Local work function effects in the neutralization of alkali ions scattered from cesiated surfaces (original) (raw)
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Low-energy Na+ neutralization on Al(1 1 1) and Cu(1 1 0) surfaces at grazing incidence
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2020
Jellium model is well known and used to understand the neutralization of alkali-metal ions on metal surfacesbut we find it cannot explain our experiments for the neutralization of 0.4 keV and 0.8 keV Na + ions on Al(1 1 1) and Cu(1 1 0) surfaces in grazing incidence. As the exit angle increases neutral fractions on Cu(1 1 0) surface decreases first and then increases which is similar to our previous results at large scattering angles. While for the Al (1 1 1) surface we observe opposite characteristics. This anomalous bell-shaped feature cannot be explained by the Jellium model. One possible explanation is the inner 2p electron promotion at smaller exit angles this may cause the Na* excited states to be generated and produce excess Na + ions while the similar electronic excitation process is inefficient for the Cu(1 1 0) surface in the present energy range.
Crystal Effects in the Neutralization of He+ Ions in the Low Energy Ion Scattering Regime
Physical Review Letters, 2008
Investigating possible crystal effects in ion scattering from elemental surfaces, measurements of the positive ion fraction P are reported for He ions scattered from single and polycrystalline Cu surfaces. In the Auger neutralization regime, the ion yield is determined by scattering from the outermost atomic layer. For Cu(110) P exceeds that for polycrystalline Cu by up to a factor of 2.5, thus exhibiting a strong crystal effect. It is much less pronounced at higher energies, i.e., in the reionization regime. However, there a completely different angular dependence of the ion yield is observed for poly-and single crystals, due to massive subsurface contributions in nonchanneling directions.
Harpooning in collisions of Li+ ions with oxygenated partially cesiated W(110) surfaces
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 1990
We have studied the formation of Li* and Li-ions, Li(2p) atoms, electrons, and O-ions when 1 keV Li+ ions collide under grazing incidence with cesiated W(110) surfaces subject to oxygen exposure. At exposures < 2 L the Processes between the incident Li + ions and the surface still proceed as for solely cesiated surfaces. We observe a strong rise of the rates of formation of Li+ ions and Li(2p) atoms for oxygen exposures > 2 L. At the same time 0-ions can be detected. One possible inte~retation is that the coilision process proceeds via a (Li+-Cs,O_,)) intermediate state.
Low-energy ion neutralization at surfaces: Resonant and Auger processes
Physical Review A, 2001
The interaction of He ϩ with a typical metal surface ͑Al or Pd͒ is described, analyzing in detail the different mechanisms that contribute to the neutralization of the projectile when backscattered from the surface. Auger and resonant neutralization processes are considered and analyzed including a detailed quantum-mechanical description of the He-metal interaction, for projectile energies between 100 eV and 3 keV. We show that the promotion of the He-1s level, due to its interaction with the metal-atom-core orbitals, is the crucial mechanism making resonant processes operative. We find, however, that resonant processes are much more important for Al than for Pd. In Al, both Auger and resonant processes are equally important for neutralization of the ion, while for Pd we find that Auger is the dominant mechanism, making the He/Pd system the ideal case for which Hagstrum's exponential law appears to be practically valid for all velocities. We also find qualitative agreement with experimental data, which we consider a satisfactory result in view of the fact that our theory is a complex ab initio calculation free of adjustable parameters.
Auger electron emission induced by slow alkali ion collisions with cesiated W(110) surfaces
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 1991
We have investigated 200 eV collisions of Li+, Na* ions under grazing incidence with partially cesiated W(110) surfaces by energy analysis of the ejected electrons. From this analysis it is concluded that Auger deexcitation of excited states of the alkali atoms populated by resonant charge transfer between the projectile and the partialiy cesiated surface is an efficient process.
Ionization probability of atoms and molecules sputtered from a cesium covered silver surface
Applied Surface Science, 2003
We have measured the ionization probabilities of Ag, Cs and AgCs sputtered from a Cs covered silver surface by simultaneously registrating the sputtered neutral and charged species. As the main result, we ®nd that AgCs molecules are predominantly emitted as neutrals. Moreover, it is found that the dependence of the AgCs ion fraction on the cesium surface concentration does not follow the ionization probability of sputtered Cs atoms. #
Physical Review A, 2004
A comparative study of the resonant charge-transfer process of H − in front of plane-model Cu surfaces of symmetries (111) and (100) is performed using a two-dimensional Crank-Nicholson wave-packet propagation approach. Very different electron evolutions near the two surfaces are related to different structures of the respective band gaps and allow for the visualization of electronic interaction mechanisms. It is shown that electrons get localized near the Cu(111) surface due to the reflectivity imposed by the band gap. This enables considerable recapture by the ion. In contrast, H − is neutralized more efficiently near Cu(100), for which the surface state is embedded in the bulk valence band. Image states are found to be important intermediaries for charge transfer at smaller ion-surface distances. As a consequence of all these effects, the dynamics of ion neutralization near (111) and (100) surfaces vastly differ to yield quite dissimilar ion-survival probabilities. It is found that while the ion-surface interaction time becomes important at normal incidence, for near-grazing incidences, the point of closest approach to the surface is a crucial determinant of the ion survival.
Multiple-scattering effects in ion-surface interactions at low energies
Physical Review B, 1981
The scattering of 600-eV He ions from clean Ni(110) is studied both experimentally and by means of computer simulation. It is shown that for a comparison with the experimental data it is essential that the scattering model be three dimensional. We infer from such comparisons for the dependence of the ion yields on the crystallographic orientation that neutralization effects are operating which strongly depend on the scattered particles' trajectories. Two types of neutralization processes are distinguished: one essentially Auger and the other more typical of the bulk neutralization seen at higher energies.