Simulation of magnetic sector deflector aberration properties for low-energy electron microscopy

In this paper, low-order aberration properties of magnetic sector deflectors are analysed by computer simulation and their use in the low-energy electron microscope (LEEM) and the spectroscopic scanning electron microscope (SPSSEM) is examined. The simulation method is based upon direct ray tracing through field distributions derived by the finite element method and semi-analytical techniques. A variety of beam conditions and geometries have been investigated in order to operate the sector as a round lens while deflecting the primary beam through 90°. Predicted results from this study are also compared to previous simulation work.