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Caesium-antimony photocathodes were processed in a vacuum of the order of 10−9 torr in two types of ultra-high vacuum systems, namely, (i) a conventional rotary pump-three stage glass mercury diffusion pump combination system and (ii) a sorption pump-titanium sputter ion pump combination system. Enhancement in white light sensitivity was observed when the photocathodes were processed in the ion pump uhv system in comparison with the diffusion pump system. A brief discussion is presented in the light of the residual gas contents in evacuated tubes processed in uhv systems. The photoelectric yield of semitransparent caesium-antimony photocathodes depends critically on the thickness of the original antimony film. Hence, the relationship, photoelectric yield (μA/lm) against percentage transmission of antimony film has been established. It is found that thin film caesium-antimony processed from an antimony film with 70% transmission yields an efficient photocathode in both types of uhv systems.

Conventional barium aluminate-impregnated tungsten matrix cathodes were coated with a metallic layer such as iridium, osmium, platinum or tungsten sputtered in an argon atmosphere. This simple practical procedure has been shown to lead to an enhancement in emission capability in the case of an iridium-coated or osmium-coated cathode, comparable with that reported in the literature using very much more complex procedures. The iridium- or osmium-coated cathodes exhibit effective work functions of 1·93 to 1·98 ev over a range 1200 to 1370 K. Results on coated (Os, Ir, Pt, W) and uncoated cathodes with 45% porosity matrices are presented and compared with an iridium-coated cathode with a 20% porosity matrix.

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