Field of View and Image Distortion : A Review of Low Magnification Imaging In the Environmental and Conventional Scanning Electron Microscopes (SEM)

Abstract Most scanning electron microscopy is performed at low magnification; applications utilising the large depth of field nature of the SEM image rather than the high resolution aspect. Some environmental SEMs have a particular limitation in that the field of view is restricted by a pressure limiting aperture (PLA) at the beam entry point of the specimen chamber. With the original ElectroScan design, the E-3 model ESEM utilised a 500 urn aperture which gave a very limited field of view (∼550um diameter at a 10mm working distance [WD]). An increase of aperture size to ∼lmm provided an improved but still unsatisfactory field of view. The simplest option to increase the field of view in an ESEM was noted to be a movement of the pressure and field, limiting aperture back towards the scan coils1. This approach increased the field of view to ∼2mm, at a 10mm WD. A commercial low magnification device extended this concept and indicated the attainment of conventional fields of view.