  Owing to the small energy differences between its polymorphs, MoTe2 can
access a full spectrum of electronic states, from the 2H semiconducting state
to the 1T semimetallic state, and from the Td Weyl semimetallic state to the
superconducting state in the 1T and Td phase at low temperature. Thus, it is a
model system for phase transformation studies as well as quantum phenomena such
as the quantum spin Hall effect and topological superconductivity. Careful
studies of MoTe2 and its potential applications require large area MoTe2 thin
films with high crystallinity and thickness control. Here, we present cm2 scale
synthesis of 2H MoTe2 thin films with layer control and large grains that span
several microns. Layer control is achieved by controlling the initial thickness
of the precursor MoOx thin films, which are deposited on sapphire substrates by
atomic layer deposition and subsequently tellurized. Despite the van der Waals
epitaxy, the precursor-substrate interface is found to critically determine the
uniformity in thickness and grain size of the resulting MoTe2 films: MoTe2
grown on sapphire show uniform films while MoTe2 grown on amorphous SiO2
substrates form islands. This synthesis strategy decouples the layer control
from the variabilities of growth conditions for robust growth results, and is
applicable to grow other transition metal dichalcogenides with layer control.
