LAUSR

Abstract Optical contrast imaging technique has been widely practiced for fast and easy thickness determination of 2D layered materials. CCDs used for such optical imaging, inherently doesn't provide any spectral information, however, by introducing RGB filters, a very narrow bandwidth spectral information of the reflected light can be recorded. Such limited database of spectral line of the reflected light fails to provide optimized contrast of the 2D flakes with the variation of flake thickness (layer number). In this report, instead of using conventional RGB filter-based CCDs, we have presented a comprehensive spectroscopic mapping of white light reflection from 2D MoS2 flake of different thickness, which provides information about spectral dependency of the optical contrast in the full visible range. It exactly defines the spectral range of filters to be selected for optimized contrast imaging. The reported spectroscopic mapping data provides a calibrated method for accurate measurement of MoS2 flake thickness. The contrast spectra has also been calculated theoretically by Fresnel's theory, which agrees well with our experimental values. The accuracy and consistency of this approach have been verified by conducting AFM measurements.