Absolute doubly differential angular sputtering yields for 20 keV Kr+ on polycrystalline Cu.

We have measured the absolute doubly differential angular sputtering yield for 20 keV Kr⁺ impacting a polycrystalline Cu slab at an incidence angle of θ_i = 45° relative to the surface normal. Sputtered Cu atoms were captured using collectors mounted on a half dome above the sample, and the sputtering distribution was measured as a function of the sputtering polar, θ_s, and azimuthal, ϕ_s, angles. Absolute results of the sputtering yield were determined from the mass gain of each collector, the ion dose, and the solid angle subtended, after irradiation to a total fluence of ∼1 × 10¹⁸ ions/cm². Our approach overcomes shortcomings of commonly used methods that only provide relative yields as a function of θ_s in the incidence plane (defined by the ion velocity and the surface normal). Our experimental results display an azimuthal variation that increases with increasing θ_s and is clearly discrepant with simulations using binary collision theory. We attribute the observed azimuthal anisotropy to ion-induced formation of micro- and nano-scale surface features that suppress the sputtering yield through shadowing and redeposition effects, neither of which are accounted for in the simulations. Our experimental results demonstrate the importance of doubly differential angular sputtering studies to probe ion sputtering processes at a fundamental level and to explore the effect of ion-beam-generated surface roughness. [ABSTRACT FROM AUTHOR]