Effective Use of External Electric Field for Charging and Levitation of Particles Under UV Irradiation

Electrostatic forces can be used to control the motion of charged particles. In this article, particle charging and motion in an electric field under ultraviolet (UV) irradiation were investigated. When the particle layers deposited on an insulating substrate were irradiated with UV light in a downward electric field, photoelectrons were emitted, and positive charges moved to the bottom of the particle layers. Subsequently, by reversing the direction of the electric field, the positive charges in the bottom moved upward; thus, the particles in the top layer were positively charged and levitated by Coulomb forces. The flux of the levitated particles increased with an increase in the strength of the electric field (downward and upward). As the upward electric field strength increased, the number of agglomerated particles in the levitation increased; however, the particle charge decreased. As the thickness of the particle layers increased, the time delay for particle levitation increased; however, the flux of the levitated particles decreased. The ratio of agglomerated particles to the total levitated particles increased. These results can be explained by the mechanisms of charge transfer and particle levitation.