry\u2019s linewidth enhancement by positioning a damped relaxation resonance at frequencies as low as 70 MHz, yielding truly quantum limited devices at frequencies of interest.
\r\n\r\nIn addition to this empirical contribution, this work explores the limits of performance of this platform. Here, the effect of two-photon-absorption and free-carrier-absorption are analyzed, using modified rate equations and Langevin force approach. The analysis predicts that as the intra-cavity field intensity builds up in the high-Q resonator, non-linear effects cause a new domain of performance-limiting factors. Steady-state behavior, laser dynamics, and frequency noise performance are examined in the context of this unique platform, pointing at the importance of nonlinear effects.
\r\n\r\nThis work offers a theoretical model predicting laser performance in light of nonlinear effects, obtaining a good agreement with experimental results from fabricated high-Q Si/III-V lasers. In addition to demonstrating unprecedented semiconductor laser performance, this work establishes a first attempt to predict and demonstrate the key impact of nonlinear effects on silicon-based lasers.
" }, { "name": "Lee, Seung Ah", "degree": "PhD", "year": "2014", "title": "Bright-Field and Fluorescence Chip-Scale Microscopy for Biological Imaging", "advisor": "Yang, Changhuei", "url": "https://resolver.caltech.edu/CaltechTHESIS:02212014-174719213", "creators": [ { "name": { "family": "Lee", "given": "Seung Ah" }, "id": "Lee-Seung-Ah", "display_name": "Lee, Seung Ah" } ], "advisors": [ { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "advisor", "display_name": "Yang, Changhuei" } ], "committee": [ { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "chair", "display_name": "Yang, Changhuei" }, { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "member", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "member", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "Ismagilov", "given": "Rustem F." }, "id": "Ismagilov-R-F", "role": "member", "display_name": "Ismagilov, Rustem F." }, { "name": { "family": "Choo", "given": "Hyuck" }, "id": "Choo-Hyuck", "role": "member", "display_name": "Choo, Hyuck" } ], "option_major": [ "eleceng" ], "doi": "10.7907/HNWJ-J182", "abstract": "Optical microscopy is an essential tool in biological science and one of the gold standards for medical examinations. Miniaturization of microscopes can be a crucial stepping stone towards realizing compact, cost-effective and portable platforms for biomedical research and healthcare. This thesis reports on implementations of bright-field and fluorescence chip-scale microscopes for a variety of biological imaging applications. The term \u201cchip-scale microscopy\u201d refers to lensless imaging techniques realized in the form of mass-producible semiconductor devices, which transforms the fundamental design of optical microscopes.
\r\n\r\nOur strategy for chip-scale microscopy involves utilization of low-cost Complementary metal Oxide Semiconductor (CMOS) image sensors, computational image processing and micro-fabricated structural components. First, the sub-pixel resolving optofluidic microscope (SROFM), will be presented, which combines microfluidics and pixel super-resolution image reconstruction to perform high-throughput imaging of fluidic samples, such as blood cells. We discuss design parameters and construction of the device, as well as the resulting images and the resolution of the device, which was 0.66 \u00b5m at the highest acuity. The potential applications of SROFM for clinical diagnosis of malaria in the resource-limited settings is discussed.
\r\n\r\nNext, the implementations of ePetri, a self-imaging Petri dish platform with microscopy resolution, are presented. Here, we simply place the sample of interest on the surface of the image sensor and capture the direct shadow images under the illumination. By taking advantage of the inherent motion of the microorganisms, we achieve high resolution (~1 \u00b5m) imaging and long term culture of motile microorganisms over ultra large field-of-view (5.7 mm \u00d7 4.4 mm) in a specialized ePetri platform. We apply the pixel super-resolution reconstruction to a set of low-resolution shadow images of the microorganisms as they move across the sensing area of an image sensor chip and render an improved resolution image. We perform longitudinal study of Euglena gracilis cultured in an ePetri platform and image based analysis on the motion and morphology of the cells. The ePetri device for imaging non-motile cells are also demonstrated, by using the sweeping illumination of a light emitting diode (LED) matrix for pixel super-resolution reconstruction of sub-pixel shifted shadow images. Using this prototype device, we demonstrate the detection of waterborne parasites for the effective diagnosis of enteric parasite infection in resource-limited settings.
\r\n\r\nThen, we demonstrate the adaptation of a smartphone\u2019s camera to function as a compact lensless microscope, which uses ambient illumination as its light source and does not require the incorporation of a dedicated light source. The method is also based on the image reconstruction with sweeping illumination technique, where the sequence of images are captured while the user is manually tilting the device around any ambient light source, such as the sun or a lamp. Image acquisition and reconstruction is performed on the device using a custom-built android application, constructing a stand-alone imaging device for field applications. We discuss the construction of the device using a commercial smartphone and demonstrate the imaging capabilities of our system.
\r\n\r\nFinally, we report on the implementation of fluorescence chip-scale microscope, based on a silo-filter structure fabricated on the pixel array of a CMOS image sensor. The extruded pixel design with metal walls between neighboring pixels successfully guides fluorescence emission through the thick absorptive filter to the photodiode layer of a pixel. Our silo-filter CMOS image sensor prototype achieves 13-\u00b5m resolution for fluorescence imaging over a wide field-of-view (4.8 mm \u00d7 4.4 mm). Here, we demonstrate bright-field and fluorescence longitudinal imaging of living cells in a compact, low-cost configuration.
\r\n" }, { "name": "Lyon, Bradley Joseph", "degree": "PhD", "year": "2014", "title": "A Multi-Scale Approach to Shaping Carbon Nanotube Structures for Hollow Microneedles", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechTHESIS:05302014-012121120", "creators": [ { "name": { "family": "Lyon", "given": "Bradley Joseph" }, "id": "Lyon-Bradley-Joseph", "display_name": "Lyon, Bradley Joseph" } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "orcid": "0000-0001-8529-106X", "role": "chair", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/BJGT-TB74", "abstract": "The concept of a carbon nanotube microneedle array is explored in this thesis from multiple perspectives including microneedle fabrication, physical aspects of transdermal delivery, and in vivo transdermal drug delivery experiments. Starting with standard techniques in carbon nanotube (CNT) fabrication, including catalyst patterning and chemical vapor deposition, vertically-aligned carbon nanotubes are utilized as a scaffold to define the shape of the hollow microneedle. Passive, scalable techniques based on capillary action and unique photolithographic methods are utilized to produce a CNT-polymer composite microneedle. Specific examples of CNT-polyimide and CNT-epoxy microneedles are investigated. Further analysis of the transport properties of polymer resins reveals general requirements for applying arbitrary polymers to the fabrication process.
\r\n\r\nThe bottom-up fabrication approach embodied by vertically-aligned carbon nanotubes allows for more direct construction of complex high-aspect ratio features than standard top-down fabrication approaches, making microneedles an ideal application for CNTs. However, current vertically-aligned CNT fabrication techniques only allow for the production of extruded geometries with a constant cross-sectional area, such as cylinders. To rectify this limitation, isotropic oxygen etching is introduced as a novel fabrication technique to create true 3D CNT geometry. Oxygen etching is utilized to create a conical geometry from a cylindrical CNT structure as well as create complex shape transformations in other CNT geometries.
\r\n\r\nCNT-polymer composite microneedles are anchored onto a common polymer base less than 50 \u00b5m thick, which allows for the microneedles to be incorporated into multiple drug delivery platforms, including modified hypodermic syringes and silicone skin patches. Cylindrical microneedles are fabricated with 100 \u00b5m outer diameter and height of 200-250 \u00b5m with a central cavity, or lumen, diameter of 30 \u00b5m to facilitate liquid drug flow. In vitro delivery experiments in swine skin demonstrate the ability of the microneedles to successfully penetrate the skin and deliver aqueous solutions.
\r\n\r\nAn in vivo study was performed to assess the ability of the CNT-polymer microneedles to deliver drugs transdermally. CNT-polymer microneedles are attached to a hand actuated silicone skin patch that holds a liquid reservoir of drugs. Fentanyl, a potent analgesic, was administered to New Zealand White Rabbits through 3 routes of delivery: topical patch, CNT-polymer microneedles, and subcutaneous hypodermic injection. Results demonstrate that the CNT-polymer microneedles have a similar onset of action as the topical patch. CNT-polymer microneedles were also vetted as a painless delivery approach compared to hypodermic injection. Comparative analysis with contemporary microneedle designs demonstrates that the delivery achieved through CNT-polymer microneedles is akin to current hollow microneedle architectures. The inherent advantage of applying a bottom-up fabrication approach alongside similar delivery performance to contemporary microneedle designs demonstrates that the CNT-polymer composite microneedle is a viable architecture in the emerging field of painless transdermal delivery.
\r\n" }, { "name": "Mujeeb-U-Rahman, Muhammad", "degree": "PhD", "year": "2014", "title": "Integrated Microsystems for Wireless Sensing Applications", "advisor": "Scherer, Axel", "url": "https://resolver.caltech.edu/CaltechTHESIS:06062014-160929992", "creators": [ { "name": { "family": "Mujeeb-U-Rahman", "given": "Muhammad" }, "id": "Mujeeb-U-Rahman-Muhammad", "display_name": "Mujeeb-U-Rahman, Muhammad" } ], "advisors": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "advisor", "display_name": "Scherer, Axel" } ], "committee": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "chair", "display_name": "Scherer, Axel" }, { "name": { "family": "Fraser", "given": "Scott E." }, "id": "Fraser-S-E", "role": "member", "display_name": "Fraser, Scott E." }, { "name": { "family": "Choo", "given": "Hyuck" }, "id": "Choo-Hyuck", "role": "member", "display_name": "Choo, Hyuck" }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Weinreb", "given": "Sander" }, "id": "Weinreb-S", "role": "member", "display_name": "Weinreb, Sander" }, { "name": { "family": "Tombrello", "given": "Thomas A." }, "id": "Tombrello-T-A", "role": "member", "display_name": "Tombrello, Thomas A." } ], "option_major": [ "eleceng" ], "doi": "10.7907/Z98050MN", "abstract": "Personal health monitoring is being considered the future of a sustainable health care system. Biosensing platforms are a very important component of this system. Real-time and accurate sensing is essential for the success of personal health care model. Currently, there are many efforts going on to make these sensors practical and more useful for such measurements. Implantable sensors are considered the most widely applicable and most reliable sensors for such accurate health monitoring applications. However, macroscopic (cm scale) size has proved to be a limiting factor for successful use of these systems for long time and in large numbers. This work is focused to resolve the issues related with miniaturizing these devices to a microscopic (mm scale) size scale which can minimize many practical difficulties associated with their larger counterparts currently.
\r\n\r\nTo accomplish this goal of miniaturization while retaining or even improving on the necessary capabilities for such sensing platforms, an integrated approach is presented which focuses on system-level miniaturization using standard fabrication procedures. First, it is shown that a completely integrated and wireless system is the best solution to achieve desired miniaturization without sacrificing the functionality of the system. Hence, design and implementation of the different components comprising the complete system needs to be done according to the requirements of the overall integrated system. This leads to the need of on-chip functional sensors, integrated wireless power supply, integrated wireless communication and integrated control system for realization of such system. In this work, different options for implementation of each of these subsystems are compared and an optimal solution is presented for each subsystem. For such complex systems, it is imperative to use a standard fabrication process which can provide the required functionality for all subsystems at smallest possible size scale. Complementary Metal Oxide Semiconductor (CMOS) process is the most appropriate of the technologies in this regard and has enabled incredible miniaturization of the computing industry. It also provides options for designing different subsystems on the same platform in a monolithic process with very high yield. This choice then leads to actual designs of subsystems in the CMOS technology using different possible methods. Careful comparison of these subsystems provides insights into different design adjustments that are made until the desired functions are achieved at the desired size scale. Integration of all these compatible subsystems in the same platform is shown to provide the smallest possible sensing platform to date.
\r\n\r\nThe completely wireless system can measure a host of different important analyte and can transmit the data to an external device which can use it for appropriate purpose. Results on measurements in phosphate buffer solution, blood serum and whole blood along with wireless communication in real biological tissues are provided. Specific examples of glucose and DNA sensors are presented and the use for many other relevant applications is also proposed. Finally, insights into animal model studies and future directions of the research are discussed.
\r\n" }, { "name": "Su, Tsu-Te Judith", "degree": "PhD", "year": "2014", "title": "Label-Free Detection of Single Molecule Using Microtoroid Optical Resonators", "advisor": "Rees, Douglas C.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05302014-140200007", "creators": [ { "name": { "family": "Su", "given": "Tsu-Te Judith" }, "id": "Su-Tsu-Te-Judith", "display_name": "Su, Tsu-Te Judith" } ], "advisors": [ { "name": { "family": "Rees", "given": "Douglas C." }, "id": "Rees-D-C", "orcid": "0000-0003-4073-1185", "role": "advisor", "display_name": "Rees, Douglas C." } ], "committee": [ { "name": { "family": "Rees", "given": "Douglas C." }, "id": "Rees-D-C", "orcid": "0000-0003-4073-1185", "role": "chair", "display_name": "Rees, Douglas C." }, { "name": { "family": "Phillips", "given": "Robert B." }, "id": "Phillips-R", "orcid": "0000-0003-3082-2809", "role": "member", "display_name": "Phillips, Robert B." }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "orcid": "0000-0003-1783-1380", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Davis", "given": "Mark E." }, "id": "Davis-M-E", "orcid": "0000-0001-8294-1477", "role": "member", "display_name": "Davis, Mark E." }, { "name": { "family": "Bjorkman", "given": "Pamela J." }, "id": "Bjorkman-P-J", "orcid": "0000-0002-2277-3990", "role": "member", "display_name": "Bjorkman, Pamela J." } ], "option_major": [ "biochem" ], "doi": "10.7907/EHWP-DH17", "abstract": "Being able to detect a single molecule without the use of labels has been a long standing goal of bioengineers and physicists. This would simplify applications ranging from single molecular binding studies to those involving public health and security, improved drug screening, medical diagnostics, and genome sequencing. One promising technique that has the potential to detect single molecules is the microtoroid optical resonator. The main obstacle to detecting single molecules, however, is decreasing the noise level of the measurements such that a single molecule can be distinguished from background. We have used laser frequency locking in combination with balanced detection and data processing techniques to reduce the noise level of these devices and report the detection of a wide range of nanoscale objects ranging from nanoparticles with radii from 100 to 2.5 nm, to exosomes, ribosomes, and single protein molecules (mouse immunoglobulin G and human interleukin-2). We further extend the exosome results towards creating a non-invasive tumor biopsy assay. Our results, covering several orders of magnitude of particle radius (100 nm to 2 nm), agree with the 'reactive' model prediction for the frequency shift of the resonator upon particle binding. In addition, we demonstrate that molecular weight may be estimated from the frequency shift through a simple formula, thus providing a basis for an ``optical mass spectrometer'' in solution. We anticipate that our results will enable many applications, including more sensitive medical diagnostics and fundamental studies of single receptor-ligand and protein-protein interactions in real time. The thesis summarizes what we have achieved thus far and shows that the goal of detecting a single molecule without the use of labels can now be realized." }, { "name": "Kelber, Scott Ian", "degree": "PhD", "year": "2013", "title": "Single Particle Mass Spectrometry and Inertial Imaging with Nanomechanical Systems", "advisor": "Roukes, Michael Lee", "url": "https://resolver.caltech.edu/CaltechTHESIS:06122013-133415217", "creators": [ { "name": { "family": "Kelber", "given": "Scott Ian" }, "id": "Kelber-Scott-Ian", "display_name": "Kelber, Scott Ian" } ], "advisors": [ { "name": { "family": "Roukes", "given": "Michael Lee" }, "id": "Roukes-M-L", "orcid": "0000-0002-2916-6026", "role": "advisor", "display_name": "Roukes, Michael Lee" } ], "committee": [ { "name": { "family": "Roukes", "given": "Michael Lee" }, "id": "Roukes-M-L", "orcid": "0000-0002-2916-6026", "role": "chair", "display_name": "Roukes, Michael Lee" }, { "name": { "family": "Beauchamp", "given": "Jesse L." }, "id": "Beauchamp-J-L", "orcid": "0000-0001-8839-4822", "role": "member", "display_name": "Beauchamp, Jesse L." }, { "name": { "family": "Phillips", "given": "Robert B." }, "id": "Phillips-R", "orcid": "0000-0003-3082-2809", "role": "member", "display_name": "Phillips, Robert B." }, { "name": { "family": "Cross", "given": "Michael Clifford" }, "id": "Cross-M-C", "role": "member", "display_name": "Cross, Michael Clifford" } ], "option_major": [ "physics" ], "doi": "10.7907/Z9PN93MP", "abstract": "This thesis work describes the development of a new technology for mass spectrometry using nanoelectromechanical systems (NEMS-MS). Mass spectrometry is a technique used to identify molecules through mass measurement. Nanoelectromechanical systems (NEMS) feature low cost, scalable on-chip compatibility, and are highly sensitivity to the mass of accreted species. Using NEMS devices, we perform NEMS-MS where the inertial mass of individual molecules is directly measured. This contrasts with traditional MS techniques utilizing electromagnetic fields to measure the average mass-to-charge ratio of many molecules.
\r\n\r\nInitially, an ultra-high-vacuum apparatus is constructed to perform NEMS-MS using laser desorption techniques for molecule delivery. An existing technique, matrix assisted laser desorption ionization (MALDI), is implemented without the usual ion optics system in order to permit detection of neutral and ionized particles. This, however, is found to be incompatible with NEMS-MS due to the matrix background.\r\nThe MALDI-NEMS-MS system is then used to measure gold nanoparticles that simultaneously act as the matrix and analyte. These experiments are combined with measurements of IgM antibodies using an ESI (electrospray ionization)-NEMS-MS system to demonstrate single-particle nanomechanical mass spectrometry in real time.
\r\n\r\nThen, the laser desorption-based NEMS-MS system is upgraded to implement laser induced acoustic desorption (LIAD) for particle delivery. LIAD is a matrix-free technique in the mass spectrometry community for desorbing nonvolatile, thermally labile molecules. The LIAD-NEMS-MS system is used for the direct mass measurement of several different types of proteins and protein-complexes with single-protein quantification. Additionally, experimental data is presented that suggests the movement of surface-adsorbed particles along the device surface due to the vibration of the resonant device modes; this remains to be confirmed.
\r\n\r\nFinally, a new methodology, inertial imaging theory, is presented, which enables measurement of the mass and shape of adsorbed particles on a NEMS device. The shifts induced by particle adsorption in the modal frequencies of a resonant device are used to calculate the spatial moments of mass distribution of individual adsorbates, one-by-one, as they adsorb It is shown that the ultimate resolution in particle size of this technique is limited only by fundamental noise processes in the device and not wavelength-dependent diffraction effects. Indeed, atomic resolution is possible using existing NEMS devices.
\r\n" }, { "name": "Levine, Joseph H.", "degree": "PhD", "year": "2012", "title": "Genetic Regulatory Circuit Dynamics: Analysis and Synthesis", "advisor": "Elowitz, Michael B.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06052012-121432503", "creators": [ { "name": { "family": "Levine", "given": "Joseph H." }, "id": "Levine-Joseph-H", "display_name": "Levine, Joseph H." } ], "advisors": [ { "name": { "family": "Elowitz", "given": "Michael B." }, "id": "Elowitz-M-B", "orcid": "0000-0002-1221-0967", "role": "advisor", "display_name": "Elowitz, Michael B." } ], "committee": [ { "name": { "family": "Winfree", "given": "Erik" }, "id": "Winfree-E", "orcid": "0000-0002-5899-7523", "role": "chair", "display_name": "Winfree, Erik" }, { "name": { "family": "Elowitz", "given": "Michael B." }, "id": "Elowitz-M-B", "orcid": "0000-0002-1221-0967", "role": "member", "display_name": "Elowitz, Michael B." }, { "name": { "family": "Fraser", "given": "Scott E." }, "id": "Fraser-S-E", "orcid": "0000-0002-5377-0223", "role": "member", "display_name": "Fraser, Scott E." }, { "name": { "family": "Phillips", "given": "Robert B." }, "id": "Phillips-R", "orcid": "0000-0003-3082-2809", "role": "member", "display_name": "Phillips, Robert B." } ], "option_major": [ "cns" ], "doi": "10.7907/35A7-K421", "abstract": "How can cells shape and utilize dynamic gene regulation to enable complex cellular behaviors? I study this question in natural and synthetic contexts.
\r\n\r\nThe first project studies how a natural genetic network can imbue cells with a sense of \u2018time\u2019. It has long been known that environmental signals induce diverse cellular differentiation programs. In certain systems, cells defer differentiation for extended time periods after the signal appears, proliferating through multiple rounds of cell division before committing to a new fate. How can cells set a deferral time much longer than the cell cycle? Here we study Bacillus subtilis cells that respond to sudden nutrient limitation with multiple rounds of growth and division before differentiating into spores. A well characterized genetic circuit controls the concentration and phosphorylation of the master regulator Spo0A, which rises to a critical concentration to initiate sporulation. However, it remains unclear how this circuit enables cells to defer sporulation for multiple cell cycles. Using quantitative time-lapse fluorescence microscopy of Spo0A dynamics in individual cells, we observed pulses of Spo0A phosphorylation at a characteristic cell cycle phase. Pulse amplitudes grew systematically and cell-autonomously over multiple cell cycles leading up to sporulation. This pulse growth required a key positive feedback loop involving the sporulation kinases, without which the deferral of sporulation became ultrasensitive to kinase expression. Thus, deferral is controlled by a pulsed positive feedback loop in which kinase expression is activated by pulses of Spo0A phosphorylation. This pulsed positive feedback architecture provides a more robust mechanism for setting deferral times than constitutive kinase expression. Finally, using mathematical modeling, we show how pulsing and time delays together enable \u2018polyphasic\u2019 positive feedback, in which different parts of a feedback loop are active at different times. Polyphasic feedback can enable more accurate tuning of long deferral times. Together, these results suggest that Bacillus subtilis uses a pulsed positive feedback loop to implement a timer that operates over time scales much longer than a cell cycle.
\r\n\r\nThe second project proposes a method to rapidly generate and test complex genetic network dynamics in living cells. Existing microorganisms have evolved genetic circuitry to meet diverse challenges and maximize their survival and fitness. These challenges arise from external environmental pressures, or internal evolved constraints. Furthermore, these challenges may be either static or dynamic in nature. While existing circuits have likely evolved to be \u2018good enough\u2019 to respond to historical challenges, it remains unclear if they can be improved upon, and whether they respond well to novel situations. Synthetic biology seeks to engineer organisms with complex novel phenotypes, both to harness these novel organisms for a function and to understand their underlying biology. Dynamic gene expression strategies may be necessary to successfully generate these phenotypes. Unfortunately, generating novel dynamic gene expression patterns with conventional genetic engineering remains a challenge. Here I propose and describe progress towards a computerized feedback control setup to enable the programming and rapid testing of dynamic gene regulatory patterns in living cells. Small sets of genes will be regulated optogenetically based on programmed control laws, and past and present cellular state. This setup will enable us to explore the functions and limits of engineered dynamic gene regulation, while hopefully, in the process, providing lessons about the underlying biology.
" }, { "name": "Briggs, Ryan Morrow", "degree": "PhD", "year": "2011", "title": "Hybrid Silicon Nanophotonic Devices: Enhancing Light Emission, Modulation, and Confinement", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:05312011-175622776", "creators": [ { "name": { "family": "Briggs", "given": "Ryan Morrow" }, "id": "Briggs-Ryan-Morrow", "display_name": "Briggs, Ryan Morrow" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "chair", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "member", "display_name": "Painter, Oskar J." }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" } ], "option_major": [ "matsci" ], "doi": "10.7907/G19Z-CY24", "abstract": "Silicon has become an increasingly important photonic material for communications, information processing, and sensing applications. Silicon is inexpensive compared to compound semiconductors, and it is well suited for confining and guiding light at standard telecommunication wavelengths due to its large refractive index and minimal intrinsic absorption. Furthermore, silicon-based optical devices can be fabricated alongside microelectronics while taking advantage of advanced silicon processing technologies. In order to realize complete chip-based photonic systems, certain critical components must continue to be developed and refined on the silicon platform, including compact light sources, modulators, routers, and sensing elements. However, bulk silicon is not necessarily an ideal material for many active devices because of its meager light emission characteristics, limited refractive index tunability, and fundamental limitations in confining light beyond the diffraction limit.
\r\n\r\nIn this thesis, we present three examples of hybrid devices that use different materials to bring additional optical functionality to silicon photonics. First, we analyze high-index-contrast silicon slot waveguides and their integration with light-emitting erbium-doped glass materials. Theoretical and experimental results show significant enhancement of spontaneous emission rates in slot structures. We then demonstrate the integration of vanadium dioxide, a thermochromic phase-change material, with silicon waveguides to form micron-scale absorption modulators. It is shown experimentally that a 2-\u00b5m long waveguide-integrated device exhibits broadband modulation of more than 6.5 dB at wavelengths near 1550 nm. Finally, we demonstrate polymer-on-gold dielectric-loaded surface-plasmon waveguides and ring resonators coupled to silicon waveguides with 1.0\u00b10.1 dB insertion loss. The plasmonic waveguides are shown to support a single surface mode at telecommunication wavelengths, with strong electromagnetic field confinement at the polymer-gold interface. These three device concepts show that diverse materials can be integrated with silicon waveguides to achieve enhanced light emission, broadband modulation, and strong confinement, all while retaining the advantages of the silicon photonics platform.
" }, { "name": "Cao, Peigen", "degree": "PhD", "year": "2011", "title": "Surface Chemistry at the Nanometer Scale", "advisor": "Heath, James R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05252011-091250250", "creators": [ { "name": { "family": "Cao", "given": "Peigen" }, "id": "Cao-Peigen", "display_name": "Cao, Peigen" } ], "advisors": [ { "name": { "family": "Heath", "given": "James R." }, "id": "Heath-J-R", "role": "advisor", "display_name": "Heath, James R." } ], "committee": [ { "name": { "family": "Weitekamp", "given": "Daniel P." }, "id": "Weitekamp-D-P", "role": "chair", "display_name": "Weitekamp, Daniel P." }, { "name": { "family": "Heath", "given": "James R." }, "id": "Heath-J-R", "role": "member", "display_name": "Heath, James R." }, { "name": { "family": "Kuppermann", "given": "Aron" }, "id": "Kuppermann-A", "role": "member", "display_name": "Kuppermann, Aron" }, { "name": { "family": "Lewis", "given": "Nathan Saul" }, "id": "Lewis-N-S", "role": "member", "display_name": "Lewis, Nathan Saul" } ], "option_major": [ "chemistry" ], "doi": "10.7907/7EFV-V231", "abstract": "This thesis describes research towards understanding surface chemical and physical processes, as well as their effects on the underlying substrate properties, at the nanometer and atomic scales. We demonstrate a method to tune the density of etch pits on Si(111) during the chlorination process so as to change the surface reactivity. Subsequent grafting of an azide group to replace chlorine demonstrates an example of non-oxidative passivation of silicon surfaces with new functionalities. Depending upon the solvent used in the azidation process, it is shown to yield different azidation kinetic rates, different final azide coverages, and different surface-area distributions. Scanning tunneling spectroscopy studies show that both chlorination and azidation processes significantly modify the surface electronic structures, with the former leading to a non-zero density of states at the Fermi level.\r\n
\r\nOur studies on a new class of corrugation, i.e., wrinkles, in exfoliated graphene on SiO2 show that a \"three-for-six\" triangular pattern of atoms is exclusively and consistently observed on wrinkles, suggesting the local curvature of the wrinkle is a perturbation that breaks the six-fold symmetry of the graphene lattice. Lower electrical conductance is also found on the top of wrinkles compared to other regions of graphene. The wrinkles are characterized by the presence of midgap states, which is in agreement with recent theoretical predictions. A general method is also reported for reliably fabricating ultrahigh-density graphene nanoribbon (GNR) arrays. We have clearly observed how the properties of GNRs evolve as a function of number of graphene layers. The band gap (and so the on-off ratio) decreases as the number of layers increases. These results suggest that, in addition to single layer graphene, properties of GNRs of different thicknesses can also be harnessed for engineering GNRs as different building blocks towards FET applications.\r\n
\r\nA novel imaging technique, graphene-templated scanning probe microscopy, has been developed and applied for the study on the condensation process of water and small organic molecules on mica. We found that these molecular adlayers grow epitaxially on the mica substrate in a layer-by-layer fashion. In particular, submonolayers of water form atomically flat, faceted islands of height 0.37 plus or minus 0.02 nm, in agreement with the height of a monolayer of ice. The second adlayers also appear ice-like, and thicker layers appear liquid-like. This general mechanism, however, is not universal. Exclusively three-dimensional droplets of water are observed on chemically modified (hydrophobic) mica surfaces, suggesting a 3D growth mechanism.\r\n
\r\nThis thesis also includes my work on the design of a quartz-tuning-fork-based force sensor and related electronics for applications on low-temperature atomic force microscopy. Results show that the force-sensor-global-feedback circuit detector system induced lowest noise floor. The high detection sensitivity of this system demonstrates its ability to be used in frequency-modulated AFM at cryogenic temperatures. Surface topographic imaging of H-terminated Si(111) has been achieved at low temperatures.\r\n
" }, { "name": "Walavalkar, Sameer Sudhir", "degree": "PhD", "year": "2011", "title": "Optical, Mechanical, and Electronic Properties of Etched Silicon Nanopillars ", "advisor": "Scherer, Axel", "url": "https://resolver.caltech.edu/CaltechTHESIS:05162011-142708481", "creators": [ { "name": { "family": "Walavalkar", "given": "Sameer Sudhir" }, "id": "Walavalkar-Sameer-Sudhir", "display_name": "Walavalkar, Sameer Sudhir" } ], "advisors": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "advisor", "display_name": "Scherer, Axel" } ], "committee": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "chair", "display_name": "Scherer, Axel" }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" }, { "name": { "family": "Wong", "given": "Joyce Y." }, "id": "Wong-J-Y", "role": "member", "display_name": "Wong, Joyce Y." }, { "name": { "family": "Tombrello", "given": "Thomas A." }, "id": "Tombrello-T-A", "role": "member", "display_name": "Tombrello, Thomas A." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/QCW6-0C39", "abstract": "This work focuses on the fabrication, characterization and applications of silicon nanopillars. We explain the techniques involved in creating sub 50 nm diameter pillars with aspect ratios of 60:1. Original work encompassed the use of a novel etch mask made of reactive ion sputtered aluminum oxide, 'pseudo-Bosch' inductively coupled reactive ion etching (ICP-RIE) to etch structures on the nanoscale. These methods demonstrate a unique approach to the largely 'bottom-up' technology used in nanowire fabrication.
\r\n\t\t\r\nWe also explored the self-terminating oxidation behavior of convex, two-dimension silicon structures. It was found that during the oxidation process, strain built up at the moving Si-SiO2 interface eventually led to a cessation of oxidation. This was used to predictably reduce the diameter of these pillars to 2 nm, making 'nanowhiskers.' We were able to characterize the results of this oxidation non-destructively by utilizing reflection mode transmission electron microscopy (R-TEM).
\r\n\t \t\t\r\nUsing spun-on PMMA and an electron beam to constrict it and bend the pillars, we were able to incorporate as much as 25% strain. More interestingly this deformation appeared to be elastic, as the pillars, once freed from the polymer, would snap back to their upright position.
\r\n\t\t\t\t\r\nA consequence of the creation of silicon nanowhiskers was that silicon, a normally poor light emitter due to its indirect bandgap, became photoluminescent. As we reduced the diameter we noticed that the bandgap became direct and the emission peak was blue-shifted. We were able to utilize a tight-binding model (TBM) that was modified by the oxidation induced strain. This modified model predicted the blue-shift in peak emission wavelength with decreasing pillar diameter. The strain induced in the pillar during the oxidation played a significant role in the peak emission wavelength and shape of the bandstructure. By corrugating the pillars with an oscillating etch technique we were able to turn our nanopillars into quantum dots which also proved to photoluminesce.
\r\n\t\r\nFinally we look at the possibilities of creating a silicon light emitting diode. By creating a double-gated structure it is possible to overcome the difficulties encountered with sub 5 nm diameter pillars. A possible fabrication process, and the current work done to implement it, is presented as well as a simulation explaining the behavior of this device in the future.
" }, { "name": "Axelrod, Blake Waters", "degree": "PhD", "year": "2009", "title": "Single Cell Pico Force Microscopy: A Novel Tool for High Resolution Measurement of Cell Forces", "advisor": "Roukes, Michael Lee", "url": "https://resolver.caltech.edu/CaltechETD:etd-04082009-102110", "creators": [ { "name": { "family": "Axelrod", "given": "Blake Waters" }, "id": "Axelrod-Blake-Waters", "display_name": "Axelrod, Blake Waters" } ], "advisors": [ { "name": { "family": "Roukes", "given": "Michael Lee" }, "id": "Roukes-M-L", "orcid": "0000-0002-2916-6026", "role": "advisor", "display_name": "Roukes, Michael Lee" } ], "committee": [ { "name": { "family": "Phillips", "given": "Robert B." }, "id": "Phillips-R", "orcid": "0000-0003-3082-2809", "role": "chair", "display_name": "Phillips, Robert B." }, { "name": { "family": "Elowitz", "given": "Michael B." }, "id": "Elowitz-M-B", "orcid": "0000-0002-1221-0967", "role": "member", "display_name": "Elowitz, Michael B." }, { "name": { "family": "Roukes", "given": "Michael Lee" }, "id": "Roukes-M-L", "orcid": "0000-0002-2916-6026", "role": "member", "display_name": "Roukes, Michael Lee" }, { "name": { "family": "Fraser", "given": "Scott E." }, "id": "Fraser-S-E", "orcid": "0000-0002-5377-0223", "role": "member", "display_name": "Fraser, Scott E." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/ESGS-Z942", "abstract": "Nearly all eukaryotic cells exert forces on their surroundings to generate and maintain tension within their cytoskeleton which is critical for normal cell function. In addition, cells exert forces on their surroundings to orient themselves within an organism, thus gaining information that influences cell fate and behavior, a process called mechanotransduction. In order to study mechanotransduction, a tool is needed that can observe the molecular level sensing events that trigger a decision by a cell as well as the ultimate response that occurs on the whole cell level. There are a number of optical techniques that are used to measure forces from adherent cells at the single cell level; some are good for measuring whole cell forces and some for measuring single molecule level forces, but none have the dynamic range necessary to span both regimes, which is critical for understanding mechanotransduction. To address this need, I have developed a Nano-ElectroMechanical Systems (NEMS) based tool, Single-Cell-Pico-Force-Microscopy (SCPFM), that measures forces exerted by adherent cells with macro-molecular level force sensitivity and sufficient dynamic range to monitor whole cell responses to stimuli with macro-molecular resolution. I have used SCPFM to measure force versus time data from a NIH-3T3 fibroblast as it is perturbed with Cytochalasin D (CD) and allowed to recover in growth media. Within the data there are three excellent examples of previously inaccessible molecular-mechanical processes that illustrate the immense potential of SCPFM to significantly enhance resolution of cell biology at the single cell level: 1) an initial contraction upon exposure to CD followed by the expected force drop, 2) small force oscillations, roughly 400pN peak-to-peak, with frequency that is monotonically dependent on the force being exerted by the lamellipodia, and 3) large, stable, quantized force steps of order 1nN are manifested when a cell\u2019s cytoskeleton is perturbed with CD and allowed to recover in growth media. I propose two complimentary experimental efforts to undertake: a systematic effort to build a library of molecular-mechanical force signatures of various common cytoskeleton reactions and an effort to stimulate and observe compliance sensing and response in adherent cells.\r\n" }, { "name": "Beyer, Andrew David", "degree": "PhD", "year": "2009", "title": "Studies of the Low-Energy Quasiparticle Excitations in High-Temperature Superconducting Cuprates with Scanning Tunneling Spectroscopy and Magnetization Measurements", "advisor": "Yeh, Nai-Chang", "url": "https://resolver.caltech.edu/CaltechETD:etd-06082009-200539", "creators": [ { "name": { "family": "Beyer", "given": "Andrew David" }, "id": "Beyer-Andrew-David", "display_name": "Beyer, Andrew David" } ], "advisors": [ { "name": { "family": "Yeh", "given": "Nai-Chang" }, "id": "Yeh-Nai-Chang", "role": "advisor", "display_name": "Yeh, Nai-Chang" } ], "committee": [ { "name": { "family": "Yeh", "given": "Nai-Chang" }, "id": "Yeh-Nai-Chang", "role": "chair", "display_name": "Yeh, Nai-Chang" }, { "name": { "family": "Kitaev", "given": "Alexei" }, "id": "Kitaev-A", "role": "member", "display_name": "Kitaev, Alexei" }, { "name": { "family": "Eisenstein", "given": "James P." }, "id": "Eisenstein-J-P", "role": "member", "display_name": "Eisenstein, James P." }, { "name": { "family": "Zmuidzinas", "given": "Jonas" }, "id": "Zmuidzinas-J", "role": "member", "display_name": "Zmuidzinas, Jonas" } ], "option_major": [ "physics" ], "doi": "10.7907/MM6C-AS16", "abstract": "This thesis details the investigation of the unconventional low-energy quasiparticle excitations in both hole-and electron-type cuprate superconductors through experimental studies and theoretical modeling. The experimental studies include spatially resolved scanning tunneling spectroscopy (STS) experiments and bulk magnetization measurements, and the theoretical modeling involves developing a phenomenology that incorporates coexisting competing orders and superconductivity in the ground state of the cuprates.
\r\n\r\nMagnetic field and temperature dependent evolution of the spatially resolved quasiparticle excitation spectra in the electron-type cuprate La0.1Sr0.9CuO2 (La-112), the simplest structured cuprate superconductor with TC = 43 K, are investigated experimentally for the first time. For temperature (T) less than the superconducting transition temperature (TC), and in zero field, the quasiparticle spectra of La-112 exhibits gapped behavior with two coherence peaks and no satellite features. For magnetic field measurements at T << TC, vortices are observed in La-112, which is the first direct observation of vortices among electron-type cuprate superconductors. Moreover, pseudogap-like spectra are revealed inside the core of vortices, where superconductivity is suppressed. The intra-vortex pseudogap-like spectra are characterized by an energy gap of VPG=(8.5\u00b10.6)meV, while the inter-vortex quasiparticle spectra show larger peak-to-peak gap values characterized by \u0394pk-pk(H) \u2265 VPG, and \u0394pk-pk(0)=(12.2\u00b10.8)meV \u2265\u0394pk-pk(H>0). The quasiparticle spectra are found to be gapped at all locations up to the highest magnetic field examined (H = 6T) and reveal an apparent low-energy cutoff at the VPG energy scale. This finding is in stark contrast to the vortex-state quasiparticle spectra in conventional superconductors, where the intra-vortex spectra near vortex cores exhibit a sharp zero-bias conductance peak due to the complete suppression of superconductivity and the presence of continuous bound quasiparticle states. The lack of a zero-bias peak and the observation of pseudogap-like spectra in the intra-vortex quasiparticle spectra of La-112 suggest that superconductivity alone cannot describe the STS results.
\r\n\r\nSimilar studies of the magnetic field and temperature dependent evolution of the spatially resolved quasiparticle excitation spectra in the hole-type cuprate YBa2Cu3O7-\u03b4 (Y-123) have also been carried out. The quasiparticle spectra for T << TC(~93 K) show satellite features at an energy higher than the superconducting gap, and the superconducting gap is found to be associated with a set of coherence peaks for H = 0. The coherence peaks are homogeneous, with a energy gap given by \u0394SC=(20\u00b11)meV, and may be attributed to superconductivity. The satellite features are less homogeneous, with a effective gap energy \u0394eff=(37.8\u00b12.0)meV. The application of magnetic fields reveal vortices in Y-123, and the intra-vortex quasiparticle spectra show two energy gaps, with one gap at the pseudogap energy scale VPG~32meV and the other gap at the subgap energy scale \u0394' ~ 7-12meV < \u0394SC. In contrast, the inter-vortex quasiparticle spectra reveal only one energy gap at \u0394SC~20meV. A dramatic shift in the peak-to-peak gaps, \u0394pk-pk(H), from \u0394SC to both VPG and \u0394' with increasing magnetic field is observed. In addition, higher spatial resolution STS measurements were performed in Y-123 to investigate the spatial dependence of the quasiparticle spectra in more detail. The experimental resolution allowed Fourier-transformed local density of states analysis to be performed. Energy-dependent dispersive diffraction modes attributable to quasiparticle scattering interferences (QPI) were seen, as well as three energy-independent modes not due to QPI. The energy-independent modes corresponded to periodic real-space conductance modulations along the Cu-O bonding and the nodal directions attributable to a pair-density wave, a charge-density wave, and a spin-density wave. The totality of data in Y-123 suggests that the ground state of Y-123 contains competing orders coexisting with superconductivity and not superconductivity alone.
\r\n\r\nIn addition to the STS experiments, the effects of unconventional quasiparticle excitations on macroscopic superconductivity and vortex phase diagrams are investigated from bulk magnetization measurements on several different families of superconducting cuprate samples. Evidence for strong field-induced quantum phase fluctuations and quantum criticality are observed in the vortex phase diagrams of all samples considered. The origin of the apparent quantum criticality and strong field-induced quantum phase fluctuations due to the nearby presence of competing orders is discussed.
\r\n\r\nFinally, a \"two-gap\" phenomenological model, describing the excitations from a ground state of coexisting superconductivity and a competing order, is used to quantitatively model the unconventional quasiparticle excitations observed in the measurements of the local tunneling density of states and the angle-resolved photoemission spectroscopy (ARPES) experiments. The phenomenological model is found to provide consistent accounts for the quasiparticle tunneling data from our measurements in La-112 and Y-123, as well as experimental data by others on different cuprates.
\r\n" }, { "name": "Emery, Teresa Holly", "degree": "PhD", "year": "2008", "title": "Fabrication of Nanowire-based Magnetic Structures for Magnetic Resonance Applications", "advisor": "Scherer, Axel", "url": "https://resolver.caltech.edu/CaltechETD:etd-06062008-115513", "creators": [ { "name": { "family": "Emery", "given": "Teresa Holly" }, "id": "Emery-Teresa-Holly", "display_name": "Emery, Teresa Holly" } ], "advisors": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "advisor", "display_name": "Scherer, Axel" } ], "committee": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "chair", "display_name": "Scherer, Axel" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." }, { "name": { "family": "Barbic", "given": "Mladen" }, "id": "Barbic-M", "role": "member", "display_name": "Barbic, Mladen" }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "member", "display_name": "Painter, Oskar J." }, { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "member", "display_name": "Tai, Yu-Chong" } ], "option_major": [ "eleceng" ], "doi": "10.7907/3XYZ-BW96", "abstract": "The development and fabrication of novel magnetic nanowire devices is presented. These devices are used both to explore the fundamental physics of single domain particles, and to provide signal amplification and increased resolution in magnetic resonance imaging. Fabrication protocols for the creation of nickel nanowires were developed using both electron beam lithography and electroplating into nanoporous templates. The templates for electroplating were created by anodizing aluminum in either oxalic or sulfuric acids. The templates are 15 to 25 $mu$m thick and composed of highly ordered pores of 40 nm and 20 nm in diameter respectively. Nanowire samples formed by each protocol are characterized using an alternating gradient magnetometer to measure magnetic hysteresis loops. The magnets formed by electroplating were found to be much closer to ideal single domain magnets than those written via electron beam. Coercivities over to 1000 Oe were observed.
\r\n\r\nIndividual cylindrical nanowires of 70 nm diameter were contacted using focused ion beam assisted platinum deposition. A contacted nanowire was tested in a cryostat to determine the temperature dependence of the magneto-resistive properties of the wire. Sections of plated nanowires still in the anodized aluminum template were examined for their reversible transverse susceptibility for applications in signal amplification in magnetic resonance imaging systems. A process of selectively plating into the aluminum templates to create shape magnets with interesting magnetic fields was developed for creating magnetic \"lenses' with focal points above the plane of the substrate. Finally, an inductive stripe loop array was fabricated for use in stripe sensor tomography. These developments will enable future work on magnetic resonance imaging using a background of patterned templates for amplification.
" } ]