Electronic transport properties have been used to classify and characterize materials and describe their functionality. Recent surge in computational power has enabled computational modelling and accelerated theoretical studies to complement and accelerate experimental discovery of novel materials. This work looks at methods for theoretical calculations of electronic transport properties and addresses the limitations of a common approximation in the calculation of these properties, namely, the constant relaxation time approximation (CRTA). This work takes a look at the limitations of this approximation and introduces energy and temperature dependent relaxation times. This study is carried out on models and real systems and compared with experiments.

This work explores a continuum representation for diffuse layer models, thereby endowing continuum embedding models the ability to capture electrostatic phenomena in the environment such as the existence of electrolyte ions, and the nature of ionic liquids. It introduces a new field-aware continuum model that adjusts the size of the quantum regime per atom based on the distribution of charge in a system. The model accounts for the asymmetric nature of solvent distribution when applied to cations versus anions; it also overcomes the need to parameterize continuum interface models for different charged systems. The continuum representation of cavitation in water does not account for the tendency for water to form a hydrogen bonding network that is broken due to the formation of cavities. This effect is a major contributor to hydrophobic solvation and is an important precondition to the investigation of solvated proteins with continuum embedding. A new model inspired by machine learning advances is trained on molecular dynamics simulations due to the difficulty of isolating the cavitation energy term in experiment. Thermodynamic integration is used to calculate the energy from a step-like repulsive potential from cavities in TIP4P water, cavities ranging from small organic molecules, to small proteins. Predictions …

Magnetic nano-clusters in silicon involving iron and cobalt were synthesized using low energy (50 keV) ion implantation technique and post-implantation thermal annealing. Before the irradiation, multiple ion-solid interaction simulations were carried out to estimate optimal ion energy and fluence for each experiment. For high-fluence low-energy irradiation of heavy ions in a relatively lighter substrate, modeling the ion irradiation process using dynamic code SDTrimSP showed better agreement with the experimental results compared to the widely used static simulation code TRIM. A saturation in concentration (~ 48%) profile of the 50 keV Fe or Co implants in Si was seen at a fluence of ~ 2 × 1017 ions/cm2. Further study showed that for structures with a curved surface, particularly for nanowires, better simulation results could be extracted using a code "Iradina" as the curve geometry of the target surface can be directly defined in the input file. The compositional, structural, and magnetic properties were studied using Rutherford backscattering spectrometry, X-ray photoelectron spectroscopy, X-ray diffraction, atom probe tomography, and vibrating sample magnetometry. Irradiation of high-current (~ 2 μA/cm2) 50 keV Fe ions into Si at a fluence of 2 × 1017 ions/cm2 showed the formation of Fe5Si3 nano structures in the near-surface …

In this work, we have utilized an ion beam process known as gettering to migrate implanted Ni ions much deeper into the bulk substrate than their initial projected end of the range. The projected mean depth is known as Rp. The gettering effect is the most crucial part of the fabrication and we have found that for an H fluence of 3x 1016 cm-2 there is a threshold fluence of approximately 7.5 x 1015 cm-2 that cannot be surpassed if the gettering process is to be completed along with the substrate recovered to the high crystalline quality. This hard threshold is due to the gettering process relaxation induced mechanism that is responsible for migrating the Ni to the Rp/2 location while the H is vacating during the thermal annealing process. If the total number of vacancies produced by the H dissociation is not substantially larger than the total number of implanted Ni atoms the Ni will migrate to the Rp location of the Ni implantation at the amorphous and crystalline interface and toward the surface. When the gettering condition is not met the resulting magnetic responses vary from an exceptionally weak ferromagnetic response to not exhibiting a magnetic response. Additionally, …

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 …

This research provides a proof of concept and background theory for the physics behind the state-of-the-art ultra-fast plasmonic spiking neurons (PSN), which can serve as a primary synaptic device for developing a platform for fast neural computing. Such a plasmonic-powered computing system allows localized AI with ultra-fast operation speed. The designed architecture for a plasmonic spiking neuron (PSN) presented in this thesis is a photonic integrated nanodevice consisting of two electro-optic and optoelectronic active components and works based on their coupling. The electro-optic active structure incorporated a periodic array of seeded quantum nanorods sandwiched between two electrodes and positioned at a near-field distance from the topmost metal layer of a sub-wavelength metal-oxide multilayer metamaterial. Three of the metal layers of the metamaterials form the active optoelectronic component. The device operates based on the coupling of the two active components through optical complex modes supported by the multilayer and switching between two of them. Both action and resting potentials occur through subsequent quantum and extraordinary photonics phenomena. These phenomena include the generation of plasmonic high-k complex modes, switching between the modes by enhanced quantum-confined stark effect, decay of the plasmonic excitations in each metal layer into hot-electrons, and collecting hot-electrons by …