Peculiarities of electron emission from the cathode in an abnormal glow discharge

Bokhan, A. P.; Бохан, П. А.; Zakrevsky, D. É.

doi:10.1063/1.1901819

Cited by 28 publications

(18 citation statements)

References 30 publications

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“…Attempts have been made to use this effective electron yield, calculated for a uniform electric field, to model also the cathode fall of abnormal glow discharge [40,46]. The failure of these attempts led to intense debate [39,40,44,46,48], recently clarified by Donkó and coworkers [39,44]. Using a hybrid model, they showed that the different electric field distributions result in dissimilar energy distributions of species bombarding the cathode, thereby modifying the effective electron yield.…”

Section: The Role Of Ion-induced Electron Emission In Glow Dischargesmentioning

confidence: 96%

Electron Emission from Surfaces Induced by Slow Ions and Atoms

Baragiola

Riccardi

2008

Reactive Sputter Deposition

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Electron emission from surfaces is of crucial importance in determining the properties of electrical discharges, where it is caused by the impact of ions, atoms, electrons, and photons. At the microscopic level, the physics of electron emission from solid targets is usually described by a three-step model: electron excitation, electron transport to the surface, and its escape through the surface. This division serves a heuristic purpose and it must be borne in mind that, in purely surface events, actually only one step is involved. What distinguishes electron emission by different incoming particles is the excitation step [1], which depends strongly on the momentum of the particle. This is because there is a minimum energy needed to extract an electron from the solid (work function for metals, band gap plus electron affinity for nonmetals) and this energy transfer implies a momentum transfer from the projectile.This chapter is concerned with heavy particle collisions (ions and atoms) at low energies (below a few keV) and will discuss first the physical mechanisms and then applications to electrical discharges in gases. The overall picture of electron emission induced by heavy particles is the following. Electrons are excited from the target or the projectile as a result of Coulomb interactions involving the nuclei and electrons through mechanisms that are grouped in two categories, potential and kinetic, depending on the source of the excitation energy. Such excitations occur mostly in binary collisions at the surface or very shallow depths, since the penetration depth of low-energy atomic projectiles is usually very shallow, tens of nm or less. The excited electrons can be ejected directly into vacuum or undergo a series of collisions in the target solid (electron transport) on their way to the surface. The collisions are either elastic scattering with atomic cores, which cause large deflections in trajectories, or energy loss collisions by scattering with other electrons, contingent on the availability of electronic states. As a result of such inelastic scattering, the electrons which succeed in escaping the solid come from a shallow depth, of the order of 2 nm for metals and semiconductors and up to a few tens of

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Section: The Role Of Ion-induced Electron Emission In Glow Dischargesmentioning

confidence: 96%

Electron Emission from Surfaces Induced by Slow Ions and Atoms

Baragiola

Riccardi

2008

Reactive Sputter Deposition

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“…Other electron ejection processes from surfaces by fast neutrals, metastable atoms and VUV photons are also suggested to be important [13,26]. Bokhan and coauthors have worked on understanding photoemission, and potential, kinetic secondary electron emission under the influence of atom implantation in plasma devices [27][28][29].…”

Section: Introductionmentioning

confidence: 99%

Material dependent modeling of secondary electron emission coefficients and its effects on PIC/MCC simulation results of capacitive RF plasmas

Daksha¹,

Derzsi²,

Zaka-ul-Islam³

et al. 2019

Plasma Sources Sci. Technol.

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The ion-induced secondary electron emission coefficient (γ) is a vital parameter in the modeling of low temperature RF plasmas. Often, the value of γ drastically affects the electron power absorption dynamics, the plasma parameters and the quality of the separate control of ion flux and mean ion energy at the electrodes. Experimental results for γ under plasma exposure are difficult to obtain. Therefore, γ is either assumed to be a constant chosen with some uncertainty, or is approximated as a quantity that is a function of the ion energy and cleanliness of the electrode surface. It is hypothesized that these assumptions are not valid for all materials and plasma conditions. In this work, Hagstrum's theory on Auger emission is suggested as a robust, ab initio model for accurately predicting γ for metal surfaces with a wide range of surface conditions and for a variety of ion species. To demonstrate the effect of the choice of γ on modeling results, we carry out particle-in-cell/Monte Carlo collision simulations of 13.56 MHz, single-frequency argon and helium capacitive discharges. Simulations are run assuming that: (i) γ is a constant, (ii) γ is an energy and surface condition dependent quantity that is independent of the electrode material, and (iii) γ is obtained from the ab initio model for different clean metals. The energy distribution of the emitted electrons resulting from Hagstrum's theory is also implemented as a uniform, metal dependent distribution with physically accurate energy domain. It is found that this is important for some metals in both helium and argon. Lastly, it is observed that, depending on the assumed surface conditions, the plasma properties change dramatically. Based on these results we conclude that a realistic, material dependent implementation of γ is required to obtain realistic simulation results and that Hagstrum's model suits this purpose.Keywords: capacitive radio frequency plasmas, secondary electron emission coefficients, plasma surface interactions, electron heating, particle in cell simulations, ab initio modeling of secondary electron emission coefficients, Auger emission

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“…The effects of the boundary conditions have recently been discussed by Hagelaar et al [32], while issues related to the secondary electron emission coefficient have been addressed in [14,16,17,33,34] (for low current, Townsend discharges these studies were preceded by [35,36]).…”

Section: Introductionmentioning

confidence: 99%

On the accuracy and limitations of fluid models of the cathode region of dc glow discharges

Derzsi

Hartmann

Korolov

et al. 2009

J. Phys. D: Appl. Phys.

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This paper compares the performance and limitations of different models of the cathode region of cold-cathode low-pressure dc glow discharges: (i) we review known modelling approaches, (ii) develop our own simulation codes based on these approaches, (iii) perform calculations using these codes for reference sets of discharge conditions, which allows a critical comparison of the models and (iv) for a further check of the simulation results we carry out Langmuir probe measurements of electron densities in abnormal Ar glow discharges. The theoretical approaches include fluid models both neglecting and including the electron energy balance equation, as well as hybrid models, which combine the fluid treatment of slow plasma species with the kinetic simulation of fast electrons. We also test the effect of the choice of the ionization source term in fluid models. We find that the electron densities calculated from the fluid models are far (several orders of magnitude) below the experimental values even if the electron energy equation is considered in the calculations. This weakness of fluid models clearly points out the importance of an accurate calculation of the ionization source term, which can only be accomplished by a kinetic approach under the conditions of highly nonlocal electron transport in the cathode region of glow discharges. In hybrid models Monte Carlo simulation is used for this purpose, and indeed, this approach gives electron densities comparable to our experimental data.

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Peculiarities of electron emission from the cathode in an abnormal glow discharge

Cited by 28 publications

References 30 publications

Electron Emission from Surfaces Induced by Slow Ions and Atoms

Electron Emission from Surfaces Induced by Slow Ions and Atoms

Material dependent modeling of secondary electron emission coefficients and its effects on PIC/MCC simulation results of capacitive RF plasmas

On the accuracy and limitations of fluid models of the cathode region of dc glow discharges

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