题目：Surface Waves in Polar Ultra-Thin Films
邀请人：赵长颖 教授（工程热物理研究所）、鞠生宏 副教授（中英低碳学院）
Dr. Sebastian Volz is a Full Professor at the French National Scientific Research Center (CNRS), CNRS Senior Research Fellow at the University of Tokyo, Laboratory of Integrated Micro Mechatronic Systems (LIMMS). He received his Ph.D degree in engineering physics from University of Poitiers (France) in 1993. He was then appointed post-doctoral fellow at the University of Caliornia, Los Angeles (USA) with Prof. Gang Chen. So far, He has published 3 books, 11 book chapters and over 140 scientific articles, including Nature Materials, Nature Photonics, Nature Communications, PRL, and Adv Mater. Currently, he is the Associate Editor of the journal of Nanoscale and Microscale Thermophysical Engineering and the journal of Nanoelecronics and Optoelectronics.
Thermal transport becomes less efficient as structures scale down since phonon-boundary scattering becomes predominant, therefore thermal management becomes more challenging in micro-electronic or optical devices. Here we aim at revealing the predominance of Surface Phonon-Polaritons (SPhPs) in thin film heat conduction. SPhPs are evanescent electromagnetic waves coupled to optical phonons and propagating along the interfaces of polar dielectrics. Through theoretical demonstration, SPhP propagation length reaches ten micrometers and SPhP spectral range reduces to the one of Surface Phonon-Polariton resonance in semi-infinite systems. Consequently, SPhPs contribution to heat flux along a surface is usually found negligible.
We have shown that thin film geometries allow for drastic changes in the surface evanescent electromagnetic field in terms of spectrum broadening and of propagation length. In thin silica films with thicknesses smaller than 1 micron, propagation length can reach centimeters and more, and evanescent waves exist in the full spectral range. Our calculations predict that those two modifications yield guided radiative heat fluxes higher than the one carried by phonons.
Moreover, thermal conductivity contributed by SPhPs can be further enhanced by increasing temperature. Nevertheless no experimental result directly proves neither the existence of a SPhP heat channel nor the enhancement of thermal conductivity in thin film due to those carriers. We experimentally measure effective in-plane thermal conductivity of SiO2 thin films and show that it can indeed be significantly increased by surface SPhPs when the film thickness scales down.