Li+-ion neutralization on metal surfaces and thin films

Abstract

Li + ions with energies ranging from 0.3 to 2 keV are scattered from Au(110) and Pd(100) surfaces and from ultrathin Ag film grown on Au(111) in order to study electron transfer phenomena. We find that neutralization occurs quite efficiently and find an anomalous ion energy dependence of the neutral fraction for Au (110) and Pd(100) surfaces previously noted for Au(111). The dependence of the neutral fraction on the azimuthal angle of the Au(110) and Pd(100) surfaces is reported. In the case of Ag monolayer on Au (111), results are similar to the case of the Ag(111) surface. To understand the anomalous ion energy dependence, we present a theoretical study using density functional theory (DFT) and a linearized rate equation approach, which allows us to follow the Li charge state evolution for the (111) surfaces of Ag, Au, and Cu, and for the Ag-covered Au(111) surface.

Electron transfer processes on Au nanoclusters supported on graphite

“…However, this anomalously large neutralization appeared to be quite general and not restricted to a given type of surface [16,24]. More recent theoretical studies show that near the metal surface, the Li(2 s) level actually lies below the Fermi level [24,27] for some distance less than Z C , and hence at small distances Li can be neutralized.…”

“…However, this anomalously large neutralization appeared to be quite general and not restricted to a given type of surface [16,24]. More recent theoretical studies show that near the metal surface, the Li(2 s) level actually lies below the Fermi level [24,27] for some distance less than Z C , and hence at small distances Li can be neutralized. Therefore, as opposed to the "standard" picture, one does not deal with the neutralization of an ion, as it recedes from the Au surface, but rather a more complex situation involving also neutral atoms that, as they recede from the surface, are first ionized and then neutralized.…”

“…Secondly, it appeared that adiabatically [24], at small velocities, the charge on Li tends to unity (neutral atom), and hence at low velocities neutralization is efficient [24], as opposed to what was expected in the standard descriptions. In a very recent calculation, this seems to be related to a much larger Li (2 s) level width [28] than predicted by earlier DFT calculations [19,20,23].…”

“…The results of this study need to be put into the perspective of a complex problem related in general to alkali ion neutralization on metal surfaces. While alkali neutralization on bulk metal surfaces seemed well understood [18][19][20], recent experiments [21][22][23][24] revealed very wide discrepancies with predictions of these "standard" jellium-like models of metals using a rate equation approach to describe neutralization. It was indeed found, as may also be seen in the Au thin film limit of Fig.…”

“…Electron capture then occurs at large distances from the surface, when the Li (2 s) level lies below the Fermi level for atom surface distances greater than Z F . For Au(111) [22,24] with a workfunction of 5.4 eV, this would only occur at very large distances where the interaction with the surface is very weak, and therefore significant neutralization was not expected.…”