Thermionic emission from carbon nanotubes with a thin layer of low work function barium strontium oxide surface coating

Abstract

We have created a thermionic cathode structure that consists of a thin tungsten ribbon, carbon nanotubes (CNTs) on the ribbon surface, and a thin layer of low work function barium strontium oxide coating on the CNTs. This oxide coated CNT cathode was designed to combine the benefits from the high field enhancement factor from CNTs and the low work function from the emissive oxide coating. The field emission and thermionic emission properties of the cathode have been characterized. A field enhancement factor of 266 and a work function of 2.1eV were obtained. At 1437K, a thermionic emission current density of 15mA∕cm2 in an electric field of 0.9V∕μm was obtained, which is 50 times greater than the emission current density from the uncoated CNT cathode at the same temperature.