Synchrotron radiation studies for thermionic cathode research

An approach to thermionic cathode research is described that combines surface-extended X-ray absorption fine structure (SEXAFS) and ultraviolet photoemission spectroscopy (UPS) measurements with theoretical calculations based on the full-potential linearized augmented plane wave (FLAPW) method. The physics and chemistry of the Ba and O layer present on the surface of a dispenser cathode and the relation of its properties to cathode performance are of interest. SEXAFS determines the surface geometry associated with the overlayer and UPS the electronic properties of the Ba-O covered surface. Through the correlation of the surface geometry with the surface electronic properties via FLAPW calculations, some of the essential issues that underline the performance of dispenser cathodes are identified. Some results obtained during the initial stage of this research are presented. In particular, the results indicate that the standing-up (or vertical) geometry is unlikely for Ba-O adsorption on tungsten surfaces