Characterization of Tungsten Dispenser Cathodes Using ISS and SIMS
Abstract
Ion Scattering Spectrometry (ISS) and Secondary Ion Mass Spectrometry (SIMS) are used to characterize surface chemistry of barium-activated tungsten dispenser cathodes. Experiments were carried out at room temperature and at temperatures in which electron emission was occurring from the cathode structures. It was found that when the cathode structure ws heated to a point at which electron emission began, barium concentration at the surface also increased. At that temperature, the barium is generated, transported through the porous tungsten matrix, and spread over the emitting tungsten surface. Apparently, sputtering rates from these barium rich surfaces were very high and when ion beams were used at conventional energies (1000 volts or more), the sputtering rate was sufficiently large to suggest that incomplete coverage of barium existed. When very low ion beam voltages were used (in the neighborhood of 200-300 volts), and beam rastering techniques were employed, then results showed that the surfaces following activation were completely covered by barium. Under these conditions of complete barium coverage, no oxygen was observed. When the surface was sputtered and tungsten appeared, oxygen also increased, but not to a point to indicate a full oxide coating. A model of Ba bonded to O bonded to W is suggested.
Document Details
- Document Type
- Technical Report
- Publication Date
- Oct 01, 1979
- Accession Number
- ADA077592
Entities
People
- William L. Baun
Organizations
- Air Force Research Laboratory