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 XPS spectra from sulphide mineral surfaces under different conditions of preparation, oxidation and reaction. Evidence from other techniques confirming assignment of high-binding-energy S 2p components to metal-deficient sulphide surfaces, polysulphides, elemental sulphur and electronic defect structures is considered for specific cases. Reliable assignment of S 2p3/2 components at 163.6–164.0 eV to elemental sulphur Sn0 can be confirmed by evaporative loss at 295 K and/or observation of S–S bonding by x-ray absorption fine structure (XAFS), x-ray diffraction or vibrational spectroscopy. Assignment to polysulphides Sn2− at 162.0–163.6 eV requires confirmation of S–S bonding by XAFS or vibrational spectroscopy. Metal-deficient lattices can be represented as electronic defects (e.g. vacancies) or restructured surface phases confirmed by diffraction or XAFS evidence. High-binding-energy S 2p3/2 components can also result from Cu(I) substitution into ZnS with associated oxidation of sulphur as electronic defect sites without S–S bonding, metal deficiency or restructuring. This assignment is confirmed by XAFS evidence. Copyright © 1999 John Wiley & Sons, Ltd.