Faculty Achievement: Dr. Thomas Wilson

Zhi Liang, Professor of Mechanical Engineering, California State University – Fresno, Thomas Wilson, Professor of Physics, Marshall University, and Pawel Keblinski, Professor and Department Head, Materials Science and Engineering Department, Rensselaer Polytechnic Institute, have published “Phonon interference in crystalline and amorphous confined nanoscopic films” in the Journal of Applied Physics, Volume 121, Issue 8, 075303, February 28, 2017. It can be viewed online at: http://dx.doi.org/10.1063/1.4976563.

Phonons are the primary thermal energy carriers in semiconductor devices. As the size of semiconductor components in microelectronics reduces to nanoscale, phonon scattering at material interfaces can strongly affect thermal transport in nanostructured components. It has been found in numerous experiments and numerical simulations that the specular reflection and transmission of phonon waves at interfaces of nanostructured components may result in phonon interference effects which can be used for the modification of phonon dispersion and for controlling nanoscale heat transport.

Abstract: Using molecular dynamics phonon wave packet simulations, we study phonon transmission across hexagonal (h)-BN and amorphous silica (a-SiO2) nanoscopic thin films sandwiched by two crystalline leads. Due to the phonon interference effect, the frequency-dependent phonon transmission coefficient in the case of the crystalline film (Si|h-BN|Al heterostructure) exhibits a strongly oscillatory behavior. In the case of the amorphous film (Si|a-SiO2|Al and Si|a-SiO2|Si heterostructures), in spite of structural disorder, the phonon transmission coefficient also exhibits oscillatory behavior at low frequencies (up to ∼1.2 THz), with a period of oscillation consistent with the prediction from the two-beam interference equation. Above 1.2 THz, however, the phonon interference effect is greatly weakened by the diffuse scattering of higher-frequency phonons within an a-SiO2 thin film and at the two interfaces confining the a-SiO2 thin film.