Time： Wednesday10: 00am-12: 00 am, November 20, 2019

Location： Room A-420, West Building 5, Qujiang Campus

Title: Nanomechanics of Covalent Crystals and Elastic Strain Engineering

Lecturer： Professor Yang LU

Inviter： Professor Xuesong MEI

Lecture Information:

Nanomechanics of Covalent Crystals and Elastic Strain Engineering

Yang Lu 陸洋

Department of Mechanical Engineering, City University of Hong Kong

(E-mail: yanglu@cityu.edu.hk)

Abstract

Covalent crystals refer to a class of crystalline solids in which the atoms are bonded by covalent bonds in a continuous network extending throughout the entire material. They are usually very hard and brittle at the macroscopic scale, with many mechanical and mechatronic applications; on the other hand, many of them are important semiconductor materials (Si and Ge) or wide-bandgap semiconductors (diamond and silicon carbide), with wide applications in nanoelectronics and nanoelectromechanical systems (NEMS). However, to achieve the full potential of these nanoscale building blocks in their functional devices will highly depend on their mechanical behavior and reliability at the relevant length scales. In this talk, we firstly show our recent nanomechanical studies of one-dimensional covalent crystals including Si and diamond: based on our in situ characterization techniques, we showed that VLS-grown single crystalline silicon nanowires with diameters ~100nm can be reversibly stretched above 10% elastic strain at room temperature (Science Advances 2016), with a few cases up to 16% tensile strain, approaching the theoretical elastic limit of silicon. We then demonstrated the unprecedented flexural behavior of nanoscale diamonds, in which single-crystalline diamond nanoneedles (with diameter 150-300nm) are capable of undergoing ultralarge elastic bending deformation, up to ~9% local tensile strain (Science 2018), with the corresponding local stress (about 90GPa) approaching the ideal strength of diamond. Lastly, we will illustrate that, in addition to the promising flexible electronics and MEMS/NEMS applications, the discovered ultralarge elasticity in nanoscale covalent crystals could open up new avenues to design and modulate nanoelectronics and optoelectronics devices through the emerging concept of “elastic strain engineering” (JPCC 2018, JAP 2019)。

Bio

Dr. Yang Lu is currently an Associate Professor in the Department of Mechanical Engineering at City University of Hong Kong (CityU) and Principle Investigator in Nano-Manufacturing Lab in CityU Shenzhen Research Institute. He obtained his B.S. degree in Physics/Microelectronics from Nanjing University in 2004 and Ph.D. degree in Mechanical Engineering and Materials Science from Rice University in 2011. Before joining CityU in 2012, he did postdoctoral research in Department of Materials Science and Engineering at Massachusetts Institute of Technology (MIT) for two years. Dr. Lu has extensive experiences in nanomechanics and nanomanufacturing, and made major contributions in the discoveries of “cold welding” in ultrathin metallic nanowires and “ultralarge elasticity” in nanoscale covalent crystals such as silicon nanowires and diamond nanoneedles, respectively. As the first or corresponding author, Dr. Lu has published more than 60 research papers in leading academic journals including Science, Nature Nanotechnology, Science Advances etc. He serves as Managing Editor for Materials Today, and Editorial Board Member for SCIENCE CHINA Technological Sciences and Scientific Reports. Dr. Lu is a recipient of UGC Early Career Award 2013/2014 awarded by Hong Kong University Grants Committee, The President’s Award 2017 and Outstanding Research Award for Young Faculty 2019 of City University of Hong Kong.