AUGER-ELECTRON SPECTROSCOPIC (AES) STUDIES OF THE ADSORPTION AND REACTION OF SNCL4 AND H2O AT A SILICA SURFACE

To investigate the surface chemical mechanisms underpinning tin oxide film formation on glass, we have monitored the effects of exposing an etched silica surface to SnCl4 and H2O using AES under ultra high vacu um (UHV) conditions. Adsorption of SnCl4 on the oxygen rich surface wa s confirmed by the appearance of Auger signals corresponding to tin an d chlorine. However in the temperature range studied (303-673 K), high temperatures did not favour adsorption conditions. Heating adlayers o f SnCl4 resulted in a reduction in tin and chlorine Auger signal inten sity, suggesting that SnCl4 was only physisorbed on the surface. The e ffect of dosing H2O onto the etched silica surface could not be direct ly monitored, due to either the inherent difficulty associated with th e detection of additional surface oxygen on the glass surface or elect ron beam stimulated desorption, or a combination of these factors. How ever H2O adsorption can be inferred from results obtained after exposi ng the etched silica surface to SnCl4, prior to dosing H2O. These resu lts suggest that H2O was physisorbed on the tin and chlorine species. Dosing SnCl4 at the same pressure used earlier in the presence of H2O resulted in detection of tin and chlorine Auger signals. By comparison to results obtained in the absence of water a reduction in tin and ch lorine Auger signal intensities was observed. This was attributed to t he formation of a H2O overlayer on the tin and chlorine species, in ag reement with the above result. High surface temperatures also produce a reduction in uptake, in line with results reported earlier.