A STUDY OF POLYCRYSTALLINE COPPER CATHODE SURFACES SUBJECT TO DC GLOW-DISCHARGE

The surface state of polycrystalline copper cathodes exposed to dc glow discharges was studied experimentally and the results compared to theoretical predictions. In order to do this, energy spectra of bombarding fast particles were calculated using a model based on the Boltzmann equation. Argon, oxygen and sulphur hexafluoride dc glow discharges were employed in the study, and experimental depth profiles were determined from the X-ray photo electron spectra recorded between successive periods of ion bombardment in a VG ESCA LAB 200 D electron spectrometer. Theoretical profiles were generated using the SUSPRE V 1.4 and TRIM computer codes. In general there was no good agreement between experimental and theoretical results. In the case of the highly chemically active gas SF6, where sputtering and deposition occur, the measured depth profiles are complex and do not lend themselves to theoretical modelling. In all cases examined the depth profiles and the physical state of the surfaces were strongly dependent on the energy of the bombarding particles.