Abstract
Application trends in the 1990's will continue to be driven by the pursuit of materials characterisation to higher levels of structural and chemical resolution. Due to the information-limit and current-density limitations of LaB6 sources, further advancements will require better electron guns. The choice of guns includes Cold, Thermally-assisted Cold and Schottky Field Emitters. For SEM and STEM the Cold Field Emitter is a reasonable choice, because the primary criterion for small-probe techniques is current density. This logic doesn't apply to TEMs, which require both high current density for small probes and high total current for large-area illumination at various TEM magnification levels. Table 1 compares Schottky and Cold Field emitters in different applications and microscope construction. In view of its performance (Figs. 1 and 2), the Field Emission Gun is expected to have a major impact on TEM in the 1990's.
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