Helium atom micro-diffraction as a characterisation tool for 2D materials

TL;DR

This paper introduces helium atom micro-diffraction as a highly surface-sensitive, high-resolution technique for characterizing 2D materials, enabling detailed measurements of surface interactions, thermal properties, and defects at the device scale.

Contribution

It demonstrates the application of helium atom micro-diffraction for detailed, spatially-resolved characterization of 2D materials, a novel approach in this context.

Findings

Measured monolayer-substrate interactions in MoS2

Determined thermal expansion coefficients and electron-phonon coupling

Quantified vacancy-type defect density

Abstract

We present helium atom micro-diffraction as an ideal technique for characterization of 2D materials due to its ultimate surface sensitivity combined with sub-micron spatial resolution. Thermal energy neutral helium scatters from the valence electron density, 2-3A above the ionic cores of a surface, making the technique ideal for studying 2D materials, where other approaches can struggle due to small interaction cross-sections with few-layer samples. Sub-micron spatial resolution is key development in neutral atom scattering to allow measurements from device-scale samples. We present measurements of monolayer-substrate interactions, thermal expansion coefficients, the electron-phonon coupling constant and vacancy-type defect density on monolayer-MoS2. We also discuss extensions to the presented methods which can be immediately implemented on existing instruments to perform spatial mapping of these material properties.