Abstract
Through the development of numerous optical metrologies, this work seeks to provide insight to one primary question: How does heat and energy transport occur across interfaces composed of varying phases of matter? The projects within this dissertation consider this question within all four phases of matter: Solid, liquid, gas, and plasma.
The vastly studied case of thermal transport across solid-solid interfaces provides itself to be an ideal test-bed for the development of novel experimental techniques for quantification and understanding of interfacial thermal resistances. Through one of these methods, a tunable mid-infrared pump-probe system, this work demonstrates a unique energy transduction process at metal-semiconductor interfaces, despite over a century of prior investigation; this process is manipulated for the modulation of plasmonic optical properties at ultrafast time-scales. In moving to interfaces composed of non-condensed phases of matter, I subsequently propose the application of these newly-developed techniques to the study of solid-liquid, solid-gas, and solid-plasma interfaces.
In the case of solid-liquid interactions, the vast disparities between nanoscale interactions and macroscale phenomenon are investigated. Additionally, through manipulation of these nanoscale interactions and development of a ‘programmable’ biopolymer, we identify a material system with the largest room temperature thermal switch ratio to-date.
In the solid-gas regime, these investigations extend to a much more fundamental level, seeking to answer the nature of nanoscale heat transfer from a solid to a gas: Is this thermal transport specular or diffusive? This question is elucidated upon by interpretation of ultrafast picosecond ultrasonic experiments with a newly-derived formulation for the acoustic and diffuse mismatch models (AMM and DMM).
Finally, we consider the fourth phase of matter: plasma. While plasmas have long been used for the synthesis and manipulation of materials because of their unique ability to deliver both energy and chemically-active species to the surface of a plasma exposed material - an attribute that separates them from other approaches to materials processing - this complex nature has greatly inhibited experimental realizations of time-resolved plasma-surface interactions. In this work, I demonstrate that non-contact thermoreflectance methods are particularly well-suited for such investigations and provide a direct measure of the energy transferred from an atmospheric plasma jet to a solid surface. Specifically, these measurements provide a direct measure of the localized, transient thermal response of a a material subjected to an incident plasma flux. In doing so, we demonstrate a regime in which plasma-induced cooling of the surface can be enabled.
