Models of Auger Neutralization and Tunneling at Metal Surfaces
Doktorsavhandling, 1993

This thesis consists of a theoretical study of electron transfer at metal surfaces. It considers two types of electron transfer (electron tunneling and Auger neutralization) that both can be used as a spectroscopy to investigate the surface electronic structure. Simple theoretical models for so-called ion neutralization spectroscopy (INS) and scanning tunneling spectroscopy (STS) are presented. In both cases a surface of a free-electron-like metal, like aluminium, is considered. The Auger neutralization rate and energy distributions (spectra) of excited Auger electrons for a He ion outside a jellium surface are calculated in a simplified model. The latter is a one-electron-like model using approximate orbitals from the jellium model of an unperturbed metal surface, however accounting for the orthogonality against the He hole state. In an intermediate distance region for not too large ion-surface separations (less than about 10 a0), an approximately quadratic scaling of the Auger rate with the electron density as a function of distance from the surface is found. For very large ion-surface separations, on the other hand, a linear scaling with the density applies. This is interpreted as that, in the intermediate distance regime, the metal orbitals are mainly probed {locally} around the ion by the Auger matrix element. The calculated spectra are found to be consistent with this interpretation. The scaling between the Auger rate and the local metal-electron density at the position of the ion might be useful for dynamic descriptions of surface processes. The second topic of this thesis is scanning tunneling spectroscopy of an Al(111) surface. The tip-sample system is modelled with two planar parallel jellium surfaces. The tunneling current in the self-consistent potential, including the bias voltage, is calculated. In the aluminium sample crystal the reflection from the crystal lattice is included in first order perturbation theory. One "crystal-induced" resonance below the vacuum level and several "field-induced" resonances are observed.


Tony Fondén

Institutionen för teoretisk fysik





Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 950

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