Adsorption of silane and methylsilane on gold surfaces

The adsorption of silane and methylsilane on the (1 1 0) and polycrystalline surfaces of gold is examined using vibrational electron energy loss spectroscopy (VEELS), angle-resolved ultraviolet photoelectron spectroscopy (ARUPS) and X-ray photoelectron spectroscopy (XPS). Adsorption of silane onto the Au(1 1 0) surface at low temperatures is dissociative and yields an SiH2 and possibly also SiH3 surface species. Further dissociation occurs at room temperature to yield adsorbed SiH, which is tilted on the surface, with complete dissociation to Si occurring by 110 °C. The similarity in the UP spectra for silane adsorbed on the polycrystalline sample suggests that the same surface species are present over that temperature range. Above 200 °C, spectral changes suggest rearrangement of the Si atoms, which, by 350 °C, have diffused into the bulk. Adsorption of methylsilane onto the (1 1 0) surface at low temperatures initially produces adsorbed CH3SiH or CH3SiH2, with undissociated methylsilane physisorbing at higher exposures. By room temperature, desorption and decomposition leaves (or direct adsorption yields) only adsorbed CH3Si. After further heating, the hydrogen–carbon bonds of the CH3 group break to leave an adsorbed SiC species. On the polycrystalline surface, methylsilane adsorption is the same at low temperatures as on (1 1 0). In contrast to the latter, though, the UP spectra indicate that direct exposures at room temperature yield adsorbed Si or SiC initially, with CH3Si again adsorbing at higher exposures. Upon further heating to 330 °C, little if any methyl-groups remain on the surface and the Si has started to diffuse into the bulk.