Abstract
Using a common purity Pt foil, the character of adspecies adsorbed from the residual gases in a stainless-steel UHV system was studied by the electron-stimulated desorption (ESD) method. Hydrogen adatoms and dissociatively adsorbed water vapor were found as a deposit from the gas phase. The alkali metal ions, Na + and K +, were readily observed by secondary ion mass spectrometry even after sputter cleaning the sample. It is suggested that alkali metal impurities could be the active sites on the Pt surface for dissociative adsorption of water. The fluorine observed on the Pt surface was thought to be a result of surface segregation of fluorine bulk impurities, with the standard enthalpy of segregation being 1600 cal/mole. A correlation between ESD of fluorine and an increase in ESD active surface hydrogen was observed. It is concluded that surface sites released by fluorine desorption are particularly active for hydrogen adsorption. Also, ESD parameters, such as total cross section, ion energy distributions, and the ion yield dependence on electron beam energy, were measured for various adspecies observed on the Pt foil.
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