Identification of graphene layer numbers from color combination contrast image for wide-area characterization

Abstract

Identification of the number of graphene layers using an optical microscope images taken at various magnifications is investigated from the viewpoint of simple wide-area inspection. For graphene on 300-nm-thick SiO2, combination of red and green color contrast gives more accurate contrast value and provides better contrast even at the low magnification as compared with the single color channel contrast. The color combination with suitable weighting factors taking account of light wavelength and intensity dependences of the system response results in the contrast that agrees well with the theoretical values from Fresnel's law. Simple image processing is also investigated to improve the signal-to-noise ratio (SNR) of the image. Median filtering improves the SNR of the image having high pixel density, whereas dithering is effective for the low magnification image having block noise due to low pixel density. (C) 2012 The Japan Society of Applied Physics.