Magnetic sector deflector aberration properties for low- energy electron microscopy

Abstract

This thesis investigates improvements in the design and use of magnetic sector deflectors in electron optics. In particular, their use in a proposed spectroscopic scanning electron microscope (SPSSEM) is investigated. The aims of this instrument are to image with nm resolution and capture the full electron energy spectrum from scattered electrons. This involves the separation of the primary beam and the scattered electrons using a circular magnetic sector deflector. Simulations predict a primary beam probe radius of a few nm, and this is essentially confirmed in experiments carried out with a stand alone magnetic sector deflector unit inside a conventional SEM. Simulations further predict that the full electron energy spectrum can be collected on to a single multi-channel detector. Additional simulations investigate the circular magnetic sector deflector in the context of multiple beam deflections. A circular magnetic sector design with very small energy dispersion is also presented.