Ar+-induced silicon Auger spectra: a probe for a sputter-related collisional and emission processes

We performed a detailed, angle resolved study of the Ar+-induced SiLMM Auger electron emission from silicon single crystals in the 1-15 keV ion energy range. Attention has been focused on the Doppler shift of the atomic lines, which arises from the motion of the decaying atoms with respect to the analyzer. It has been found to be a powerful tool to investigate the spatial and energy distribution of sputter-ejected atoms. The Doppler shifted contributions have been up to now associated with an anisotropic ''spike'' of fast atoms which originates from projectile-target collisions, superimposed on the nearly isotropic distribution of slow atoms which originate from collisions between target particles in the cascade. We report on new features in the shifted spectrum, whose behaviour vs ion energy suggests a more complex picture of the surface collisional processes and of the consequent fast particle ejection. The total yield, the relative weight of the atomic and bulk contributions to the SiL23 derived Auger spectra and the behaviour of the asymmetric projectile-target collisions have been investigated as a function of the ion energy at different incident angles. (orig.)