The intrinsic defect structure of exfoliated MoS2 single layers revealed by Scanning Tunneling Microscopy

Abstract

MoS2 single layers have recently emerged as strong competitors of graphene in electronic and optoelectronic device applications due to their intrinsic direct bandgap. However, transport measurements reveal the crucial role of defect-induced electronic states, pointing out the fundamental importance of characterizing their intrinsic defect structure. Transmission Electron Microscopy (TEM) is able to image atomic scale defects in MoS2 single layers, but the imaged defect structure is far from the one probed in the electronic devices, as the defect density and distribution are substantially altered during the TEM imaging. Here, we report that under special imaging conditions, STM measurements can fully resolve the native atomic scale defect structure of MoS2 single layers. Our STM investigations clearly resolve a high intrinsic concentration of individual sulfur atom vacancies, and experimentally identify the nature of the defect induced electronic mid-gap states, by combining topographic STM images with ab intio calculations. Experimental data on the intrinsic defect structure and the associated defect-bound electronic states that can be directly used for the interpretation of transport measurements are essential to fully understand the operation, reliability and performance limitations of realistic electronic devices based on MoS2 single layers.

Intrinsic and Extrinsic Defect-Related Excitons in TMDCs

“…First, what is the nature of the defect-related PL feature (D peak)? It has been attributed both to two-and three-particle states as well as to various defect types 18,20,21,[27][28][29][30] . Second, can the D peak be used as an indicator of a sample quality, i.e.…”

Rhenium-doped MoS2 films

“…In a recent study, it has been shown that single sulfur atom vacancies are the dominant defects in the exfoliated single layer of MoS 2 , generating similar states in the bandgap. 28 At low temperatures where the Fermi distribution is close to the step-like function, less charges will be captured by the S-vacancy-induced energy state due to losing thermal energy, causing E F to move towards the mid-gap level (the band structure at 10 K is shown in Fig. S5 in the supplementary material).…”

Electronic Dynamics in Graphene and MoS2 Systems

“…Further localized perturbations may come from structural defects, for example Sulfur vacancies, which cause mid‐gap states in MoS 2 . These mid gap states have triangular and hexagonal atomic scale patterns observed recently in STM measurements . Ghorbani et al analysed the effect of different localized defects on the MoS 2 transport for currents in the zigzag‐ and armchair directions, utilizing a nonequilibrium Green function DFT approximation.…”