A facile method for precise layer number identification of two-dimensional materials through optical images

Optical microscopy is believed to be an efficient method for identifying layer number of two-dimensional (2D) materials. However, since illuminants, cameras and their parameters are different from lab to lab, it is impossible to identify layer numbers merely by comparing a given optical image with standard or calculated images under standard conditions. Here we reported an image reconstruction method, converting raw optical images acquired by arbitrary illuminants and cameras into reconstructed images under the condition of specified illuminant and specified camera. After image reconstruction, the color differences of each layer number roughly equaled those calculated under the specified condition. By comparing the color differences in the reconstructed image with those calculated under the specified condition, the layer numbers of 2D materials in our lab and published papers, including MoS2, WS2, and WSe2, were unambiguously identified. This study makes optical microscopy a precise method to identify layer numbers of 2D materials on known substrates.