Measuring vacancy-type defect density in monolayer semiconductors

TL;DR

This paper demonstrates a rapid, non-destructive helium atom micro-diffraction method to quantify vacancy-type defect density in monolayer 2D semiconductors like MoS2, supported by an analytic model and ab initio calculations.

Contribution

The authors introduce a novel helium atom micro-diffraction technique and a lattice gas model for measuring defect density in 2D materials, enabling quick, wafer-scale characterization.

Findings

Helium micro-diffraction effectively measures defect density in monolayer MoS2.

The lattice gas model accurately relates diffraction intensity to defect density.

Method applicable to various 2D materials regardless of chemistry or structure.

Abstract

Two-dimensional (2D) materials have attracted wide-spread interest due to their unique and tunable properties. Their optoelectronic, mechanical, and thermal properties are greatly influenced by crystal defects, which are, in turn, used to control these properties. However, experimental quantification of the density of defects, whether deliberately introduced or inherent, is very difficult in these atomically thin materials. Here we show that helium atom micro-diffraction can be used to measure the defect density in 15x20um monolayer MoS2, a prototypical 2D semiconductor, quickly and easily compared to standard methods. We present a simple analytic model, the lattice gas equation, that fully captures the relationship between atomic Bragg diffraction intensity and defect density. The model, combined with ab initio scattering calculations, shows that our technique can immediately be applied to a wide range of 2D materials, independent of sample chemistry or structure. Additionally, wafer-scale characterization is immediately possible.