Study on the Emission Properties of the Impregnated Cathode With Nanoparticle Films

The effect of thin-film characteristics on the thermionic emission of dispenser cathodes has been investigated. Nanoparticle Ir thin films were grown by magnetron sputtering at room temperature. Microstructures of these thin films grown at different sputtering pressures were observed using a scanning electron microscope. The results showed that the particle size of the films depended on the deposition rate in the nucleation stage of the Ir films, which could be well controlled by the sputtering pressure. N-type cathodes were fabricated by impregnating tungsten matrices of 25% porosity with 6:1:2-type barium calcium aluminate and then coating them with nanoparticle Ir thin films, 200–500 nm in thickness, in hydrogen at 1200
$^{\circ} \hbox{C}$
. A comparison was made in the emission uniformity between an N-type cathode (defined here as a Ba dispenser cathode coated with a layer of metal nanoparticles) and a traditional M-type cathode using a thermionic electron microscope. The chemical components of the vacuum background, the evaporants from an N-type cathode, and an M-type cathode were respectively analyzed using a time-of-flight mass spectrometer. The evaporating rates of the two types of cathodes and their dependence on the cathode temperatures were also investigated. Finally, the electron emission performance of the N-type cathodes was studied.