Síntese e caracterização de filmes depositados em sílica de nanocompósitos formados por grafeno e nanopartículas metálicas mistas para aplicações ópticas

Abstract

The use of nanocomposites formed by metallic nanoparticles (Nps) and carbon nanomaterials, such as graphene, has gained prominence, as their interaction can result in new properties. Both the synthesis and application of graphene have gained prominence since its first production in 2004, when a single sheet was separated from graphite using the peeling technique. Nps have been synthesized for centuries, however new routes have been proposed resulting in high control over the characteristics of the final material. The present work aimed at the synthesis and characterization of thin films of mono or bimetallic Nps together with graphene, on a silica substrate, in a single synthesis step. Silica coverslips previously treated with piranha solution (2 H2SO4:1 H2O2) were used, with subsequent surface functionalization with (3-aminopropyl)triethoxysilane (APTES), together with the proposed metals (Ag, Cu and Ag+Cu) in the form of the respective metal cations. In some samples, an extra carbon source (expanded polystyrene) was added in order to obtain a greater amount of graphene in the films. After this, the reduction of metallic ions was carried out using the thermal method, together with obtaining the carbon material, where the samples were taken to the muffle furnace at 350 °C for a period of 30 minutes, resulting in relatively homogeneous films containing the species of interest. At the end of the synthesis steps, the films were characterized by electronic absorption spectroscopy in the ultraviolet-visible region (UV-Vis) to verify plasmon absorption, being the first indication of obtaining metallic Nps using the proposed method. X-ray diffraction (XRD) for thin films showed signals related to silver and copper, with broadened peaks showing that particles were obtained on a nanometric size scale. Raman Spectroscopy (Raman) measurements confirmed the obtainment of graphene in the samples, and transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were used to verify the shape, size and presence of 2D materials, as well as the characteristics of each film with changes in synthesis conditions. Atomic force microscopy (AFM) images allowed the roughness of each film to be evaluated. The presence of carbon, both amorphous and crystalline, was thus evident in the samples, but not continuously, in addition to the formation of metallic Nps. With the addition of greater amounts of extra carbon source, it was observed that a greater amount of 2D carbon structures were obtained, in addition to a decrease in the roughness of the films.