Making 2D Nanolayers Visible by Optical Imaging

Abstract

Recent developments have proved optical imaging to be a promising method to identify and locate 2D materials efficiently and non-invasively. By putting a 2D material on a substrate, the nanolayer will add to an optical path and create a contrast with the case when the nanolayer is absent, which can be used to identify the 2D material and its number of layers. To make the optical imaging process in the laboratories more convenient, this report uses Fresnel Law as a model to simulate the optical imaging results of various 2D materials (graphene, MoS2, MoSe2) on top of different thickness of SiO2 and Si wafer. The results provide details of the optimal conditions (the optimal light wavelength and optimal thickness of SiO2) to identify and locate the 2D nanolayer, which can be used directly in laboratories. The model used in this report was benchmarked by simulating the system of graphene on top of SiO2 and Si to ensure its accuracy and comparing with existing literature. The model was then used to simulate the optical contrasts of 1–5 layers of MoS2 and MoSe2, the latter of which has not been reported in previous literature. In particular, we highlight the sensitivity of the used model on the accuracy of the refractive indices used. In conclusion, we show through computational modelling that optical contrast can in principle allow effective determination of layer numbers in few layered 2D materials.