Investigation of submonolayer SiOX species formed from oxidation of silane on Pt(1 1 1)

The adsorption and reaction of SiH4 and O2 was investigated on Pt(1 1 1) with a focus on characterizing surface oxidation of silicon. Temperature programmed desorption was used to identify trends in desorption peak temperature and desorption yields to show trends in reactant availability and consumption. These experiments showed increases in H2 desorption and decreases in O2 desorption with increasing SiH4 exposure. No significant H2O desorption was observed with high exposures of SiH4, consistent with O atoms remaining on the surface through bonding with Si atoms. This observation also indicates Si-O reaction kinetics are faster than water formation kinetics. High resolution electron energy loss spectroscopy (HREELS) was used to study the vibrational modes of surface species isolated after various exposures and thermal treatments. Spectra observed after low exposures of SiH4 on an O-saturated surface consist of three primary peaks at 480, 800, and 1130 cm−1, modes similar to those observed in the initial stages of surface oxidation of Si single crystals. However, spectra observed after higher exposures of SiH4 have a single dominant peak at 750 cm−1, indicating a different surface structure at higher Si coverage. Finally, Auger electron spectroscopy showed no shift in the Si LVV peak after exposure to oxygen, suggesting that a true silicon oxide phase is not formed. HREEL spectra collected after higher silane exposures are consistent with computed spectra for a chain of SiO species in which Si is bound to the surface and O is in a bridging position between Si atoms. Comparisons to previous work on Pd(1 1 1), in which clearly silica-like regions on the surface are formed during oxidation of surface silicon, indicate silane oxidation thermal chemistry depends strongly on surface composition.