Abstract
Lately, the optical properties of Graphene Oxide (GO) and Reduced Graphene Oxide (RGO) films have been studied in the ultraviolet and visible spectral range. However, the accurate optical properties in the extended near-infrared and mid-infrared range have not been published yet. In this work, we report a Variable Angle Spectroscopic Ellipsometry (VASE) characterization of GO thin films dip-coated on SiO2/Si substrates and thermally reduced GO films in the 0.38–4.1 eV photon energy range. Moreover, the optical properties of RGO stabilized with poly(sodium 4-styrenesulfonate) (PSS) films dip-coated on SiO2/Si substrates are studied in the same range for the first time. The Lorentz optical models fit well with the experimental data. In addition, the morphological properties of the samples were investigated by Scanning Electron Microscopy (SEM) analysis.
Highlights
Graphene Oxide (GO) reduction is a promising approach for the mass production of graphene [1]and the product obtained by this method is known as Reduced Graphene Oxide (RGO)
In our previous works we have studied graphene-based materials by means of Variable Angle Spectroscopic Ellipsometry (VASE) [22,23,24,25]
It is worth noticing that in our previous work [24] we have demonstrated the reduction of GO films by thermal annealing at 400 ◦ C
Summary
Graphene Oxide (GO) reduction is a promising approach for the mass production of graphene [1]. The product obtained by this method is known as Reduced Graphene Oxide (RGO). Non-covalent functionalization is obtained using polymer wrapping, adsorption of surfactants or small molecules via π-π stacking interactions, avoiding surface defects and disruption of electron conjugation of graphene [15]. The capacitance performance, electrochemical and biological properties of PSS-RGO composites have been investigated by other groups [16,19,20]. The optical constants of PSS-functionalized RGO films have not been studied yet. Access to precise complex refractive index data is central for the design of GO and RGO-based optical materials. The optical properties of PSS-functionalized RGO films dip-coated on SiO2 /Si substrates were studied by VASE in the photon energy range between 0.38 and 4.1 eV. Our study could be important for specific applications, such as hyperbolic metamaterials [30] and gas sensors in the mid-infrared [31] range, metamaterials assembled in microfluidic channels [32], and photodetectors in the near-infrared [33] range
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