SCANDIUM SUPPLY AFTER ION-BOMBARDMENT ON SCANDATE CATHODES

A scandium, barium, and oxygen coverage of monolayer order is essential to the high-emission capability of scandate cathodes. The relationship between surface coverage and emission will be demonstrated by combined scanning Auger and emission measurements. A problem with the known cathodes is that the emission recovery after ion bombardment, as may occur during CRT processing, is not yet complete. This is due to insufficient scandium supply to the surface which is related to the oxidized state of the scandium in the processed and activated cathode. The problem cannot be solved by simply constructing a mixed-matrix cathode of W and Sc grains because of huge evaporation of Sc during sintering and oxidation of the remainder during subsequent impregnation. It will be discussed how in this case the scandium can be effectively surrounded by a protective layer resulting in considerably improved scandium supply. Moreover, experimental results indicate the possibility for further simplification of the cathode manufacture. The latter is shown with the aid of cathodes containing compounds which exhibit Sc surface segregation on heating. © 1990 IEEE