Optical band structure with enhanced plasmonic effect of SiO₂/rGO bilayer deposited by spray pyrolysis

Reduced graphene oxide (rGO) has been extensively studied as an alternative plasmonic material which offers activity at broad wavelength region. A bilayer film combining SiO₂ and rGO was successfully deposited on a glass substrate by spray pyrolysis. For a comparative review, the rGO from commercial product (rGO-com) and from our samples (rGO-csc) derived from biomass (coconut shell) are used in this study. X-ray diffractometry (XRD), scanning electron microscopy (SEM), and X-ray photoemission spectroscopy (XPS) were used to characterize these materials. The existence of plasmonic state was clarified by investigating the real component of the dielectric function and by applying the base layer correction of optical conductivity, derived from UV–Vis spectra at wavelength of 300–1000 nm. The real part of the dielectric constant was approximately −20 and −10 for SiO₂/rGO-csc and SiO₂/rGO-com films respectively. Meanwhile, the optical conductivity for both samples has confirmed a peak of around ∼3.5 eV, indicating the presence of correlated plasmon. Broadly speaking, the rGO can be employed to generate the plasmon effect in term of either conventional or correlated plasmons. This result also offers the groundwork for the development of potentially far-reaching discipline of graphene plasmonics, where the usage of biomass-derived rGO-like compounds leading to increasing optical characteristics is interestingly superior to that of the commercial rGO.