Abstract: Emerging 2D materials, such as atomically thin transition metal dichalcogenides (TMDs) and graphene, have been the subject of intense research, due to their intriguing electronic and optical behaviors. Atomic point defects and interfaces in 2D materials, including domain boundaries and edges, usually govern physical and chemical properties of the materials, and hence performance of devices based on them. To design and optimize 2D materials rationally, it is essential to investigate the point defects and interfaces at the atomic scale, the knowledge of which is yet lacking.
In this talk, I will present our recent scanning tunneling microscopy (STM) and spectroscopy (STS) investigations of point defects in 2D TMDs. We observed an interface between the MoS2 monolayer and the MoS2/WS2 heterobilayer with atomic resolution. Our STS results and density functional theory (DFT) calculations reveal the electronic structures of monolayer and heterobilayer. I will further discuss how the defects and interfaces are affected by external stimuli. Using monolayer vacancy islands on TiSe2 surfaces under electrical stress as a model system, we experimentally and theoretically investigated the shape evolution and demonstrated dependence of the growth rate on the tunneling current.

Brief Bio: Dr. Chenggang Tao is an assistant professor in the Department of Physics at Virginia Tech. He received his PhD from the University of Maryland and then moved to the University of California at Berkeley as a postdoctoral researcher. His current research mainly focuses on emerging 2D materials and surface dynamics. He has published a number of papers on 2D materials and surface dynamics, including papers in Science, Nature Physics, PRL and PNAS. In his spare time, Chenggang enjoys playing tennis.