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 vacuum (UHV) conditions. Adsorption of SnCl4 on the oxygen rich surface was confirmed by the appearance of Auger signals corresponding to tin and chlorine. However in the temperature range studied (303-673 K), high temperatures did not favour adsorption conditions. Heating adlayers of SnCl4 resulted in a reduction in tin and chlorine Auger signal intensity, suggesting that SnCl4 was only physisorbed on the surface. The effect of dosing H2O onto the etched silica surface could not be directly monitored, due to either the inherent difficulty associated with the detection of additional surface oxygen on the glass surface or electron beam stimulated desorption, or a combination of these factors. However H2O adsorption can be inferred from results obtained after exposing the etched silica surface to SnCl4, prior to dosing H2O. These results 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 chlorine Auger signal intensities was observed. This was attributed to the formation of a H2O overlayer on the tin and chlorine species, in agreement with the above result. High surface temperatures also produce a reduction in uptake, in line with results reported earlier.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 vacuum (UHV) conditions. Adsorption of SnCl4 on the oxygen rich surface was confirmed by the appearance of Auger signals corresponding to tin and chlorine. However in the temperature range studied (303-673 K), high temperatures did not favour adsorption conditions. Heating adlayers of SnCl4 resulted in a reduction in tin and chlorine Auger signal intensity, suggesting that SnCl4 was only physisorbed on the surface. The effect of dosing H2O onto the etched silica surface could not be directly monitored, due to either the inherent difficulty associated with the detection of additional surface oxygen on the glass surface or electron beam stimulated desorption, or a combination of these factors. However H2O adsorption can be inferred from results obtained after exposing the etched silica surface to SnCl4, prior to dosing H2O. These results 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 chlorine Auger signal intensities was observed. This was attributed to the formation of a H2O overlayer on the tin and chlorine species, in agreement with the above result. High surface temperatures also produce a reduction in uptake, in line with results reported earlier.