The charge of micro-particles in a low pressure spatial plasma afterglow

In this letter, we present charge measurements of micro-particles in the spatial afterglow (remote plasma) of an inductively coupled low pressure radiofrequency plasma. The particle afterglow charge of (-30 +/- 7) e, being deducted from their acceleration in an externally applied electric field, is about three orders of magnitude lower compared to the typical charge expected in the bulk of such plasmas. This difference is explained by a relatively simplistic analytical model applying orbital motion limited theory in the afterglow region. From an application perspective, our results enable further understanding and development of in situ plasma-based particle contamination control for ultra-clean low pressure environments.