Thermal Transport and Energy Transfer Mechanisms across Interfaces Composed of Varying Phases of Matter

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.