Effects of Direction and Strength of External Electric Field on Particle Charging and Levitation under UV Irradiation

When particles are charged, their motion can be controlled by electrostatic forces. In this study, particle charging and motion in an electric field under UV irradiation were elucidated. When the particle layers deposited on an insulating substrate were irradiated with UV light in a downward electric field, positive charges generated by photoemission were distributed within the particle layers. Subsequently, by reversing the direction of the electric field, particles in the top layer were positively charged and levitated. The flux of the levitated particles increased with an increase in the strength of the electric field (downward and upward). The number of agglomerated particles in the levitation region increased but the particle charge decreased with an increase in the upward electric field strength. These results can be explained via the mechanism of particle levitation.