Session: 03-03: Micro/Nanoscale Interfacial Transport Phenomena

Paper Number: 133021

133021 - Measuring Nanoscale Interfacial Heat Transport Across Solid-Liquid, -Gas, and -Plasma Interfaces: How Matter Heats and Cools 

Abstract: 

The fundamental interactions among photons, electrons and phonons at interfaces dictate heat transport across a wide array of heterojunctions between various phases of matter.  These energy carrier interactions at interfaces of various phases of matter become more important to fundamentally understand and quantify as energy production, communication, and computing technologies continue to advance.  In this work, I will discuss our recent experimental developments that are designed to measure the energy coupling of liquid, gas or plasma interactions at solid surfaces. Through the use of wavelength tunable sub-picosecond pump-probe techniques, we demonstrate the ability to measure the temporal energy exchange across a solid/gas or liquid interface.  By tuning the wavelength, we measure the spectral dependence of the energy transfer. 

In this work, we first theoretically and experimentally study the scattering nature of how acoustic phonons in a solid transmit energy to molecules in a gas. Specifically, we seek to answer the question, do acoustic phonons in a solid transmit their energy to gas molecules via specular or diffusive surface interactions? We derive new models based on semi-classical phonon interfacial transmission theories that predict the transmission probability of acoustic waves across a solid/gas interfaces assuming either specular or diffusive interactions between the long wavelength phonon modes in a solid with the energetic particles in the gas. We then study the validity of these theories through our recently modified picosecond ultrasonic measurement platform to monitor the change in photo-thermally-excited acoustic wave transmission in a gold film in argon atmospheres with varying temperatures and pressures. We demonstrate clear evidence that diffusive rather than specular scattering between the acoustic phonons in the solid and molecules in the gas drives interfacial energy trans- mission across the gold/Ar interface. The temperature and pressure dependence on this phononic energy transmission into the gas also provide experimental validation to previous theoretical and computational findings on the thermal boundary conductance across solid/gas interfaces and thermal accommodation of gas molecules on heated surfaces.

We then extend this study to measure the heat transfer processes across solid/plasmas interface, in which a directed atmospheric plasma jet is focused on a gold film surface, while we interrogate the thermal dynamics with a cw probe pulse.  We find that due to the various energetic particles that impinge on the Au surface during plasma excitation, a local and temporal cooling occurs, resulting a “plasma cooling”, which results in a local temperature drop at the interface during plasma excitation. The results indicate photon-stimulated desorption of adsorbates from the surface is the most likely mechanism responsible for this plasma cooling (Nature Communications, 13:2623, 2022)

Presenting Author: Patrick Hopkins Professor

Presenting Author Biography: Patrick E. Hopkins is a Professor in Department of Mechanical and Aerospace Engineering at the University of Virginia, with courtesy appointments in the Department of Materials Science and Engineering and the Department of Physics. Patrick received his Ph.D. in Mechanical and Aerospace Engineering at the University of Virginia in 2008 under the mentorship of Professor Pamela Norris. After his Ph.D., Patrick was one of two researchers in the nation to receive a Truman Fellowship from Sandia National Laboratories in 2008, working under the mentorship of Dr. Leslie Phinney. In 2011, Patrick returned to the University of Virginia and joined the faculty. Patrick’s current research interest are in energy transport, charge flow, laser-chemical processes and photonic interactions with condensed matter, soft materials, liquids, vapors and their interfaces. Patrick’s group at the University of Virginia uses various optical thermometry-based experiments to measure the thermal conductivity, thermal boundary conductance, emissivity, thermal accommodation, strain propagation and sound speed, and coupled electron, phonon, and photon mechanisms in a wide array of bulk materials and nanosystems. In 2021, Patrick co-founded Laser Thermal, Inc., a company based in Charlottesville Virginia that is commercializing thermal conductivity measurement systems that provide non-contact, automated metrologies for thermal properties of thin films, coatings and bulk materials.

In the general fields of nanoscale heat transfer, laser interactions with matter, and energy transport, storage and capture, Patrick has authored or co-authored over 300 technical papers (peer reviewed) and been awarded 5 patents focused on materials, energy and laser metrology for measuring thermal properties. Patrick has been recognized for his accomplishments in these fields via AFOSR and ONR Young Investigator Awards, the ASME Bergles-Rohsenhow Young Investigator Award in Heat Transfer, and a Presidential Early Career Award for Scientists and Engineering (PECASE, awarded by DoD/ONR). Patrick is a fellow of ASME and was recently awarded the ASME Gustus L. Larson Memorial Award. During 2021-2022, Patrick was awarded a Humboldt Fellowship to work on laser thermometry of materials in extreme environments at the Joint Research Center in Karlsruhe, Germany.

Authors:

Patrick Hopkins Professor