The field emission electron source is a key element in powerful electron microscopes that characterize matter on the atomic scale, but the brightness, coherence, and stability are no longer sufficient to investigate materials at the level of resolution demanded by modern industry. Specifically, brightness needs to be improved by a factor of ten, the energy spread needs to be decreased 2-3 times, and the overall stability, reliability and user-friendliness all must be improved substantially. This project will develop a new low-workfunction, cold-field emission electron source with reduced emitter radius that can meet these criteria. The source will operate at liquid nitrogen temperature in an exceptionally high vacuum and will be used in a 200 keV scanning transmission electron microscope. Phase I will study the performance of selected low-workfunction cold field emitters in a dedicated ultra high-vacuum test chamber. Candidate low workfunction systems include Zr/O, Sc/O and Ba/O coatings on tungsten, all cooled to 78 K. Their workfunction, brightness, stability and reproducibility will be determined. The best system will be incorporated in a 200 keV electron gun to be developed in Phase II. Commercial Applications And Other Benefits as described by awardee: The complete 200 keV electron gun would be incorporated in an aberration-corrected scanning transmission electron microscope. It should allow entry into the highly competitive electron microscope market with the first US-designed and made electron microscope in over 40 years.
