Effects of particle shape and chemical composition on the electron impact charging properties of submicron inorganic particles

The electron impact charging properties of submicron ( 0.04–0.25 μm diameter) particles of inorganic salts, and metal and semiconductor oxides were investigated using a particle beam apparatus. The results indicate that the particle saturation charge is approximately a linear function of diameter, and is relatively insensitive to particle shape and chemical composition. A linear least-squares fit to all our data on inorganic and organic particles (14 different compounds) provides a simple equation that can be used to calculate saturation charge to within 15% for these broad classes of materials. This result is important for the application of a new particle beam mass spectrometric technique we have developed for sizing submicron particles sampled from low-pressure environments. The saturation charging curves can be explained by using the results of a series of measurements on KCl particles to extend a charging model developed earlier for organic particles.