Making graphene visible

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 SiO2. We study graphene’s visibility and show that it depends strongly on both thickness of SiO2 and light wavelength. We have found that by using monochromatic illumination, graphene can be isolated for any SiO2 thickness, albeit 300 nm (the current standard) and, especially, ≈100 nm are most suitable for its visual detection. By using a Fresnel-law-based model, we quantitatively describe the experimental data.