GOLD PARTICULATE FILM FORMATION UNDER MONOLAYERS

Gold nanoparticulate films were generated under monolayers, prepared from octadecyl mercaptan (1), N,N'dioctadecyl-N,N'-dithioethylammonium bromide (2), and N,N'-dioctadecyl-N,N'-dimethylammonium bromide (3), by the exposure of aqueous HAuCl4 to carbon monoxide and to steady-state irradiation by a 150-W xenon lamp. Absorption spectrophotometric and transmission electron microscopic investigations of the gold particulate films, transferred to solid substrates, indicated the marked influence of the surfactants used to form the monolayer. Those prepared under monolayer 1 had a broad absorption maximum at 580 nm and diameters between 3 and 50 nm. Those formed under monolayer 2 were highly dense and had an absorption maximum at 564 nm. Gold particles formed under monolayer 3 had a very narrow size distribution with a mean diameter of 10 nm and had a broad absorption maximum at 574 nm. Annealing the gold particulate films at high temperature decreased their absorption bandwidth and shifted their maximum to higher energy.