Optical detection and characterization of graphene by broadband spectrophotometry

The spectra of optical constants, index of refraction $(n)$⁠, and extinction coefficient $(k)$ of graphene and graphite are obtained in the wavelength range of 190–1000 nm (6.53–1.24 eV) using broadband optical spectrophotometry in conjunction with the Forouhi–Bloomer dispersion relations for $n$ and $k$⁠. Measurement is made possible by the use of a multilayer substrate consisting of bulk Si and a $3000ÅSiO2$ film. The effect of multiple internal reflections between the $Si/SiO2$ and $SiO2$/graphene interfaces amplifies the attenuating effect of the graphene layer, thereby improving the sensitivity of the reflectance measurement by a factor of 27 in the deep ultraviolet region of the spectrum. Maximum sensitivity is observed in the deep ultraviolet region of the spectrum, where a strong peak in the spectrum of the extinction coefficient of graphene is identified. The proposed method enables fast nondestructive angstrom-level thickness measurements of graphene and graphite. In this work, layers ranging in thickness between $3.8Å$ (graphene) and $792.8Å$ are detected, measured, and characterized. Reflectance spectra of graphene and graphite on Ni, Co, and Fe substrates are calculated. Differences of 1.1%–2.0% between the bare substrate and the graphene on the substrate are predicted in the deep ultraviolet region of the spectrum, which makes graphene detectable and measurable on these substrates.