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Water transport properties in cement are important for the cement industry. At the nanoscale, a nondestructive experimental method, 1 H nuclear magnetic resonance [NMR] relaxometry, can be used to quantify these properties. However, recent results have proven difficult to reconcile with current understanding of cement. The purpose of this work is to use Molecular Dynamics [MD] simulations to try and better understand water in cement and hence better interpret some of the NMR data. In particular, MD simulations are used to investigate water dynamics in two sizes of nanopores in analogues of calcium-silicate-hydrate [C-S-H], which is the active phase of cement paste. These pores are gel pores (3-5 nm) and interlayer spaces (1 nm). First, a bulk water system is studied and the water diffusion coefficient and NMR relax ation times are calculated. The results are compared to literature values and used to validate the methods. Then, different C-S-H analogues based on SiO 2] α -quartz crystal, tobermorite 11 ̊ A and modified tobermorite 14 ̊ A are presented. Two different sets of interatomic poten tials are used for these model simulations: CLAY FF+SPC/E and Freeman+TIP4P. These simulations are then compared. A model called MD4 which is based on modified tobermorite 14 ̊ A and using CLAY FF+SPC/E potentials is selected for further work. The density profile of water oxygen in MD4 is used to identify four water layers with different properties in the gel pore (L1, L2, TL and B) and one water layer in the interlayer pore (IL). Diffusivity and desorption analyses are performed on water populations related to these layers. The importance of the calcium ions close to the surface is highlighted. The NMR dipolar correlation function is generated for water using data from the MD4. This function underpins relaxation analysis. These outputs are compared to Korb’s single water layer model of surface NMR relaxation. Korb’s model is not supported by the new data. However, a new relaxation model of surface relaxation that takes into account water in two layers is supported by the data. Exchange is possible between these layers and is important for diffusivity as well as relaxation. Simulations are carried out as a function of temperature and used to calculate water trans- port activation energies in bulk and in MD4. Finally, the analysis of water exchange between the interlayer and gel pores is performed. It is shown that the exchange time in simulations is ≈69000 times smaller than measured experimentally. Some possible failings in the model that would account for this are discussed.

Inspired by graphene, I investigate the properties of several different real and artificial Dirac materials. Firstly, I consider a two-dimensional honeycomb lattice of metallic nanoparticles, each supporting localised surface plasmons, and study the quantum properties of the collective plasmons resulting from the near field dipolar interaction between the nanoparticles. I analytically investigate the dispersion, the effective Hamiltonian and the eigenstates of the collective plasmons for an arbitrary orientation of the individual dipole moments. When the polarisation points close to normal to the plane the spectrum presents Dirac cones, similar to those present in the electronic band structure of graphene. I derive the effective Dirac Hamiltonian for the collective plasmons and show that the corresponding spinor eigenstates represent chiral Dirac-like massless bosonic excitations that present similar effects to those of electrons in graphene, such as a non-trivial Berry phase and the absence of backscattering from smooth inhomogeneities. I further discuss how one can manipulate the Dirac points in the Brillouin zone and open a gap in the collective plasmon dispersion by modifying the polarisation of the localized surface plasmons, paving the way for a fully tunable plasmonic analogue of graphene. I present a phase diagram of gapless and gapped phases in the collective plasmon dispersion depending on the dipole orientation. When the inversion symmetry of the honeycomb structure is broken, the collective plasmons become gapped chiral Dirac modes with an energy-dependent Berry phase. I show that this concept can be generalised to describe many real and artificial graphene-like systems, labeling them Dirac materials with a linear gapped spectrum. I also show that biased bilayer graphene is another Dirac material with an energy dependent Berry phase, but with a parabolic gapped spectrum. I analyse the relativistic phenomenon of Klein Tunneling in both types of system. The Klein paradox is one of the most counter-intuitive results from quantum electrodynamics but it has been seen experimentally to occur in both monolayer and bilayer graphene, due to the chiral nature of the Dirac quasiparticles in these materials. The non-trivial Berry phase of pi in monolayer graphene leads to remarkable effects in transmission through potential barriers, whereas there is always zero transmission at normal incidence in unbiased bilayer graphene in the npn regime. These, and many other 2D materials have attracted attention due to their possible usefulness for the next generation of nano-electronic devices, but some of their Klein tunneling results may be a hindrance to this application. I will highlight how breaking the inversion symmetry of the system allows for results that are not possible in these system's inversion symmetrical counterparts.

One of the main focuses of hypersonic research is understanding the relevant physicochemical phenomena that characterize hypersonic flows. Shock-induced heating and strong thermochemical non-equilibrium are significant occurrences in high-enthalpy, high-speed flows. To accurately simulate such flows, one must ensure that the relevant effects are described in the physical model of the gas. In conventional CFD, we solve a set of governing equations, the Navier-Stokes equations, that include the terms related to viscous dissipation, heat transfer, and mass diffusion of multiple chemical species present in the flow. These diffusive processes are a continuum manifestation of transport processes at the molecular scale. According to kinetic theory, the Boltzmann equation fully describes the statistical behavior of dilute gas mixtures. A mathematical link between the Boltzmann and the Navier-Stokes equations provides a complete description of the transport phenomena with additional terms neglected in the conventional continuum flow representation. Thus, with this work, we study the effects of diffusion transport properties and chemical kinetics by simulating different hypersonic flows in the near-continuum regime. In particular, we compare the solutions obtained with US3D, a code routinely used for complex hypersonic computational fluid dynamics simulations, and MGDS, a code capable of large-scale 3D Direct Simulation Monte Carlo calculations. This work is part of a long-term effort to strike a balance between computational efficiency and accuracy in simulations and perform eventually coupled hybrid CFD-DSMC simulations of hypersonic flows.

Nonwoven fibrous materials represent a platform of flexible material substrates. Nonwovens are widely used in the production of napkins, paper, filters, wound covers and face masks. In addition, for many applications, nonwoven materials interact with fluids. For example, in filtration applications, nonwoven materials are used to clean fluids containing solid particles or emulsified droplets. The filtration performance is affected not only by the geometrical arrangement of fibers in non-woven materials but also wettability of fibers. Understanding the transport properties of nonwoven materials and interactions between the dispersed droplets and solid substrate is crucial for the design and optimization of filter media. The present work is focused on: (1) obtaining pore space information from 3D structure in nonwoven media and 2) predicting the liquid transport properties in fibrous materials, including permeability and tortuosity (3) investigating droplet morphology on fibers. Chapters 1-3 provide the basis of fiber-liquid interactions and introduce the lattice Boltzmann method (LBM). Chapter 4 deals with characterization of microstructures generated from 3D reconstructed plywood and random oriented fibrous media. An algorithm based on watershed segmentation is utilized to extract pore network information including: pore diameter, throat diameter and connectivity. The effect of fiber overlapping arrangements, fiber radius and porosity on the pore space morphology was explored by statistical pore-network analysis. A thorough analysis of the correlation between effective geometrical properties and mean pore size, demonstrated that randomness on microscopic level can have a significant effect on the macroscopic properties of the fibrous media. In Chapter 5, simulations on pore-scale single phase fluid flow through fibrous media using the lattice Boltzmann method were performed. From the simulated flow field, permeability and tortuosity of nonwoven fibrous materials can be evaluated over a wide range of porosity 0.1 < φ < 0.9. The validity of Darcy’s law which describes the flow behavior through a porous medium was confirmed in the studied porosity regime. The simulation results were used to test the accuracy of semi-empirical scaling relations, that enabled predictions in trans-plane permeability and tortuosity based on porosity and specific surface area. Chapter 6 deals with the wetting and capillarity effects of droplets deposited on a single fiber. A multicomponent pseudopotential lattice Boltzmann model was applied to study the interface dynamics of droplets and wetting/dewetting behavior. By adopting different initial droplet configurations, we studied the stability of barrel-shaped and clam-shell droplets on a single fiber for contact angles ranging from 10° to 68°. The simulated barrel drop profile was validated with experimental results. The morphology diagram established from simulations showed that both barrel and clam-shell configurations are stable in coexistence. Dr. Ulf Schiller introduced me to the LBM, and guided my research described in Chapter 3-5. These chapters are based on publications [1, 2, 3], but significantly modified to include additional materials that has never been published. Chapter 6 has been developed to explain recent experimental results obtained in Dr. Kornev’s group. The developed simulation protocol revealed new physics related to the classical problem of fiber-drop interactions and a new diagram of morphological transitions of droplets on fibers was determined. The numerical simulations and data analysis were carried out on Palmetto high-performance computing (HPC) cluster.

This dissertation focuses on multiscale analysis in shale to improve understanding of mechanical and transport properties in shale gas reservoirs. Laboratory measurements of the effects of constant confining pressure (CCP), and constant effective stress (CES) on permeability were coupled with multiscale finite element simulations and the development of a comprehensive apparent permeability model to study the mechanical behavior of shale and transport mechanisms in shale. Predicting long-term production from gas shale reservoirs is a challenging task due to changes in effective stress and permeability during gas production. Unlike coal, the variation of sorbing gas permeability with pore pressure in shale does not always feature a biphasic trend under a constant confining pressure. The present contribution demonstrates that the biphasic dependence of permeability on pore pressure depends on a number of physical and geometrical factors, each with a distinct impact on gas permeability. This includes pore size, adsorption isotherm, and the variation of gas viscosity with pore pressure. In the first part, a single-capillary model was proposed for the apparent permeability of real gas in shale. Results indicated that the biphasic relation between apparent permeability and pore pressure is prevalent when the sorbing gas flows in sufficiently small pores. In addition, the effects of sorption isotherm and internal resistance of non-ideal gas to flow were shown to be non-trivial and could not be ignored.In the second part, experimental measurements were conducted on an intact Utica shale sample under constant confining pressure (CCP) and constant effective stress (CES) conditions to better understand how apparent permeability evolves over time. The average pore diameter of the sample is determined using nitrogen adsorption analysis. In low-permeability porous media, such as shale, gas slippage is more significant at low pore pressure, and using the Klinkenberg’s theoretical model overestimates the apparent permeability. Therefore, a conceptual model based on the second-order slip boundary condition was developed to study the apparent permeability behavior with pore pressure. Results from the apparent permeability predicted by the proposed model reasonably matched against the experimental data, but deviated from the model using Klinkenberg’s assumption at low pore pressures. These findings indicated that permeability under the CCP and CES conditions are dominated by gas slippage at low pore pressures, but as pore pressure increases, poroelastic effects become more significant. Moreover, it was found that the nonlinearity between the apparent permeability and pore pressure was more pronounced at small pores sizes and could be explained through more pronounced gas slippage in viscous flow.Finally, the thermomechanical behaviors of a solid-gas mixture were studied using the asymptotic expansion homogenization (AEH) method coupled with the finite element method to understand how porosity and pore density have effects on thermo-hydro-mechanical behaviors and transport properties of shale and how solid and gas interaction effect on permeability. It was found that increasing porosity results in a reduction of homogenized properties such as elastic stiffnesses, thermal expansion coefficients, and thermal conductivity, while the apparent permeability increases. In addition, under applied loading, micro stress distribution strongly influenced by pore clusters and pores sizes. It was shown that the apparent permeability at the microscale is two orders of magnitude smaller than the apparent permeability at the macroscale.

The phase transitions and associated magnetic and transport properties of Ni2Mn0.70Cu0.30Ga, Ni2Mn0.70Cu0.25Cr0.05Ga and Ni2Mn0.70Cu0.30Ga0.95In0.05 have been investigated via x-ray diffraction, scanning electron microscopy, magnetic, calorimetric, and electrical resistivity measurements. While Ni2Mn0.70Cu0.30Ga exhibited a tetragonal structure at room temperature, cubic and orthorhombic phases coexisted in the other two samples. The scanning electron microscope micrographs indicated that no impurity phases existed in the samples. All three samples exhibited the first order martensitic phase transformation upon cooling and heating. The phase transitions were accompanied by large magnetic entropy changes and anomalies in the electrical resistivity data. For a field change of 50 kOe, peak magnetic entropy changes of -17 J kg-1K-1, -39 J kg-1K-1, and -26 J kg-1K -1 were observed for Ni2Mn0.70Cu0.30Ga, Ni2Mn0.70Cu0.25Cr0.05Ga and Ni2Mn0.70Cu0.30Ga0.95In0.05 respectively, when the measurements were done while heating. When the measurements were done while cooling from 400 K to lower temperatures, the peak values were -33 Jkg-1K-1, -17 Jkg-1K-1, and -15 Jkg-1K-1 for Ni2Mn0.70Cu0.30Ga, Ni2Mn0.70Cu0.25Cr0.05Ga and Ni2Mn0.70Cu0.30Ga0.95In0.05 respectively. The experimental results are discussed taking the decoupling and coupling of the phase transitions into consideration.

The main objective of this dissertation is to provide sound understanding and mitigation solutions to the perplexing problem of well interference and its implications on completions design, well-spacing decisions, and ultimately the economics of unconventional reservoirs. Optimal fracture spacing has eluded reservoir and completions engineers since the inception of multi-stage hydraulic fracturing. Very small cluster spacing results in fracture-to-fracture interference and higher completions cost, whereas very large cluster spacing leads to inefficient oil recovery which is detrimental to the economics of the well. Furthermore, when US onshore oil producers transitioned from appraisal to development, they were surprised not only by oil price volatility, but also by the magnitude of infill degradation due to well interference. In simple words, lucrative results from appraisal efforts were not representative of infill operations. Hence, several numerical models were constructed to better understand inter- and intra-well interference based on finite-difference, and finite-volume methods. The physical principals utilized in these models are conservation of mass, Darcy's law, thermodynamic equilibrium of fluid components between phases, and the definitions of phase saturation and mole fraction to complete the system. Numerical models presented in this work are three-phase, transient, and consider compressible fluid flow. Fluid thermodynamics were addressed via equation of state. iii Since the numerical solutions are non-unique, actual production data were utilized from different basins to calibrate the numerical models via history-matching process. Additionally, available geologic data were integrated to construct fit-for-purpose geologic models that were used as flow domains. Findings from intra-well interference simulation suggest that drawdown strategy is more impactful to short-term oil productivity than hydraulic-fracture spacing. Drawdown strategy is even more impactful on short-term oil recovery than 20% error in porosity, or water saturation. Results suggest that the profile of producing gas-oil ratio depends on fracture spacing and has been interpreted within the context of linear-flow theory. Also, results clearly show that drawdown strategy and magnitude of intra-well interference can be optimized based on the desired economic metric (NPV, or IRR). For instance, if the objective is to maximize rate of return, then tighter fracture spacing may be accepted Simulation results from inter-well interference show that the unpropped fracture geometry could be higher than matrix permeability by a factor of 10 to 20. History-match results confirm that hydraulic fracture half-length could exceed 2,000 ft depending on the completions design. Results also show that a certain level of inter-well interference improves oil recovery. Based on observations from sector modeling, the acceptable level of inter-well interference is dependent on the business commercial objectives, oil pricing, and well cost structure.

Diblock copolymers (DBPs) are used in numerous current and potential applications, from composite materials to electrolyte membranes. Depending on the chemical incompatibility of the blocks and their volume fractions, they self-segregate into microdomains inducing anisotropy and different symmetries to the microstructure, resulting in significant variability in the macroscopic properties. DBPs are emerging as a candidate for replacing conventional liquid electrolytes in electrochemical devices, due to their improved chemical and mechanical stability. In contrast to isotropic melts, the self-segregation of DBPs allows the decoupling of ionic transport and mechanical properties. In this work, molecular dynamic simulations of coarse-grained DBPs were devised and carried out to unveil correlations between the microstructure and both ionic mobility ($\mu$), and dynamics/viscoelasticity (directly correlate with mechanical properties) of DBPs. It was found that across different morphologies and chain lengths ($N$), $\mu$ is mainly controlled by the extent of microdomains mixing and the tortuosity of the conductive path. Furthermore, the local fluctuations in the density of the polymer matrix have a non-negligible effect on the transport of ions. Our study of dynamic and viscoelastic properties of DBPs revealed that the interface between the two blocks constrains chain conformations in a way akin to topological constraints caused by entanglements. Specifically, the DBP interface gives rise to a temperature-dependent early crossover from Rouse to reptation scaling of the self-diffusion coefficient with $N$ compared to isotropic melts. Rheologically, the interface manifests into a modulus plateau similar to that of the rubbery plateau of entangled polymer melts that arises at the same Rouse to reptation scaling crossover $N$. Overall, the results of this study shed some light on the effects of various design and operating parameters, such as block composition, temperature, and external forces, on the transport properties of DBPs. It is expected that these results will provide a fundamental basis to complement ongoing experimental and modeling efforts devoted to engineer DBPs for target applications.

Abstract: The increase in oil consumption during the past few decades, coupled with oil/gas extraction from shale in the recent years has increased drilling and cementing demands. Well cementing operation is one of the most crucial and important steps in any well completion. However, since it takes place at the end of the drilling process (each segment), a satisfying and acceptable job is rarely done. In the cementing process, cement is used to fill in the annular space between the casing string and the ground formation within the drilled hole. The cementitious system placed in an oil well has exclusive functions to perform. These include restricting the movement of hydrocarbons and/or water in between the permeable zones, providing a suitable mechanical support for the casing string, protecting the casing from any sort of physical damage including corrosion, and supporting the well-bore walls in order to prevent the collapse of the formation. The prepared paste has to be satisfactorily pumpable and flowable. However, on the other hand, the viscosity and yield stress associated with the paste should be appropriately tailored in order to reduce the risk of lost circulation. Therefore, the rheological behavior of an oil well cement paste should be assessed carefully. Also, the fluid loss (filtration) rate of the prepared cement paste is of great importance since it directly impacts various characteristics of the hardened cement sheath. High filtration and fluid loss rate lead to a change in the water-to-cement ratio of the matrix, influencing not only the flowability of paste while still fresh but also the microstructure of the hardened cement paste. Furthermore, the hardened oil well cement sheath placed in a wellbore should demonstrate adequate mechanical properties. Therefore, while designing the slurry, the strength development rate along with the ultimate compressive and tensile strength of the hardened paste should be taken into consideration. Moreover, understanding and improving the transport properties of oil well cement paste is essential. The aggression of any type of destructive and detrimental agents through the hardened paste will eventually degrade the cementitious system. Thus, the permeability and pore structure of the hardened oil well cement paste placed in the annulus is extremely critical. This study was primarily associated with the material behavior of oil well cement paste in the presence of cellulose nanocrystals. The main goal of this research was to develop an oil well cement system and address the associated durability concerns mentioned above. Firstly, the workability and the rheological properties of CNC-dosed fresh oil well cement paste were assessed, followed by static filtration tests to evaluate fluid loss. It was found that adding CNC to oil well cement paste leads to shear thinning which manifests as lower slump for the cement based slurry. Also, based on the experimental results, the presence of CNC increased the time required to collect a given amount of filtrate. Furthermore, the effect of cellulose nanocrystal (CNC) particles on the dynamic mechanical properties of oil well cement paste was studied. Using oscillatory rheology, the linear viscoelastic range of CNC-dosed oil well cement paste was determined and the frequency sweep test was performed at the critical strain. According to the results obtained, the presence of CNC enhanced the complex viscosity, rigidity, hydration rate and solidification of oil well cement paste. Moreover, the effect of cellulose nanocrystal (CNC) particles on the pore structure and porosity of hardened oil well cement paste was investigated using the gas sorption technique. The strength development (compressive and tensile) of CNC-dosed oil well cement paste was also measured at different ages in order to recognize the impact of this nanomaterial on the mechanical properties of hardened oil well cement paste. Test results revealed that CNC particles reduced the porosity and surface area of hardened oil well cement paste and enhanced the mechanical properties. Finally, the mass flow rate of early aged hollow cylindrical specimens dosed with CNC was measured by using a pressurized permeability cell and the water permeability of the specimens was evaluated using Darcy’s law for laminar flow. The water permeability of oil well cement paste was reduced with the addition of cellulose nanocrystal (CNC) particles.

Replacing organic liquid electrolytes with nonflammable solid electrolytes can improve safety, offer higher volumetric and gravimetric energy densities, and lower the cost of lithium-ion batteries. However, today’s all-solid-state batteries suffer from low Li-ion conductivity in the electrolyte, slow Li-ion transport across the electrolyte/electrode interface, and slow solid-state Li-ion diffusion within the electrode. Defect chemistry is critical to understanding ionic conductivity and predicting the charge transport through heterogeneous solid interfaces. The goal of this dissertation is to analyze and improve solid state materials for energy storage applications by understanding their defect structure and transport properties. I have investigated defect chemistry of cubic Li7La3Zr2O12 (c-LLZO), one of the most promising candidate solid electrolytes for all-solid-state lithium batteries. By combining conductivity measurements with defect modeling, I constructed a defect diagram of c-LLZO featuring the intrinsic formation of lithium vacancy-hole pairs. The findings provided insights into tailoring single-phase mixed lithium-ion/electron conducting materials for emerging ionic devices, i.e., composite cathodes requiring both fast electronic and ionic paths in solid-state batteries. I suggested that oxygen vacancies could increase the Li-ion conductivity by reducing the amount of electron holes bound with lithium vacancies. Using a simpler but also attractive solid electrolyte Li2ZrO3 (LZO) as an example, I significantly improved Li-ion conductivity by creating extra oxygen vacancies via cation doping. In particular, Fe-doped LZO shows the highest Li-ion conductivity reported for the family of LZO compounds, reaching 3.3 mS/cm at 300 °C. This study brought attentions to the long-neglected oxygen vacancy defects in lithium-ion conductors and revealed their critical role in promoting Li-ion transport. More importantly, it established a novel defect engineering strategy for designing Li-oxide based solid electrolytes for all-solid-state batteries. I surface-modified LiNi0.6Co0.2Mn0.2O2 cathode material with a LZO coating prepared under dry air and oxygen, and systematically investigated the effect of coating atmosphere on their transport properties and electrochemical behaviors. The LZO coating prepared in oxygen is largely amorphous. It not only provided surface protection against the electrolyte corrosion but also enabled faster lithium-ion transport. Additionally, oxygen atmosphere facilitated Zr diffusion from the surface coating to the bulk of LiNi0.6Co0.2Mn0.2O2, which stabilized the crystal structure and enhanced lithium ion diffusion. Consequently, LiNi0.6Co0.2Mn0.2O2 cathodes coated with Li2ZrO3 in oxygen achieved a significant improvement in high-voltage cycling stability and high-rate performance.

Two-dimensional materials including graphene and transition metal dichalcogenides semiconductors are of tremondous interest for potential electronic applications because of their electronic properties and rich physics. In this work, using tight binding models, first principle calculation and non equilibrium Green’s function(NEGF) simulations, interlayer resistance of misoriented MoS2, electronic properties of tetralayer graphene and edge states of trilayer graphene nanoribbons are successively studied.In transition metal dichalcogenides like MoS2, interlayer misorientation alters the interlayer distance, the electronic bandstructure, and the vibrational modes, but, its effect on the interlayer resistance is not known. We analyze the coherent interlayer resistance of misoriented 2H-MoS2 for low energy electrons and holes as a function of the misorientation angle. The electronic interlayer resistance monotonically increases with the supercell lattice constant by several orders of magnitude similar to that of misoriented bilayer graphene. The large hole coupling gives low interlayer hole resistance that weakly depends on the misorientation angle. Interlayer rotation between an n-type region and a p-type region will suppress the electron current with little effect on the hole current. We also estimate numerical bounds and explain the results in terms of the orbital composition of the bands at high symmetry points. Density functional theory calculations provide the interlayer coupling used in both a tunneling Hamiltonian and a non-equilibrium Green function calculation of the resistivity.In multilayer graphene, as the Fermi level and band structure are readily tunable, they constitute an ideal platform for exploring the Lifshitz transition, a change in the topology of a material’s Fermi surface. In tetralayer graphene that hosts two intersecting massive Dirac bands, we provide numerical analysis of multiple Lifshitz transitions and multiband transport, which is manifest as a nonmonotonic dependence of conductivity on the charge density n and out-of-plane electric field D, anomalous quantum Hall sequences and Landau level crossings that evolve with n, D, and B.Lastly, due to mirror symmetry the bands of ABA stacked trilayer graphene can be identified by their parity with respect to mirror symmetry. The even parity bands exhibit gapped bilayer graphene-like dispersion, while the odd parity bands exhibit a gapped graphene-like dispersion. Using a tight binding model with Slonczewski-Weiss-McClure parameters, we look at the edge states in trilayer graphene nanoribbons in the quantum hall regime. When mirror symmetry is preserved, the system exhibits quantized longitudinal conductance at charge neutrality point, due to counterpropagating even and odd parity edge modes. We study the effects of perpendicular electric field and magnetic field and mirror symmetry breaking disorder on the band structures and longitudinal conductance.

Theoretical predictions for AlSb material properties have not been realized using bulk growth methods. This research was motivated by advances in molecular beam epitaxial (MBE) growth technology to produce high-quality thin-film AlSb for the purpose of evaluating transport properties and suitability for radiation detection. Simulations using MCNP5 were performed to benchmark an existing silicon surface barrier detector and to predict ideal AlSb detector behavior, with the finding that AlSb should have improved detection efficiency due to the larger atomic number of Sb compared with Si. GaSb diodes were fabricated by both homoepitaxial MBE and ion implantation methods in order to determine the effect on the radiation detection performance. It was found that the radiation response for the MBE grown GaSb diodes was very uniform, whereas the ion-implanted GaSb diodes exhibited highly variable spectral behavior. Two sets of AlSb heterostructures were fabricated by MBE methods; one for a Hall doping study and the other for a radiation response study. The samples were characterized for material quality using transmission electron microscopy (TEM), Nomarski imaging, atomic force microscopy (AFM), x-ray diffraction (XRD), I-V curve analysis, and Hall effect measurements. The Hall study samples were grown on semi-insulating (SI) GaAs substrates and contained a thin GaAs layer on top to protect the AlSb from oxygen. Doping for the AlSb layer was achieved using GaTe and Be for n- and p-type conductivity, respectively, with intended doping densities ranging from 1015 to 1017 cm-3. Results for net carrier concentration ranged 2×109 to 1×1017 cm-3, 60 to 3000 cm2/Vs for mobility, and 2 to 106 Ω-cm for resistivity, with the undoped AlSb samples presenting the best values. The radiation detector samples were designed to be PIN diodes, with undoped AlSb sandwiched between n-type GaAs substrate and p-type GaSb as a conductive oxygen-protective layer. Energy spectra were measured from 241Am, 252Cf, and 239Pu sealed sources, with good peak resolution and signal to noise response. Both GaSb PN diodes and AlSb PIN diodes exhibited larger pulses for smaller surface area samples, in good agreement with voltage-capacitance relationships for junctions. Microwave photoconductive decay (MW-PCD) measurements were performed on the Hall samples to determine the effect of doping on the minority carrier lifetime. Contrary to expectations, more heavily doped samples presented with longer decay times, some as large as hundreds of microseconds. There also appeared to be multiple exponential decay curves, potentially associated with different decay mechanisms. Collectively, the studies presented here reinforce the predicted nature of AlSb with respect to radiation detection.

Landau Fermi-liquid theory was first introduced by L. D. Landau in the effort of understanding the normal state of Fermi systems, where the application of the concept of elementary excitations to the Fermi systems has proved very fruitful in clarifying the physics of strongly correlated quantum systems at low temperatures. In this thesis, I use Landau Fermi-liquid theory to study the transport phenomena of two different correlated quantum liquids: the strongly interacting ultracold Fermi gases and the ferromagnet/normal metal (F/N) junctions. The detailed work is presented in chapter II and chapter III of this thesis, respectively. Chapter I holds the introductory part and the background knowledge of this thesis. In chapter II, I study the transport properties of a Fermi gas with strong attractive interactions close to the unitary limit. In particular, I compute the transport lifetimes of the Fermi gas due to superfluid fluctuations above the BCS transition temperature Tc. To calculate the transport lifetimes I need the scattering amplitudes. The scattering amplitudes are dominated by the superfluid fluctuations at temperatures just above Tc. The normal scattering amplitudes are calculated from the Landau parameters. These Landau parameters are obtained from the local version of the induced interaction model for computing Landau parameters. I also calculate the leading order finite temperature corrections to the various transport lifetimes. A calculation of the spin diffusion coefficient is presented in comparison to the experimental findings. Upon choosing a proper value of F0a, I am able to present a good match between the theoretical result and the experimental measurement, which indicates the presence of the superfluid fluctuations near Tc. Calculations of the viscosity, the viscosity/entropy ratio and the thermal conductivity are also shown in support of the appearance of the superfluid fluctuations. In chapter III, I study the spin transport in the low temperature regime (often referred to as the precession-dominated regime) between a ferromagnetic Fermi liquid (FFL) and a normal metal metallic Fermi liquid (NFL), also known as the (F/N) junction, which is considered as one of the most basic spintronic devices. In particular, I explore the propagation of spin waves and transport of magnetization through the interface of the F/N junction where nonequilibrium spin polarization is created on the normal metal side of the junction by electrical spin injection. I calculate the probable spin wave modes in the precession-dominated regime on both sides of the junction especially on the NFL side where the system is out of equilibrium. Proper boundary conditions at the interface are introduced to establish the transport of the spin properties through the F/N junction. A possible transmission conduction electron spin resonance (CESR) experiment is suggested on the F/N junction to see if the predicted spin wave modes could indeed propagate through the junction. Potential applications based on this novel spin transport feature of the F/N junction are proposed in the end.

The focus of this dissertation is the determination of the electronic structure and trans-port properties of solids. We first review some of the theory and computational methodologyused in the calculation of electronic structure and materials properties. Throughout the dis-sertation, we make extensive use of state-of-the-art software packages that implement den-sity functional theory, density functional perturbation theory, and the GW approximation,in addition to specialized methods for interpolating matrix elements for extremely accurateresults. The first application of the computational framework introduced is the determi-nation of band offsets in semiconductor heterojunctions using a theory of quantum dipolesat the interface. This method is applied to the case of heterojunction formed between anew metastable phase of silicon, with a rhombohedral structure, and cubic silicon. Next, weintroduce a novel method for the construction of localized Wannier functions, which we havenamed the optimized projection functions method (OPFM). We illustrate the method on avariety of systems and find that it can reliably construct localized Wannier functions withminimal user intervention. We further develop the OPFM to investigate a class of materialscalled topological insulators, which are insulating in the bulk but have conductive surfacestates. These properties are a result of a nontrivial topology in their band structure, whichhas interesting effects on the character of the Wannier functions. In the last sections of themain text, the noble metals are studied in great detail, including their electronic propertiesand carrier dynamics. In particular, we investigate, the Fermi surface properties of the no-ble metals, specifically electron-phonon scattering lifetimes, and subsequently the transportproperties determined by carriers on the Fermi surface. To achieve this, a novel samplingtechnique is developed, with wide applicability to transport calculations. Additionally, thegeneration and transport of hot carriers is studied extensively. The distribution of hot carri-ers generated from the decay of plasmons is explored over a range of energy, and the transportproperties, particularly the lifetimes and mean-free-paths, of the hot carriers are determined.Lastly, appendices detailing the implementation of the algorithms developed in the work ispresented, along with a useful derivation of the electron-plasmon matrix elements.

Fast growing power densities of modern electronic devices demand high-performance thermal interface materials (TIMs). Owing to a superior thermal conductivity of graphene, composites with graphene fillers dispersed in polymer matrix are expected to be promising TIM candidates. However, the thermal conductivity of graphene-polymer composites is hindered by a high thermal resistance across the interfaces between graphene fillers and polymer matrix. The research in this thesis is concerned with reducing the thermal transport across the graphene-polymer interfaces by employing a variety of treatment methods. Using molecular dynamics (MD) simulations, the effectiveness of covalent functionalisation, non-covalent functionalisation, dopants, defects and acetylenic linkages in reducing the graphene-polymer interfacial thermal resistance is investigated systematically. It is found that the covalent and non-covalent functionalisation techniques could considerably reduce the graphene-polymer interfacial thermal resistance. Among the various covalent functional groups, butyl is more effective than the others (i.e., carboxyl, hydroxyl and amines) in reducing the interfacial thermal resistance. Different non-covalent functional molecules, including 1-pyrenebutyl, 1-pyrenebutyric acid and 1-pyrenebutylamine, yield a similar amount of reduction. Moreover, it is found that the graphene-polymer interfacial thermal resistance is insensitive to defecting and doping in graphene, while it can be reduced moderately by replacing the sp2 bonds in graphene with acetylenic linkages. Using the effective medium theory, it is demonstrated that the overall thermal conductivity of graphene-polymer nanocomposites can be increased while the interfacial thermal resistance is reduced. The mechanical properties (i.e., Young’s modulus and tensile strength) of the graphene-polymer nanocomposites are not affected by the noncovalent functionalisation technique, while they can be deteriorated by the covalent functionalisation of graphene. Based on the pull-out simulation results, it can be found that the interfacial shear stress between graphene and polymer is increased by the covalent functionalisation of graphene, while it is insensitive to the non-covalent functionalisation techniques.

Nanomedicine has shown great promise for the treatment of a variety of complex diseases including cancer. The use of nanomaterials for non-covalent drug delivery has shown great success in the delivery of photodynamic therapy drugs in animal models, and has great potential as a general delivery vector for hydrophobic drugs. A detailed understanding of what physical forces dictate efficacy in the loading, transport, and delivery of non-covalent drugs is required for optimization and clinical translation. This thesis examines the non-covalent interactions between silicon phthalocyanine 4 (Pc 4) and polyethylene glycol coated gold nanoparticles (PEGylated Au NPs) through photophysics and transport studies. A detailed investigation of Pc 4’s photophysical behavior in water both with and without Au NPs is presented, elucidating the role of intramolecular photoinduced electron transfer and aggregation behavior. Gel electrophoresis studies of PEGylated Au NPs described in this work provide insights on fundamental physical properties of NPs as well as the local environment through which they translate. This thesis provides a “bottom-up” approach to non-covalent drug delivery which will be helpful in translating non-covalent drug delivery to more complex systems.

Membrane desalination using reverse osmosis (RO) has been the leading candidate technology for supplying fresh water in recent years. However, there is a strong motivation for improving the established membrane process and/or developing alternative membrane technologies to overcome the limitations of high energy cost and brine discharge problems of RO technology. In the later context, pervaporation is a potential membrane technology as it has the advantage that the energy need is essentially independent of the concentration of the salt feed water. The pervaporation process combines the evaporation of volatile components of a mixture with their permeation through a nonporous polymeric membrane under reduced pressure conditions. In desalination applications, pervaporation has the advantage of near 100% of salt rejection. The pervaporation of an aqueous salt solution can be regarded as separation of a pseudo-liquid mixture containing free water molecules and bulkier hydrated ions formed in solution upon dissociation of the salt in water. Previous studies have demonstrated the possibility of applying pervaporation to produce distilled water from aqueous salt solutions. However, the water flux reported in the literature so far is generally quite low (

In this dissertation, four topics related to the physics and astrophysics of neutron stars are studied. Two first topics deal with microscopical physics processes in the star outer crust and the last two with macroscopical properties of a star, such as mass and radius.In the first topic, the thermodynamical and transport properties of a dilute gas in which particles interact through a delta-shell potential are investigated. Through variations of a single parameter related to the strength and size of the delta-shell potential, the scattering length and effective range that determine the low-energy elastic scattering cross sections can be varied over wide ranges including the case of the unitary limit (infinite scattering length). It is found that the coefficients of shear viscosity, thermal conductivity and diffusion all decrease when the scattering length becomes very large and also when resonances occur as the temperature is increased. The calculated ratios of the shear viscosity to entropy density as a function of temperature for various interaction strengths (and therefore scattering lengths) were found to lie well above the recently suggested minimal value of (4π)-1 ℏ/kB. A new result is the value of (4/5) for the dimensionless ratio of the energy density times the diffusion coefficient to viscosity for a dilute gas in the unitary limit. Whether or not this ratio changes upon the inclusion of more than two-body interactions is an interesting avenue for future investigations. These investigations shed pedagogical light on the issue of the thermal and transport properties of an interacting system in the unitary limit, of much current interest in both atomic physics and nuclear physics in which very long scattering lengths feature prominently at very low energies.In the second topic, the shear viscosity of a Yukawa liquid, a model for the outer crust of a neutron star, is calculated in both the classical and quantum regimes. Results of semi-analytic calculations in both regimes are presented for various temperatures and densities, and compared with those of classical molecular dynamical simulations performed for the same system by collaborators from Indiana University. For heavy-ion plasmas, as energetically favored in the outer crust of a neutron star, excellent agreement was found between the results of semi-analytic calculations and those of molecular dynamical simulations. However, in the case of light-ion plasmas, substantial differences were found between the results of quantum and classical cases, which underscores the importance of incorporating quantum effects in molecular dynamical simulations, even in the dilute limit. In the third topic, first steps are taken to reconstruct the uncertain high-density nuclear equation of state from the measured masses and radii of several individual stars. Inherent errors of the measurements are incorporated into the analysis. A new inversion procedure of the Tolman-Oppenheimer-Volkov stellar structure equation is developed so that a model independent dense matter of equation can be derived from observations. Successful tests of the inversion procedure emphasize the need to determine the masses and especially the radii of several individual stars. The aim here is to provide a benchmark equation of state for theoretical advances to be made. The fourth topic is concerned with the emerging field of gravitational-wave detections and its ability to shed light on the dense matter equation of state. In an external tidal gravitational field, as for example in binary star configurations, each star deforms and acquires a quadrupole moment. The quadrupole polarizability given by the coefficient of proportionality between the induced moment and the field called the tidal Love number after the English mathematician Love. By calculating Love numbers for several model equations of state, connections between the underlying equation of state, star structure and the tidal Love numbers of normal neutron stars and self-bound strange quark matter stars are established. It is shown that the measurement of the Love number from the gravitational signals produced from inspiraling binaries can distinguish between normal and self-bound structures of neutron stars as they are characterized by distinctly different magnitudes of Love numbers.

Cross-linked poly(ethylene oxide) (XLPEO) based on poly(ethylene glycol) diacrylate (PEGDA) is an amorphous rubbery material with potential applications for carbon dioxide removal from mixtures with light gases such as methane, hydrogen, oxygen and nitrogen. Changing the polymer network structure of XLPEO through copolymerization has previously been shown to influence gas transport properties, which correlated with fractional free volume according to the Cohen-Turnbull model. This project explores strategic modifications of the cross-linked polymer structure and their effect on the chemical, physical and gas transport properties with an aim to develop rational, molecular-based design rules for tailoring separation performance. Experimental results from calorimetric and dynamic thermal analysis studies are presented, along with pure gas permeability and solubility obtained at 35°C. Incorporation of dangling side chains by copolymerization of PEGDA with methoxy-terminated poly(ethylene glycol) methyl ether acrylate, n=8 (PEGMEA) was previously shown to be effective in increasing fractional free volume of XLPEO through the opening of local free volume elements, which in turn increased CO₂ permeability. Through a comparative study ofshort chain analogs to these co-monomers, incorporation of an ethoxy-terminated co-monomer was shown to be more effective than a comparable methoxy-terminated co-monomer in increasing gas permeability. For instance, copolymerization of PEGDA with 71 wt% ethoxy-terminated diethylene glycol ethyl ether acrylate increased CO₂ permeability from 110 barrer to 320 barrer. Gas permeability increase was not observed when hydroxy or phenoxy-terminated pendants were introduced, which was attributed to reduction in chain mobility due to increased inter-chain chemical interactions or steric restrictions, respectively. Based on these results, incorporation of a co-monomer containing a bulky non-polar terminal group, tris-(trimethylsiloxy)silyl, was examined in order to further increase gas permeability. Addition of 80 wt% TRIS-A co-monomer increased CO₂ permeability of cross-linked PEGDA to 800 barrer. However, the resulting changes in chemical character of the copolymer reduced CO₂/light gas selectivity, even as gas permeability increased. The effect of incorporating a bulky, stiff functional group in the cross-linker chain was studied using cross-linked bisphenol-A ethoxylate diacrylate, which showed 40% increase in permeability compared to cross-linked PEGDA. This study affirmed the importance of polymer chain interaction, in addition to free volume, in determining the gas transport properties of the polymer.

Carbon foams are porous materials which are attractive for many engineering applications because their thermal and mechanical properties can be customized by varying manufacturing process parameters. However, a highly random geometry at pore level makes it very difficult to analyze the properties and the behavior of this material in an application. Published research work on the analysis of foams has employed various ideal geometries to approximate the pore microstructure. However, these models are unable to predict accurately the foam properties and behavior in engineering applications.The objective of this research work is to determine thermal and mechanical properties of carbon foam on the basis of its true microstructure. A new approach is proposed by creating a three dimensional (3D) solid model based on an accurate representation of the real geometry of carbon foam. Finite element models are then developed to investigate the bulk thermal and mechanical properties of carbon foam using the three dimensional solid model. On the basis of the true 3D model of carbon foam, a study is undertaken to examine the effect of the unique microstructure on the flow field within the foam pores and the resultant convective heat transfer. A finite volume model is developed using the accurate representation of carbon foam microstructure inside a flow channel. The fluid flow and heat transfer is simulated to evaluate pressure drop and heat transfer capabilities. The carbon foam permeability, inertial coefficient and friction coefficient are determined and found to be in good agreement with experimental and semi-empirical models. The results also show a large enhancement in the heat transfer due to the presence of carbon foam in the channel. These results are comparable to the experimental results available in published literature.Another application that has been analyzed in this study is the use of carbon foam as tooling material for manufacturing advanced composite materials. Finite element simulations are carried out to predict the process induced residual stresses and deformations when a composite part is manufactured on conventional tooling versus carbon foam tooling. The results show that both the lower coefficient of thermal expansion and the elastic modulus of carbon foam contribute to the reduction of residual stress and deformation of the composite part.

My doctoral research has focused on the development of surface plasmon resonance (SPR) reflectance imaging technique to detect near-field transport properties such as concentration, temperature, and salinity in micro/nano fluidic phenomena in label-free, real-time, and full-field manner. A label-free visualization technique based on surface plasmon resonance (SPR) reflectance sensing is presented for real-time and full-field mapping of microscale concentration and temperature fields. The key idea is that the SPR reflectance sensitivity varies with the refractive index of the near-wall region of the test mixture fluid. The Fresnel equation, based on Kretschmann’s theory, correlates the SPR reflectance with the refractive index of the test medium, and then, the refractive index correlates with the mixture concentration or temperature. The basic operation principle is summarized and the laboratory-developed SPR imaging/analyzing system is described with the measurement sensitivity, uncertainties and detection limitations of the implemented SPR reflectance imaging. Total five proposed uses of SPR reflectance imaging technique are presented: (1) micromixing concentration field development of ethanol penetrating into water contained in a micro-channel, (2) full-field detection of the near-wall salinity profiles for convective/diffusion of saline droplet into water, (3) full-field and real-time surface plasmon resonance imaging thermometry, (4) correlation of near-field refractive index of nanofluids with surface plasmon resonance reflectance, and (5) unveiling hidden complex cavities formed during nanocrystalline self-assembly.

My dissertation research focuses on the investigation of the transport and magnetic properties of transition metal and rare earth doped oxides, particularly SnO2 and HfO2 thin films. Cr- and Fe-doped SnO2 films were deposited on Al2O3 substrates by pulsed-laser deposition. Xray- diffraction patterns (XRD) show that the films have rutile structure and grow epitaxially along the (101) plane. The diffraction peaks of Cr-doped samples exhibit a systematic shift toward higher angles with increasing Cr concentration. This indicates that Cr dissolves in SnO2. On the other hand, there is no obvious shift of the diffraction peaks of the Fe-doped samples. The magnetization curves indicate that the Cr-doped SnO2 films are paramagnetic at 300 and 5 K. The Fe-doped SnO2 samples exhibit ferromagnetic behaviour at 300 and 5 K. Zero-field-cooled and field-cooled curves indicate super paramagnetic behavior above the blocking temperature of 100 K, suggesting that it is possible that there are ferromagnetic particles in the Fe-doped films. It was found that a Sn0.98Cr0.02O2 film became ferromagnetic at room temperature after annealing in H2. We have calculated the activation energy and found it decreasing with the annealing, which is explained by the increased oxygen vacancies/defects due to the H2 treatment of the films. The ferromagnetism may be associated with the presence of oxygen vacancies although AMR was not observed in the samples. Pure HfO2 and Gd-doped HfO2 thin films have been grown on different single crystal substrates by pulsed laser deposition. XRD patterns show that the pure HfO2 thin films are of single monoclinic phase. Gd-doped HfO2 films have the same XRD patterns except that their diffraction peaks have a shift toward lower angles, which indicates that Gd dissolves in HfO2. Transmission electron microscopy images show a columnar growth of the films. Very weak ferromagnetism is observed in pure and Gd-doped HfO2 films on different substrates at 300 and 5 K, which is attributed to either impure target materials or signals from the substrates. The magnetic properties do not change significantly with post deposition annealing of the HfO2 films.

Transport properties of novel sulfonated wholly aromatic copolymers and the state-of-the-art poly(perfluorosulfonic acid) copolymer membrane for fuel cells, Nafion, were compared. Species transport (protons, methanol, water) in hydrated membranes was found to correspond with the water-self diffusion coefficient as measured by pulsed field gradient nuclear magnetic resonance (PFG NMR), which was used as a measure of the state of absorbed water in the membrane. Generally, transport properties decreased in the order Nafion > sulfonated poly(arylene ether sulfone) > sulfonated poly(imide). The water diffusion coefficients as measured by PFG NMR decreased in a similar fashion indicating that more tightly bound water existed in the sulfonated poly(arylene ether sulfone) (BPSH) and sulfonated poly(imide) (sPI) copolymers than in Nafion. Electro-osmotic drag coefficient (ED number of water molecules conducted through the membrane per proton) studies confirmed that the water in sulfonated wholly aromatic systems is more tightly bound within the copolymer morphology. Nafion, with a water uptake of 19 wt % (λ = 12, where λ = N H2O/SO3H) had an electro-osmotic drag coefficient of 3.6 at 60°C, while BPSH 35 had an electro-osmotic drag coefficient of 1.2 and a water uptake of 40 wt % (λ = 15) under the same conditions. Addition of phosphotungstic acid decreased the total amount of water uptake in BPSH/inorganic composite membranes, but increased the fraction of loosely bound water. Zirconium hydrogen phosphate/BPSH hybrids also showed decreased bulk water uptake, but contrary to the results with phosphotungstic acid, the fraction of loosely bound water was decreased. This dissimilar behavior is attributed to the interaction of phosphotungstic acid with the sulfonic acid groups of the copolymer thereby creating loosely bound water. No such interaction exists in the zirconium hydrogen phosphate materials. The transport properties in these materials were found to correspond with the water-self diffusion coefficients. Proton exchange membrane (PEM) transport properties were also found to be a function of the molecular weight of sulfonated poly(arylene thioether sulfone) (PATS). Low molecular weight (IV ~ 0.69) copolymers absorbed more water on the same ion exchange capacity basis than the high molecular weight copolymers (IV ~ 1.16). Surprisingly, protonic conductivity of the two series was similar. Moreover, the methanol permeability of the low molecular weight copolymers was increased, resulting in lower membrane selectivity and decreased mechanical properties. The feasibility of converting the novel sulfonated wholly aromatic systems to membrane electrode assemblies (MEAs) for use in fuel cells was studied by comparing free-standing membrane properties to those of MEAs assembled with standard Nafion electrodes. Significantly higher interfacial resistance was measured for BPSH samples. Fluorine was introduced into the copolymer backbone by utilizing bisphenol-AF in the copolymer synthesis (6F copolymers). These 6F copolymers showed a markedly lower interfacial resistance with Nafion electrodes and correspondingly greater direct methanol fuel cell performance. It was proposed that the addition of the hexafluoro groups increased the compatibility of the PEM with the highly fluorinated Nafion electrode.

A molecular mechanics study on conformational and gas transport properties of selected silicon-base polymers is presented in this dissertation. A new molecular mechanics force field, COMPASS was used in this study. It has been extensively validated by simulation of molecular and crystalline structures of cyclo-silanes and glass transition of a series of silicon-base polymers. Simulations have demonstrated that simulation conditions have direct impact on the results. Generally larger system and longer equilibration time gave better agreement between experimental and simulation results. Conformational properties of polysiloxane, polycarbosilane and selected polysilanes were studied by static and dynamic approaches. Backbone torsional angle energy contour maps for these polymers were obtained by molecular mechanics calculations. From energy maps, qualitative chain flexibility information of these polymers was obtained. Molecular dynamics studies on the orientational changes of polymer chain segments with time revealed their dynamic flexibility. Studies have shown asymmetrically substituted polysilanes backbones are very rigid due to the side groups. Self-diffusion and solubility coefficients of a number of gas species in these polymers have been calculated by molecular dynamics and Monte Carlo simulations. It has been shown that polydimethylsiloxane has the highest gas diffusivity and lowest gas solubility among these polymers. While asymmetrically substituted polysilanes have moderated diffusivity and high gas solubility. Their overall gas permeabilities are comparable. Glass transition behaviors of polymers are directly controlled by their backbone flexibility, while free volumes of these polymers are affected by both their backbone/side chain flexibility and molecular structures. Both chain flexibility and free volume affect gas diffusion rate in polymers. Higher chain flexibility leads to higher gas diffusivity. Gas solubility in polymers depends largely on their backbone structures. Side groups influence gas sorption by affecting chain packing and free volume fraction and distribution.

The Shubnikov-de Haas magneto-resistance oscillations and photoconductivity were experimentally studied in order to investigate the interaction of CO laser radiation with n-InSb at liquid helium temperatures. The roles of various absorption mechanisms on these effects were considered, particularly near the intrinsic band edge. From these measurements an effective electron temperature Tₑ was defined that increased or decreased under illumination, depending upon the strength of the applied electric field.