Portal de Periódicos da CAPES

Electron emission and surface composition of osmium and osmium-tungsten coated dispenser cathodes

1985; Elsevier BV; Volume: 20; Issue: 4 Linguagem: Inglês

10.1016/0378-5963(85)90166-7

1878-1071

D. Brion, J.C. Tonnerre, A.M. Shroff,

Electron and X-Ray Spectroscopy Techniques

The surface compositions of impregnated cathodes having coatings of pure osmium with thicknesses between 50 and 30,000 Å or mixed osmium-tungsten coatings (between 10 and 70% osmium) were measured by Auger spectroscopy. These compositions were determined during activation and short-duration aging at 1000°CB. Care was taken to first eliminate all of the residues of aluminates from the cathode surface, by chemical cleaning. During the activation of cathodes covered with a pure osmium coating (thickness greater than 3000 Å), the tungsten diffuses in the osmium until saturation of the θ phase throughout the coating depth. The electron emission of cathodes covered with a coating of pure osmium is three greater than that of “type S” cathodes, whatever the coating thickness. The electron emission of mixed-coating cathodes is slightly less than that of cathodes with a pure osmium coating. At 1000°CB, the quantities of barium and oxygen adsorbed at the surface of these cathodes and thus the O/Ba ratio are equal, whatever the surface concentration of Os, between 10 and 70%, and whatever the nature of the coating (Os or Os-W). Relative and absolute measurements using AES as well as ESCA show that the barium concentration at the surface of type M cathodes is 20% higher than at the surface of type S cathodes at 1000°CB, and the concentration of oxygen is 10% less. The chemical states of barium and oxygen are alike on type M and S cathodes. At least two different chemical states of oxygen co-exist at the surface of these cathodes.