The absolute energy positions of conduction and valence band edges were compiled for about 50 each semiconducting metal oxide and metal sulfide minerals. The relationships between energy levels at mineral semiconductor-electrolyte interfaces and the activities of these minerals as a catalyst or photocatalyst in aqueous redox reactions are reviewed. The compilation of band edge energies is based on experimental flatband potential data and complementary empirical calculations from electronegativities of constituent elements. Whereas most metal oxide semiconductors have valence band edges 1 to 3 eV below the H2O oxidation potential (relative to absolute vacuum scale), energies for conduction band edges are close to, or lower than, the H2O reduction potential. These oxide minerals are strong photo-oxidation catalysts in aqueous solutions, but are limited in their reducing power. Non-transition metal sulfides generally have higher conduction and valence band edge energies than metal oxides; therefore, valence band holes in non-transition metal sulfides are less oxidizing, but conduction band electrons are exceedingly reducing. Most transition-metal sulfides, however, are characterized by small band gaps (<1 eV) and band edges situated within or close to the H2O stability potentials. Hence, both the oxidizing power of the valence band holes and the reducing power of the conduction band electrons are lower than those of non-transition metal sulfides.

The absolute energy positions of conduction and valence bands of selected semiconducting minerals

NEXAFS investigations of transition metal oxides, nitrides, carbides, sulfides and other interstitial compounds

X-ray photoelectron spectra of 3d transition metal pyrites

Transition metal sulfides

Interfacial properties of semiconducting transition metal chalcogenides

The $K\ensuremath{\beta}$ emission spectra of sulfur in $\ensuremath{\alpha}\ensuremath{-}\mathrm{MnS}$, FeS, CoS, NiS, and CuS, and in two modifications (zinc-blende and wurtzite structures) of ZnS and CdS are obtained with a two-crystal spectrometer. The spectra of FeS, CoS, and NiS consist of a broad band and are alike. The spectra from the modifications of ZnS and CdS are similar to each other. The spectrum of CuS consists of two prominent peaks and it is discussed in relation to the sulfur $K\ensuremath{\beta}$ emission spectra from $\ensuremath{\alpha}\ensuremath{-}\mathrm{sulfur}$ and NiS. The $K\ensuremath{\beta}$ emission bands of ZnS and CdS are comparatively narrow, while those of the other metal sulfides are very wide. Results are evaluated by comparing the $K\ensuremath{\beta}$ emission spectra of these metal sulfides with the $\mathrm{sulfur}\ensuremath{-}K$ absorption spectra and with the energy-band structures.

Sulfur K β x-ray emission spectra and electronic structures of some metal sulfides

The application of chemical effects in high resolution X-ray spectrometry

The sulfur K β emission spectra in fluorescence from FeS 2 , CoS 2 , NiS 2 (with pyrite structure) and 2H-MoS 2 (with layered structure) have been measured on a vacuum two-crystal spectrometer. Results are evaluated by comparing the sulfur K β emission spectra with the X-ray photoelectron spectra of the valence-band region for the transition-metal disulfides, with the sulfur L II, III emission spectra and with the recent electronic-structure calculations. A reasonable agreement is obtained between them. It is indicated that the sulfur 3 p -like valence bands of the metal disulfides are very broad and their upper parts overlap with the 3 d - or 4 d -like band of the metals.

Sulfur Kβ X-Ray Emission Bands and Valence-Band Structures of Transition-Metal Disulfides

Kβ Emission and K Absorption Spectra of Sulfur in MnS

The Kb emission and K absorption spectra of sulfur in Cu1.8S are measured with a two‐crystal spectrometer and a bent‐crystal spectrograph, respectively. The Kb emission spectrum consists of two well‐separated peaks and the K absorption spectrum has a shoulder at the threshold. These spectra are interpreted on the basis of Terakura’s theory. The two emission peaks are attributed to the transitions from the bonding and antibonding states formed by the redistribution of the sulfur 3p states as a result of hybridization with the copper 3d bands. The spectra of Cu1.8S are compared with those of FeS, CoS, NiS, and CuS reported previously. From the similarity of the overall aspect of the Cu1.8S spectra and those of the transition‐metal sulfides, it is indicated that the local p‐like density of states of sulfur in the copper and transition‐metal sulfides are similar to each other.

Yohichi Gohshi

Papers

Sulfur K β x-ray emission spectra and electronic structures of some metal sulfides

The application of chemical effects in high resolution X-ray spectrometry

Sulfur Kβ X-Ray Emission Bands and Valence-Band Structures of Transition-Metal Disulfides

Kβ Emission and K Absorption Spectra of Sulfur in MnS

Sulfur Kβ emission and K absorption spectra and electronic structure of copper sulfide: Cu1.8S