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.
@article{arxiv.2409.18637,
title = {Measuring vacancy-type defect density in monolayer semiconductors},
author = {Aleksandar Radic and Nick von Jeinsen and Vivian Perez and Ke Wang and Min Lin and Boyao Liu and Yiru Zhu and Ismail Sami and Kenji Watanabe and Takashi Taniguchi and David Ward and Andrew Jardine and Akshay Rao and Manish Chhowalla and Sam Lambrick},
journal= {arXiv preprint arXiv:2409.18637},
year = {2025}
}