State of sulphur on the palladium surface studied by auger electron spectroscopy, electron energy loss spectroscopy, ultraviolet photoelectron spectroscopy and X-ray photoelectron spectroscopy

Abstract

The state of sulphur on the Pd surface was studied by Auger electron spectroscopy, electron energy loss spectroscopy, ultraviolet photoelectron spectroscopy and X-ray photoelectron spectroscopy. When a Pd foil (> 99.9%) was heated at 773 K under vacuum, sulphur was segregated onto the surface; this was demonstrated by the S(L2,3M2,3M2,3) Auger peak at a kinetic energy of 150 eV. Ultraviolet photoelectron spectra revealed that the S 3p peak appeared at a binding energy of 5.5 eV and increased linearly with the amount of sulphur determined by the Auger electron spectra. The Pd 4d band near the Fermi level decreased sharply during the initial stage of sulphur segregation, indicating that the electron had been transferred from Pd to S. The binding energy of the S 2p band of sulphur segregated onto the Pd surface to various extents ranged from 161.5 ± 0.3 eV at low coverage to 162.8 ± 0.3 eV at full coverage. They correspond to the binding energies of S in PdS and in solid sulphur, respectively; thus sulphur was negatively charged on the Pd surface, especially in its lower coverages. Electron energy loss spectra showed no distinct changes.