Angle-resolved Auger study of 10-keV Ar+-ion-induced Si LMM atomic lines.

Abstract

We present a detailed, angle-resolved Si L-shell Auger study by bombarding a single-crystalline Si sample with 10-keV ${\mathrm{Ar}}^{+}$ ions. We have observed a new atomic line at kinetic energy of \ensuremath{\sim}99 eV which is tentatively assigned to an Auger transition involving two 2p holes in ${\mathrm{Si}}^{+}$. The existence of two atomic peaks at 61.36 and 91.1 eV has also been clearly confirmed. Our Auger spectra show well-split Doppler peaks for the principal ${\mathrm{Si}}^{0}$ and ${\mathrm{Si}}^{+}$ atomic lines and a strong dependence of the shift amplitude on both incidence and detection angles. Successful computer fitting of the angular dependence of Doppler shift has been achieved by using a simple binary-collision model with the Moli\`ere approximation to the Thomas-Fermi screening potential. These results suggest that the first violent Ar-Si asymmetric collisions contribute remarkably to the Si 2p-vacancy creation process and are responsible for the ejection of energetic ${\mathrm{Si}}^{(\mathrm{*})}$ particles which is highly directional. The critical minimum Ar-Si approach distance for Si 2p-hole excitation is 0.355 \AA{}, in very good agreement with the value predicted by molecular-orbital theory.