Ion reduction in metallic nanoparticles nucleation and growth on cellulose films: Does substrate play a role?

The effect of the substrate (GaAs, Si, glass or Au) on the reduction of silver and gold ions in AgNO3 and HAuCl4 center dot 3H(2)O salts aqueous solutions was here studied. The main goal of this study was the understanding of the reduction mechanism of silver and gold ions in interaction with ultrathin cellulose films deposited on different substrates. Surface morphology was observed and measured using atomic force microscopy (AFM) and its chemical composition characterized by X-ray photoelectron spectroscopy (XPS). Results show that, besides the contribution of the cellulose film to the metallic ions reduction and nanoparticle (NP) growth, the substrate also plays an active role. This is clearly evident in the case of silicon, gallium arsenide, and gold substrates, either bare or covered by cellulose films. For bare glass substrates, no NPs were observed contrarily to glass substrates covered by a cellulose film, where NPs appear on the cellulose film. Yet, XPS showed that, in this last case, metallic ion reduction did not occur, at least in the surface region of the film, where oxidized silver was detected, suggesting a weak or absent reduction power of cellulose. In all cases, XPS C 1s spectra of the cellulose did not show any oxidation of the film. Anyway, the images point out the important role of the cellulose covering film on the final distribution of NPs on the surface.