Band Alignment in As-Transferred and Annealed Graphene/MoS2 Heterostructures

The band alignment in the graphene/MoS2 van der Waals heterostructures (vdWHs) is investigated by Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) to understand the transfer- and annealing-induced change of electronic properties. Raman spectroscopy indicates that partial electron redistribution between the MoS2 and graphene layers occurs when brought into contact, resulting in a hole concentration decrease in graphene from 1 x 10(13) to 7 x 10(12) cm(-2). The additional thermal annealing at 400 degrees C further decreases the hole concentration down to 3 x 10(12) cm(-2) and leads to a MoS2 valence band offset increase by 0.2 eV. The annealing procedure also results in a visible decrease in adsorbed carbon- and oxygen-containing contaminants, and this decrease is clearly detected by XPS. Thus, the combination of Raman spectroscopy and XPS provides a powerful diagnostic tool for the electronic properties at each stage of vdWHs preparation, allowing the attainment of 2D vdWHs with the desired properties.