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

Abstract

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 This regime is superseded by a second mechanism involving the breaking of C–O bonds leading to the attachment of alkyl moieties to the surface.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).