Work function and microstructure of a monoatomic order surface layer grown on a (WSc 2W 3O 12)-coated impregnated cathode

Abstract

Activation processes of a (WSc 2W 3O 12)-coated impregnated cathode are clarified by analysing the change in coated film structure before and after activation, the change in atom concentration on the cathode surface as well as the work function of the cathode during activation processes, and the activation time required to attain electron emission enhancement. It is found that there are three steps necessary to complete the activation of the cathode; (1) separation of Sc 2W 3O 12 from W in the coated film; (2) production of free Sc atoms as a result of the reaction between Sc 2W 3O 12 and Ba atoms from the substrate cathode; and (3) formation of an ordered monoatomic surface layer composed of Ba, Sc and O. It is also found that the overall activation energy is about 4.6 eV, and the work function after activation is about 1.15 eV.