Differences in the neutralization of 2.4–10 keVNe+scattered from the Cu and Au atoms of an alloy surface

The neutralization behavior of low-energy ${\mathrm{Ne}}^{+}$ ions scattered from a compositionally ordered ${\mathrm{Cu}}_3$Au(100) surface has been studied over a range of incident energy ${\mathit{E}}_0$ from 2.4 to 10 keV. Ion fractions of Ne scattered from Cu atoms in the first, or first two, atom layers exhibited a sharp increase setting in at an ${\mathit{E}}_0$ of 4–5 keV, reaching 70% at 10 keV for first-layer scattering. Inelastic energy losses, up to 130 eV, and Auger electron emission from Ne scattered from Cu, were also observed at incident energies above 4 keV. Ne scattered from the Au atoms on the same ${\mathrm{Cu}}_3$Au(100) surface showed only the usual velocity-dependent Auger and resonance neutralization. An explanation of the Cu results is given in terms of Ne 2s vacancy creation during the close collision of Ne, which is neutralized on the inward path, followed by autoionization on the outward path after scattering into the vacuum. Conversely, Ne cannot approach Au closely enough to form an appropriate inner-shell vacancy. This is due to the higher Coulombic repulsion created by the greater charge of the Au nucleus.