Dissociation of ethoxysilane and methoxysilane on Si(001)-2 × 1 and Si(111)-7 × 7 at room temperature: A comparative study using synchrotron radiation photoemission

The adsorption of tetraethoxysilane and tetramethoxysilane (TEOS, Si[OC₂H₅]₄ and TMOS, Si[OCH₃]₄) on the Si(001)-2 × 1 and Si(111)-7 × 7 surface at 300 K was studied by synchrotron radiation X-ray photoelectron spectroscopy (XPS). On Si(001)-2 × 1, and for both alkoxysilanes, two adsorption regimes are present. The initial one corresponds to the full dissociation via Si-O bond breaking that leads to the grafting of ethoxy moieties and the release of a silicon monomer. This regime is superseded by a second mechanism involving the breaking of C-O bonds leading to the attachment of alkyl moieties to the surface. We propose that C-O bond breaking occurs on the silicon monomers produced during the initial regime. On Si(111)-7 × 7, although the surface reconstruction is different from that of Si(001), we observe the same products as those seen on Si(001)-2 × 1 and the same trends (Si-O bond breaking predominates over C-O bond breaking at low coverage).