Theory of electronic processes in atom scattering from surfaces

Abstract

The theory of electronically non-adiabatic processes in atom scattering on surfaces of solids, in particular metals, is reviewed. It is assumed that resonant tunnelling of electrons between an electronic orbital of the adatom and the conduction band of the substrate is the dominant charge exchange mechanism. The kinetic energy of the adatom is assumed to be in the intermediate range (eV to keV), which makes it possible to treat the adatom trajectory classically and to obtain a time-dependent electronic Hamiltonian. The aim of the theory is to find the deviations from adiabaticity, i.e. the fraction of the minority charge states of the atom after scattering and the spectrum of the electron-hole pairs created in the substrate. Under some simplifying approximations, these quantities can be calculated explicitly. Their dependence upon the adatom velocity and other parameters of the model is analysed, with particular attention paid to features which are characteristic of an extended substrate, in contrast to atom-atom or atom-molecule scattering. The present understanding of more complete models, for example inclusion of the intra-atomic Coulomb correlation, is also reviewed.

H−formation in collisions of hydrogen atoms with Al(100) surfaces

“…We describe the projectile motion classically and model the electronic dynamics during the projectile-surface collision within a spinless Newns-Anderson model [20][21][22][23] based on the Hamiltonian…”

“…The continuum-continuum interaction between these states can be neglected if the excitation into positive-energy states is suppressed during the collision. In this case the Hamiltonian (1) reduces to the Newns-Anderson model for a discrete level interacting with one continuum of negative-energy metal states [23].…”

Determination of Compton profiles at solid surfaces from first-principles calculations

“…The local density of states above the topmost layer, the occupied states of which represent the electron density spilling out into vacuum, is an important quantity characterizing many properties of the surface and image states [1,2], surface magnetism [3,4], and chemical reactivity mediated by charge transfer [5,6]. Yet, many of its properties are difficult to directly access experimentally because they are overshadowed by bulk contributions.…”

Effect of an Adsorbed Atom on Resonant Charge Exchange in Atom Scattering on Metal Surfaces

“…The sta rti ng poi nt to descri b e the resona nt charge tra nsf er wi ll b e the ti m e-dependent Anderso n{ Newns (AN) Ha mi l to nia n. Several autho rs ha ve revi ewed the resonant charg e tra nsfer pro cesses i n the fra m ework of thi s mo del (e.g. [1,4]). Usua l l y, the evol uti on o f the scattered ato m i s well descri b ed by a classical tra j ectory gi ven by a ti me functi on z ( t ), z bei ng the di sta nce b etween an ato m and the m etal surf ace, so the z -dep endent para m eters of the AN Ha mi lto ni an can b e easil y converted i nto the ti m e-dependent ones.…”

“…Usua l l y, the evol uti on o f the scattered ato m i s well descri b ed by a classical tra j ectory gi ven by a ti me functi on z ( t ), z bei ng the di sta nce b etween an ato m and the m etal surf ace, so the z -dep endent para m eters of the AN Ha mi lto ni an can b e easil y converted i nto the ti m e-dependent ones. In our cal culati ons we reno unced a wi de-band l i m it appro xi mati on [1,4] often used for sim pl i Ùed descri pti on of the meta l surf ace el ectro n band structure and assumed the free-el ectro n ba nd structure. It wi l l be shown tha t for some v alues of pa ra meters the oscil lato ry dep endence of the i oni zati on pro babi l ity of the scattered a tom agai nst the di sta nce of the col l i sion regi on fro m the adsorb ed ato m i s observed | the e˜ect of the i ndi rect i ntera cti on b etween the adsorb ed and the scattered ato m s.…”