EFFECTS OF SECONDARY ELECTRON DETECTOR POSITION ON SCANNING ELECTRON MICROSCOPE IMAGE.

The image contrast in a SEM employing an open bore geometry objective lens is seen to vary substantially, depending on whether the images are produced using an SE detector above or below the lens, and on working distance. At a short working distance, and with the specimen in the gap between the objective lens polepiece, there is a very high contribution of Type 1 SEs to the top detector signal. This is advantageous for the production of high resolution images. In addition, the images are very sensitive to surface effects such as the presence of contaminants.