Analysis of the Surface of Thermoemitters by Ion and Electron Beams

The temperature dependences of the composition of the outer monolayers of the surface of thermoemitters, namely, oxide, scandate, thoriated tungsten, and carbide cathodes, have been studied by the methods of low-energy ion and recoil atom scattering, Auger spectroscopy, and secondary ion mass spectroscopy. It has been established that the surfaces of oxide, scandate, and tungsten-thorium cathodes at operating temperatures contain a monoatomic film of active material (barium, thorium), which forms on the surface of the emitter when heated to operating temperature and dissolves in volume when the temperature drops to room temperature. As a result of activation, free barium accumulates in the volume of oxide crystals. It is shown that there is a slight increase in tantalum on the surface of tantalum carbide and it contains foreign electronegative adatoms (oxygen, chlorine, and sulfur) that cannot be removed at temperatures of 2500 K.