Dr. Yaguo Wang [from University of Texas at Austin]

Title: Ultrafast Phonon Dynamics in Thermoelectrics
Time: 10:00 - 11:00, December 12
Place: Conference Room 201, Building 6, HPSTAR (Shanghai)
Host: Jung-Fu Lin

Abstract:

This talk will demonstrate a comprehensive methodology to study the ultrafast phonon dynamics in thermoelectrics, combing femtosecond phonon spectroscopy and molecular dynamics simulations. The time-resolved ultrafast phonon spectroscopy can reveal the ultrafast dynamics of phonons occurring on femtosecond (10-15 s) to picosecond (10-12 s) time scales, provide valuable information about phonon frequency, lifetime and scattering rates at interfaces and defects. Extended Molecular Dynamics (MD) simulations are developed to predict the properties of each single phonon mode, identify the dominant phonons, and hence help design optimum phonon scattering channels. A case study demonstrating this methodology in Bi2Te3/Sb2Te3 superlattices (SL) will be presented. Comparing with bulk Bi2Te3, phonon scattering in Bi2Te3/Sb2Te3 SLs is greatly enhanced, which is attributed to the interfaces of the hetero-structure in SL. The sound velocity decreases by 10% in SLs, resulting from folding and flattening of phonons branches. Both interface scattering and the reduced phonon velocity contribute to suppressing the heat conduction in SLs. From MD simulations of Bi2Te3, it was found that 70% of the heat is carries by phonons with mean free path between 1~ 10nm.

Biography of the Speaker:
Dr. Yaguo Wang is currently an Assistant Professor of Mechanical Engineering Department at University of Texas at Austin. Dr. Wang received her Bachelor's degree in Safety Science and Engineering at the University of Science and Technology of China (USTC) in 2005 and her Ph.D. degree from the Department of Mechanical Engineering, Purdue University, Indiana, in 2011. After one-year's postdoctoral experience at Purdue University, she joined the faculty of UT Austin in January 2013. Dr. Wang received the Career Award from National Science Foundation in 2014. Dr. Wang's research focuses on the study of ultrafast phenomenon occurring from femtosecond (10-15 s) to picosecond (10-12 s) time scale in solid state materials with optical spectroscopy. Currently Dr. Wang's research interests include: ultrafast phonon/electron dynamics in semiconductors for energy applications; 2D materials in extreme environments; Computational studies of atomic-level heat transport with Molecular Dynamics simulations.