The optimization of electrostatic energy selection systems for low energy electrons

Design criteria are presented which allow electrostatic energy selection systems to be optimized to give the highest currents for electron beams having a low mean energy (? 500 eV) and a small energy spread (? 30 meV). Limitations in various parts of the system are discussed and a relationship between the current delivered by the system and the energy spread is presented. Different types and sizes for the energy selectors in these systems are considered and the best results are obtained with hemispherical deflectors. The advantage of using, within reasonable limits, a large selector with small image sizes is also demonstrated.