Recent trend of minimization in microprocessors has introduced increasing self-heating effects in FinFET and MOSFET transistors. To study these self-heating effects, we developed self-consistent 3D models of FinFET and MOSFET basic logic gates, and simulated steady-state thermal transport for the worst heating case scenario. Incorporating size-dependent effective thermal conductivity of thin films instead of bulk values, these simulations provide a more accurate prediction of temperature rise in the logic gates. Results of our simulations predict higher temperature rise in FinFETs, compared to MOSFETs. Existence of buried oxide layer and confined geometry of FinFET structure are determined to be the most contributing to this higher temperature rise. To connect the results of our simulations to higher scale simulations, we proposed an equivalent thermal conductivity for each basic logic gate. These values were tested and found to be independent of the magnitude of chosen boundary conditions, as well as heat generation rate.

Advancements in the semiconductor industry have lead to the miniaturization of components and increased power densities, resulting in thermal management issues. In response to this shift, finding multifunctional materials with excellent thermal conductivity and tailored electrical properties are becoming increasingly important. For this research thesis, three different studies were conducted to develop and characterize thermally conductive polymer composites. In the first study, a PPS matrix was combined with different types of carbon-based fillers to determine the effects of filler’s size, shape, and orientation on thermal conductivity. In the second study, effects of adding ceramic- and carbon- based fillers on the tailored thermal and electrical properties of composites were investigated. Lastly, the possibility of improving the thermal conductivity by introducing and aligning polymer fibers in the composites was investigated. The composites were characterized with respect to their physical, thermal, and electrical properties to propose possibilities of application in the electronic packaging industries.

Recent trend of minimization in microprocessors has introduced increasing self-heating effects in FinFET and MOSFET transistors. To study these self-heating effects, we developed self-consistent 3D models of FinFET and MOSFET basic logic gates, and simulated steady-state thermal transport for the worst heating case scenario. Incorporating size-dependent effective thermal conductivity of thin films instead of bulk values, these simulations provide a more accurate prediction of temperature rise in the logic gates. Results of our simulations predict higher temperature rise in FinFETs, compared to MOSFETs. Existence of buried oxide layer and confined geometry of FinFET structure are determined to be the most contributing to this higher temperature rise. To connect the results of our simulations to higher scale simulations, we proposed an equivalent thermal conductivity for each basic logic gate. These values were tested and found to be independent of the magnitude of chosen boundary conditions, as well as heat generation rate.

A single polymer electrolyte membrane fuel cell (PEMFC) is comprised of several sub-millimetre thick layers of varying porosity sandwiched together. The thickness of each layer, which typically ranges from 10 to 200μm, is kept small in order to minimize the transport resistance of heat, mass, electrons, and protons, that limit reaction rate. However, the thickness of these materials presents a significant challenge to engineers characterizing the transport properties through them, which is of considerable importance to the development and optimization of fuel cells. The objective of this research is to address the challenges associated with measuring the heat conduction and gas diffusion transport properties of thin porous media used in PEMFCs. An improvement in the accuracy of the guarded heat flow technique for measuring thermal conductivity and the modified Loschmidt Cell technique for measuring gas diffusivity are presented for porous media with a sub-millimetre thickness. The improvement in accuracy is achieved by analyzing parameters in each apparatus that are sensitive to measurement error and have the largest contribution to measurement uncertainty, and then developing ways to minimize the error. The experimental apparatuses are used to investigate the transport properties of the gas diffusion layer (GDL) and the microporous layer (MPL), while the methods would also be useful in the study of the catalyst layer (CL). Gas diffusion through porous media is critical for the high current density operation of a PEMFC, where the electrochemical reaction becomes rate-limited by the diffusive flux of reactants reaching reaction sites. However, geometric models that predict diffusivity of the GDL have been identified as inaccurate in current literature. Experimental results give a better estimate of diffusivity, but published works to date have been limited by high measurement uncertainty. In this thesis, the effective diffusivity of various GDLs are measured using a modified Loschmidt cell and the relative differences between GDLs are explained using scanning electron microscopy and the method of standard porosimetry. The experimental results from this study and others in current literature are used to develop a generalized correlation for predicting diffusivity as a function of porosity in the through-plane direction of a GDL. The thermal conductivity and contact resistance of porous media are important for accurate thermal analysis of a fuel cell, especially at high current densities where the heat flux becomes large. In this thesis, the effective through-plane thermal conductivity and contact resistance of the GDL and MPL are measured. GDL samples with and without a MPL and coated with 30%-wt. PTFE are measured using the guarded steady-state heat flow technique described in the ASTM standard E 1225-04. Thermal contact resistance of the MPL with the iron clamping surface was found to be negligible, owing to the high surface contact area. Thermal conductivity and thickness of the MPL remained constant for compression pressures up to 15bar at 0.30W/m°K and 55μm, respectively. The thermal conductivity of the GDL substrate containing 30%−wt. PTFE varied from 0.30 to 0.56W/m°K as compression was increased from 4 to 15bar. As a result, the GDL contain- ing MPL had a lower effective thermal conductivity at high compression than the GDL without MPL. At low compression, differences were negligible. The constant thickness of the MPL suggests that the porosity, as well as heat and mass transport properties, remain independent of the inhomogeneous compression by the bipolar plate. Despite the low effective thermal conductivity of the MPL, thermal performance of the GDL can be improved by exploiting the excellent surface contact resistance of the MPL while minimizing its thickness.

Currently, in the field of reactor physics, there is a drive for high fidelity, numerical simulations of reactors for the purposes of design and analysis. Since the behavior of a reactor is dependent on various physical phenomena, high fidelity simulations must be able to accurately couple these different types of physics. This is the essence of multiphysics simulations. In order to accurately simulate the thermal behavior of a reactor, the physics of neutron transport must be coupled to the fluid flow and solid phase conduction occurring within the reactor. This thesis develops a computational fluid dynamics solver for this purpose. The solver is based on the PCICE solution algorithm and employs cell-centered finite volumes. In addition to the fluid dynamics solver, a newly developed form of conjugate heat transfer is implemented. This implementation tightly couples the physics of solid phase heat conduction with the fluid dynamics in an efficient and consistent manner. Finally, the radiation transport code EVENT is used to provide heat generation data to the fluids solver. Using this fluids solver, several benchmark problems are analyzed and the formulation is validated.

The present work investigates the effect of carbon nanotube (CNT) inclusions on the electrical and thermal conductivity of a thermoset epoxy resin. The characterization of electrical and thermal conductivity of CNT/epoxy composites is presented. Pristine, oxidized, and fluorine-functionalized unpurified CNT mixtures ("XD grade") were dispersed in an epoxy matrix, and the effect of stirring rate and pre-curing of the epoxy on the dispersion of the CNTs was evaluated. In order to characterize the dispersion of the CNTs at different length scales, Optical Microscopy (OM), Raman Spectroscopy, and Scanning Electron Microscopy (SEM) was performed. Samples of varying CNT weight fractions were fabricated in order to find the effect of CNT weight fraction on thermal and electrical conductivity. Electrical conductivity was measured using a dielectric spectrometer, and thermal conductivity was determined by a transient plane source thermal analyzer. It was found that electrical conductivity increases by orders of magnitude for the pristine and oxidized XD CNT composites relative to the neat epoxy matrix, while fluorinated XD CNT composites remain electrically non-conductive. A small, but significant, increase in thermal conductivity was observed for pristine, oxidized, and fluorinated XD CNT composites, showing a linear increase in thermal conductivity with increasing CNT weight fraction. Pristine XD CNTs were ball-milled for different times in order to reduce the degree of agglomeration and entanglement of CNTs, and composites were fabricated using the same technique as with non-milled XD CNTs. Using ball-milled CNTs shows improved dispersion but results in an electrically non-conductive composite at the CNT weight fractions tested. The thermal conductivity of the ball-milled CNT samples shows an initial increase higher than that of non-milled pristine, oxidized, and fluorinated XD CNTs, but remains constant with increasing CNT weight fraction. A micromechanics model based on the composite cylinders method was implemented to model the electrical and thermal conductivity of the CNT/epoxy composites. Nanoscale effects in electrical and thermal conduction, such as electron hopping and interface thermal resistance, respectively, were incorporated into the model in order to accurately predict the acquired results. Modeling results show good agreement with acquired experimental results.

Geopolymers (GPs) are a special class of inorganic polymers with unique properties. Their 3-D amorphous structure and properties are often attributed to SiO2/Al2O3 molar ratios. However; contradictory results reported in literature on the structure and properties, do not conclusively support these reported findings. Furthermore, alternative processing methods are necessary for synthesizing pure geopolymers without impurities often found in precursor material. A rigorous study on chemical composition and processing parameters as well as alternative processing methods are necessary for advancing GPS in various engineering applications. The effects of H2O/(SiO2 + Al2O3) and SiO2/Al2O3 molar ratios , as well as precursor material on the density, open porosity, microstructure and the thermal and mechanical properties in K and Na activated geopolymers is investigated. X-ray diffraction, Nuclear Magnetic Resonance as well as alcohol immersion to determine density and open porosity is utilized for structural characterization. Thermogravimetric analysis and Thermomechanical analysis are used to investigate thermal behavior. Thermal conductivities and mechanical properties were measured using Thermal Constant analysis and compression testing respectively. Conclusive results demonstrate that the amount of water used to process GPs is the governing factor affecting their structure while SiO2/Al2O3 molar ratio plays no significant role. The K- and Na-activated samples have similar amounts of residual water after aging for 21 days at ambient conditions. In addition, the effects of the initial water content, SiO2/Al2O3 ratio, and alkaline activator (Na or K) on the thermal and mechanical properties of GPs, indicate that the dominant factor controlling thermal conductivity is H2O/(SiO2 + Al2O3) ratio used in processing, and to a lesser degree, the type of activation ion (Na or K). The SiO2/Al2O3 ratio did not have an effect on thermal conductivity. However, GPs compressive strengths are strongly affected by H2O/(SiO2 + Al2O3) ratio, especially at higher water ratio. At high and intermediate H2O/(SiO2 + Al2O3) ratios, liquid/solid ratio is the most important factor controlling the strength of GPs. At low H2O/(SiO2 + Al2O3) ratios, SiO2/Al2O3 ratio also plays an important role. Finally, partial geopolymer synthesis was possible using pure SiO2 and Al(OH)3 precursors, providing a possible low temperature alternative to other aluminosilicate precursors.

With excellent electrical, thermal and mechanical properties as well as large specific surface area, graphene has been applied in next-generation nano-electronics, gas sensors, transparent electrical conductors, thermally conductive materials, and superior energy capacitors etc. Convenient and productive preparation of graphene is thereby especially important and strongly desired for its manifold applications. Chemically developed functionalized graphene from graphene oxide (GO) has significantly high productivity and low cost, however, toxic chemical reduction agents (e.g. hydrazine hydrate) and raised temperature (400-1100°C) are usually necessary in GO reduction yet not preferred in current technologies. Here, microwaves (MW) are applied to reduce the amount of graphene oxide (GO) at a relatively low temperature (~165°C). Experimental results indicate that resurgence of interconnected graphene-like domains contributes to a low sheet resistance with a high optical transparency after MW reduction, indicating the very high efficiency of MW in GO's reduction. Moreover, graphene is usually recumbent on solid substrates, while vertically aligned graphene architecture on solid substrate is rarely available and less studied. For TIMs, electrodes of ultracapacitors, etc, efficient heat dissipation and electrical conductance in normal direction of solid surfaces is strongly desired. In addition, large-volume heat dissipation requires a joint contribution of a large number of graphene sheets. Graphene sheets must be aligned in a large scale array in order to meet the requirements for TIM application. Here, thermally conductive fuctionalized multilayer graphene sheets (fMGs) are efficiently aligned in a large scale by vacuum filtration method at room temperature, as evidenced by SEM images and polarized Raman spectroscopy. A remarkably strong anisotropy in properties of aligned fMGs is observed. Moreover, VA-fMG TIMs are prepared by constructing a three-dimensional vertically aligned functionalized multilayer graphene architecture between contact Silicon/Silicon surfaces with pure Indium as a metallic medium. Compared with their counterpart from recumbent A-fMGs, VA-fMG TIMs have significantly higher equivalent thermal conductivity and lower contact thermal resistance. Electrical and thermal conductivities of polymer composite are also greatly interested here. Previous researches indicated that filler loading, morphology of fillers, and chemical bonding across filler/polymer interfaces have significant influence on electrical/thermal conductivity of polymer composite. Therefore, the research also pays substantial attention to these issues. First, electrical resistivity of CPCs is highly sensitive on volume or weight ratio (filler loading) of conductive fillers in polymer matrix, especially when filler loading is close to percolation threshold (pc). Thermal oxidation aging usually can cause a significant weight loss of polymer matrix in a CPC system, resulting in a filler loading change which can be exhibited by a prompt alteration in electrical resistivity of CPCs. Here, the phenomena are applied as approach for in-situ monitoring thermal oxidation status of polymeric materials is developed based on an electrical sensors based on conductive polymeric composites (CPCs). The study developed a model for electrical resistivity of sensors from the CPCs as a function of aging time at constant aging temperature, which is in a good agreement with a Boltzmann-Sigmoidal equation. Based on the finding, the sensors show their capability of in-situ in-situ monitor and estimate aging status of polymeric components by a fast and convenient electrical resistance measurement. Second, interfacial issues related to these thermal conductive fillers are systemically studied. On the one hand, the study focuses on relationship between morphology of h-BN particles and thermal conductivity of their epoxy composites. It is found that spherical-agglomeration of h-BN particles can significantly enhance thermal conductivity of epoxy resin, compared with dispersed h-BN plates, by substantially reducing specific interfacial area between h-BN and epoxy resin. On the other hand, surface of high thermal conductive fillers such as SiC particles and MWNTs are successfully functionalized, which makes their surface reactive with bisphenol A diglycidyl ether and able to form chemical bonding between fillers and epoxy resin. By this means, thermal conductivity of polymer composites is found to be significantly enhanced compared with control samples, indicating the interfacial chemical bonding across interface between thermal conductive fillers and polymer matrix can promote heat dissipation in polymeric composites. The finding can benefit a development of high thermal conductive polymer composites by interfacial chemical bonding enhancement to meet the demanding requirements in current fine pitch and Cu/low k technology.

The search of materials relevant for thermoelectric and magnetocaloric applications, as well as materials that interact with light, is an important aspect of the materials science. Such materials can be used for solid-state power generation and refrigeration, as light sources, detectors, or controllers. Intermetallic clathrates have long been of interest for the materials science research. The promise these materials hold for useful applications ranges from thermoelectrics to photovoltaics and optoelectronics to potentially ultra-hard materials and magnetic cooling applications. Their unique physical properties are intimately related to their intriguing structural properties. Thus a fundamental understanding of the chemistry and physics of inorganic clathrates offers the possibility to assess their potential for use in the various applications mentioned above. In this work the selective, phase pure, single-crystal growth of AxSi46 and AySi136 (A = Na, K) intermetallic clathrates by the new vapor-phase intercalation method is presented. The approach appears promising for accessing regions of the equilibrium diagrams for Na-Si and K-Si clathrates that can be otherwise difficult to reach due to the greatly differing properties of the constituent elements. Physical properties of these materials were investigated in terms of single-crystal diffraction, electrical and thermal properties measurements. The synthesis and structural properties of single crystals of NaxSi136 are presented. A two-step synthetic approach was employed for the synthesis of NaxSi136 which also allowed for low temperature transport measurements of polycrystalline NaxSi136. The potential of the Eu8Ga16Ge30 type-I and VIII - EuO composites for magnetocaloric applications is discussed. The type-I clathrate - EuO composites hold promise for active magnetic refrigeration around 70 K.

We conduct a comprehensive and systematic study of the Fermi-Pasta-Ulam (FPU) model using both equilibrium and non-equilibrium molecular dynamics simulations, with the aim being to explain the cause of the anomalous energy-transport behaviour in the model. In the equilibrium scenario, our motivation stems from the lack of a complete understanding of the effects of initial conditions on the energy dissipation among Fourier modes. We also critically reconsider the ????probes' that had been widely used to quantitatively describe the types of energy sharing in a system, and then decide on a preferred choice to be used in our equilibrium study. We establish, from strong numerical evidence, that there exists a critical energy density of approximately 0:1, above which the energy dissipation among the modes becomes independent of initial conditions and system parameters, and that the full equipartition of mode energy is never attained in the FPU model. We report, for the first time, the violation of particle positions in the FPU model at high energies, where the particles are found to pass through one another. In the non-equilibrium scenario, we critically review the Nos???Se-Hoover algorithm thermostatting method largely used by other works, and identify its weaknesses. We also review some other alternative methods and decide on the most appropriate one to be implemented throughout our work. We confirm the divergence of the thermal conductivity of the FPU model as the chain length increases, and that kfpu [symbol] No.41, in agreement with other works. Our study further shows that there exists an upper limit of the anharmonicity in the FPU model, and that any attempt to increase the strength of this anharmonicity will not succeed. We also introduce elastic collisions into the original FPU model and find that the Modified model (FPUC) still exhibits anomalous thermal conductivity. We conclude that a one-dimensional FPU-type model with ????only' nearest-neighbour interaction, regardless of being soft or hard, does not exhibit a finite thermal conductivity as the system size increases, due to the non-chaotic nature of its microscopic dynamics, the origin of which we are unable to account for. Finally, we briefly outline possible research directions.