Towards a new method to measure low energy electron sticking coefficients using dusty plasmas

• Applicant: Privatdozent Dr. Franko Greiner
• Subject Area: Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 443791209

The charging properties of different materials are widely discussed in the dusty plasma community. They are directly related to the electron sticking coefficient of the particles, which is highly relevant for plasma technology because of its strong impact on the discharge properties of rf driven plasma reactors using different electrode materials. The high precision measurement of the dust charge opens the door to a new method for the determination of low energy electron sticking coefficients. In the last years, we developed a set of diagnostic tools for the high precision measurement of the charge-to-mass-ratio and the size of dust particles in the sheath of a plasma. Combining these methods allows to determine the particle charge with high precision. This makes it possible to measure the electron sticking coefficient for different materials at very low electron impact energies (less than 10 eV). Compared to other methods, the proposed method has the advantage that it measures the full charge of a small solid in a plasma, avoiding the problem that charges on a large solid surface will diffluence and obscure the charge measurement. Another advantage is that the new method does not rely on the electric conductivity of the material, therefore, conductive and dielectric materials canbe investigated.In this project, we will• Perform experiments to verify the theoretical prediction that dust particles of different materials charge up differently in a low pressure plasma.• Set up a diagnostic which measures the ratio of the low energy electron sticking coefficient of two materials.• Develop a method to measure the absolute, energy resolved electron sticking coefficient by a variation of the plasma parameters and calibration with a perfect absorbing material.• Test an ’enclosing spherical hull’ approximation for the charging of nonspherical particles in the plasma.

• DFG Programme: Research Grants
• Co-Investigator: Privatdozent Dr. Franz Xaver Bronold