Detecting MoS2 and MoSe2 with optical contrast simulation

Optical imaging is 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 to the case when the nanolayer is absent. This optical contrast imaging can be used to identify the 2D material and its number of layers. To make the optical imaging process in the laboratories an effective tool, Fresnel Law as a model was used to simulate the optical imaging results of 2D materials (graphene, MoS2 and MoSe2) on top of different thickness of SiO2 and Si wafer in the present investigation. The results provide the details of the optimal conditions (optimal light wavelength and optimal SiO2 thickness) to identify and locate single to few 2D nanolayers, which can be used directly in laboratories. The optical contrasts of 1-5 layers of molybdenum disulfide (MoS2) and molybdenum diselenide (MoSe2) were simulated. To the best of our knowledge, it is the first time that the optical contrast results of MoSe2 have been reported. In particular, this work highlights the sensitivity of the model on the accuracy of the refractive indices used. It is demonstrated that through computational modeling that optical contrast can allow effective determination of number of layers in few layer 2D materials.