Thesis advisor: Kevin S. Bedell / 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. / Thesis (PhD) — Boston College, 2016. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Physics.

Ce travail expérimental a porté sur la dégradation de deux matériaux cimentaires, un mortier (pour la grande majorité des essais) et un béton, suite à un chauffage intense jusqu’à 600°C et parfois 700°C. L’idée qui a sous tendu cette étude était de « mesurer » cette dégradation via les propriétés de transport : la perméabilité au gaz et la porosité au gaz sous contrainte de confinement et certaines propriétés poro-mécaniques. Pour mener à bien ce travail, plusieurs techniques expérimentales ont été développées ou améliorées. Il s’agit en particulier de la mesure de porosité au gaz sous contrainte de confinement. L’emploi d’un gaz neutre permet de remplir les vides connectés dans le matériau et de calculer sa porosité. La réhydratation avec de l’eau déminéralisée a un effet considérable sur les matériaux fortement chauffés car elle restaure une grande partie de la porosité qui retrouve son niveau initial voire parfois une valeur inférieure à celui-ci. Très logiquement le « self-healing » permet aussi de restaurer une large part de la perméabilité qui ne retrouve cependant pas son niveau initial. / This experimental work focused on the degradation of two cementitious materials, mortar (for most tests) and a concrete following an intense heating to 600 ° C and 700 ° C sometimes. The idea that underpinned the study was to "measure" this degradation via the transport properties : gas permeability and porosity to gas under confining stress and some poro-mechanical properties. To carry out this work, several experimental techniques have been developed or improved. This is particularly the porosity measurement gas under a confining stress. The use of a neutral gas is used to fill the voids in the material and connected to calculate its porosity. Rehydration with demineralized water has a considerable effect on the highly heated material because it restores much of the porosity which regains its initial level or sometimes a value less than one. Logically the "self-healing" also restores much of the permeability which does not recover its original level

Huang, Chun Fuk = 間層對龐磁阻多層薄膜的傳導與擴散特性的影響 / 黃真福. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2007. / Includes bibliographical references. / Text in English; abstracts in English and Chinese. / Huang, Chun Fuk = Jian ceng dui pang ci zu duo ceng bo mo de chuan dao yu kuo san te xing de ying xiang / Huang Zhenfu. / Chapter Chapter 1 --- Introduction / Chapter 1.1 --- Magnetoresistance --- p.1 / Chapter 1.1.1 --- Giant magnetoresistance (GMR) --- p.3 / Chapter 1.1.2 --- Colossal magnetoresistance (CMR) --- p.5 / Chapter 1.1.3 --- Double exchange mechanism --- p.6 / Chapter 1.1.4 --- Jahn-Teller effect --- p.10 / Chapter 1.1.5 --- Tolerance factor --- p.12 / Chapter 1.1.6 --- Effect of Doping --- p.14 / Chapter 1.1.7 --- Charge-ordering effect --- p.16 / Chapter 1.1.8 --- Phase separation and percolation theory --- p.17 / Chapter 1.2 --- Our motivation --- p.18 / Chapter 1.3 --- Review of manganite multilayer system --- p.20 / Chapter 1.4 --- Scope of this thesis --- p.21 / References --- p.22 / Chapter Chapter 2 --- Instrumentation / Chapter 2.1 --- Thin film deposition --- p.24 / Chapter 2.1.1 --- Facing-target sputtering (FTS) --- p.24 / Chapter 2.1.2 --- Vacuum system --- p.26 / Chapter 2.2 --- Oxygen annealing system --- p.28 / Chapter 2.3 --- Characterization --- p.30 / Chapter 2.3.1 --- α-step profilometer --- p.30 / Chapter 2.3.2 --- X-ray diffraction (XRD) --- p.30 / Chapter 2.3.3 --- Resistance measurement --- p.32 / References --- p.34 / Chapter Chapter 3 --- Epitaxial growth of LCMO and LSMO single layer thin films / Chapter 3.1 --- Fabrication and characterization of LCMO and LSMO targets --- p.35 / Chapter 3.2 --- Epitaxial growth of LCMO and LSMO thin films --- p.41 / Chapter 3.2.1 --- Substrate materials --- p.41 / Chapter 3.2.2 --- Deposition conditions --- p.42 / Chapter 3.2.3 --- Deposition procedures --- p.44 / Chapter 3.3 --- Characterization of single layer films --- p.45 / References --- p.50 / Chapter Chapter 4 --- Lao.67Ca0.33MnO3/La0.4Ca0.6MO3 multilayers and La0.67Ca0.33MnO3 /La0.2̐ơإSr0.75MnO3 multilayers / Chapter 4.1 --- Sample preparation --- p.51 / Chapter 4.2 --- As-grown multilayers --- p.53 / Chapter 4.2.1 --- Structural characterization of as-grown samples --- p.53 / Chapter 4.2.2 --- Transport properties of as-grown samples --- p.59 / Chapter 4.3 --- Oxygen post annealing of multilayer thin films --- p.68 / Chapter 4.3.1 --- Introduction to post annealing of manganite oxides --- p.68 / Chapter 4.3.2 --- Oxygen post annealing conditions --- p.69 / Chapter 4.4 --- Results and discussion of oxygen post-annealing samples --- p.71 / Chapter 4.4.1 --- Structural characterization of oxygen post-annealing samples --- p.71 / Chapter 4.1.1.1 --- Effect of chemical composition --- p.71 / Chapter 4.4.1.2 --- Effect of relative thickness --- p.73 / Chapter 4.4.2 --- Transport properties of oxygen post-annealing samples --- p.84 / References --- p.95 / Chapter Chapter 5 --- Conclusion --- p.97

Neste trabalho, apresentamos os resultados de estudos com poços quânticos parabólicos (PQW, Parabolic Quantum Well ) de AlGaAs crescidos sobre substratos de GaAs pela técnica de epitaxia por feixe molecular. Medidas de transporte em PQWs do tipo n e do tipo p com larguras de 1000 ºA ate 4000 ºA em baixas temperaturas indicam um aumento abrupto do coeficiente Hall para um campo magnético critico de aproximadamente 3 T. Nosso estudo concentra-se na interpretação deste aumento observado. Com este propósito, estudamos através de cálculos autoconsistentes e de aproximações anal¶³ticas o processo de transferência de cargas em amostras com PQWs. Determinamos as densidades superficiais de cargas ns e ps, e comparamos estes resultados com os obtidos experimentalmente. Verificamos que os melhores resultados para a densidade de cargas (ns) s~ao aqueles determinados pelos cálculos autoconsistentes. No entanto, as aproximações analíticas se mostram importantes para descrever de forma qualitativa os resultados experimentais para amostras do tipo p. Numa segunda parte do nosso trabalho, estudamos a influencia da aplicação de campos magnéticos ao longo da direção de crescimento nas amostras com PQWs. Observamos uma diminuição na largura de densidade de cargas n(z) e do potencial total V (z). Estes resultados em combinação com o processo de transferência de cargas, levam a uma diminuição da densidade de portadores no poço, produto da redistribuição das cargas entre o poço e as camadas com dopagem de silencio. Desta forma, atribuímos o aumento no coeficiente Hall como sendo oriundo de uma diminuição da densidade de cargas dentro do PQW. / We present the results of experiments and calculations done on AlGaAs Parabolic Quantum Wells (PQWs) grown on GaAs by molecular beam epitaxial tecniques. Transport measurements in n-type and p-type samples with widths between 1000 ºA and 4000 ºA at low temperatures indicate an abrupt increase of the Hall coeficient at a critical field B ¼ 3 T. Our study focuses on the interpretation of this observed increase. To this end, we study by means of self-consistent numerical simulations and analytical approximations the charge transfer process in PQWs. We compare our results for the sheet densities with those observed experimentally. The best results are obtained for n-type samples for which we could numerical simulations. However, the analytical expressions we obtained also describe qualitatively the experimental results, and can be applied to p-type samples. In the second part of this work we study the efect of a magnetic feld applied perpendicular to the well. The simulations indicate a diminishing of the charge density and the total potential in the well. These results, combined with the charge transfer process, lead to a redistribution of charge between the well and the dopant layers. Therefore, we interpret the observed increase of the Hall coefcient as the result of a depletion of charge in the parabolic quantum well.

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.

We developed and implemented a first-principles based theory of the Landauer ballistic conductance, to determine the transport properties of nanostructures and molecular-electronics devices. Our approach starts from a quantum-mechanical description of the electronic structure of the system under consideration, performed at the density-functional theory level and using finite-temperature molecular dynamics simulations to obtain an ensemble of the most likely microscopic configurations. The extended Bloch states are then converted into maximally-localized Wannier functions to allow us to construct the Green's function of the conductor, from which we obtain the density of states (confirming the reliability of our microscopic calculations) and the Landauer conductance. A first application is presented to the case of pristine and functionalized carbon nanotubes. / Singapore-MIT Alliance (SMA)

Poly(vinyl alcohol) and polyethylene polymer systems werebuilt in order to study their transport properties (diffusion).First a verification of the AMBER force field was conducted fora poly(vinyl alcohol) system built from a chain with 145repeating units. NPT-molecular dynamics simulations attemperatures between 400 and 527 K were performed. The resultsof the simulations were compared withpressure-volume-temperature data, solubility parameter, X-rayscattering pattern and data for the characteristic ratio. Thefractional free volume distribution was computed and thediffusion characteristics of water in the polymer werestudied. Further another poly(vinyl alcohol) system, with 600repeating units, was used to study oxygen diffusion in dry andwet poly(vinyl alcohol). In these systems the focus was toinvestigate the oxygen paths relative to the backbone and alsothe effect of water on the diffusion coefficients. Jump mapsand correlation function between the velocity of the oxygen wascalculated. The water has a huge impact on the oxygen diffusionand the preferred paths. A larger molecule (limonene) was studied in a polyethylenematrix consisting of 6000 anisotropic united atoms. A 100 nslong trajectory was recorded and also shortertrajectories atdifferent temperatures, which gave the temperature dependenceof the diffusion coefficients. Correlation functions for thelimonene molecule shows that it rotates and tumbles when movingthru the matrix. The main results from the molecular dynamics simulationsshowed that diffusion of larger molecules are possible and alsothat molecular dynamics simulations can predict plasticizationeffects. A new fast experimental method for determining diffusioncoefficients with non iso thermal thermogravimetry weredeveloped. The advantage is that the experiments only takesminutes instead of days with a small effect on theaccuracy.

We have used a molecular modeling of both random and blocky sequence hydrogel networks of poly(N-vinyl-2-pyrrolidone-co-2-hydroxyethyl methacrylate) (P(VP-co-HEMA)) with a composition of VP:HEMA = 37:13 to investigate the effect of the monomeric sequence and the water content on the equilibrium structures and the mechanical and transport properties by full-atomistic molecular dynamics (MD) simulations. The degree of randomness of the monomer sequence for the random and the blocky copolymers, were 1.170 and 0.104, respectively, and the degree of polymerization was fixed at 50. The equilibrated density of the hydrogel was found to be larger for the random sequence than for the blocky sequence at low water contents (< 40 wt %), but this density difference decreased with increasing water content. The pair correlation function analysis shows that VP is more hydrophilic than HEMA and that the random sequence hydrogel is solvated more than the blocky sequence hydrogel at low water content, which disappears with increasing water content. Correspondingly, the water structure is more disrupted by the random sequence hydrogel at low water content but eventually develops the expected bulk-water-like structure with increasing water content. From mechanical deformation simulations, the stress-strain analysis showed that the VP is found to relax more efficiently, especially in the blocky sequence, so that the blocky sequence hydrogel shows less stress levels compared to the random sequence hydrogel. As the water content increases, the stress level becomes identical for both sequences. The elastic moduli of the hydrogels calculated from the constant strain energy minimization show the same trend with the stress-strain analysis. Ascorbic acid and D-glucose were used to study the effect of the monomeric sequence on the diffusion of small guest molecules within the hydrogels. By analyzing the pair correlation functions, it was found that the guest molecule has greater accessibility to the VP units than to the HEMA units with both monomeric sequences due to its higher hydrophilicity compared to the HEMA units. The monomeric sequence effect on the P(VP-co-HEMA) hydrogel is clearly observed with 20 wt % water content, but the monomeric sequence effect is significantly reduced with 40 wt % water content and disappears with 80 wt % water content. This is because the hydrophilic guest molecules are more likely to be associated with water molecules than with the polymer network at the high water content. By analyzing the mean square displacement, the displacement of the guest molecules and the inner surface area, it is also found that the guest molecule is confined in the system at 20 wt % water content, resulting in highly anomalous subdiffusion. Therefore, the diffusion of the guest molecules is directly affected by their interaction with the monomer units, the monomeric sequence and the geometrical confinement in the hydrogel at a low water content, but the monomeric sequence effect and the restriction on the diffusion of the guest molecule are significantly decreased with increasing the water content. We also investigated the de-swelling mechanisms of the surface-grafted poly(N-isopropylacrylamide) (P(NIPAAm)) brushes containing 1300 water molecules at 275 K, 290 K, 320 K, 345 K, and 370 K. We clearly observed the de-swelling of the water molecules for P(NIPAAm) above the lower critical solution temperature (LCST) (~305 K). Below the LCST, we did not observe the de-swelling of water molecules. Using the upper critical solution temperature (UCST) systems (poly(acrylamide) brushes) for comparison purposes, we did not observe the de-swelling of water molecules at a given range of temperatures. By analyzing the pair correlation functions and the coordination numbers, the de-swelling of the water molecules occurred distinctly around the isopropyl group of the P(NIPAAm) brush above the LCST because C(NIPAAm) does not offer sufficient interaction with the water molecules via the hydrogen bonding type of secondary interaction. We also found that the contribution of the N(NIPAAm)-O(water) pair is quite small because of the steric hindrance of the isopropyl group. By analyzing the change in the hydrogen bonds, the hydrogen bonds between polar groups and water molecules in the P(NIPAAm) brushes weaken with increasing temperature, which leads to the de-swelling of the water molecules out of the brushes above the LCST. Below the LCST, the change in the hydrogen bonds is not significant. Again, the contribution of the NH(NIPAAm)-water pairs is insignificant; the total number of hydrogen bonds is ~20, indicating that the interaction between the NH group and the water molecules is not significant due to steric hindrances. Lastly, we observed that the total surface area of the P(NIPAAm) brushes that is accessible to water molecules is decreased by collapsing the brushes followed by the de-swelling of water molecules above the LCST.

We analyze experimental evidence of transport through evanescent waves in graphene, reconciling existing experimental data with theory. We propose novel experimental geometries that provide even more compelling evidence of evanescent waves. We investigate the shot noise generated by evanescent modes in graphene for several experimental setups. For two impurity-free graphene strips kept at the Dirac point by gate potentials, separated by a long highly doped region, we find that the Fano factor takes the universal value F=1/4. For a large superlattice consisting of many strips gated to the Dirac point, interspersed among doped regions, we find F=1/(8ln2). These results differ from the value F=1/3 predicted for a disordered metal, providing an unambiguous experimental signature of evanescent mode transport in graphene. For a graphene nano-ribbon transistor geometry, we explain that the experimentally observed anomalous voltage scale of the shot noise can arise from doping by the contacts to the electrical circuit. These observations provide strong evidence of evanescent mode transport in graphene.

Non-woven carbon paper is a porous material composed of carbon composite and is the preferred material for use as the gas diffusion layer (GDL) of polymer electrolyte membrane (PEM) fuel cells. This material is both chemically and mechanically stable and provides a free path for diffusion of reactants and removal of products and is electrically conductive for transport of electrons. The transport of species in the GDL has a direct effect on the overall reaction rate in the catalyst layer. Numerical simulation of these transport phenomena is dependent on the transport properties associated with each phenomenon. Most of the available correlations in literature for these properties have been formulated for spherical shell porous media, sand and rock, which are not representative of the structure of the GDL. Hence, the objective of this research work is to investigate the transport properties (diffusion coefficient, thermal conductivity, electrical conductivity, intrinsic and relative permeability and the capillary pressure) of the GDL using experimental and numerical techniques. In this thesis, a three-dimensional reconstruction of the complex, anisotropic structure of the GDL based on stochastic models is used to estimate its transport properties. To establish the validity of the numerical results, an extensive comparison is carried out against published and measured experimental data. It was found that the existing theoretical models result in inaccurate estimation of the transport properties, especially in neglecting the anisotropic nature of the layer. Due to the structure of the carbon paper GDL, it was found that the value of the transport properties in the in-plane direction are much higher than that in the through-plane direction. In the in-plane direction, the fibers are aligned in a more structured manner; hence, the resistance to mass transport is reduced. Based on the numerical results presented in this thesis, correlations of the transport properties are developed. Further, the structure of the carbon paper GDL is investigated using the method of standard porosimetry. The addition of Teflon was found have little effect on the overall pore volume at a pore radius of less than 3 micro meters. A transition region where the pore volume increased with the increase in pore radius was found to occur for a pore radius in the range 3<5.5 micro meters regardless of the PTFE content. Finally, the reduction of the overall pore volume was found to be proportional to the PTFE content. The diffusion coefficient is also measured in this thesis using a Loschmidt cell. The effect of temperature and PTFE loading on the overall diffusibility is examined. It was found that the temperature does not have an effect on the overall diffusibility of the GDL. This implies that the structure of the GDL is the main contributor to the resistance to gas diffusion in the GDL. A comparison between the measured diffusibility and that predicted by the existing available models in literature indicate that these models overpredict the diffusion coefficient of the GDL significantly. Finally, both the in-plane and through-plane thermal conductivity were measured using the method of monotonous heating. This method is a quasi-steady method; hence, it allows the measurement to be carried out for a wide range of temperatures. With this method, the phase transformation due to the presence of PTFE in the samples was investigated. Further, it was found that the through-plane thermal conductivity is much lower than its in-plane counterpart and has a different dependency on the temperature. Detailed investigation of the dependency of the thermal conductivity on the temperature suggests that the thermal expansion in the through-plane direction is positive while it is negative in the in-plane direction. This is an important finding in that it assists in further understanding of the structure of the carbon paper GDL. Finally, the thermal resistance in the through-plane direction due to fiber stacking was investigated and was shown to be dependent on both the temperature and compression pressure.