Abstract
The emission characteristics of three types of dispenser cathode, i.e. Ir coated, OsRu coated and uncoated have been studied under realistic vacuum. The cathodes were installed in electron guns normally used for CRT. The emission current was measured in dc method under controlled gas pressures of Ar, N 2, or H 2 at 10 −9 to 10 −6 torr. In cases of Ar and N 2, significant decrease in emission current was observed for each cathode. The onset pressure for the emission decrease was several 10 −8 torr for coated cathodes and several 10 −7 torr for uncoated cathodes. For coated cathodes, the Ir coated cathode has been confirmed to have greater tolerance to the gases than the OsRu coated one. In the case of the H 2, no significant decrease in emission current was observed. The surface compositions of cathodes during and after sputtering by Ar ion were observed by SAM. The results showed the differences in the manner of sputtering away of Ba(−O) layer for three types of cathode.
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