Quantum Effects and Phase Tuning in Epitaxial Hexagonal and Monoclinic MoTe Monolayers.

Monolayer (ML) transition-metal dichalcogenides exist in different phases, such as hexagonal (2H) and monoclinic (1T') structures. They show very different properties: semiconducting for 2H-MoTe and semimetallic for 1T'-MoTe. The formation energy difference between 2H- and 1T'-phase MoTe is small, so there is a high chance of tuning the structures of MoTe and thereby introducing applications of phase-change electronics. In this paper, we report the growth of both 2H- and 1T'-MoTe MLs by molecular-beam epitaxy (MBE) and demonstrate its tenability by changing the conditions of MBE. We attribute the latter to an effect of Te adsorption. By scanning tunneling microscopy and spectroscopy, we reveal not only the atomic structures and intrinsic electronic properties of the two phases of MoTe but also quantum confinement and quantum interference effects in the 2H- and 1T'-MoTe domains, respectively, as effected by domain boundaries in the samples.