报告题目：Ultralarge Elasticity in Nanoscale Covalent Crystals: Si and Diamond

时间: 2019-11-14 10:00-11:30

报告地点：实验十五楼715会议室

报告人: 上海科技大学张洪题助理教授

联系人：牛德超

Ultralarge Elasticity in Nanoscale Covalent Crystals: Si and Diamond

Dr. Hongti ZHANG 张洪题, Assistant Professor

School of Physical Science and Technology,

ShanghaiTech University

E-mail: zhanght3@shanghaitech.edu.cn

Abstract

Due to the interesting physical, chemical, optical and electrical properties, one-dimensional (1-D) nanoscale materials and structures (such as nanowire, nanotube, nanoneedle and nanopillar) have stimulated great interests in the past decades. However, the ability to achieve the full potential of these 1-D building blocks in their fascinating functional applications is ultimately limited by how they will behave at the relevant length scales, in particular, their mechanical performance and reliability. In view of this, an in situ nanomechanical testing platform based on a high-resolution nanoindenter inside SEM was developed out, which allows the quantitative nanomechanical characterization of various kinds of individual 1-D nanostructures under different loading geometries (such as uniaxial tensile, compression, bending). Based on this platform, tensile mechanical property of Si nanowires and bending flexural behavior of diamond nanoneedles were separately studied. Results show that VLS-grown single crystalline Si nanowires with diameters ~100nm can be repeatedly stretched above 10% elastic strain at room temperature, with a few cases up to 16% tensile strain, approaching their theoretical elastic limit; single-crystalline diamond nanoneedles with size ~300 nm are capable of undergoing ultra large elastic bending deformation (up to ~9% local tensile strain) upon a dedicated “push-to-bend” nanomechanical actual strategy, which approaches their theoretical elastic strain limit, too. Besides, mechanical behavior of 1-D metallic nanostructures was also investigated, which includes the nano-fatigue study of single crystalline nickel nanowires, “smaller is stronger” size effect in high entropy alloy (HEA) micro/nanopillars and ‘zipping-unzipping’ behavior of nano-twin nickel nanowires. The discovery of ultralarge elasticity in nanoscale networked covalent crystals will boost their applications in fields of flexible electronics, elastic strain engineering, etc.

Biography

Dr. Hongti Zhang is currently an Assistant Professor in the School of Physical Science and Technology at ShanghaiTech University. Dr. Zhang obtained his Bachelor degree in Polymer Material and Engineering from Qingdao University of Science and Technology in 2010, Master degree in Material Science and Engineering from East China University of Science and Technologyin 2013, and Ph.D. degree in Mechanical Engineering from City University of Hong Kong in 2016. Prior to joining in ShanghaiTech University as a faculty member in November 2018, he continued his research works about in situ nanomechanics in the same research group at City University of Hong Kong with changed titles from Research Assistant to Senior Research Associate and Postdoctoral Fellow. His research interests are focused on in situ Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM) Experimental Nanomechanics for the investigation of size-dependent mechanical properties of 1-D nanomaterials as well as the structure-property relationship of networked covalent crystals and metallic nanomaterials, as well as the Elastic Strain Engineering study for functional semiconductor nanomaterials. By far, as the role of first or co-first author, Dr. Zhang has published research works in academic journals like Science, Science Advances, Experimental Mechanics and Materials Research Letters, etc.