Auger-electron emission induced by Ar+ impact on silicides.

Abstract

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.