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Title: Role of surface states in Auger neutralization of He{sup +} ions on Ag surfaces

Abstract

Recent measurements of He{sup +} ion fractions that survive to a whole scatterig event when they impinge on Ag surfaces have shown two different and interesting effects: (1) a notable difference of surviving ion fraction depending on which crystallographic face of the target surface is studied [Yu. Bandurin et al., Phys. Rev. Lett. 92, 017601 (2004)], and (2) an uncommonly high ion fraction in the very-low-energy range (tens of eV) [S. Wethekam et al., Phys. Rev. Lett. 90, 037602 (2003)]. Apart from the geometry, one of the differences between the surfaces of a crystal can be seen in the electronic structure: while the (111) surface has an occupied surface state near the Fermi level at the {gamma} point the (110) and (100) faces have not. Motivated by these facts, in this work we study the role that the occupied surface state plays on the Auger neutralization rate and we present an estimation of the ion fractions that survive for the different Ag faces.

Authors:
; ;  [1];  [2];  [3]
  1. Fisika Aplikatua I Saila, Unibertsitate Eskola Politeknikoa, UPV/EHU, Europa Plaza 1, 20018 Donostia (Spain)
  2. (DIPC), Manuel de Lardizabal pasealekua 4, 20018 Donostia (Spain)
  3. (Spain)
Publication Date:
OSTI Identifier:
20976665
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review. B, Condensed Matter and Materials Physics; Journal Volume: 75; Journal Issue: 4; Other Information: DOI: 10.1103/PhysRevB.75.045104; (c) 2007 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; AUGER EFFECT; CRYSTALLOGRAPHY; CRYSTALS; ELECTRONIC STRUCTURE; EV RANGE; FERMI LEVEL; HELIUM IONS; SILVER; SURFACES

Citation Formats

Sarasola, A., Silkin, V. M., Arnau, A., Donostia International Physics Center, and Materialen Fisika Saila, Kimika Fakultatea, UPV/EHU and Centro Mixto CSIC-UPV/EHU, 1072 Posta Kutxatila, 20080 Donostia. Role of surface states in Auger neutralization of He{sup +} ions on Ag surfaces. United States: N. p., 2007. Web. doi:10.1103/PHYSREVB.75.045104.
Sarasola, A., Silkin, V. M., Arnau, A., Donostia International Physics Center, & Materialen Fisika Saila, Kimika Fakultatea, UPV/EHU and Centro Mixto CSIC-UPV/EHU, 1072 Posta Kutxatila, 20080 Donostia. Role of surface states in Auger neutralization of He{sup +} ions on Ag surfaces. United States. doi:10.1103/PHYSREVB.75.045104.
Sarasola, A., Silkin, V. M., Arnau, A., Donostia International Physics Center, and Materialen Fisika Saila, Kimika Fakultatea, UPV/EHU and Centro Mixto CSIC-UPV/EHU, 1072 Posta Kutxatila, 20080 Donostia. Mon . "Role of surface states in Auger neutralization of He{sup +} ions on Ag surfaces". United States. doi:10.1103/PHYSREVB.75.045104.
@article{osti_20976665,
title = {Role of surface states in Auger neutralization of He{sup +} ions on Ag surfaces},
author = {Sarasola, A. and Silkin, V. M. and Arnau, A. and Donostia International Physics Center and Materialen Fisika Saila, Kimika Fakultatea, UPV/EHU and Centro Mixto CSIC-UPV/EHU, 1072 Posta Kutxatila, 20080 Donostia},
abstractNote = {Recent measurements of He{sup +} ion fractions that survive to a whole scatterig event when they impinge on Ag surfaces have shown two different and interesting effects: (1) a notable difference of surviving ion fraction depending on which crystallographic face of the target surface is studied [Yu. Bandurin et al., Phys. Rev. Lett. 92, 017601 (2004)], and (2) an uncommonly high ion fraction in the very-low-energy range (tens of eV) [S. Wethekam et al., Phys. Rev. Lett. 90, 037602 (2003)]. Apart from the geometry, one of the differences between the surfaces of a crystal can be seen in the electronic structure: while the (111) surface has an occupied surface state near the Fermi level at the {gamma} point the (110) and (100) faces have not. Motivated by these facts, in this work we study the role that the occupied surface state plays on the Auger neutralization rate and we present an estimation of the ion fractions that survive for the different Ag faces.},
doi = {10.1103/PHYSREVB.75.045104},
journal = {Physical Review. B, Condensed Matter and Materials Physics},
number = 4,
volume = 75,
place = {United States},
year = {Mon Jan 15 00:00:00 EST 2007},
month = {Mon Jan 15 00:00:00 EST 2007}
}
  • We present a detailed theoretical analysis of the role played by s and d electrons in Auger neutralization processes of He{sup +} at Ag(111) and Ag(110) surfaces. We calculate crystal-lattice-site Auger neutralization rates as a function of the perpendicular distance between ions and surfaces. We find that the rate is very insensitive to the lateral position for large values of the perpendicular distance because the contribution of the delocalized s electrons dominates in this case. In contrast, the contribution of d electrons dominates at short perpendicular distances and the strong spatial localization of these electrons causes a similar strong dependencemore » of the Auger rate with lateral position. We perform molecular dynamic simulations of scattered ion trajectories, which, used together with the Auger neutralization rates, allow us to obtain the theoretical ion fraction that we compare with our measurements. This parameter-free theory is able to reproduce the magnitude of the ion survival probability and its dependence with the azimuthal angle of incidence for both surfaces of Ag, thus showing the important role played by localized electrons in Auger neutralization of He.« less
  • Energy distributions of electrons ejected from an atomically clean Cu(100) surface by incident thermal-energy helium 2 {sup 3}{ital S}, 2 {sup 1}{ital S}, and 2 {sup 3}{ital P} atoms are presented, which show that each species is deexcited exclusively through resonance ionization followed by Auger neutralization. These data, when coupled with earlier measurements in this laboratory using electron-spin-polarized He (2 {sup 3}{ital S}) atoms, require that the electrons involved in the Auger neutralization process tend to have antiparallel spins. This work provides direct confirmation of spin correlation in Auger neutralization of ions outside a paramagnetic surface.
  • We develop a theory of the Auger neutralization rate of ions on solid surfaces in which the matrix elements for the transition are calculated by means of a linear combination of atomic orbitals technique. We apply the theory to the calculation of the Auger rate of He{sup +} on unreconstructed Al(111) (100), and (110) surfaces, assuming He{sup +} to approach these surfaces on high symmetry positions and compare them with the results of the jellium model. Although there are substantial differences between the Auger rates calculated with both kinds of approaches, those differences tend to compensate when evaluating the integralmore » along the ion trajectory and, consequently, are of minor influence in some physical magnitudes like the ion survival probability for perpendicular energies larger than 100 eV. We find that many atoms contribute to the Auger process and small effects of lateral corrugation are registered.« less
  • Electron emission by 130-430-eV Ar{sup +} ion impact on polycrystalline Al surfaces is studied extending the theory of Auger neutralization to include the singular response of the metal conduction band to the sudden change of charge in the incoming hole state, following its neutralization. The effect is manifested in the high-energy tail of the electron energy distributions, where the theory accounts very well with experiments.
  • The screening of a He{sup +} ion embedded in a paramagnetic electron gas is studied using density functional theory within the local spin density approximation. We calculate the induced electron density and the induced density of states for each spin orientation, parallel and antiparallel to that of the electron bound to the He{sup +} ion. Our results show that the screening is preferably due to parallel spin electrons, especially for low electron densities of the medium. In a second step, the rates for Auger neutralization of a He{sup +} ion in an electron gas are calculated, paying special attention tomore » their dependence on the spin of the electron excited in the Auger process. The results obtained are used to interpret experiments in which the spin polarization of the emitted yield is measured when a He{sup +} projectile is neutralized in front of a metal surface.« less