Optical constants of graphene measured by spectroscopic ellipsometry

A mechanically exfoliated graphene flake (∼150×380 μm2) on a silicon wafer with 98 nm silicon dioxide on top was scanned with a spectroscopic ellipsometer with a focused spot (∼100×55 μm2) at an angle of 55°. The spectroscopic ellipsometric data were analyzed with an optical model in which the optical constants were parameterized by B-splines. This parameterization is the key for the simultaneous accurate determination of the optical constants in the wavelength range 210–1000 nm and the thickness of graphene, which was found to be 3.4 Å.