COMPUTER MODELING OF FIELD-EMISSION GUN SCANNING ELECTRON-MICROSCOPE COLUMNS

Some computer programs are described which enable the performance of 2-, 3-, and 4-magnetic lens (scanning) electron microscope columns to be modeled. The case of a 3-lens field emission SEM with a magnetic gun lens is explicitly considered; this case is extended to a 4-lens STEM with an objective lens working at fixed demagnification. The usefulness of these programs for optimizing the details of the column layout and for predicting performance is illustrated. The trajectory displacement (or transverse Boersch) effect is included and is predicted to affect the performance of practical columns containing one or more crossovers.