Multicomponent metal alloys play an essential role in many technologies and their properties must be optimized by rational selection of the alloy’s components and its fractional composition of each. High-throughput materials synthesis allows us to prepare Composition Spread Alloy Films (CSAFs), sample libraries that contains all possible compositions of a binary or ternary alloy. In our lab, a Rotatable Shadow Mask (RSM) – CSAF deposition tool has been developed for the creation of CSAFs. Such CSAFs can be prepared with composition gradients and/or thickness gradients in arbitrarily controlled directions and on a variety of substrates. Once prepared, the CSAF libraries can be characterized thoroughly using a variety of highthroughput spectroscopic methods. Their bulk composition is mapped across the library using Energy Dispersive X-ray spectroscopy (EDX). The near-surface compositions are mapped across composition space using X-ray Photoemission Spectroscopy (XPS). Finally, the electronic structure can be mapped using UV photoemission spectroscopy (UPS) and valence band XPS. Once characterized, these CSAFs are being used for high-throughput studies of alloy catalysis and thermal properties of the alloys and of alloy-substrate interfaces. First of all, PdzCu1-z CSAF was prepared to show that alloy nanoparticles (aNPs) and thin films can adopt phases that differ from those of the corresponding bulk alloy. The mapping of XPS-derived core level binding energy shifts across PdzCu1-z SCSNaP library shows a promising result that the FCC phase can be dimensionally stabilized over the composition range where B2 phase exists in the bulk. This observation can potentially improve the performance of PdzCu1-z NP catalysts in H2 separation. Secondly, the relationship between catalyst activity-electronic structure-composition has been investigated. A high throughput characterization of electronic structure (valence band energy) of binary PdxAg1-x and ternary PdxCuyAu1-x-y CSAFs were performed by XPS. This XPS-derived valence band center is compared with UPS-derived data across PdxCuyAu1-x-y CSAFs. In addition, H2-D2 exchange reaction was studied on PdxAg1-x CASF. A higher HD formation rate is experimentally observed but cannot be predicted by the Langmuir-Hinshelwood model when the surface coverage is saturated. However, the proposed H2-D2 exchange mechanism (breakthrough model) involved with surface and subsurface hydrogen reaction is investigated to produce a same reaction order as Langmuir-Hinshelwood mechanism, which cannot explain the experimental observation. Furthermore, the thermal interface conductance (G) was studied as a function of metal alloy composition. A high-throughput approach to preparation, characterization, and measurement of G was also demonstrated to study the thermal property of alloyed materials. Our result in studying the G across the AuxY1-x (Y = Pd and Cu) CSAFs-dielectric interfaces has shown a linear relationship with alloy composition, which monotonically increases with decreasing Au (at. %). Lastly, the effect of interdiffusion in metal films on G at metal-dielectric interface was also examined. The XPS depth profiling was designed to experimentally determine the temperature effect on compositional profiles in the Au-Cu system, and how to further influence G. This study provides fundamental understanding of stability of adhesion layer of Cu and the effect of interdiffusion in Cu-Au alloy on the heat dissipation. All in all, the key value to these CSAF libraries is that they enable measurement of important alloy properties across entire binary or ternary alloy composition spaces, without the need to prepare and characterize numerous discrete composition samples.

Thermoelectric devices are useful for a variety of applications due to their ability to either convert heat directly into electricity, or to generate a temperature gradient from an electric current. These devices offer several attractive features including compact size, no moving parts, limited maintenance requirements, and high reliability. Thus thermoelectric devices are used for temperature-control, cooling, or power generation in various industrial systems such as automobiles, avionics, refrigerators, chillers, laser diodes, dehumidifiers, and a variety of sensors. In order to improve the efficiency of thermoelectric devices, many endeavors have been made to design and fabricate materials with a higher dimensionless thermoelectric figure of merit (ZT), as well as to optimize the device structure and packaging to manage heat more effectively. When evaluating candidate thermoelectric materials, one must accurately characterize the electrical conductivity, thermal conductivity, and the Seebeck coefficient over the temperature range of potential use. However, despite considerable research on thermoelectric materials for decades, there is still significant scatter and disagreement in the literature regarding accurate characterization of these properties due to inherent difficulties in the measurements such as requirements for precise control of temperature, simultaneous evaluation of voltage and temperature, etc. Thus, a well-designed and well-calibrated thermoelectric measurement system that can meet the requirements needed for multiple kinds of thermoelectric materials is an essential tool for the development of advanced thermoelectric devices. In this dissertation, I discuss the design, fabrication, and validation of a measurement system that can rapidly and accurately evaluate the Seebeck coefficient and electrical resistivity of thermoelectric materials of various shapes and sizes from room temperature up to 600 K. The methodology for the Seebeck coefficient and electrical resistivity measurements is examined along with the optimization and application of both in the measurement system. The calibration process is completed by a standard thermoelectric material and several other materials, which demonstrates the accuracy and reliability of the system. While a great deal of prior research has focused on low temperature thermoelectric materials for cooling, such as Bi2Te3, high temperature thermoelectric materials are receiving increasing attention for power generation. With the addition of commercial systems for the Seebeck coefficient, electrical resistivity, and thermal conductivity measurements to expand the temperature range for evaluation, a wide range of materials can be studied and characterized. Chapter Two of this dissertation describes the physical properties characterization of a variety of thermoelectric materials, including room temperature materials such as Bi0.5Sb1.5Te3, medium temperature level materials such as skutterudites, and materials for high temperature applications such as half-Heusler alloys. In addition, I discuss the characterization of unique oxide thermoelectric materials, which are Al doped ZnO and Ca-Co-O systems for high temperature applications. Chapter Four of this dissertation addresses the use of GaSn alloys as a thermal interface material (TIM), to improve thermal transport between thermoelectric devices and heat sinks for power generation applications at high temperature. I discuss the mechanical and thermal behavior of GaSn as an interface material between electrically insulating AlN and Inconel heat exchangers at temperatures up to 600 °C. Additionally, a theoretical model for the experimental thermal performances of the GaSn interface layer is also examined. / Ph. D. / Thermoelectric materials can directly convert heat into electricity for power generation, or they can be used for cooling or refrigeration applications when supplied with electric power. This dissertation primarily focuses on the evaluation of materials used in thermoelectric generators (TEGs). Specifically, Chapter Two of this work describes the design, development, and validation of a developed measurement system that can evaluate two important properties, the Seebeck coefficient and electrical resistivity, for a variety of thermoelectric materials. Next, Chapter Three discusses the work using other commercial measurement systems to evaluate several types of thermoelectric materials, including Bi2Te3 based materials, skutterudites, half-Heusler alloys, ZnO, and Ca-Co-O for a TEG module. Finally, I discuss the use of GaSn, a liquid metal alloy, as a thermal interface material to improve heat transport between dissimilar materials for TEGs. The GaSn was applied between a thermoelectric device and a heat exchanger for use in energy harvesting devices. The mechanical robustness and thermal reliability were tested, and the GaSn was shown to improve thermal performances both in experiments and through modeling.