Secondary Positive Ion-Emission from Platinum

Abstract

Mass analysis of the secondary particles ejected from Pt surfaces by inert gas ion bombardment or by heating revealed species characteristic of the base metal, of certain bulk and surface impurities, and of the bombarding beam (so-called ``reflected'' ions). The Pt+ ions seemed to come directly from the substrate rather than from surface compounds. Their yield increased with temperature, bombarding ion energy, and bombarding ion mass. The ratio of sputtered Pt ions to sputtered neutrals is estimated to be of the order of 1 to 1000 at room temperature. The kinetics of the formation and desorption of a certain surface compound [possibly Pt(CO)2] was studied by secondary ion analysis. The compound formed spontaneously on the surface from the background gas in the instrument (CO at 10—8 mm Hg). Its formation rate was greatly enhanced by inert gas ion bombardment. It desorbed readily at 1000°C with an activation energy of 0.74±0.05 ev. The ``reflected'' ions appeared to be sputtered rather than reflected. Their energy was always extremely low (<1 ev) and the dependence of their yield on ambient gas pressure and target temperature is consistent with the notion that they originated from inert gas atoms trapped in the surface layers.