Optical thickness determination of hexagonal boron nitride flakes*

Optical reflectivity contrast provides a simple, fast, and noninvasive method for characterization of few monolayer samples of two-dimensional materials. Here, we apply this technique to measure the thickness of thin flakes of hexagonal Boron Nitride (hBN), which is a material of increasing interest in nanodevice fabrication. The optical contrast shows a strong negative peak at short wavelengths and zero contrast at a thickness dependent wavelength. The optical contrast varies linearly for 1-80 layers of hBN, which permits easy calibration of thickness. We demonstrate the applicability of this quick characterization method by comparing atomic force microscopy and optical contrast results.