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 <i>F_c</i> exceed the sum of the gravitation <i>F_g</i> forces and the adhesive van der Waals <i>F_vdW</i> forces acting on the particle on a nonconducting surface. However, a paradoxical situation usually arises: the three primary forces of different nature <i>F_c, F_g,</i> and <i>F_vdW</i>, 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 <i>F_c</i> << <i>F_g << F_vdW.</i> 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.