Electron kinetics at the plasma interface

Abstract

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.

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

“…Specifically, plasma parameters such as the mean ion energy and ion flux have to be controlled independently. However, in order to obtain such control, it is important to understand how the surface interacts with the plasma and vice versa [4,5].…”

Continuum Kinetic Simulations of Plasma Sheaths and Instabilities

“…In reality, the situation is more complicated as the incident electrons can be reflected back, they can penetrate the material and then being rediffused with lower energy, or the electrons originally in the material can gain energy and be released into the plasma. The latter process, known as secondary electron emission (SEE), can occur either through direct transfer of the kinetic energy of the impacting particle [Furman and Pivi, 2002] or through a change in its internal energy state [Bronold et al, 2018]. While the source of the first type of SEE can be both electrons and ions, the second type requires distinct internal energy levels.…”

“…While the source of the first type of SEE can be both electrons and ions, the second type requires distinct internal energy levels. Bronold et al [2018] provide an example of helium ions colliding with a dielectric wall. As an ion approaches the wall, an electron from the surface can tunnel into ion shell energy levels directly neutralizing it and releasing Auger electron.…”

“…Description of rediffusion in Bronold et al [2018] is much more complicated in comparison to back-scattered electrons, (5.39) where ρ(E) = m 3 e E/2(2π) 3 is the conduction band density of states and is the probability of rediffusion. Q(E, µ, E , µ ) is given by a recursive relation summed over the back-scattering events inside the material.…”

The Transregional Collaborative Research Centre “Fundamentals of Complex Plasmas” (Greifswald – Kiel)

“…-The progress in the field of plasma-chemical processes in molecular gases with mid-infrared laser absorption spectroscopy and optical emission spectroscopy is reviewed by Röpcke et al [8]. -A review is given by Bronold et al [9] on the modeling of the electric double layer formed by the ions in the sheath and the electrons on the surface or inside the solid surface. -Nemschokmichal et al [10] study the breakdown of dielectric barrier discharges with streak-camera imaging, laser photo-detachment of negative ions and fluid modeling.…”