arXiv subjects

M. Pamperin

Publications and source records attributed to M. Pamperin.

4 recordsLinked to original sources

arXiv2018

Ion-induced secondary electron emission from metal surfaces

Using a helium ion hitting various metal surfaces as a model system, we describe a general quantum-kinetic approach for calculating ion-induced secondary electron emission spectra at impact energies where the emission is driven by the internal potential energy of the ion. It is based on an effective model of the Anderson-Newns-type for the subset of electronic states of the ion-surface system most strongly affected by the collision. Central to our approach is a pseudo-particle representation for the electronic configurations of the projectile which enables us, by combining it with two additional auxiliary bosons, to describe in a single Hamiltonian emission channels involving electronic configurations with different internal potential energies. It is thus possible to treat Auger neutralization of the ion on an equal footing with Auger de-excitation of temporarily formed radicals and/or negative ions. From the Dyson equations for the projectile propagators and an approximate evaluation of the self-energies, rate equations are obtained for the probabilities with which the projectile configurations occur and an electron is emitted in the course of the collision. Encouraging numerical results, especially for the helium-tungsten system, indicate the potential of the approach.

physics.plasm-ph↗

arXiv2018

Electron kinetics at the plasma interface

The most fundamental response of an ionized gas to a macroscopic object is the formation of the plasma sheath. It is an electron depleted space charge region, adjacent to the object, which screens the object's negative charge arising from the accumulation of electrons from the plasma. The plasma sheath is thus the positively charged part of an electric double layer whose negatively charged part is inside the wall. In the course of the Transregional Collaborative Research Center SFB/TRR24 we investigated, from a microscopic point of view, the elementary charge transfer processes responsible for the electric double layer at a floating plasma-wall interface and made first steps towards a description of the negative part of the layer inside the wall. Below we review our work in a colloquial manner, describe possible extensions, and identify key issues which need to be resolved to make further progress in the understanding of the electron kinetics across plasma-wall interfaces.

physics.plasm-ph↗

arXiv2015

Mixed-valence correlations in charge-transferring atom-surface collisions

Motivated by experimental evidence for a mixed-valence state to occur in the neutralization of strontium ions on gold surfaces we analyze this type of charge-transferring atom-surface collision from a many-body theoretical point of view using quantum-kinetic equations together with a pseudo-particle representation for the electronic configurations of the atomic projectile. Particular attention is paid to the temperature dependence of the neutralization probability which--experimentally--seems to signal mixed-valence-type correlations affecting the charge-transfer between the gold surface and the strontium projectile. We also investigate the neutralization of magnesium ions on a gold surface which shows no evidence for a mixed-valence state. Whereas for magnesium excellent agreement between theory and experiment could be obtained, for strontium we could not reproduce the experimental data. Our results indicate mixed-valence correlations to be in principle present, but for the model mimicking most closely the experimental situation they are not strong enough to affect the neutralization process quantitatively.

cond-mat.str-el↗

arXiv2015

Many-body theory of the neutralization of strontium ions on gold surfaces

Motivated by experimental evidence for mixed-valence correlations affecting the neutralization of strontium ions on gold surfaces we set up an Anderson-Newns model for the Sr:Au system and calculate the neutralization probability $α$ as a function of temperature. We employ quantum-kinetic equations for the projectile Green functions in the finite$-U$ non-crossing approximation. Our results for $α$ agree reasonably well with the experimental data as far as the overall order of magnitude is concerned showing in particular the correlation-induced enhancement of $α$. The experimentally found non-monotonous temperature dependence, however, could not be reproduced. Instead of an initially increasing and then decreasing $α$ we find over the whole temperature range only a weak negative temperature dependence. It arises however clearly from a mixed-valence resonance in the projectile's spectral density and thus supports qualitatively the interpretation of the experimental data in terms of a mixed-valence scenario.

cond-mat.str-el↗