Adsorption of organosilanes on iron and aluminium oxide surfaces

Thin films of a simple organosilane, propyltrimethoxysilane (PTMS), on polycrystalline aluminium and iron oxide substrates have been investigated using XPS. Comparison of the adsorption isotherms for the two substrates reveals significant differences between them. Although PTMS on iron oxide exhibits a Langmuir-like isotherm, PTMS on aluminium oxide shows an unexpected decrease in adsorption at intermediate exposures. The results demonstrate that even for the simplest organosilanes and single-component surfaces the formation of silane coatings on metals is complex and strongly dependent upon the nature of the surface. The implication of the results to silane coupling events (SCAs) is discussed briefly.