Measuring the thickness of flakes of hexagonal boron nitride using the change in zero-contrast wavelength of optical contrast

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 SiO2/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 SiO2 thickness, and increases proportionally with SiO2 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.