Surface potential of small particles charged by the medium-energy electron beam

The present paper deals with the charging of glass particles of micron sizes by the monoenergetic electron beam with the energy in the range from 400 eV-5 keV. The particles are trapped in an electrodynamic quadrupole placed in an ultra-high vacuum chamber and bombarded by the electron beam. The surface of a trapped grain can be modified by the ion beam. The charge of the particles as well as their dimensions are determined from the dynamics of their motion inside the quadrupole and the corresponding surface potential is determined. The equilibrium surface potential is measured for different beam energies and the in fluence of the secondary electrons and background electrons on this potential is discussed for the grains of different sizes. A simple computer model of the charging process which has been developed is able to predict the equilibrium surface potential. (C) 1998 Elsevier Science Ltd. All rights reserved.