Additive Manufacturing of Batteries and IR-Active Microparticles: Polyborane-Based Electrolytes for Solid State Batteries and Additively Manufactured, TiN-Coated Microbridges

Advances in additive manufacturing (AM) processes are continuously opening up the material design space, providing scientists with opportunities to explore the relationship between structure, processing, and materials properties in new contexts. The first project presented in this thesis presents the design and refinement of a novel, polyborane-based solid electrolyte, whose design and investigation were motivated by the advent of additively manufactured, 3D electrodes, which could play a pivotal role in enabling next-generation batteries that can store more energy without sacrificing power. The first iteration of this electrolyte was synthesized by hydroborating polybutadiene with 9-borabicyclo(3.3.1)nonane (9-BBN). The resultant poly(9-BBN) was then reacted with precise amounts of n-butyllithium (n-BuLi), an organolithium reagent, to create the final polymer electrolyte. The polymer electrolyte films were assembled into a custom apparatus for impedance measurements, and though found to be ionically conductive, these measurements were not consistent, even within films made from the same batch of polymer in solution. This necessitated the modification of the electrolyte into a UV-cured version, which was achieved by hydroboration of polybutadiene using 9-BBN. The resulting poly(9BBN)-co-polybutadiene is treated with lithium tert-butoxide (LiOtBu) and crosslinked to produce a precursor resin, which is then drop cast onto PTFE spacers, UV-cured for 5 minutes, dried, and assembled into coin cells for electrochemical impedance spectroscopy (EIS) and into pans for differential scanning calorimetry (DSC). The ionic conductivity of the PBEs as measured by EIS as a function of molar salt ratio, r = molLi/molB, does not track with their measured glass transition temperatures, Tg or the activation energies, Ea, extracted from fitting the Vogel-Tammann-Fulcher (VTF) equation to the conductivity data. Beyond r = 0.33, values for Tg and Ea demonstrate insensitivity to increasing concentration, while conductivity continues to change with concentration and reaches a maximum at r = 0.75. Moreover, measurement of ionic conductivity of control PBE films without boron on the polybutadiene backbone confirms that the presence of Lewis-acidic boron groups is necessary for ionic solvation and conduction. Further analysis that compared the PBEs to a well-studied PEO-based electrolyte in the literature through the calculation of a reduced conductivity to control for polymer viscosity and segmental motion revealed that PBEs obtain optimal conductivity at higher salt concentrations than PEO, and that their ionic conductivities are far below that of PEO. We posit that we are observing a mechanism of ionic conduction in a glassy regime partially decoupled from the relaxation of the polymer host. We attribute these effects to the strong interaction between the Lewis-acidic boron centers and the strongly Lewis-basic tert-butoxide anions, which limits ionic conductivity by suppressing motion of the anions and presenting a large activation barrier for motion of Li+, which is optimized at high concentrations where the distance between the boron-anion centers is sufficiently small to increase the probability of a hopping event from one center to another. Nanorods fashioned from noble metals are ideal for maximizing extinction of electromagnetic radiation, which is necessary for plasmonically active materials in numerous applications, from contrast agents for biological imaging to effective obscurants. Key challenges that prevent nanorods from being employed for these technological applications include the prohibitively expensive cost of Au and Ag, their lack of requisite thermal and chemical stability, and the limitations in resolution and attainable feature sizes produced by existing wet chemistry techniques. The second project in this thesis focuses on the development of an AM process to create arrays of TiN-coated microbridges with lengths of 4.749 microns, cross-sections with dimensions of 0.692 by 2.256 microns, and effective aspect ratios of 3.368, that are capable of attenuating light reflected from a TiN-coated sapphire substrate by more than 80% in the mid-infrared (mid-IR), as measured by Fourier Transform Infrared (FTIR) spectroscopy. FTIR spectroscopy measurements further reveal attenuation of light transmitted through the same TiN-coated structures by up to 35% in the near- to mid-IR. These results indicate a promising pathway for AM of plasmonically active microparticles with broad reflectance and transmittance attenuation of light in the near- and mid-IR.</p

Asymmetric Pericyclic Transformations from Reactive Palladium Intermediates

The Pd-catalyzed decarboxylative asymmetric allylic alkylation of enolate nucleophiles is a cornerstone of our groups’ efforts to develop methodologies that directly facilitate the synthesis of stereochemically complex molecular building blocks. This thesis first focuses on our efforts to deepen our mechanistic understanding of these transformations. We then employ our insights as a base from which we expand the scope of the decarboxylative asymmetric allylic alkylation reaction, as well as develop entirely novel reaction paradigms

I. Dynamics of Subduction Initiation and II. Constraining Sedimentary Basin Structure with Seismic Ambient Noise

Subduction initiation, the inception of a subduction zone, heralds dramatic changes in tectonic plate kinematics and dynamics. In the first half of the thesis, I focus on understanding the dynamics of the subduction initiation process through a synthesis of numerical computations and theoretical frameworks. In Chapter 2, we employ force balance analysis and 2D geodynamic models to yield an analytical solution on the force evolution of the subducting plate. This formulation illuminates a pivotal phase in subduction initiation —- the compression-to-extension transition of plate forces -— as a defining milestone. In Chapter 3, we extend this analytical framework into a sliced 3D context (2.5D) while incorporating the influence of strike-slip motion. Modified from Chapter 2, the analytical solution validates that strike-slip motion facilitates subduction initiation by accelerating the process of weakening. Chapter 4 ventures into 3D geodynamic modeling, focusing on the Puysegur trench -— a living example of subduction initiation. The models demonstrate a capability to match multiple geophysical and geological observations quantitatively with mechanical models. With a parametric search, we discover the best-fitting models require a relatively fast strain weakening rate, which can be explained by pore-pressure weakening at shallow depths and grain-size reduction at greater depths. The second part of this thesis transitions to ambient seismic noise correlation. In Chapter 5, we conduct an ambient noise tomography in northern Los Angeles basins with a newly obtained, dense seismic data set. The new shear wave velocity model exhibits a lower velocity in the basins than previous community models, which can potentially resolve the inconsistency between observed and calculated ground motions. In Chapter 6, we introduce a new method to identify the near-field noise sources from the spurious arrivals in ambient noise correlations. The correlation between the inverted noise sources and geological features in northern LA basins suggests the viability of this technique as a novel means of identifying geological structures, including faults.</p

Dissecting and Reconstructing the Cosmic Infrared Background with Spaceborne Experiments

The utilization of several tracers of large-scale structure has led to important advancements in our understanding of the history of the Universe, in both characterizing cosmological initial conditions and late-time astrophysics. With the onset of dramatic changes in data volume and quality through existing and near-future experiments, methodologies that harness the information content in imaging and spectroscopic datasets while mitigating systematic effects will have larger impacts than ever before. In this thesis, we present a variety of analysis techniques for galaxy surveys of discrete objects and diffuse light measurements that are demonstrated on both synthetic and real datasets. In Chapter 2, we develop techniques for measurement of near-infrared extragalactic background light (EBL) anisotropies, focusing on imager data from the Cosmic Infrared Background ExpeRiment (CIBER). Through improvements in methodology and data quality, we present fluctuation measurements in Chapter 3 that are five to ten times more sensitive on several arcminute to degree scales than existing studies, with clear detection of diffuse anisotropies exceeding those from the Poisson noise of individual stars and galaxies. In Chapter 4, we present a new suite of empirically-based galaxy simulations which we use to examine the diversity of galaxies that will be observed with SPHEREx, NASA's upcoming MIDEX mission. We then develop and apply redshift estimation techniques to synthetic SPHEREx observations generated from these simulations, demonstrating the ability to measure the distances to several hundred million galaxies over the full sky. In Chapter 5, we describe a formalism for modeling point-like and diffuse signals in astronomical images, which can be used for robust photometry in the presence of diffuse contaminants, extraction of diffuse signals in the presence of point source contaminants, and more general component separation. In Chapter 6 we apply this modeling framework to Herschel-SPIRE observations of galaxy cluster RX J1347.5-1145, measuring the diffuse thermal Sunyaev-Zel'dovich (tSZ) effect at high significance and using relativistic corrections of the tSZ spectrum to constrain the intra-cluster medium temperature, for which we find consistent estimates with independent X-ray measurements.</p

Development and Applications of Imaginary Time Path Integral Methods

Recent engineering advances have opened up avenues to novel technologies that bridge the gap between the quantum and the classical. In order to understand large-scale quantum systems, a variety of approximate theoretical treatments have been proposed. This thesis focuses on development and applications of path-integral methods, which have enjoyed broad applicability in recent years for exploring nuclear quantum effects in the domains that span physical, bio-, geo-, and materials chemistry. Feynman's path-integral formulation of quantum statistical mechanics offers powerful and widely used strategies for including nuclear quantum effects in complex chemical systems. These strategies are based on the observation that the quantum Boltzmann statistical mechanics of a quantum system is exactly reproduced by the classical Boltzmann statistical mechanics of an isomorphic ring-polymer system. For the numerically exact calculation of quantum Boltzmann statistical properties, the classical Boltzmann distribution of the ring-polymer system can be sampled using Monte Carlo (i.e., path-integral Monte Carlo, or PIMC) or molecular dynamics (PIMD). Chapters 1 and 2 of this thesis identify and &#8212; with no computational overhead &#8212; eliminate the issues in virtually all previous numerical implementations of PIMD that stem from time discretization. The resultant integration scheme requires only a small modification to existing PIMD algorithms and provides accurate statistical and dynamical data in a single-shot simulation with an up to 3-fold increase in the timestep duration. Chapter 3 transitions from the PIMD method development to the applications of the related PIMC method to understand equilibrium of stable heavy isotopes (D, 13C, 17, and 18O in small gaseous molecules. We present a collaborative experiment-theory calibration of the temperature dependence of the clumped isotope effect in methane in Chapter 4. We continue in Chapter 5, adding the study of isotopic fractionation between methane, water, and molecular hydrogen. Here we present the first concrete example of the effect of Born-Oppenheimer approximation on PI calculations. Finally, Chapter 6 extends our treatment to ethane and propane. For propane, in addition to multiple clumped isotope effects, there is also a strong site preference for the heavy isotopes to occupy the central (methylene) group. All the isotopic equilibrium calculations utilize accurate potential energy surfaces and are validated against experimental data in close collaboration with Daniel Stolper's experimental group at Berkeley, representing (to the best of our knowledge) the most accurate reference data available to date.</p

Carbon Currencies: Isotopic Constraints on the Biogeochemistry of Organic Acids

On both human and geologic timescales, the microbial degradation of organic carbon in anoxic environments significantly influences the Earth’s climate. The rate-limiting step of this process is the initial breakdown of complex organic polymers (e.g. cellulose) into small organic acids (e.g. acetate), which are then rapidly converted into either carbon dioxide or methane. While the steady-state concentration of organic acids is kept low by microbial turnover, the flux of reactions producing and consuming them is large. In my doctoral work, I leveraged this dynamic pool of metabolites as a window into the broader carbon cycle. Specifically, I developed novel analytical and computational tools that quantify and interpret the isotope composition of organic acids. These techniques provide new information about the mechanism and rates of organic acid turnover in nature. First, in Chapter 2, I adapted electrospray ionization (ESI) Orbitrap mass spectrometry (MS) to simultaneously measure the carbon and hydrogen isotope compositions of acetate. This approach is 50 to 1000-fold more sensitive than established techniques, making measurements of environmental samples feasible for the first time. This technique clearly distinguishes the metabolic sources of acetate (fermentation and acetogenesis). In Chapter 3, I developed a complementary computational tool to interpret this new isotopic information. Quantifying Isotopologue Reaction Networks (QIRN) builds numerical models of complex reaction networks, including metabolic pathways, and predicts the isotope composition of molecules produced by these networks. In Chapter 4, I combined my analytical and computational approaches to investigate the isotopic fractionations of the microbial metabolism that generate organic acids in nature, fermentation. I found that fermentation imposes a significant isotopic fractionation during the degradation of organic matter. By coupling flux-balance analysis and QIRN, I isolated the enzymes responsible for these fractionations. These results suggested that fermentation may have imprinted a carbon isotope trophic enrichment that is observable in the compound-specific carbon isotope composition of Proterozoic biomarkers. In Chapter 5, I used my Orbitrap method to quantify in situ acetate turnover rates based on the exchange of hydrogen atoms between water and acetate's methyl group. I took this tool to the environment, where I studied the biogeochemical drivers of carbon cycling in the deep continental subsurface. In Kidd Creek mine, which has subsurface fracture fluids that have been isolated for over a billion years, I found that acetate is being actively produced and consumed in the subsurface. My analyses of acetate's isotope composition suggested that turnover may be driven by low-temperature water-rock reactions with implications for the habitability of subsurface environments elsewhere in the Solar System. Chapter 6 is a second application of the Orbitrap and QIRN in natural systems. This time I expanded the Orbitrap technique to include not only acetate but also the organic acids propionate and butyrate. I investigated carbon turnover in the rumen fluid of cows, where microbial fermentation breaks down cellulose and transfers organic acids to the animal host. I found clear trends in the carbon and hydrogen isotope composition of acetate and propionate that may hold information about the metabolic strategies of fermenters in the rumen. Finally, in Chapter 7, I highlight the challenges and opportunities of transitioning Orbitrap MS isotopic applications from pure standards to compelx samples. These studies demonstrate bespoke strategies for isolating organic acids, and possibly other ESI-Orbitrap analytes, from environmental samples without fractionating their isotope ratios. Together, these chapters use a combination of novel analytical and computational tools to study the rate and mechanism of organic acid cycling in nature. Elucidating these drivers is necessary to understand the modern and ancient carbon cycle and to predict its response to climate change.</p

Beowulf and the Moral Dilemma Between Kingship and Heroism

[Introduction] While Beowulf is largely a poem chronicling the exploits of the titular hero, one of the integral roles in Beowulf is that of the king. From the very exposition of the poem, the reader is introduced to the kings of the Danes and their respective lineages, implicitly highlighting the role of the kings in shaping the story. The poem describes a variety of kings, both “good” and ‘bad’, but what is especially interesting to note is the use of kings as both a complement and a contrast to heroes. The values and responsibilities of the king seem to differ vastly from that of a hero, with the exception of the titular character Beowulf himself. Despite ascending the throne and serving as a “good king” (2390) “for fifty years” (2733), Beowulf still seems to toe the line between serving as a king and serving as a hero, which makes him a prime candidate while analysing the moral code of kings and heroes in the poem Beowulf. This essay aims to explore how the expectations from kings and heroes contrast each other in Beowulf, and how Beowulf himself seems to be unwilling to transition between the two states

Single Rare-Earth Ions in Solid-State Hosts: A Platform for Quantum Networks

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 ¹7¹Yb³⁺ ions in YVO₄, coupled to a nanophotonic cavity. First, we demonstrate coherent operation of single ¹7¹Yb³⁺ 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. Next, we focus on realizing an auxiliary quantum register. The high-fidelity spin control of our ¹7¹Yb³⁺ 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. Moving 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’ optical transition frequencies, thereby enabling entanglement generation between any pair of qubits in a scalable fashion. These results showcase single rare-earth ions as a promising platform for the future quantum internet.</p

Investigation of Transport Phenomena in Semiconductors and Semiconductor Devices: Drain Noise, Two-Phonon Scattering, and Phonon Drag

The dynamics of charge carriers in semiconductors set the foundation for semiconductor device performance. Devices crucial for fields like radio astronomy rely on transistor amplifiers where hot electron dynamics impact noise significantly. The overarching goal of this work is to contribute towards the development of better transistor amplifiers by investigating electron transport in existing devices and emerging materials. The physical mechanisms governing noise in a class of semiconductor devices called high electron mobility transistors (HEMTs) are not completely understood. HEMTs are transistors that use a junction between two materials of different band gaps as the channel. HEMTs are used as amplifiers by translating a small signal applied at the gate terminal to a large current at the drain terminal or output. The noise added at the input is well-characterized by the device physical temperature, while the origin of the noise added at the output is still up for debate. We attempt to fill this knowledge gap by proposing a theory of noise occurring at the drain terminal of these devices as a type of partition noise arising from two possible electron paths. This theory emphasizes the critical role of the conduction band offset between epitaxial layers of the device: a larger offset maximizes the channel sheet density and minimizes electron transfer between layers, potentially improving noise performance. The theory accounts for the magnitude and dependencies of the drain temperature and suggests strategies to realize devices with lower noise. We then investigate phonon-limited charge transport in the semiconductor boron arsenide. Boron arsenide has drawn significant interest due to reports of simultaneous high thermal conductivity and ambipolar charge mobility, desirable properties for integration in electronic devices. The theoretical prediction of high electron and hole mobility assumed the dominance of charge carrier scattering by one phonon. We consider the effects of two-phonon electron and hole scattering processes in boron arsenide, and find that inclusion of these higher-order processes reduces the computed room-temperature electron and hole mobility significantly from the one-phonon value. Despite its potential, our predictions of electron and hole mobility contradict recent experimental reports based on photoexcited charge carrier diffusion. Several factors may explain this discrepancy, including another type of two-phonon scattering not considered in this work, superdiffusion of hot carriers, induced carrier concentration, or a combination of all or some of the above elements. At high carrier concentrations, the phonon system may interact with the electron system on the timescale of the phonon-phonon interaction. When this happens, the nonequilibrium state of phonons becomes important for electron transport, and vice versa as these systems interact in a coupled manner. This coupled interaction could lead to an inflated value of the experimentally reported mobility. We quantify this effect, known as phonon drag, with a coupled electron-phonon Boltzmann transport equation framework and demonstrate that the electron mobility is indeed enhanced significantly at the relevant carrier densities.</p

Institutional Design of Criminal Justice Processes

This dissertation contains three essays that contribute to ongoing debates about the design of institutions and procedures related to criminal justice. Chapter 1 investigates how peremptory challenges in the jury selection process affect the diversity of and outcomes from juries. A game-theoretic model of attorneys’ decisions to strike potential jurors finds that the process 1) can lead selected jurors from a majority group to be a skewed sample and 2) can increase minority representation, contrary to common intuition. The first theoretical finding about the skew is supported by empirical analysis of data from jury selection transcripts: a novel measure of the pro-defense lean of jury pool members is developed, and selected White jurors are found to be more pro-defense than the average White pool member. Chapter 2 develops a game-theoretic model of decisions about the verdict and sentence in a criminal trial, considering both single-actor and two-actor versions of this two-step process. Restrictions on sentencing discretion can lead to nullification where an actor with acquits who would have convicted under full discretion. When actors care about the lawfulness of their own actions, a two-actor process may lead to additional convictions, as the convicting actor can free ride off of a separate sentencing actor who will pay the cost of sentencing away from the lawful sentence. The model also leads to non-monotonic effects on the verdict when lawfulness or the expected sentence change. Chapter 3 (joint work with Alexander V. Hirsch) uses mechanism design to examine single-threshold information escrows in a workplace setting. In this setting, reports of misconduct by a manager are kept secret until the number of reports exceeds a threshold and the manager is fired. When the firm designing the system wishes to minimize misconduct, a single-threshold mechanism leads to optimal results when misconduct reports are costless. In contrast, costly misconduct reports can make truthful reporting impossible under certain threshold values, raising the threshold above the firm’s ideal or even eliminating the possibility of any truthful mechanism. We find that single-threshold mechanisms are generally worse for the firm than mechanisms that mix two thresholds and can be worse than choosing whether to fire the manager without eliciting any information about misconduct.</p