Characterization of thermally reduced graphene oxide by imaging ellipsometry

The dispersion functions for the refractive index and the extinction coefficient of single- and multiple-layer graphene oxide samples were measured by imaging spectroscopic ellipsometry in the wavelength range of 350-1000 nm and were compared to previously reported results measured by confocal microscopy. The dispersion functions for thin platelets were also compared to those obtained by standard spectroscopic ellipsometry on a deposit consisting of many overlapping graphene oxide layers. Changes were observed in both the thickness of the deposits and the values of the dispersion parameters following heating. A model is proposed to explain these observations, based on the removal of water between the graphene-oxide layers upon thermal treatment.