High energy (˜ 107 eV) Si peak in Ar excited auger emission from silicon and silicides

The Ar⁺ excited electron emission from Si and Si-Ni compounds (from NiSi₂ to Ni₃Si) was studied, with emphasis on the high energy peak in the Si (L₂₃-related) spectrum. This peak is associated with the decay of Si atoms having two 2p holes (Si²*); therefore it originates in asymmetric (Ar-Si) collisions only. It has been investigated to determine the occurrence of these collisions with respect to the symmetric (Si-Si) ones and their relative weight.

The threshold energy for the Si^2* related Auger emission was found to be about 2.9 keV in Si and silicides, significantly lower than previously reported. Above this threshold, the relative weight of the asymmetric collisions increases with ion energy and depends on the target stoichiometry, being greater in metal-rich silicides. However in the investigated ion energy range (1 to 5 keV) the total Auger yield was found to be mainly related to the symmetric collisions.

We also investigated the dependence of the high energy Si peak on the excitation and acceptance geometry. The results indicate that asymmetric collisions are mainly “surface events”, resulting in the ejection of an anisotropic flux of energetic Si atoms.