Control of emission current from a LirW 111;field emitter by sequential deposition of Li

For a W 111:field electron emitter deposited with liquid Li, a field-stabilized cone of liquid Li is formed on the emitter tip and an electron beam with several hundreds of microamperes is emitted from the cone apex. However, the emission current decreases gradually with time because of the evaporation of deposited Li and the lifetime is about an hour. In order to prolong the lifetime, in this paper, we tried sequential deposition of Li whose amount corresponded to consumption by thermal evaporation. As a result, electron emission with a fluctuation of about 10% continued for more than 10 h. The critical pressure for stable electron emission was also investigated. An abrupt decrease of emission current was observed at the exposure of about 1 l of dry air. The decrease is probably caused by the solidification of the liquid Li at the emitter surface. q1999 Elsevier Science B.V. All rights reserved