Pressure dependence of secondary ion emission from selected transition metals under nitrogen dioxide

For Ar⁺ bombarded polycrystalline surfaces of Ta, Co, Ni, Pd and Pt the emission of positive secondary ions was observed using nitrogen dioxide as reactant gas with varied partial pressure (0.001 mPa <p_{spno}2 < 10 mPa) and dynamic SIMS conditions (2 keV; 32 A/cm²). The results indicate that NO₂ molecules appear to be completely destroyed in adsorption to Ta. Different behaviour was found for the other target metals. This can be explained by assuming surface species of partially molecular type. In some cases the results indicate two different modes of surface interaction with the reactant gas.