Thickness Identification of 2D Materials by Optical Imaging

In recent decades, 2D materials have been researched extensively for their exceptional properties and diverse applications. Their thickness strongly influences their characteristics and therefore it must be determined prior to any experiment. This paper examines the approach of thickness identification by optical imaging on behalf of a theoretical model and experimental data, and tests its reliability for application in research, for both the insulating material FePS₃ and the conductive metallic NbSe₂. 

The results confirm that the theoretical model accurately describes the contrast and colour of an insulator on a two-layered (SiO₂/Si) substrate. The correlation indicates, that the model’s underlying assumptions (eg. insulation) were well chosen - even more so, since there is a significant divergence to the experimental results for the conductive material. 

Further, they suggest that the thicknesses of an insulating flake up to 200 nm correspond to distinct RGB values. This fact is used to develop an application, which is capable to yield, from a list of RGB values, the thicknesses, to which they are likely to correspond. The application is evaluated and its reliability is demonstrated. This report therefore confirms the practicality of thickness identification by optical imaging, providing a fast, large-scale and cheap method to determine the thickness of 2D materials.