Selective phase growth and precise-layer control in MoTe2

Minor structural changes in transition metal dichalcogenides can have dramatic effects on their electronic properties. This makes the quest for key parameters that enable a selective choice between the competing metallic and semiconducting phases in the 2D MoTe2 system compelling. Herein, we report the optimal conditions at which the choice of the initial seed layer dictates the type of crystal structure of atomically-thin MoTe2 films grown by chemical vapour deposition (CVD). When Mo metal is used as a seed layer, semiconducting 2H-MoTe2 is the only product. Conversely, MoO3 leads to the preferential growth of metallic 1T′-MoTe2. The control over phase growth allows for simultaneous deposition of both 2H-MoTe2 and 1T′-MoTe2 phases on a single substrate during one CVD reaction. Furthermore, Rhodamine 6G dye can be detected using few-layered 1T′-MoTe2 films down to 5 nM concentration, demonstrating surface enhanced Raman spectroscopy (SERS) with sensitivity several orders of magnitude higher than for bulk 1T′-MoTe2. The polymorphism of MoTe2 can be used to realize planar metallic/semiconducting homojunctions in 2D devices, greatly reducing the contact resistance. Here, the simultaneous growth of both phases is achieved on the same substrate by single-step chemical vapor deposition and seeding layer engineering.