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The Ba-Related Partial Density of States in Thermionic Dispenser Cathodes Revealed by Resonant Photoemission Spectroscopy

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Final rept. 1 Sep 1989-31 Aug 1991

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A range of synchrotron radiation-based spectroscopies has been used to study the geometric and electronic structure of the sub-monolayer bariumoxygen coating on tungsten-based thermionic dispenser cathodes. Surface EXAFS Extended X-ray Absorption Fine Structure results are identical to those published by us earlier Norman et al, Phys. Rev. Lett. 58 1987 519. Near edge XAFS shows substantial differences between the environment of oxygen atoms on B-type pure W matrix and CD-type WOs alloy cathodes, but these results still await detailed understanding. Photoemission shows that the shape of the valence band also is distinctly different for the two types of cathode, consistent with a lower coverage BaO overlayer on the alloy cathode, and a somewhat higher coverage of BaO with excess oxygen on the B-type cathode. The binding energies of the Ba 5p32, 12 and O 2s levels reinforce this suggestion. Constant initial state spectra show a resonance at a photon energy of about 106 eV in the Ba 5p levels and in parts of the valence band lying at binding energies greater than ca. 3.5 eV, but there are no Ba-derived states within ca. 3.5 EV of the Fermi level.

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  • Physical Chemistry
  • Electrical and Electronic Equipment
  • Electric Power Production and Distribution
  • Atomic and Molecular Physics and Spectroscopy

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