In recent years, continuum models of solvation have had exceptional success in materials simulations as well as condensed matter physics. They can easily capture the effects of disordered systems, such as neutral liquids or electrolytes solutions, on material interfaces without the need for expensive statistical sampling. The Environ library (www.quantum-environ.org) implements different continuum models and correction schemes, which is the focus of this presentation. Recently refactored into a stand-alone library, many changes have been introduced in Environ, making it more flexible and computationally efficient. Introduction of a double-cell formalism allows for faster ab initio DFT calculations while reparameterization of soft-sphere continuum model allows for smaller density cutoffs. Furthermore, Environ's periodic boundary conditions correction schemes have been expanded by including the AFC90 library, which allows for faster DFT calculations of partially periodic systems, such as slabs, wires, and isolated molecules. Finally, stand-alone Environ can now provide atomic and molecular descriptors, which can be used to characterize solvated interfaces, e.g. in machine learning applications. The specific details of the implementations are reviewed as well as their efficiency and some choice applications for different calculation setups and systems.

The Gemini Near Infrared Spectrograph - Distant Quasar Survey (GNIRS-DQS) is the largest uniform, homogeneous survey of its kind, covering 260 quasars at 1.5 ≤ z ≤ 3.5. This unique survey, coupled with data from the Sloan Digital Sky Survey (SDSS), enables new investigations into redshifts, supermassive black hole masses (MBH), and accretion rates at high redshift through spectroscopic coverage of important rest-frame UV-optical emission lines. The importance of this survey is highlighted in the fact that the optical emission lines provide more reliable measurements of these quasar parameters than their UV counterpart. With such a unique sample compiled here, I construct prescriptions to calibrate these quasar parameters derived from rest-frame UV emission lines to those derived from rest-frame optical emission lines. These prescriptions provide important insight into how these parameters depend on redshift and are potentially biased as we look out further into the universe. Additionally, all the work completed with this sample will help shape our understanding of how these quasars and their host galaxies co-evolve over cosmic time.

I present spectroscopic measurements for 260 sources from the Gemini Near Infrared Spectrograph–Distant Quasar Survey (GNIRS-DQS). Being the largest uniform, homogeneous survey of its kind, it represents a flux-limited sample of Sloan Digital Sky Survey (SDSS) quasars at 1.5 < z < 3.5. A combination of the GNIRS and SDSS spectra covers principal quasar diagnostic features, chiefly the C IV λ1549, Mg II λλ2798, 2803, Hβ λ4861, and [O III] λλ4959, 5007 emission lines, in each source. The spectral inventory is utilized primarily to develop prescriptions for obtaining more accurate and precise redshifts, black hole masses, and accretion rates for all quasars. Additionally, the measurements facilitate an understanding of the dependence of rest-frame ultraviolet–optical spectral properties of quasars on redshift, luminosity, and Eddington ratio, and test whether the physical properties of the quasar central engine evolve over cosmic time.

In this dissertation, I report the results of my research on twisted moiré photonic crystals which can be formed through multi-beam holographic interference without a physical rotation and later fabricated by electron-beam lithography. Their optical properties, such as photonic bandgaps, multiple resonance modes, and quality factor are presented. Randomized moire photonic crystals in lattice are also studied. The applications of moire photonic crystals in improving light extraction efficiency are simulated and verified in light emitting devices. Furthermore, I simulated the light extraction efficiency in OLED when the Al layer is patterned with a triangular GPSC, square moiré PhC with defects in the uniform area, and random locations of the photonic lattice, and obtain light extraction efficiency of 78.9%, 79.9%, 81.7%, respectively. Also, the ratios of photoluminescence intensity of LED integrated with twisted moiré PhCs and random moiré PhCs over that without moiré PhCs are measured to be (1.3-1.9) and 1.74, respectively, in a good agreement with simulated ratios of 1.69 and 1.8.

Using multiple theoretical methods, comprehensive calculations are performed to create a new and more comprehensive data set for elastic scattering and related transport cross sections for collisions of (H$^+$ + H), (H + H) and (He$^{2+}$ + H) in the center-of-mass energy frame. In proton-atomic hydrogen collisions, we have significantly updated and extended previous work of elastic scattering, charge transfer and related transport integral and differential cross sections in the center-of-mass energy range $10^{-4} - 10^4$ eV where the multi-channel molecular orbital approach (MO3) is used. For atomic hydrogen-hydrogen collisions, similar updates have been made of elastic scattering and spin exchange differential and integral cross sections, also for the H + H collision the ionization and negative ion formation cross sections are provided in energy range (1-20 KeV) by use of the 'hidden crossing' theoretical framework. For collisions of alpha particles with atomic hydrogen we have computed the elastic scattering cross section in the center-of-mass energy range $10^{-4} - 10^8$ eV. In this case, at the lowest energies where elastic scattering greatly dominates other reaction channels, a single-channel quasi-molecular-orbital approach (MO1) is used. With the opening of inelastic channels at higher energies the multi-channel atomic-orbital, close-coupling method is applied, and …

Silicon telluride (Si2Te3) and many other tellurium containing compounds show emergent Raman peaks located at ~120 cm-1 and ~140 cm-1 as they age. The origin of these two emergent peaks is controversial in the literature and has been attributed to myriad causes such as the intrinsic Raman modes of the telluride materials, surface oxidation, defects, double resonances, and tellurium precipitates. The controversial nature of these peaks has led to the misidentification of highly degraded materials as pristine and to the misinterpretation of changes in Raman spectra. For the first time, quality thin film and bulk crystals of Si2Te3 are grown using a chemical vapor deposition (CVD) process. We then present a comprehensive and multimodal study of various Si2Te3 samples and find that the two emergent Raman peaks originate from tellurium nano-crystallites formed in the degraded surface layers of Si2Te3. The formation of the tellurium nano-crystallites are shown to be a result of a hydrolysis process in which Si2Te3 reacts with atmospheric water vapor. The challenges involved in the fabrication of Si2Te3 based devices are also discussed and ways in which degradation can be either prevented or reversed are demonstrated. Finally, we present preliminary data which shows promising low voltage switching …