Single-layer Mo5Te8 — A new polymorph of layered transition-metal chalcogenide

Abstract

Single-layer (SL) transition-metal chalcogenides (TMCs) represent an important family of two-dimensional (2D) materials that have attracted intensive research attention recently. It has been established that many TMCs are polymorphic that can exist in different crystal structures and correspondingly exhibit diverse physical properties. Discovery of new structural phases of a crystal is of great scientific and practical importance. In this work, we report a new polymorph of SL-TMC, i.e. SL-Mo5Te8, attained by molecular-beam epitaxy (MBE). Like the 1H-MoTe2, it possesses the hexagonal symmetry but a much larger unit cell with a basis containing as many as 39 atoms (15 Mo and 24 Te). We call it the variational hexagonal (v1H) phase. Coincidently, it may be viewed also as one containing the highest density possible of mirror-twin domain boundaries (MTBs) in an otherwise pristine 1H-MoTe2. Electronically, it is metallic and a comparison between theory and experiments of its density-of-states (DOS) at the Fermi level reveals features pointing to an importance of electron interactions that invites further investigations.