Reactive collisions of hyperthermal ions with oxide surfaces

Hyperthermal energy ions (NO+ and O+) are reacted with thin oxide films grown on Al(111) and Si(100), respectively. The scattered ionic products (NO2− and O2−, respectively) are detected with mass-, energy-, and angular-resolution. The translational energy distributions of the products are correlated with the collision energy, suggesting that the abstraction product emerges from the surface before it, or the incident ion has had time to equilibrate. Thresholds for O-atom abstraction are 9 eV for NO+ incident on O/Al(111) and 16 eV for O+ on SiOx. The data support an Eley-Rideal mechanism, in which the incident ion neutralizes along the inbound trajectory, abstracts an adsorbed oxygen atom through a direct collision, and scatters from the surface as a molecular anion.