美国爱荷华州立大学Xinwei Wang教授讲座

From Thermal Transport to Structure Domain Size

主讲人 : Prof.Xinwei Wang

Electrical resistivity of  ls and its variation against temperature directly reflects the phonon scattering behavior, and is dependent on the phonon structure. On the other hand, the thermal resistivity concept in heat conduction cannot be used directly to capture the same phonon behavior. This talk will introduce a new concept: thermal reffusivity, which is the inverse of thermal diffusivity. It will cover studies we have conducted for various  llic, polymer, and semiconductor materials from micron down to nanoscales from room temperature down to 10 K. Direct measurement of thermal reffusivity is made possible using the transient electro-thermal (TET) technique, which was first developed in our lab to provide one of the most reliable measurements of thermal transport properties of micro/nanosize materials. The variation of the thermal reffusivity against temperature, in comparison with that of bulk counterpart, directly uncovers the contribution of defects. Also the Debye temperature of materials can be directly determined from the thermal reffusivity-temperature curve, similar to the electrical resistivity-temperature curve. The 0 K-limit of the thermal reffusivity, termed residual thermal reffusivity, is directly used to determine the structure domain size uncovered by low-momentum phonon scattering. This size is very close to that determined by x-ray diffraction. Materials including  ls, dielectrics, and organic and bio-materials have been studied to uncover their structure domain size. The thermal reffusivity sheds new light on the structure effect on energy transport, and provides great potential to look into material’s structure from the energy transport respect.

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主讲人简介：

Dr. Xinwei Wang is a full professor at Iowa State University (http://web.me.iastate.edu/wang). He obtained his Ph.D. from the School of Mechanical Engineering, Purdue University in 2001, and had his M.S. (1996) and B.S. (1994) from the University of Science and Technology of China. Over the past 18 years, he has led his laboratory to develop novel technologies for micro/nanoscale thermal characterization, study ultrafast-laser material interaction, investigate light-structure coupling, and probe energy transport in various materials down the sub-nm scale. His current work focuses on energy transport in macromolecules, 2D atomic   materials, atomic scale interface phonon energy transport, and in-situ probing and characterization of fuels in nuclear reactors. He has published 146 papers in highly-visible journals. He received the inaugural Viskanta Fellow Award of Purdue University in recognition of his pioneering and independent work in thermal sciences. He is the recipient of the 2014 Mid-career Award for Research of Iowa State University (ISU) and 2018 ISU Award for Outstanding Achievement in Research. He is the Fellow of American Society of Mechanical Engineers (ASME) and Associate Fellow of American Institute of Aeronautics and Astronautics (AIAA).