Place：Room 316, No. 11 Teaching Bld

Time：10:00 am, July 6th ，2018

Title：Surface studies of epitaxial transition-metal dichalcogenides and phosphorous films

Speaker：Maohai Xie, Physics Department, The University of Hong Kong, Pokfulam Road, Hong Kong

Transition-metal dichalcogenide (TMDC) monolayers and phosphorene are two important 2D materials that have drawn tremendous research interests in late years. In this talk, I shall describe our recent efforts in growing TMDC and phosphorous monolayers by molecular-beam epitaxy (MBE). Using scanning tunneling microscopy (STM), we observe some interesting features that can be specific to the MBE-grown layers. Examples include the observation of a dense network of inversion domain boundaries in epitaxial MoSe2 and MoTe2, giving rise to mid-gap metallic states modulated by quantum effects and the charge-density wave states. Formation of such defects is found closely related to MBE conditions, allowing one to modulate or tune the defect density for different application purposes. Point defects in epitaxial TMDCs are also revealed and the induced quasi-particle interference evidences a spin-conserving inter-Q valley scattering. Phosphorous deposition on Au exhibits an interesting kinetic pathway, from single atom adsorption to formation of a blue-phosphorene like monolayer. It involves a dewetting process that can be understood by the minimization of surface energy