  Monolayer (ML) transition-metal dichalcogenides exist in different phases,
such as the hexagonal (2H) and distorted octahedral or monoclinic (1T') phases.
The different structures show vastly different properties. For example, the 2H
MoTe2 ML is a direct-gap semiconductor while 1T' MoTe2 is a semi-metal. It has
been suggested that the formation energies between 2H and 1T' MoTe2 differ very
little, so there is a high chance to tune the structures of MoTe2 and thereby
to bring in new applications such as phase-change electronics. In this work, we
report growth of both 2H and 1T' MoTe2 ML by molecular-beam epitaxy (MBE). We
demonstrate the tunability of the structural domains in epitaxial MoTe2 by
changing the growth conditions of MBE and by annealing. We present experimental
and theoretical evidences showing the important role of Te surface adsorption
in promoting and stabilizing the otherwise metastable 1T'-MoTe2 during MBE.
