Thermionic emission and surface cooling from functionalized carbon nanotube oxide thin films

Thermionic emission is widely used in applications where strong electron emission is essential. Thin film type of thermionic emitters, however, despite of its versatility and potential, has yet to appear in real device applications. The main shortcoming for thin film thermionic emitter is its weak emission capability as compared to its bulky conventional counterparts. A high performance thermionic emission thin film with emission capability in par with that from a regular thermionic source is presented here. This thin film is based on carbon nanotubes (CNTs) with its surface further functionalized with low work function oxide materials. The low-work-function oxide coating combines with a large Schottky effect induced by the CNTs, results in a dramatic increase of thermionic emission. Emission current density as high as 4.5 A/cm² is obtained, and such emission capability exceeds most of the conventional thermionic cathodes used today.
A large cooling effect on the emitting surface was also observed due to the strong thermionic emission of hot electrons from this surface. Temperature drops as high as 90 °C was obtained. The efficiency of the cooling effect is also estimated.