XPS of sulphide mineral surfaces: Metal-deficient, polysulphides, defects and elemental sulphur

This paper reviews evidence for the assignments of components of the S 2p X PS spectra from sulphide mineral surfaces under different conditions of pre paration, oxidation and reaction. Evidence from other techniques confirming assignment of high-binding-energy S 2p components to metal-deficient sulph ide surfaces, polysulphides, elemental sulphur and electronic defect struct ures is considered for specific cases. Reliable assignment of S 2p(3/2) com ponents at 163.6-164.0 eV to elemental sulphur S-n(0) can be confirmed by e vaporative loss at 295 K and/or observation of S-S bonding by x-ray absorpt ion fine structure (XAFS), x-ray diffraction or vibrational spectroscopy. A ssignment to polysulphides S-n(2-) 162.0-163.6 eV requires confirmation of S-S bonding by XAFS or vibrational spectroscopy. Metal-deficient lattices c an be represented as electronic defects (e.g. vacancies) or restructured su rface phases confirmed by diffraction or XAFS evidence. High-binding-energy S 2p(3/2) components can also result from Cu(I) substitution into ZnS with associated oxidation of sulphur as electronic defect sites without S-S bon ding, metal deficiency or restructuring. This assignment is confirmed by XA FS evidence. Copyright (C) 1999 John Wiley & Sons, Ltd.