Quantitative LEIS analysis of thermionic dispenser cathodes

An UHV LEIS setup has been converted into a dedicated apparatus to study the surface composition, structure and dynamics of real dispenser cathodes and cathode model systems based on W single crystals. LEIS, AES and LEED are available to investigate the surface characteristics, and the cathode emission properties are derived in situ from a close-spaced diode configuration. In this paper, the focus is on the quantitative surface composition of B-type and M-type dispenser cathodes by LEIS. A straightforward quantification is hampered by the influence of the cathode workfunction on the neutralisation of the ions. It is shown that the ion fraction decreases as the workfunction of the cathode decreases. The Ba surface density is observed to increase with decreasing workfunction. However, before an accurate quantitative surface analysis can be performed a validation of the model used to correct for the influence of the ion fraction has to be performed. q1999 Elsevier Science B.V. All rights reserved.