Effects of defect structures at surfaces and thin films on grazing scattering of fast ions

Studies on grazing scattering of 25 keV ${\mathrm{H}}^{+}$ and ${\mathrm{He}}^{+}$ ions from clean Fe(001) and submonolayer films of Cr and Mn on Fe(001) are reported. We find that angular distributions of reflected ions directly depend on the defect structure of the topmost surface layer. Surface defects of different dimensions (thermal displacements, surface steps, islands) can be separated due to characteristic effects on the scattering process. Computer simulations based on the binary collision approximation permit a quantitative analysis of data.