Effects of growth substrate on the nucleation of monolayer MoTe2

Abstract

The discovery and characterization of two-dimensional (2D) materials beyond graphene has increased dramatically over the past decade with increasingly fine control over the growth dynamics of these materials. MoTe₂ represents a model material for studying phase change properties of 2D materials due to small energy differences between its 2H semiconducting phase and 1T′ semimetallic phase. Although some substrates are demonstrated to be better than others for the wafer-scale growth of high quality MoTe₂ films, substrate effects on the nucleation and growth of MoTe₂ are still not well understood. Here, we grow monolayer MoTe₂ by converting MoO_x thin films deposited on three different substrates: sapphire Al₂O₃ (0001), amorphous SiO₂, and amorphous AlO_x, and examine the early stages of the conversion reaction to elucidate the substrate effects on the nucleation of MoTe₂. We observe that the chemical composition of the substrate is more important than the surface topography and crystallinity of the substrate, with high quality monolayer 2H MoTe₂ formed on both Al₂O₃ (0001) and AlO_x in contrast to mixed phase 2H/1T′ MoTe₂ formed on SiO₂, as determined by Raman spectroscopy, X-ray photoelectron spectroscopy, and atomic force microscopy.