originally created by Britt Baugher for Jarillo-Herrero Group

Introduction

It has been shown that you can quantitatively determine the number or layers of few layer graphene (about 1-5 layers thick) on 300 nm thick SiO₂ simply using an optical microscope and some post processing software.  The interference effect that allows us to distinguish different graphene thicknesses by eye can be easily read by the computer to give a more quantitative analysis of the layer number.  This is accomplished by reading the intensity of green light reflected by the bare SiO₂ substrate and by the graphene flake, and calculating the difference between the two. The interference of reflected light formed between graphene and the SiO₂ substrate peaks in contrast at 560 nm, right in the green spectrum of light. The green pixel in an RGB monitor is peaked very close to this value at roughly 510 nm. Thus, by simply reading off the difference in the G value between the light reflected by the graphene and the bare substrate we can selectively pull out graphene's contrast.  The contrast of single layers of graphene are expected to add linearly.  Thus, this works to pick out single layer graphene from the substrate as well as mono-layer from bi-layer, bi-layer from tri-layer, and so on up to about five layers thick. 

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