Abstract

Using the reflectivity mode of an optical microscope, we analyzed the optical contrast to identify the layer number of flakes of hexagonal boron nitride on a <TEX>$SiO_2$</TEX>/Si substrate. Overall optical contrast in the visible range varies with the thickness of flakes. However, the wavelength of zero contrast exhibits a linear redshift of 0.53 nm per layer, independent of the <TEX>$SiO_2$</TEX> thickness, and increases proportionally with <TEX>$SiO_2$</TEX>thickness. Experiments show good agreement with calculations and the results of AFM measurements. These results show that this zero-contrast approach is more accurate and easier than the reflectivity-contrast approach using the overall optical contrast.

© 2015 Optical Society of Korea

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