Measuring Electron Sticking Coefficients using Dust in Plasma

The subject of this thesis is a novel method for the determination of electron sticking coefficients of different materials at very low energies (< 10 eV). Previously, conventional measurements of electron sticking coefficients were limited to either metallic surfaces, or higher energies in the case of dielectric materials. Using single, micrometer-sized particles of the respective material confined in a laboratory low-pressure plasma sheath (dust-in-plasma situation), low-energy electron sticking coefficients of several materials could now be determined. Especially the electron sticking coefficients of dielectric materials at low energies are now accessible with the experimental approach termed "Sticking Machine". This presents an application of dusty plasma physics for the investigation of surface processes.

At the core of the method lies a relative measurement scheme comparing a particle of a material with known sticking coefficient to one of which the sticking coefficient is to be determined. In a first step, an improved measurement technique for the particle charge-to-mass ratio is developed, as the charge of a particle is an indicator for its sticking coefficient. To allow for the relative measurement scheme, models for the charge collection currents of ions and electrons onto the particle are chosen and applied, leading to results for the low-energy electron sticking coefficients of silica, polymethyl methacrylate (PMMA) and melamin formaldehyde (MF) using spherical particles. To extend the method to a wider range of materials, a generalization to non-spherical particles is needed, which is detailed in the last portion of the work.

Using the results of this work, the Sticking Machine setup now allows for the determination of low-energy electron sticking coefficients of a wide range of technologically interesting materials, without requiring conductivity of the material or spherical particles.

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Mengel, A., 2025. Measuring Electron Sticking Coefficients using Dust in Plasma.
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