Charging of metal microparticles in electron flow

We have studied the charging of copper microparticles in electron flow. It is established that the parameters of secondary electron emission from microparticles can significantly differ from those for metal films and volume targets. Conditions are determined under which negative charging of micron-sized copper particles in electron flow takes place. In the case of spherical microparticles, secondary emission is significantly increased as a result of the oblique incidence of primary electrons. A general approach is proposed that can be used to estimate the electron energy necessary for charging microparticles to high negative potentials.