C. Auth

Charge state dependence of the energy loss of slow nitrogen ions reflected from an aluminum surface under grazing incidence

The experimentally observed monotonic increase of the energy loss with charge q for N qa ions impinging on an Al(1 1 1) surface under grazing angle of incidence is explained by a model that accounts for the eAect of K- and L-shell vacancies in the stopping power. Our model allows us to estimate the characteristic time scales (and distances from the surface) for the neutralization and relaxation of multicharged ions. We use a transport cross section formulation of the electronic stopping of ions in an electron gas, as well as a self-consistent calculation of the scattering potential within density functional theory. ” 1999 Elsevier Science B.V. All rights reserved.

FORMATION OF NEGATIVE IONS IN GRAZING SCATTERING FROM A LIF(100) SURFACE

Abstract We have studied charge exchange between fast atoms/ions and the surface of an insulator. Based on investigations on the formation of negative hydrogen, oxygen and fluorine ions in the grazing scattering from a clean and flat LiF(100) surface, we discuss specific features of the interaction of fast atomic projectiles with the surface of an insulator. Under specific kinematic conditions large fractions of negative ions are observed.

CHARGE EXCHANGE AND EXCITATION PHENOMENA AT INSULATOR SURFACES

Abstract We discuss charge exchange and excitation phenomena during the scattering of fast atoms and ions from the surface of an insulator under a grazing angle of incidence. We show that the electronic structure of an insulator target, comprising an electronic band gap, affects charge exchange, excitation, and projectile energy loss in a characteristic manner.

Stopping of low energy protons during grazing scattering from a LiF(001) surface

Abstract Protons with energies ranging from 300 eV to 25 keV are scattered under glancing angles of incidence from a flat and clean LiF(001) surface. We have recorded energy spectra for specularly reflected projectiles and analyze the data in terms of stopping cross-sections. From our analysis we deduce a threshold behaviour for electronic stopping at the low energy end. We find pronounced effects on energy loss owing to charge exchange and excitation of valence band electrons. At energies below 1 keV energy dissipation proceeds predominantly via excitation of optical phonons.

Scattering of fast Na+-ions from alkali-halide surfaces under a grazing angle of incidence

Abstract We have studied charge exchange of Na + -ions with energies ranging from 1 keV to 100 keV in the scattering from LiF(100)-, KI(100)-, and KCl(100)-surfaces under a grazing angle of incidence. In the experiments we observe generally small fractions of neutral atoms and conclude that the density of occupied surface states within the band gap of the insulator is negligible.

Z1-OSCILLATIONS IN THE STOPPING OF SLOW IONS DURING GRAZING ION-SURFACE SCATTERING

Abstract We have scattered ions with energies Z 1 Z 1 . Comparison of the stopping powers at different distances from the surface plane, i.e. for different electron densities, reveals characteristic shifts in those oscillatory structures as predicted by nonlinear density functional theory.

Scattering of fast He-atoms from single terraces of an Al(1 1 1)-surface

Abstract We have scattered fast He-atoms with keV energies under a grazing angle of incidence from a clean and flat Al(1 1 1)-surface. From the analysis of the angular distributions for scattered projectiles and for scattered light of a HeNe-laser we find evidence for a reflection of the fast atoms from single terraces of the crystal surface. From our experiments we deduce in a simple manner an averaged width for terraces forming a stepped surface.