Band Alignment at Au/MoS2 Contacts: Thickness Dependence of Exfoliated Flakes

We investigated the surface potential (V-surf) of exfoliated MoS2 flakes on bare and Au-coated SiO2/Si substrates using Kelvin probe force microscopy. The V-surf of MoS2 single layers was larger on the Au-coated substrates than on the bare substrates; our theoretical calculations indicate that this may be caused by the formation of a larger electric dipole at the MoS2/Au interface leading to a modified band alignment. V-surf decreased as the thickness of the flakes increased until reaching the bulk value at a thickness of similar to 20 nm (similar to 30 layers) on the bare and similar to 80 nm (similar to 120 layers) on the Au-coated substrates, respectively. This thickness dependence of V-surf was attributed to electrostatic screening in the MoS2 layers. Thus, a difference in the thickness at which the bulk V-surf appeared suggests that the underlying substrate has an effect on the electric-field screening length of the MoS2 flakes. This work provides important insights to help understand and control the electrical properties of metal/MoS2 contacts.