Woodruff School of Mechanical Engineering
COE/Structural Mechanics Seminar
In-Situ Nanomechanics of Crystalline Nanowires
Prof. Yong Zhu
Associate Professor, North Carolina State University, Department of Mechanical and Aerospace Engineering
Thursday, November 13, 2014 at 11:15:00 AM
MRDC Building, Room 4211
Dr. Ting Zhu
Recent advance in nanotechnology has brought forth a host of nanostructures, such as nanoparticles, nanowires, nanotubes and graphene that exhibit ultrahigh strength. These nanostructures are not only an ideal platform to study fundamental mechanics, but also important building blocks for a broad spectrum of nanotechnology applications. In this talk, I will present in-situ scanning and transmission electron microscopy (SEM/TEM) mechanical testing of crystalline nanowires. I will focus on two types of nanowires, metallic and semiconductor nanowires with Ag and Si as examples, respectively. Both types of nanowires exhibit size dependent elastic properties, fracture or yield strength. For Ag nanowires, yielding was attributed to surface dislocation nucleation. In addition, unusual strain hardening was observed, which we found, through collaboration with atomistic simulations, is due to the interaction between dislocations and the pre-existing twin boundaries in the nanowires. For Si nanowires, we found evidence for size dependent brittle to ductile transition. It has become accepted in recent years that deformation mechanisms at the nanoscale transit from dislocation multiplication to (surface) dislocation nucleation. In this talk, I will discuss the importance of internal defects in addition to the free surfaces. I will conclude my talk with an application that harnesses the excellent mechanical properties of nanostructures, namely, nanowire-enabled stretchable electronics and sensors.
Yong Zhu received his B.S. degree in Mechanics and Mechanical Engineering from the University of Science and Technology of China in 1999, and his M.S. and Ph.D. degrees in Mechanical Engineering from Northwestern University in 2001 and 2005, respectively. He was a postdoctoral fellow at the University of Texas at Austin from 2005 to 2007. He is currently an Associate Professor in the Departments of Mechanical and Aerospace Engineering and Materials Science and Engineering (affiliated) at North Carolina State University. Dr. Zhuís research interests lie at the interface between solid mechanics and micro/nano-technology, including mechanical and multiphysical properties of nanostructures, micro/nano-electromechanical systems, and flexible/stretchable devices for healthcare applications. He has received several awards including Best Poster Award in the Gordon Research Conference on Thin Film & Small Scale Mechanical Behavior (2006), Sigma Xi Faculty Research Award (2012) and Society of Experimental Mechanics Young Investigator Award (2013).
Refreshments will be served.