Nucleation and growth of gold nanoparticles on adsorption layers and in ultrathin films of poly(2-vinylpyridine)

Peculiarities of the nucleation and growth of gold nanoparticles on adsorption layers and in ultrathin films of poly(2-vinylpyridine) (PVP) in the chemical reduction of sorbed Au(III) ions and the consequent thermal treatment of systems are studied by X-ray photoelectron spectroscopy and optical spectroscopy. It is shown that nitrogens of PVP pyridine groups coordinate gold atoms. It is revealed that, even at relatively short contact between PVP film saturated with chloroauric acid and the solution of strong reductant NaBH4, Au(III) ions are reduced to metal. As a result, quasi-metal gold particles are formed. At the same time, when exposing a PVP-Au system to the solution of weak reductant NH2OH, the process of reduction proceeds in several stages. First, Au(III) ions are reduced to Au(I) followed by the reduction to Au(0) as a result of disproportionation reaction. It is demonstrated for the first time that, upon using NH2OH, the rate of reduction, as well as the structure of prepared PVP-Au nanocomposite films depends to substantial extent on solution pH. Prolonged annealing of ultrathin nanocomposites at 150 A degrees C, i.e., above the glass transition temperature of polymer matrix, leads to an increase in the sizes of metal particles and the formation of systems characterized by intense absorption within the 500-600-nm range due to the localized plasmon resonance of gold nanoparticles.