The emerging two-dimensional (2D) materials are playing more and more important roles in both fundamental research and practical application potentials in recent years. The 2D transition metal dichalcogenides (TMDCs) have attracted extensive interest due to their remarkable fundamental properties distinct from those of their bulk counterparts. Using molecular beam epitaxial (MBE) method, we achieved the controllable growth of transition metal dichalcogenides MoSe₂ and WSe₂.  Combining with the in-situ angle-resolved photoemission spectroscopic (ARPES) measurements, we directly characterized the electronic structures of them and studied the evolution of their electronic structures in atomically thin limit [1-2]. Collaborating with further photoluminescence spectroscopy and scanning tunnelling spectroscopy (STS), we experimentally observed a rather large exciton binding energy in monolayer MoSe₂ and WSe₂ [3]. We also realized the growth of meta-stable 1T’-WSe₂ monolayer, and studied its thermo-driven structure phase transition to stable 2H-WSe₂[4]. Our findings not only help understanding of TMDC materials but also enrich the family of epitaxial 2D materials toward a fully MBE grown epitaxial heterostructures for light emission and photon-voltage devices.
 

[1]Yi Zhang et al., Nature Nanotechnology. 9, 111 (2014).
[2] Yi Zhang et al., Nano Letters 16, 2485 (2016).
[3]M. M. Ugeda et al., Nature Materials, 13, 1091 (2014).
[4]W. Chen et al., Scientific Reports, 9, 2685 (2019)
 

Yi Zhang got his B.S. degree in Peking University in 2006. Then he became a graduate student in Prof. Qi-Kun Xue’s group in the Institute of Physics, Chinese Academy of Sciences. After he finished my Ph.D. degree in 2011, he joined Prof. Zhi-Xun Shen’s group as a joint postdoc in Lawrence Berkeley Lab and Stanford University. He joined Nanjing University as a professor since 2015. His research interests are the molecular beam epitaxial (MBE) growth of novel 2D materials and topological materials, and the studies on their electronic structures using in-situ scanning tunnelling microscopic (STM) and angle-resolved photoemission spectroscopic (ARPES) technologies.