Multi-electron dynamics for neutralization of highly charged ions near surfaces

in Vacuum (2004), 73(1), 3-7

We present a simulation of the neutralization of highly charged ions in front of a lithium fluoride surface including the close-collision regime above the surface. The present approach employs a Monte ... [more ▼]

We present a simulation of the neutralization of highly charged ions in front of a lithium fluoride surface including the close-collision regime above the surface. The present approach employs a Monte-Carlo solution of the Liouville master equation for the joint probability density of the ionic motion and the electronic population of the projectile and the target surface. It includes single as well as double particle-hole (de)excitation processes and incorporates electron correlation effects through the conditional dynamics of population strings. For slow projectiles and normal incidence, the ionic motion depends sensitively on the interplay between image acceleration towards the surface and repulsion by an ensemble of positive hole charges in the surface ("trampoline effect"). For Ne10+ we find that image acceleration is dominant and no collective backscattering high above the surface takes place. (C) 2004 Elsevier Ltd. All rights reserved. [less ▲]

Liouville master equation for multielectron dynamics: Neutralization of highly charged ions near a LiF surface

in Physical Review. A (2003), 67(1),

We present a simulation of the neutralization of highly charged ions in front of a lithium fluoride surface including the close-collision regime above the surface. The present approach employs a Monte ... [more ▼]

We present a simulation of the neutralization of highly charged ions in front of a lithium fluoride surface including the close-collision regime above the surface. The present approach employs a Monte Carlo solution of the Liouville master equation for the joint probability density of the ionic motion and the electronic population of the projectile and the target surface. It includes single as well as double particle-hole (de)excitation processes and incorporates electron correlation effects through the conditional dynamics of population strings. The input in terms of elementary one- and two-electron transfer rates is determined from classical trajectory Monte Carlo calculations as well as quantum-mechanical Auger calculations. For slow projectiles and normal incidence, the ionic motion depends sensitively on the interplay between image acceleration towards the surface and repulsion by an ensemble of positive hole charges in the surface ("trampoline effect"). For Ne10+ we find that image acceleration is dominant and no collective backscattering high above the surface takes place. For grazing incidence, our simulation delineates the pathways to complete neutralization. In accordance with recent experimental observations, most ions are reflected as neutral or even as singly charged negative particles, irrespective of the charge state of the incoming ions. [less ▲]

Semiclassical theory for transmission through open billiards: Convergence towards quantum transport

in Physical Review. E. (2003), 67(1),

We present a semiclassical theory for transmission through open quantum billiards which converges towards quantum transport. The transmission amplitude can be expressed as a sum over all classical paths ... [more ▼]

We present a semiclassical theory for transmission through open quantum billiards which converges towards quantum transport. The transmission amplitude can be expressed as a sum over all classical paths and pseudopaths which consist of classical path segments joined by "kinks," i.e., diffractive scattering at lead mouths. For a rectangular billiard we show numerically that the sum over all such paths with a given number of kinks K converges to the quantum transmission amplitude as K-->infinity. Unitarity of the semiclassical theory is restored as K approaches infinity. Moreover, we find excellent agreement with the quantum path-length power spectrum up to very long path length. [less ▲]

Vertical incidence of slow Ne10+ ions on an LiF surface: Suppression of the trampoline effect

in Nuclear Instruments and Methods in Physics Research. Section B, Beam Interactions with Materials and Atoms (2001), 182

We present a Monte Carlo simulation of the neutralization of a slow Ne10+ ion in vertical incidence on an LiF(100) surface. The rates for resonant electron transfer between surface F- ions and the ... [more ▼]

We present a Monte Carlo simulation of the neutralization of a slow Ne10+ ion in vertical incidence on an LiF(100) surface. The rates for resonant electron transfer between surface F- ions and the projectile are calculated using a classical trajectory Monte Carlo simulation, We investigate the influence of the hole mobility on the neutralization sequence. It is shown that backscattering above the surface due to the local positive charge up of the surface ("trampoline effect") does not take place. (C) 2001 Elsevier Science B.V. All rights reserved. [less ▲]

Hollow-ion formation in microcapillaries

in Physical Review. A (2001), 64(4),

Transmission of highly charged ions through microcapillaries is studied theoretically by a classical trajectory simulation. The interaction of highly charged ions with the internal surface of the ... [more ▼]

Transmission of highly charged ions through microcapillaries is studied theoretically by a classical trajectory simulation. The interaction of highly charged ions with the internal surface of the capillary is treated within the framework of dielectric-response theory. The simulation is based on the classical over-the-barrier model modified for open cylindrical surfaces. The multielectron evolution and relaxation is taken into account as a stochastic event sequence. We consider N6+ and Ne10+ with an energy of 2.1 keV/amu passing through a metallic microcapillary of Ni. We analyze the distance of closest approach. the angular distribution, and the distribution of the mean occupation numbers of n shells of highly charged ions. We find the resulting charge state distribution of transmitted projectiles in good agreement with recent measurements. Implications for nanotube targets will be discussed. [less ▲]

Charge-state evolution of highly charged ions transmitted through microcapillaries

in Physical Review. A (2000), 61(2),

The charge-state evolution of highly charged ions transmitted through microcapillaries is studied theoretically by a classical trajectory Monte Carlo simulation.: The interaction of highly charged ions ... [more ▼]

The charge-state evolution of highly charged ions transmitted through microcapillaries is studied theoretically by a classical trajectory Monte Carlo simulation.: The interaction of highly charged ions with the internal surface of the capillary is treated within the framework of dielectric response theory. We analyze the distance of closest approach and the angular distributions of the highly charged ions at the exit of the microcapillary. We find the charge-state fraction of transmitted N6+ projectiles, in: good agreement with first measurements. Moreover, our calculations indicate that grazing collisions with the microcapillary surface hold the promise of direct observation of charge transfer and hollow-atom formation at a large distance from the surface. [less ▲]

Observation of a threshold in potential sputtering of LiF surfaces

in Nuclear Instruments and Methods in Physics Research. Section B, Beam Interactions with Materials and Atoms (2000), 164

A quartz-crystal microbalance technique is used for measuring total sputtering yields for LiF under impact of slow (20 eV, 100 eV, 500 eV and 1000 eV kinetic energy) singly and doubly charged ions. At low ... [more ▼]

A quartz-crystal microbalance technique is used for measuring total sputtering yields for LiF under impact of slow (20 eV, 100 eV, 500 eV and 1000 eV kinetic energy) singly and doubly charged ions. At low kinetic energies (less than or equal to 100 eV) potential sputtering (PS) (i.e., sputtering due to the projectiles potential energy) clearly dominates over kinetically induced sputtering. New insight into the mechanisms for PS is gained by determining the minimum potential energy necessary to induce PS. The measured potential energy threshold at around 10 eV provides evidence that PS can already be induced by the production of cold holes in the valence band of LiF via resonant neutralisation. (C) 2000 Elsevier Science B.V. All rights reserved. [less ▲]

Interaction of highly charged ions with microcapillaries

in PHYSICA SCRIPTA (1999), T80B

The transmission of highly charged ions (HCI) through microcapillaries is investigated. The interaction of an HCI with the internal surface of the capillary is described in terms of a classical image ... [more ▼]

The transmission of highly charged ions (HCI) through microcapillaries is investigated. The interaction of an HCI with the internal surface of the capillary is described in terms of a classical image potential. For Neq+ projectiles transmitted through a Ni capillary the impact parameter distribution and angular distribution of ions leaving the microcapillary is determined. We consider both a narrowly focussed and a dispersive incident beam relative to the acceptance angle of the capillary. Our results are compared with recent experiments. [less ▲]

Threshold for potential sputtering of LiF

in Physical Review Letters (1999), 83(19), 3948-3951

We have measured total sputtering yields for impact of slow (less than or equal to 100 eV) singly and doubly charged ions on LiF. The minimum potential energy necessary to induce potential sputtering (PS ... [more ▼]

We have measured total sputtering yields for impact of slow (less than or equal to 100 eV) singly and doubly charged ions on LiF. The minimum potential energy necessary to induce potential sputtering (PS) from UF was determined to be about 10 eV. This threshold coincides with the energy necessary to produce a cold hole in the valence band of LiF by resonant neutralization. This allows the first unambiguous identification of PS induced by cold holes. Further stepwise increase of the sputtering yield with higher projectile potential energies provides evidence for additional defect-mediated sputtering mechanisms operative in alkali halides. [less ▲]

Geometry-dependent scattering through ballistic microstructures: Semiclassical theory beyond the stationary-phase approximation

in Physical Review. B (1997), 56(12), 7589-7597

The conductance of a ballistic microstructure shows strong fluctuations as a function of the Fermi wave number. We present a semiclassical-theory that describes these fluctuations in terms of bundles of ... [more ▼]

The conductance of a ballistic microstructure shows strong fluctuations as a function of the Fermi wave number. We present a semiclassical-theory that describes these fluctuations in terms of bundles of short trajectories. These trajectories provide the dominant contribution to electron transport through a weakly open microstructure. For the coupling between the quantum wires and the cavity, contributions beyond the stationary phase approximation are taken into account giving rise to diffraction effects. A comparison with full quantum calculations for st rectangular billiard is made. The peak positions of the power spectrum agree very well between the quantum and semiclassical theories. Numerical evidence is found for the breakdown of the semiclassical approximation for long paths. A simple explanation in terms of the dispersion of the semiclassical wave packet in the interior of the cavity is proposed. [less ▲]