Effect of cross-linking and thermal budget on plasmonic sensing and sub-surface segregation of in situ synthesized gold in polymer nanocomposite

Surface gold–poly (dimethylsiloxane) nanocomposites are a special category of composites, with gold nanoparticles segregated in a polymer’s sub-surface layer. In this work, sub-surface nanocomposites were created by the in situ synthesis of gold, by using the solution of a gold precursor. The in situ reduction of gold ions by the polymer’s cross-linking agent (a vinyl silicon compound) and the subsequent diffusion of gold nanoparticles into the PDMS matrix through heat treatment are investigated, principally, by UV-Vis spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). It is shown that the diffusion stabilizes the freshly formed gold nanoparticles into the sub-surface layer, where they form small aggregates. The kinetics of the in situ reduction reaction at the solution-film interface is studied. The interplay between the reduction of gold ions and the cross-linking agent’s continuous diffusion toward the surface is also discussed in detail. Further, the effect of the sub-surface segregation of gold nanoparticles and their subsequent spatial distribution on the nanocomposite’s sensing capability is discussed as well.