Photoelectric Charging of Dust Particles in Vacuum

Photoelectric charging measurements are presented of dust grains in vacuum for isolated grains and for grains near a photoemissive surface. Isolated grains reach a positive-equilibrium floating potential, dependent upon the work function of the particle, which causes the emitted electrons to be returned. Grains dropped past a photoemitting surface reach a negative floating potential for which the sum of the emitted and collected currents is zero. The particles tested are $90–106\mu \mathrm{m}$ in diameter and are composed of Zn, Cu, graphite, and glass.