题目：Surface/Edge Induced Intrinsic Size-Dependent Properties of Nanowires
报告人：Prof. Tong-Yi Zhang
Department of Mechanical Engineering
Hong Kong University of Science and Technology
主持人：苏先樾  教授
时  间：6月20日（周五）下午3:00
地  点：力学楼434会议室

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联系人：王健平  82529038

报告内容摘要：
The present work studies the size-dependent surface energy, surface stress, surface stiffness, and Young’s Modulus of a prism crystalline nanowire, which is theoretically treated to be composed of a hypothetical nanowire phase, a true two-dimensional geometric surface phase, and a true one-dimensional geometric edge phase. The hypothetical nanowire phase could be elastically deformed due to relaxation of a free-standing nanowire, without any applied load, with respect to its bulk counterpart. The initially deformed nanowire phase is taken as reference in the present work in the determination of excess surface and edge energies. The theoretical results indicate that the edge phase causes the nominal specific surface energy, surface stress and surface stiffness to be size-dependent, and the surface phase and the edge phase make the nominal Young’s modulus size-dependent. The edge and surface effects are more significant as the cross-sectional area of a nanowire becomes smaller. Molecular dynamics simulations on hexagonal prism b-SiC nanowires were conducted and the results verified the theoretical approach and illustrated the intrinsic mechanism of the size-dependent surface properties and Young’s modulus of nanowires. The theoretical analysis and methodology are universal when the continuum concepts of surface energy, surface stress, and Young’s modulus are used to characterize mechanical properties of nanowires.

报告人简介：
Tong-Yi Zhang received his Master and PhD degrees from the Department of Materials Physics, University of Science and Technology Beijing in 1982 and 1985, respectively. Then, he worked at the Universit?t G?ttingen, Germany, 1986-1988, as a research fellow of the Alexander von Humboldt Foundation; at the University of Rochester, USA, 1988-1990, as a postdoctoral fellow; and at Yale University, USA, 1990-1993, as an associate research scientist. He has had an academic appointment with the Department of Mechanical Engineering, HKUST, since 1993 and is currently a full professor. His current research areas include mechanical properties of materials, micro/nanomechanics, relationship between microstructures and material properties, ferroelectric and piezoelectric materials, thin films, nanowires and nanotubes, micro/nanobridge tests, and diffusion and phase transformation. The honors he has received include second prize of the 1987 State Natural Science Award, second prize of the 2007 State Natural Science Award, and the 1988 National Award for Young Scientists in China. In 2001, he received the Fellow Award from ASM International, USA. This ASM Fellow Award was in recognition of Zhang’s distinguished contributions in the field of materials science and engineering. Zhang’s citation reads: "For significant contributions to knowledge of hydrogen diffusion, fracture of piezoelectric ceramics, intercalated graphite, and thin film systems using both analytical and state-of-the-art experimental techniques." In 2003, he was awarded the Croucher Senior Research Fellowship Award. Tong-Yi Zhang received a congratulation card in March 2005 and four such cards in Nov. 2007 from the Web of Science, congratulating him for “The number of citations your article places it in the top 1% within its field according to Essential Science IndicatorsSM. Your work is highly influential, and is making a significant impact among your colleagues in your field of study.” The total SCI cited times of his publications are over 1,900, among which over 1,600 times are cited by other researchers. Zhang has four papers cited, by 14 June 2008, 121, 127, 173, and 224 times, respectively, according to the Science Citation Index Expanded Database.