  Monolayer MoTe2 exhibits a variety of derivative structural phases and
associated novel electronic properties that enable a wealth of potential
applications in future electronic and optoelectronic devices. However, a
comprehensive study focusing on the complexities of the controllable phase
evolution in this atomically thin film has yet to be performed. This work aims
to address this issue by systematically investigating molecular beam epitaxial
growth of monolayer Mo-Te compounds on bilayer graphene substrates. By
utilizing scanning tunnelling microscopy, we explored a series of thermally
driven structural phase evolutions including distinct T'-MoTe2, H-MoTe2, Mo6Te6
nanowires, and multistoichiometric MoTe2-x. Furthermore, we carefully
investigated the critical effects of the growth parameters-annealing
temperature and time and tellurium concentration-on the controllable and
reversible phase transformation within monolayer MoTe2-x. The findings have
significant implications for understanding the thin film synthesis and phase
transformation engineering inherent to two-dimensional crystals, which can
foster further development of high-performance devices.
