Role of He excited configurations in the neutralization of He<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msup><mml:mrow /><mml:mo>+</mml:mo></mml:msup></mml:math>ions colliding with a HOPG surface

Iglesias-García, A.; García, Evelina A.; Goldberg, E. C.

doi:10.1103/physrevb.87.075434

Cited by 15 publications

(34 citation statements)

References 43 publications

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“…Since the projectile and the target are composite systems, to analyze these processes theoretically is a complicated many-body problem. It can be either approached with first-principle methods [40][41][42]44,45,48 , ideally containing the full electronic structure of the target and the projectile, or with model Hamiltonians focusing only on the subset of electronic states which are actively involved in the collision as pioneered by Gadzuk 57,58 . The former is computationally very expensive.…”

Section: Modelmentioning

confidence: 99%

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Ion-induced secondary electron emission from metal surfaces

Pamperin

Bronold

Fehske

2018

Plasma Sources Sci. Technol.

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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 selfenergies 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 our approach.

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Section: Modelmentioning

confidence: 99%

“…We do not attempt a description from first principles [40][41][42]44,45,48 . Instead, we use an Anderson-News-Hamiltonian for the subset of electronic degrees of freedom which are dominantly involved in the collision process.…”

Section: Introductionmentioning

confidence: 99%

Ion-induced secondary electron emission from metal surfaces

Pamperin

Bronold

Fehske

2018

Plasma Sources Sci. Technol.

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“…In the experiment, H + and H – are both observed, and the high H – fraction is completely contrary to the resonant charge transfer (RCT) prediction based on the free-electron-gas model because of the low electron affinity of H (0.75 eV). Except He ions and Li ions, − to date, few studies have been conducted on HOPG using heavy ions with dozens of keV energies. , In the previous study, we measured the positive-ion fraction as a function of incident velocity and angle for negative-ion scattering on HOPG . Similar to proton scattering, we observe both negative and positive ions in the experiment.…”

Section: Introductionmentioning

confidence: 75%

Unexpected Negative-Ion Conversion in Grazing Scattering of Negative Ions on HOPG

et al. 2021

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An experimental study of 8.5–22.5 keV-energy C–, O–, and F– ion scattering from an HOPG surface has been performed at a grazing scattering angle. For a given incident angle or impact velocity, the F– fraction is the highest and the C– fraction is the smallest among these three projectiles, which is explained with the order of the electron affinity level of the projectile. Moreover, the unexpected observations are that the F– ion fraction increases monotonically with impact velocity and that the negative-ion fraction increases with the decrease in exit angle. It can be explained by the influence of the effective high work function of HOPG and the production of positive ions at short distances from the surface.

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“…The use of Anderson-Newns models for the description of charge-transferring atom-surface collisions is well established and has a long history, recent applications [66,[71][72][73][74][75][76][77][78] differ only in the way the matrix elements are obtained and the number of channels included. Both of course depend on the scattering process to be modelled.…”

Section: Quantum Boltzmann Equationmentioning

confidence: 99%

Towards an integrated modeling of the plasma-solid interface

Bönitz

Filinov

Abraham

et al. 2019

Front. Chem. Sci. Eng.

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Solids facing a plasma are a common situation in many astrophysical systems and laboratory setups. Moreover, many plasma technology applications rely on the control of the plasma-surface interaction, i.e. of the particle, momentum and energy fluxes across the plasma-solid interface. However, presently often a fundamental understanding of them is missing, so most technological applications are being developed via trial and error. The reason is that the physical processes at the interface of a low-temperature plasma and a solid are extremely complex, involving a large number of elementary processes in the plasma, in the solid as well as fluxes across the interface. An accurate theoretical treatment of these processes is very difficult due to the vastly different system properties on both sides of the interface: quantum versus classical behavior of electrons in the solid and plasma, respectively; as well as the dramatically differing electron densities, length and time scales. Moreover, often the system is far from equilibrium. In the majority of plasma simulations surface processes are either neglected or treated via phenomenological parameters such as sticking coefficients, sputter rates or secondary electron emission coefficients. However, those parameters are known only in some cases and with very limited accuracy. Similarly, while surface physics simulations have often studied the impact of single ions or neutrals, so far, the influence of a plasma medium and correlations between successive impacts have not been taken into account. Such an approach, necessarily neglects the mutual influences between plasma and solid surface and cannot have predictive power.In this paper we discuss in some detail the physical processes a the plasma-solid interface which brings us to the necessity of coupled plasma-solid simulations. We briefly summarize relevant theoretical methods from solid state and surface physics that are suitable to contribute to such an approach and identify four methods. The first are mesoscopic simulations such as kinetic Monte Carlo (KMC) and molecular dynamics (MD) that are able to treat complex processes on large scales but neglect electronic effects. The second are quantum kinetic methods based on the quantum Boltzmann equation that give access to a more accurate treatment of surface processes using simplifying models for the solid. The third approach are ab initio simulations of surface process that are based on density functional theory (DFT) and time-dependent DFT. The fourths are nonequilibrium Green functions that able to treat correlation effects in the material and at the interface. The price for the increased quality is a dramatic increase of computational effort and a restriction to short time and length scales. We conclude that, presently, none of the four methods is capable of providing a complete picture of the processes at the interface. Instead, each of them provides complementary information, and we discuss possible combinations. PACS numbers:

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Role of He excited configurations in the neutralization of He+ions colliding with a HOPG surface

Cited by 15 publications

References 43 publications

Ion-induced secondary electron emission from metal surfaces

Ion-induced secondary electron emission from metal surfaces

Unexpected Negative-Ion Conversion in Grazing Scattering of Negative Ions on HOPG

Towards an integrated modeling of the plasma-solid interface

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