Charge control of micro-particles in a shielded plasma afterglow

In this work, charge control of micro-particles from ~ -40 to +10 elementary charges is presented. This is achieved at 0.9 mbar argon in the spatial afterglow of an inductively coupled plasma by solely changing the strength of an externally applied electric field. Crucial in the presented experiments is the use of a grounded mesh grid in the cross section of the setup, separating the active plasma region from the "shielded" spatial afterglow. While in the regions above the mesh grid all particles reached a constant negative equilibrium charge, the actual control achieved in the shielded spatial afterglow can most probably be explained by variations of the local ion density. The achieved charge control not only opens up possibilities to study nano-scale surface charging physics on micro-meter length scales, it also contributes to the further development of plasma-based contamination control for ultra-clean low-pressure systems.