Philips electron microscopes: Applications trends—design advances

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.