Highly charged ions impinging on a stepped metal surface under grazing incidence

We report on energy loss measurements and charge state distributions for 60 keV N⁶⁺ and 75 keV N⁵⁺ ions scattered off a Pt(110)(1×2) single crystal surface. In particular, the influence of surface steps on the energy loss and the outgoing charge states is discussed. The scattering angle and the angle of incidence are varied. We use grazing incidence conditions, i.e., the momentum perpendicular to the surface is low enough to prevent penetration through the first atomic layer. Image charge effects are observed leading to an additional projectile acceleration towards the surface. Outgoing charge states are detected from 1+ up to 3+. Axial channeling conditions are defined by scattering along the azimuthal [001] direction, i.e., the projectiles are guided along the [001]-atomic rows. The energy loss for axial channeling is found to be somewhat larger and the energy distribution to be broadened in comparison with the spectra for planar channeling conditions. The broadening is attributed to the interaction of the projectiles with the side wall potentials of the surface channels. We find a strong increase in the energy loss with increasing scattering angle, which exceeds the calculated contribution of the elastic energy transfer by orders of magnitudes. These increased energy losses are attributed to the interaction of the ions with the surface steps.