Abstract
Two-dimensional materials have emerged as promising candidates for next-generation electronic and optoelectronic applications. Besides the monolayer of 2D crystals have demonstrated unique electronic and optical properties, 2D heterostructures are also interesting because of their tunable interlayer stacking and rotations. This talk will discuss the synthesis of large-area, high-quality monolayers of W and S-doped MoSe2 sheets using chemical vapor deposition (CVD) and pulse laser deposition (PLD). Scanning tunneling microscopy (STM) and spectroscopy (STS) reveal that the dopants in the MoSe2 samples arrange in different geometrical configurations exhibiting different electronic properties. Combined with first-principles calculations, the detailed electronic structures of 2D doped crystals have been illuminated. In addition, the vertical and lateral 2D heterostructures by controlled assembly and pattern will be discussed. Our results show that the 2D heterostructures exhibit high persistent photoconductivity and excellent photovoltaic behavior, which have the potential to deliver innovative applications in ultra-thin and flexible solar-energy devices and in micro- and nano-electronics.

Bio
Dr. Kai Xiao is a staff scientist in the Functional Hybrid NanomaterialsGroup at Center for Nanophase Materials Sciences, Oak Ridge National Laboratory and a joint faculty at Department of Computer Science and Electrical Engineering, University of Tennessee at Knoxville. He graduated from East China Institute of Technology in 1998, and received his M.S. degree in Materials in 2001 from Institute of Metal Research, Chinese Academy of Sciences and his Ph.D. degree in Physic Chemistry in 2004 from Institute of Chemistry, Chinese Academy of Sciences. Then he worked as a postdoc associate at CNMS and became a staff scientist in 2008. He has published about 80 papers, and 4 book chapters.  He has been awarded the Top 50 Excellent Ph. D. Thesis Award of the Chinese Academy of Sciences and the National Top 100 Excellent Ph. D. Thesis Award in China, Ministry of Education. His research interests include understanding and controlling the synthesis of thin films and nanostructured materials such as conjugated small molecules/polymers, hybrid perovskites, graphene and other 2D inorganic crystals, and investigating their applications in field-effect transistors, photodetectors, photovoltaics, and other energy-related devices.