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.

表面上的静电荷会随着时间的推移通过体或表面传导到接地，或通过与周围气相中的离子物质的电荷转移而衰减。一般来说，这些过程是同时发生的，不可能解开它们的影响。在这里，我们研究了仅由与周围气体相互作用引起的表面电荷衰减的时间依赖性。我们的方法基于带静电样品表面的磁悬浮，以避免任何接地的导电路径。通过测量表面电荷随时间的变化，我们发现电荷衰减比以前基于与气态离子碰撞的模型预测的要慢，并且表现出不同的时间依赖性函数形式。较慢的衰减归因于带电表面附近的离子消耗，