Auger-electron emission induced byAr+impact on silicides

Impact of ions of several kilo-electron-volts (keV) with solids produces inner-shell excitations. The consequent decay results in the emission of Auger electrons whose spectra differ considerably from electrons or x-ray-excited spectra. Si ($L_{23}$-derived) Auger emission, induced by ${\mathrm{Ar}}^{+}$ bombardment in pure Si and silicides of different metals (Cr,Ni,Pt) and stoichiometry (from ${\mathrm{NiSi}}_2$ to ${\mathrm{Ni}}_3$Si), has been studied by varying both the energy of the primary ions (in the 1–5-keV range) and the takeoff angle (from grazing to normal geometry). We separated the background of inelastic scattered electrons from the Auger electrons, and in a further step the contributions to the spectra coming from deexcitation inside and outside the solid. The portion of the Auger emission which originates from sputtered atoms (‘‘atomic spectrum’’) was found to depend on the target composition and takeoff angle, being larger in metal-rich silicides and at grazing geometry. The parents of ‘‘atomic’’ Auger electrons were found to be mainly neutral and excited sputtered atoms in Si and Si-rich silicides, while in metal-rich silicides there is a dominant contribution from sputtered ions. These results have been discussed in terms of the inner-shell ionization mechanism and the in-depth distribution of exciting collisions. The ‘‘atomic’’ spectral shape dependencies on ion energy and takeoff angle have been interpreted in terms of the Doppler shift imparted to the Auger-electron velocity by an anisotropic jet of high-energy parent atoms.