Berlin 2024 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 34: Poster: Surface Dynamics & Electron-Driven Processes

O 34.3: Poster

Dienstag, 19. März 2024, 18:00–20:00, Poster C

Invariant embedding approach to secondary electron emission from surfaces — •Franz Xaver Bronold and Felix Willert — Institut für Physik, Universität Greifswald, 17489 Greifswald, Germany

Secondary electron emission from the walls confining a gas discharge is an important surface process in low-temperature plasma physics. It affects, for instance, the operation modii of barrier discharges, Hall thrusters, and divertor plasmas in fusion devices. Little is however known quantitatively about the process because it typically occurs at energies below 50  eV which are hard to access experimentally. In this contribution, we present a theoretical scheme for calculating the secondary electron emission yield in this energy range. It is based on applying the invariant embedding principle, originally developed for calculating the albedo of planetary atmospheres, to the electron surface scattering kernel characterizing the interaction of a primary electron with a surface [1]. To illustrate the approach we apply it to polycrystalline silicon and germanium surfaces using a semiempirical randium-jellium model containing the Schottky barrier, impact ionization across the band gap as well as scattering on phonons, defects, and ion cores. The emission yields we obtain by solving the full nonlinear embedding equation numerically without an approximate decoupling of angle and energy variables are in satisfactory agreement with measured data to also support the use of the scattering kernel in the boundary condition of the electron Boltzmann equation of a plasma simulation. [1] F. X. Bronold and F. Willert, arXiv:2309.00534.

Keywords: secondary electron emission; electron surface scattering kernel; semiclassical transport equation; Boltzmann equation