ADSORPTION AND DECOMPOSITION OF HEXAMETHYLDISILOXANE ON PLATINUM - ANXPS, UPS AND TDS STUDY

We have studied with XPS, UPS and TDS, in UHV conditions, the adsorpti on of HMDS on various platinum surfaces and different temperatures. At low temperature, a multilayer is formed which desorbs at 150 K, leavi ng on the surface an undistorted monolayer. With temperature increase, several products appear in the gas phase (methane, lighter organodisi loxanes and hydrogen) leaving on the surface methyl radicals that unde rgo progressive dehydrogenation leading to the formation of amorphous carbon and graphitization at above 700 K. The carbon residue is readil y removed by an oxygen treatment at moderate temperatures, Almost no s ilicon or oxygen remain on the surface above 300 K, a result which can not explain the poisoning effect of HMDS on platinum sensors used to d etect methane in coal mines, It shows that the low pressure mechanism differs from the ambient pressure mechanism. Differences are possibly due to the presence of oxygen at ambient pressures and deserve further investigations.