Optical identification of atomically thin dichalcogenide crystals

摘要

We present a systematic study of the optical contrast of niobium diselenide and molybdenumndisulfide flakes deposited onto silicon wafers with a thermally grown silicon oxide layer. Wenmeasure the optical contrast of flakes whose thickness, which is obtained by atomic forcenmicroscopy, ranges from 200 layers down to a monolayer using different illumination wavelengthsnin the visible spectrum. The refractive index of these thin crystals has been obtained from the opticalncontrast using Fresnel law. In this way the optical microscopy data can be quantitatively analyzednto determine the thickness of the flakes in a fast and nondestructive way. © 2010 American Institutenof Physics. u0004doi:10.1063/1.3442495