Microfabrication of graphene devices used in many experimental studies currently relies on the fact that graphene crystallites can be visualized using optical microscopy if prepared on top of Si wafers with a certain thickness of . The authors study graphene’s visibility and show that it depends strongly on both thickness of and light wavelength. They have found that by using monochromatic illumination, graphene can be isolated for any thickness, albeit (the current standard) and, especially, are most suitable for its visual detection. By using a Fresnel-law-based model, they quantitatively describe the experimental data.
Filtered light images are taken with a Nikon DS-2MBWc monochrome camera. White light images are taken with a Nikon DS-2Mv color camera. Cheaper cameras are more likely to do extensive postprocessing of images in firmware or software that could enhance contrast.
In Ref. 9, the refractive index of bulk graphite is within 5% of between 300 and . At , the extinction coefficient jumps to 1.73, but this coincides with a change of reference in the handbook, which we have chosen to ignore in our model.
The experimental contrast was found by computer analysis of the images obtained using a monochrome camera Ref. 8. The thickness of usually differs by up to 5% from nominal values provided by suppliers and, accordingly, in our theoretical calculations in Fig. 2, the following values for were used to acheive the best fit: (a) , (b) , and (c) .