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Title: Azimuth-dependent Auger neutralization of He{sup +} on Ag(111) and (110) surfaces

Abstract

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 dependence 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.

Authors:
;  [1];  [1];  [2];  [3]
  1. Departamento de Fisica Teorica de la Materia Condensada, Universidad Autonoma de Madrid, E-28049 Madrid (Spain)
  2. (Spain)
  3. Laboratoire des Collisions Atomiques et Moleculaires, Universite Paris Sud, 91405 Orsay (France)
Publication Date:
OSTI Identifier:
20957820
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review. B, Condensed Matter and Materials Physics; Journal Volume: 75; Journal Issue: 16; Other Information: DOI: 10.1103/PhysRevB.75.165404; (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; COMPARATIVE EVALUATIONS; CRYSTAL LATTICES; ELECTRONS; HELIUM IONS; INCIDENCE ANGLE; SILVER 110; SILVER 111; SIMULATION; SURFACES

Citation Formats

Valdes, Diego, Monreal, R. C., Blanco, J. M., European Space Astronomy Centre, ESAC-ESA, Ingenieria y Servicios Aeroespaciales, and Esaulov, V. A. Azimuth-dependent Auger neutralization of He{sup +} on Ag(111) and (110) surfaces. United States: N. p., 2007. Web. doi:10.1103/PHYSREVB.75.165404.
Valdes, Diego, Monreal, R. C., Blanco, J. M., European Space Astronomy Centre, ESAC-ESA, Ingenieria y Servicios Aeroespaciales, & Esaulov, V. A. Azimuth-dependent Auger neutralization of He{sup +} on Ag(111) and (110) surfaces. United States. doi:10.1103/PHYSREVB.75.165404.
Valdes, Diego, Monreal, R. C., Blanco, J. M., European Space Astronomy Centre, ESAC-ESA, Ingenieria y Servicios Aeroespaciales, and Esaulov, V. A. Sun . "Azimuth-dependent Auger neutralization of He{sup +} on Ag(111) and (110) surfaces". United States. doi:10.1103/PHYSREVB.75.165404.
@article{osti_20957820,
title = {Azimuth-dependent Auger neutralization of He{sup +} on Ag(111) and (110) surfaces},
author = {Valdes, Diego and Monreal, R. C. and Blanco, J. M. and European Space Astronomy Centre, ESAC-ESA, Ingenieria y Servicios Aeroespaciales and Esaulov, V. A.},
abstractNote = {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 dependence 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.},
doi = {10.1103/PHYSREVB.75.165404},
journal = {Physical Review. B, Condensed Matter and Materials Physics},
number = 16,
volume = 75,
place = {United States},
year = {Sun Apr 15 00:00:00 EDT 2007},
month = {Sun Apr 15 00:00:00 EDT 2007}
}
  • 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
  • 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 electronicmore » 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.« less
  • He atoms and ions with keV energies are scattered under grazing angles of incidence from Al(111), Al(100), and Al(110) surfaces. Fractions of surviving ions and normal energy gains of He{sup +} ions prior to neutralization, derived from shifts of angular distributions for incident atoms and ions, are compared to results from three-dimensional Monte Carlo simulations based on theoretically calculated Auger neutralization rates and He ground-state energy shifts. From the good agreement of experimental data with simulations, we conclude a detailed microscopic understanding for a model system of ion-surface interactions. Our work provides further evidence for the recently reported surface Millermore » index dependence for the neutralization of He{sup +} ions at metal surfaces. The study is extended to the face dependence of the He ground-state energy shift.« less
  • 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