Scattering of low-energy atoms by metallic surfaces

Computer Physics Communications, 1994

In this paper we review the recent advances in the theory of He-atom inelastic scattering used to study the lattice dynamics of metal surfaces. We discuss the importance of the He-surface interaction potential and the various techniques employed up to now to determine the surface phonon dispersions. The anharmonic contributions to the one-phonon linewidth are also discussed.

Physics Reports, 2001

6.2. Scattering of He atoms from Cu surfaces 115 6.3. Scattering of He atoms from monolayers of Xe atoms 123 6.4. Debye}Waller factors for scattering of heavier noble gas atoms from surfaces 138 7. Energy transfer in gas}surface collisions 140 7.1. Angular resolved vs. angular integrated energy transfer 141 7.2. Quantum vs. classical results for energy transfer in benchmark systems 143 8. Concluding remarks and protocol for the use of EBA-formalism in interpretations of atom}surface scattering experiments 147 Acknowledgements 149 References 150

Surface Science, 1996

We present results of a detailed study of the production of electronically excited states in the scattering of ionic or neutral inert gas projectiles in the keV energy range at AI and Mg surfaces. The complementary observation of scattered particles (neutrals or ions), secondary electrons and photons leads to a rather complete description of the successive stages of inelastic scattering events. Efficient neutralisation of the incident ions occurs, when they approach the surface. This is clearly demonstrated by the strong similarities between results obtained for incoming ions and incoming ground-state neutrals. The characteristics of the scattered particle distributions, the observation of scattered ions, and also of some excited states by electron and photon spectroscopy, delineates the decisive importance of short-distance binary collisions with atoms of the surface, in the production of these species. A detailed comparison with the "inverse" collisional systems in the gas phase shows that the same kind of primary excitations as described in the quasi-molecular orbital promotion model are operative and allows, for example, predictions about which of projectile and/or target atoms can be excited. Some very strong differences to gas-phase collisions are also demonstrated. They stress the importance of surface-specific effects, such as the role of resonant or Auger electron transfers between the metal surface and the receding particle in defining the final state population. In particular, an interesting surface-induced core rearrangement effect is emphasised, and different rearrangement mechanisms are presented and discussed.

Journal of Physics and Chemistry of Solids, 1987

Abstraet-A technique for calculating the response of the substrate to atomic scattering from solid surfaces is presented. It utilizes a time-dependent phonon Green's function approach to calculate the propagation into the substrate of a disturbance induced by an atom-surface collision and it can, in principle, be incorporated into a recently introduced subspace Hamiltonian technique for calculating atomic forces from electronic energies. It therefore promises to be useful in conjunction with computer simulations of atomic motion at solid surfaces. The method is illustrated in the case of a simple model where the propagation of the disturbance from the collision can be calculated in terms of simple functions.

Surface Science, 1980

of a thermal He beam from a LiF surface has been observed in terms of velocity and intensity distributions as a function of scattering angle. The results allow a correlation with theoretical predictions assuming single Rayleigh phonon coupling for both phonon creation and annihilation processes. A marked decrease of inelastic intensities with momentum or energy transfer is demonstrated, which depends strongly on the temperature of the scattering surface.

Journal of Electron Spectroscopy and Related Phenomena, 1983

The recent progress in the production of highly monochromatic atomic beams is opening new perspectives in surface physics, having paved the way for a full determination of the surface vibrational structure. After a discussion on the possible determination of Rayleigh wave dispersion curves from angular distributions exploiting the kinematical focussing effect, a short review is presented on the direct measurement of surface phonon dispersion curves, first achieved by Brusdevlins, Doak and Toennies in alkali halides. from time-offlight (TOf) spectra of-scattered He atoms. A comparison is-made with the existing theories of surface phonons in ionic crystals. The state of the art in the theory of inelastic processes is briefly illustrated in order to discuss the theoretical interpretation of TOF spectra. The one-phonon energy loss spectra of He scattering from LiF(OO1) calculated for a hard corrugated surface model are found to be in general good agreement with the experimental TOF spectra. From such a comparison evidence is obtained that: i) one-phonon processes are predominant, and ii) in addition to Rayleigh waves important contributions to the inelastic scattering come from the surface-projected density of bulk phonons. Important effects due to inelastic resonances with surface bound states are put in evidence and explained by simple kinematical arguments. The possible observation of surface optical modes in NaF(OO1) is finally discussed. INTRODUCTION Inelastic scattering of atoms from crystal surfaces has been since long recognized to have a remarkable potential in the spectroscopy of microscopic surface vibrations.' Light atoms, like helium and hydrogen at thermal energies have a wavevector which is larger than, but still comparable to the size of the surface Brillouin zone-an ideal condition for the surface phonons to be probed in the whole spectral range of energy and momentum. The early experimental investigations by Fisher and Bledsoe' (He/LiF(OOl); velocity analysis) and Subbarao and Miller3 (He/Ag(lll); angular distribution) have provided a clear separation between elastic and inelastic processes. A few years later Lapujoulade and Lejay,' using He, Ne and Xe at the same energy on Cu(OOl), gave evidence of the one-phonon processes with He, and many-phonon processes for Ne and Xe. Williams and Mason (He/LiF(OOl) and NaF(OO1)) proved that the inelastic sidebands of the specular peak found in out-of-plane angular distributions involve Rayleigh waves (RW).5'6 Rayleigh waves were shown to

Journal of Electron Spectroscopy and Related Phenomena, 2003

A calculation of the inelastic scattering rate of Xe atoms on Cu(111) is presented. We focus in the regimes of low and intermediate velocities, where the energy loss is mainly associated to the excitation electron-hole pairs in the substrate. We consider trajectories parallel to the surface and restrict ourselves to the Van der Waals contribution. The decay rate is calculated within a self-energy formulation. The effect of the response function of the substrate is studied by comparing the results obtained with two different approaches: the Specular Reflection Model and the Random Phase Approximation. In the latter, the surface is described by a finite slab and the wave functions are obtained from a one-dimensional model potential that describes the main features of the surface electronic structure while correctly retains the imagelike asymptotic behaviour. We have also studied the influence of the surface state on the calculation, finding that it represents around 50% of the total probability of electron-hole pairs excitation.

Physical Review B, 1988

This paper first develops the general S-matrix theory for evanescent (negative-energy} waves "incident" on a localized scattering center. Next, an exact expression is derived for the interaction energy of an evanescent vmve ~ith a short-range scattering center in terms of elements of the scattering matrix. Finally, these results are applied to the calculation of the repulsive interaction between a He atoms and a metal surface. A diSculty, in principle caused by the r polarization potential between an electron and a He atom, is discussed.

Physical Review Letters, 2012

We investigate the role played by electron-hole pair and phonon excitations in the interaction of reactive gas molecules and atoms with metal surfaces. We present a theoretical framework that allows us to evaluate within a full-dimensional dynamics the combined contribution of both excitation mechanisms while the gas particle-surface interaction is described by an ab initio potential energy surface. The model is applied to study energy dissipation in the scattering of N 2 on W(110) and N on Ag(111). Our results show that phonon excitation is the dominant energy loss channel, whereas electron-hole pair excitations represent a minor contribution. We substantiate that, even when the energy dissipated is quantitatively significant, important aspects of the scattering dynamics are well captured by the adiabatic approximation.

Journal of Physics: Condensed Matter, 2004

Calculations are carried out and compared with data for the scattering of CH 4 molecules from a LiF(001) surface and for O 2 scattering from Al(111). The theory is a mixed classical-quantum formalism that includes energy and momentum transfers between the surface and projectile for translational and rotational motions as well as internal mode excitation of the projectile molecule. The translational and rotational degrees of freedom couple most strongly to multiphonon excitations of the surface and are treated with classical dynamics. Internal vibrational excitations of the molecules are treated with a semiclassical formalism with extension to arbitrary numbers of modes and arbitrary quantum numbers. Calculations show good agreement for the dependence on incident translational energy, incident beam angle and surface temperature when compared with data for energy-resolved intensity spectra and angular distributions.