Ion sputtering on metal oxides: A source of translationally hot O(3P J) atoms for chemical studies above 1 eV

Abstract

A novel technique is described for generation of translationally ‘‘hot’’ oxygen atoms that can be used for chemical studies. These atoms are produced through ion sputtering on Ta2 O5 targets. Mass-resolved beams of noble gas ions in the kilovolt energy range are generated for this purpose using a 150-cm isotope separator. The technique can yield fluxes of oxygen atoms in the range of 1015 –1016 atoms cm−2 s−1 from a 40-keV argon ion beam with 15-μA intensity. The sputtered atoms are predominantly neutral and reside exclusively in their 3PJ ground electronic state upon ejection. Translational energy profiles, measured for an incident ion beam angle of 30° from the surface normal, were found to be similar in both the forward and backward scattered directions at a 60° angle from the surface normal. These distributions peaked at about 7 eV, but extended beyond 20 eV. Theoretical calculations using a modified Thompson model yielded a similar distribution at this angle. This suggests that kilovolt ion sputtering on Ta2 O5 proceeds predominantly through a collision cascade mechanism. The energy range provided by this technique opens up a new area of hot-atom chemistry for oxygen atoms that has been relatively unexplored until now because of the lack of methods for their generation.