Scattering of low energy K + and Na from W(110)

Abstract

Low energy scattering experiments of K + and Na from W(110) have been performed. The triple differential cross section σ( θ, φ, E′) has been measured for 35 eV K + as a function of the angle of incidence θ i. As θ i, increases, the complex σ( θ, φ, E′) structure reported previously at normal incidence simplifies considerably. At the largest experimental θ i (30°), the triple differential cross section and the energy spectra are simple and reminiscent of energy spectra as measured in low energy ion-scattering (LEIS) at higher energies. Most of the structures observed can be attributed to electronically elastic scattering, and can be reproduced in classical trajectory calculations using a simple model potential. The calculations indicate that many of the features observed can be identified as surface rainbows. The surprising additional existence of “quasi-specular” scattering for this system is due to symmetrical zig-zag collisions. In addition electronic excitation of the projectile can be observed. Scattering of 20–70 eV Na atoms from the W(110) surface shows that in this energy range Na atoms behave similarly to K + ions, although the higher electronic excitation energy of Na + precludes its observation.