Behavior of gold nanoparticles in formation of surficial sulfide micro- and nanophases on substrates of single crystals of arsenopyrite and chalcopyrite

The features of superficial phases (SPs) formation with different mineral buffers from metallic Fe and Cu films containing nanoparticles (NPs) of gold are studied. The data on gold occurrence forms in sulfide SPs are obtained by scanning probe microscopy (SPM), electron probe microanalysis (EPMA) and X-ray photoelectron spectroscopy (XPS). SPM shows that metal films of gold, iron and copper obtained by magnetron sputtering on polished sulfide substrates of arsenopyrite (FeAsS) and chalcopyrite (CuFeS₂) have a fractal nature. Under annealing, the fractal dimension (D_f) of films varies in the interval 2.3-2.4, providing suggestion that the process of sulfidation of metal films proceeds by a partial ripening of metal grains and the formation of iron and (or) copper sulfides. A portion of Au NPs is "trapped" by growing sulfide micro- and nanophases (binding energy (BE) for XPS spectrum line Au 4f_7/2 equal to 84.5±0.2 eV indicates the form Au_nano). Other NPs are represented by spherical microsized gold-containing phases on the surface of sulfide substrates (the form Au°) formed by the self-assembly mechanism (BE=84.0±0.2 eV), and partially are chemisorbed on SPs displaying Au-S chemical bonding (the form Au⁺ with BE=85.0±0.2 eV).