Surface Miller Index Dependence of Auger Neutralization of Ions on Surfaces

Abstract

Neutralization of He+ ions in grazing incidence scattering on Ag(111) and Ag(110) surfaces is studied. These measurements reveal the existence of an order of magnitude difference in the probability of ion survival on Ag(110) and Ag(111). The experimental results are discussed in terms of survival from Auger neutralization, whose rates are derived theoretically. Molecular dynamics simulation of scattered ion trajectories is performed and the surviving ion fractions are then calculated using the theoretical Auger neutralization rates, without adjustable parameters. The calculations agree quite well with the experimental data and show that the observed differences in the neutralization probabilities on these surfaces are related to different extensions of the electron density beyond the surface, resulting from different atomic packing.

Band structure effects in Auger neutralization of He ions at metal surfaces

“…This value is also confirmed by recent investigations of He + scattered from Ag(111) and Ag(110), where agreement between experiment and theory was obtained assuming a level shift of 2 eV. 45 Experiments for He + scattered from various Al surfaces yielded, depending on the perpendicular energy, the shift of the He 1s level is in the range between −1 eV and 2 eV. 24 All these experiments were conducted in grazing scattering geometry, where the perpendicular energy of the projectiles is small.…”

“…This finding was explained by the fact that for different Miller indices the jellium edge is located at different distances to the surface planes, which contain the outermost atomic layers. 19,20 Thorough investigations revealed that a theory of AN beyond the jellium model is required to explain existing experiments on noble metals and to be able to make quantitative predictions there. To this end, a theory of AN was formulated using a Linear Combination of Atomic Orbitals (LCAO) basis for the metal electrons.…”

The healing mechanism for excited molecules near metallic surfaces

“…Nevertheless, it has been suggested by numerical calculations that, as a good approximation, the dependence on the distance d and the energy ω factorize [9] as…”

“…where 1/τ B (ω) is obtained using the formula for the molecule immersed in the bulk and f(d) is an unknown function, usually approximated by an exponential [9], which decays away from the metal surface. Propst [17], however, has shown that the distance of the molecule from the surface comes into play mostly through the WKB transmission probability.…”

Studies on Auger Neutralization of He + Ions in Front of Metal Surfaces

“…In experiments with He þ ions scattered from Ag(111) and Ag(110) surfaces, Bandurin et al [35] observed differences for the fractions of survived ions of about one order of magnitude. Similar results were also reported for different faces of a Cu crystal [36].…”