Preparation and Electronic Characterization of Substrate-Scale MoS$_{2}$ Single-Layer Films

Using a novel high vacuum chemical vapor deposition process we synthesize substrate scale (2x2 cm) homogeneous monolayer MoS$_{2}$ films. Our process involves exposure of a hot Mo filament to organic chalcogen precursors that volatilize MoS$_{x}$ species which then precipitate on a thermally-controlled substrate. The resultant films are photoluminescent at 1.87 eV as expected for monolayer material; their Raman modes are indistinguishable from exfoliated material. Metal contact formation to these films was investigated under UHV conditions utilizing X-Ray Photoelectron Spectroscopy. These measurements permit us to follow the formation of a Schottky Barrier with increasing metal film thickness on the Angstrom scale. We utilize core level spectroscopy to indicate the evolution of the MoS$_{2}$ valence band under metal deposition. Our measurements provide direct indication on the charge transfer direction at metal contacts and the ensuing band-bending in two-terminal devices.~