Nonaqueous gold colloids. Investigations of deposition and film growth on organically modified substrates and trapping of molecular gold clusters with an alkyl amine
Gold–acetone colloidal solutions were prepared by a metal vapor codeposition procedure (solvated metal atom dispersion) and from these solutions gold films were prepared by allowing adsorption/deposition on (sulfanylpropyl)trimethoxysilane- (aminopropyl)trimethoxysilane or (isobutyl)trimethoxysilane-modified substrates. The mechanism of gold film formation was studied by AFM and TEM. At short contact times, self-assembly of colloidal gold particles onto the functionalized substrate surfaces took place and both individual particles and aggregates appeared. As contact time increased, a dynamic equilibrium was evident on the thiol- and amine-modified substrates and resulted in the development of more stable, close-packed layers. At still longer contact times, a smooth film was formed on the surface. Besides film growth studies, the gold colloid particle growth in acetone was investigated. By adding dodecylamine, particle growth was stunted and very small (2–3 nm) individual crystallites coated by the amine were obtained. These materials were molecular in nature in the sense that they could be precipitated and redissolved many times without change. TEM data showed that the particles were spatially separated and the interparticle spacing was dependent on the amount of dodecylamine. The FT-IR data indicated that a significant amount of amine (N–H bond) and acetone (CO bond) were adsorbed on the gold particle surfaces.