Surface topography effects on energy-resolved polar angular distributions of electrons induced in heavy ion-Al collisions: Experiments and models

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Abstract
The influence of the surface topography on the polar angular distributions of secondary electrons emitted in Ar+ (and Xe+)-Al collisions was studied. After each set of experiments, carried out in controlled bombardment conditions, the surface target was viewed by scanning electron microscope. Some models were elaborated to schematize the main structures observed. Under normal incidence, continuum background and Al L23 VV Auger electron polar angular distributions were not modified by the topography and closely followed a cosine law which is that expected from a flat surface for electrons generated inside the crystal. This result was in agreement with the angular distributions calculated taking into account different structured surface models. For Al L23 MM Auger electrons, experimental angular distributions as a function of the emission polar angle Θ, either were near a constant law or followed a decreasing law depending on the irradiation conditions. The N(Θ) curves calculated from the models showed that the isotropic angular distributions obtained for electrons generated outside the crystal from a flat surface could be strongly modified by the surface topography. These calculated curves reasonably agree with the different experimental distributions obtained from various surface topographies.