MBE and STM Study of Ultrathin Transition-Metal Dichalcogenide Layers

Speaker: Maohai Xie
Affiliation: University of Hong Kong

Abstract: Ultrathin layers of transition metal dichalcogenides (TMDs) are of great current research interests for their promises in two-dimensional electronics, optoelectronics, spin and valley electronics. In this talk, I shall describe our latest efforts of molecular-beam epitaxy (MBE) of ultrathin layers of MoSe2, WSe2 and MoTe2. By scanning tunneling microscopy and spectroscopy (STM/S) study, we not only probe some intrinsic properties of the materials, including energy band gap and band alignment, but also reveal defect and their properties and effects. In particular, networks of domain boundary defects are seen to persist in as-grown MoSe2, giving rise to midgap states modulated by the moiré potential and the quantum size effect. The formation of such defects is closely dependent on the MBE conditions, allowing one to achieve a varying density of the DB defects for different application purposes. Point defect in monolayer WSe2 induces quasi-particle interference, which evidences spin-conserving inter-Q valley scattering, affirming spin-valley coupling and large spin-splitting at the Q valleys in monolayer WSe2. Finally, phase tuning of epitaxial MoTe2 by Te surface adsorption is demonstrated. The latter would make it attractive for phase-change electronics applications.

Biography: Professor Maohai Xie is currently a faculty member in the Physics department at the University of Hong Kong. He received his MSc from the Institute of Semiconductors, Chinese Academy of Sciences, China and the PhD in Physics from the University of London. Professor Xie’s research interests include epitaxial growth and properties of ultrathin films and quantum structures of semiconductors, metals, topological insulators and monolayer transition-metal dichalcogenides; surfaces and electronic structures of ultrathin films; properties related to quantum size effects; Electron diffraction, scanning probe microscopy and photoelectron spectroscopy.

For more information, contact Prof. Kang Wang ()

Date/Time:
Date(s) - Jun 24, 2016
5:00 pm - 6:00 pm

Location:
E-IV Tesla Room #53-125
420 Westwood Plaza - 5th Flr., Los Angeles CA 90095