A quick method for estimating the layer number of black phosphorus is demonstrated by simple color-comparison using optical microscope in this paper. A thickness-dependent reflection model of black phosphorus/SiO2 /Si is constructed and a colorbar confirmed by experiments is obtained for quick identifying layer number. The enhanced visibility affected by substrates or wavelength of light is further verified by calculating the contrast.
Keywords: black phosphorus; colors; layer numbers; monochromatic light; optical methods.
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