Probing thickness-dependent tip-induced band bending in MoS2

Abstract

Scanning tunneling spectroscopy (STS) has played an important role in determining the electronic band structures of semiconductors. However, the tip-induced band bending (TIBB) could strongly affect the measured valence and conduction band edges, which are of vital importance for a semiconductor. In the literature, the presence or absence of the TIBB effect in a given STS measurement is often not discussed thoroughly. In this work, we quantitatively investigate the TIBB effect in MoS2 with varying thicknesses using light-modulated contact-mode STS. Our results demonstrate that the TIBB effect is strongly dependent on the thickness of MoS2. With thin MoS2 of a few atomic layers (several nanometers), the TIBB approaches zero, and the measured STS can accurately reflect the band edges. While for thicker MoS2 of ∼100 nm, the TIBB can be as large as ∼1 eV. This work clarifies the ambiguity about the TIBB effect and provides a foundation for the interpretation of STS data on atomically thin semiconductors.