Optical detection and characterization of graphene by broadband spectrophotometry
Gray, Alexander × Balooch, Mehdi Allegret, Stephane De Gendt, Stefan Wang, Wei-E #
American Institute of Physics
Journal of Applied Physics vol:104 issue:5
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 3000 angstrom SiO2 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 3.8 angstrom (graphene) and. 792.8 angstrom 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. (c) 2008 American Institute of Physics.