Energy-Level Alignment at Interfaces between Transition-Metal Dichalcogenide Monolayers and Metal Electrodes Studied with Kelvin Probe Force Microscopy.

We studied the energy-level alignment at interfaces between various transition-metal dichalcogenide (TMD) monolayers, MoS, MoSe, WS, and WSe, and metal electrodes with different work functions (WFs). TMDs were deposited on SiO/silicon wafers by chemical vapor deposition and transferred to Al and Au substrates, with significantly different WFs to identify the metal-semiconductor junction behavior: oxide-terminated Al (natural oxidation) and Au (UV-ozone oxidation) with a WF difference of 0.8 eV. Kelvin probe force microscopy was employed for this study, based on which electronic band diagrams for each case were determined. We observed the Fermi-level pinning for MoS, while WSe/metal junctions behaved according to the Schottky-Mott limit. WS and MoSe exhibited intermediate behavior.