Optical determination of thick graphene layer number based on surface plasmon resonance

An optical method of measuring the number of layers in a graphene sample is formulated and compared with the conventional surface plasmon resonance (SPR) detection scheme, the latter being appropriate only for a very few graphene layers. Numerical results based on transfer-matrix method support that an alternative method, wherein the SPR substrate includes a dielectric overlayer, is feasible over a wide range of graphene layer numbers. While the multilayer graphene may lead to a broad and shallow SPR curve owing to the nonzero imaginary part in its relative permittivity, the dielectric overlayer makes the resonant surface plasmons less affected by graphene, resulting in a strong and deep absorption band at resonance. Linear regression analysis shows that the measurable graphene layer number can be as high as 50.