High-performance negative electron affinity photocathodes for high resolution electron beam lithography and metrology

Factors affecting the brightness of negative electron affinity photocathodes have been investigated experimentally and theoretically. The results of a two-dimensional model of electron dynamics in the cathode, including the effects of surface-trapped electrons, are presented. Emission is seen to be cut off in the central emission area at high current levels. The angular distribution is compared to a cosine distribution based on an energy spectrum obtained from the same cathode. While superior to the cosine distribution with respect to its forward focusing properties, it is far wider than previous theory has suggested.