Investigation of band alignment at two-dimensional ReS2/XSe2 (X=W, Mo) heterojunctions using x-ray/ultraviolet photoelectron spectroscopy

In this work, the monolayer WSe2 and MoSe2 were transferred to the surface of ReS2/sapphire to form two-dimensional (2D) ReS2/WSe2 and ReS2/MoSe2 van der Waals heterojunctions, respectively. The high quality of monolayer ReS2, WSe2 and MoSe2 was characterized by Raman spectroscopy. We determined a valence band offset of 0.16±0.15 eV at ReS2/WSe2 heterojunction using x-ray photoelectron spectroscopy, with a type-II band alignment. The valence band offset of ReS2/MoSe2 was determined to be 0.61±0.15 eV, with a type-I band alignment. By combining ultraviolet photoelectron spectroscopy, the results calculated by Anderson's affinity rule and the results of XPS showed agreement. This work not only reveals energy-band structures of the ReS2/WSe2 interface and ReS2/MoSe2 interface, but also paves the way for the future designing of 2D heterojunction-based optoelectronic devices.