Charge Density Fluctuations on a Dielectric Surface Exposed to Plasma or UV Radiation

Dust particles on a nonconductive surface are known to acquire electric charge and detach from the surface under plasma conditions and/or when affected by ultraviolet radiation. Similar phenomena occur as a result of electrostatic surface cleaning (shedding) as well as in nature, e.g., when observing levitation of dust particles above the lunar surface. A detachment of dust particles from the surface should occur when the electrostatic forces of their repulsion Fc exceed the sum of the gravitation Fg forces and the adhesive van der Waals FvdW forces acting on the particle on a nonconducting surface. However, a paradoxical situation usually arises: the three primary forces of different nature Fc, Fg, and FvdW, acting on a speck of dust with a characteristic size of the order of hundreds or thousands of nanometers, are completely incomparable in magnitude, herewith Fc << Fg << FvdW. In the last decade, numerous attempts have been made to explain how a particle on a nonconducting surface can acquire a charge sufficient for the electrostatic forces that arise to approach the adhesive forces’ values. However, despite some successes, many questions remain unanswered. This article presents a brief analysis of the charge appearance process on a solitary dust speck and a speck lying on the surface. To explain the detachment of dust particles from the surface caused by electrostatic forces and the accumulation of a charge on those particles sufficient for levitation, one should take into account the charge density fluctuations on the surface.