Electron impact charging properties of size-selected, submicrometer organic particles

Size-selected, submicrometer particles of an organic liquid (dioctyl sebacate) were produced using a differential mobility analyzer and impacted by electrons in a particle beam apparatus. Particle charges were measured as a function of electron current and energy and the results used to calculate secondary electron yields and saturation potentials. These quantities were found to depend on particle size, and a simple model based on the theory of secondary electron emission from bulk materials, with corrections for the effects of surface curvature, was developed to explain the results. The model was used to calculate a number of parameters from the particle data for comparison with measurements made on organic liquid films. Values for the maximum yield, the primary electron energy at the maximum, the range of secondary electrons, and the energy dependence of the primary electron penetration depth were in good agreement. The results indicate that electron impact charging may be a useful technique for on-line characterization of particle properties.