SEMINAR

The State Key Lab of
High Performance Ceramics & Superfine Microstructure
Shanghai Institute of Ceramics, Chinese Academy of Sciences
中国科学院上海硅酸盐研究所高性能陶瓷和超微结构国家重点实验室

Thermal Energy Transport and Conversion in Nanostructured and Complex Materials

Speaker

Prof. Li Shi

Department of Mechanical Engineering and Texas Materials Institute

University of Texas at Austin

时间：6月8日（星期二）下午4：00

地点：四号楼14楼第一会议室

联系人：陈立东研究员

Abstract

Reducing or recovering the large amount of waste heat lost by transportation vehicles and electronic devices has gained increasing interest. High and low thermal conductivities, respectively, are desirable for increasing the energy efficiency of electronic and thermoelectric devices, both of which require high electron mobility. Recently, ultrahigh electron mobility and thermal conductivity have been reported in mechanically exfoliated small flakes of monolayer graphene. Here, we have developed a micro-Raman spectroscopy method to show that large-area suspended graphene grown using chemical vapor deposition possesses thermal conductivity higher than the highest bulk values found in graphite and diamond. We have further fabricated a suspended micro-thermometer device to reveal that the thermal conductivity of mechanically exfoliated graphene is reduced by the contact with a dielectric support because of phonon leakage across the interface, but is still considerably higher than the values of common electronic materials. In the other end of the thermal conductivity spectrum, we have developed another suspended micro-thermometer device to show highly anisotropic thermal transport in disordered-layered thin films that were found to possess ultralow cross-plane thermal conductivity. We have also found that the lattice thermal conductivity of nanowire structures is suppressed considerably for III-V semiconductors with long anharmonic phonon scattering mean free paths, but only slightly for bismuth telluride with already low bulk thermal conductivity and good thermoelectric figure of merit (ZT). In contrast, the thermal conductivity of higher manganese silicide (HMS) nanowires can be suppressed from the already low bulk values to the amorphous limit. This finding of a glassy thermal conductivity is attributed to the combined effect of a complex crystal structure and phonon-interface scattering in the HMS nanowires, and points to a potential approach to enhancing the ZT.

Biography

Prof. Li Shi received the B.E. degree in Thermal Engineering from Tsinghua University, Beijing in 1991, M.S. degree from Arizona State University in 1997, and Ph.D. degree in Mechanical Engineering from University of California at Berkeley in 2001. Dr. Shi was a Research Staff Member at IBM Research Division from 2001 to 2002. He has held positions of assistant professor between 2002 and 2006 and associate professor since 2006 at the Department of Mechanical Engineering and Texas Materials Institute, University of Texas at Austin. Dr. Shi specializes in thermal transport and thermoelectric energy conversion in nanostructured and complex materials. His other research efforts include nanotechnologies for drug delivery and biomedical imaging, and nano-catalysis for cleaner fossil fuel utilization. He received the CAREER award from the US National Science Foundation in 2003, the Young Investigator Award from US Office of Naval Research in 2004, the ASME Transaction Journal of Heat Transfer Outstanding Reviewer Award in 2005, and the Myron L. Begeman Fellowship in Engineering at UT Austin in 2007.