Study of optical properties of graphene oxide and its derivatives using spectroscopic ellipsometry

Graphene oxide (GO), an insulating analogue to highly conducting graphene, is considered as a chemically tunable platform for optoelectronic applications. However, to be useful for such applications, detailed analysis of its optical properties with a controlled degree of de-oxidation need to be investigated. In this report, we investigated the optical behaviour of GO and chemically reduced GO (with different degrees of de-oxidation, termed as RGO-5 and RGO-10) deposited onto SiO2/Si substrates, using variable angle spectroscopic ellipsometry. GO and its chemically tuned derivatives (RGO-5 & RGO-10) have been synthesized using Hummer's method and by its corresponding reduction using different concentrations (5 and 10 ml) of reducing agent, respectively. Optical properties such as bandgap, the refractive index, the extinction coefficient, and complex dielectric behaviour over the wavelength region 250-1650 nm have been investigated. The optical bandgap is found to reduce systematically from 3.25 eV for GO to 2.78 and 1.81 eV for RGO-5 and RGO-10 samples, respectively. Whereas, the dielectric behaviour of RGO-5 sample found to be better with a lower value of extinction coefficient as compared to GO and RGO-10 samples.