Decay of electrostatic charge on surfaces due solely to gas phase interactions

The electrostatic charge on surfaces can decay over time by bulk or surface conduction to electrical ground, or by charge transfer with ionic species in the surrounding gas phase. In general, these processes occur simultaneously, and it is not possible to disentangle their effects. Here, we study the time dependence of surface charge decay resulting only from interactions with the surrounding gas. Our methodology is based on the magnetic levitation of an electrostatically-charged sample surface to avoid any conductive path to ground. By measuring the surface charge over time, we find that the charge decays more slowly than predicted by previous models based on collisions with gaseous ions, and exhibits a different functional form for the time dependence. The slower decay is attributed to a depletion of ions in the vicinity of the charged surface, and the experimentally-observed charge decay is explained by a new model that considers a spatially-dependent ion velocity.