The structural and electronic properties, stability, optimum coverage and workfunction of oxygen atoms at different sites on the (1×1) unreconstructed and the (2×1) reconstructed C(111) surfaces have been investigated using density functional theory. Oxygen atoms prefer on-top sites on the C(111)-(1×1) surface, with an optimum coverage of 1/3 monolayers (ML), while on the (2×1) reconstructed surface, bridge sites are preferred with a coverage of 1/2 ML. With increasing oxygen coverage greater than 1/3 ML on the (1×1) surface, a repulsive interaction develops between the oxygen atoms, while for the (2×1) surface such a repulsive interaction occurs for coverages greater than 0.5 ML. For both surfaces, the workfunction initially increases with oxygen adsorption relative to that of each of the clean surfaces, reaching about ∼6 eV and then decreasing slightly at full monolayer coverage. Minimal buckling of the upper π-bonded chains and no dimerization of the clean (2×1) reconstructed surface was observed. An average valence band width of ∼21 eV occurs, and a surface state associated with the (2×1) surface reconstruction was established at ∼-2.5 eV. In addition, O 2s states were established at around -21 eV for the (1×1) surface and at ∼-22.5 eV on the (2×1) surface. These corresponded to similarly located C 2s states at -21.25 eV for both (1×1) and (2×1) surfaces. O 2p states were observed at the Fermi level, ∼-1.25, -2.5, -4.0, and ∼-7.5 eV on the (1×1) surface, and at ∼-2.5 eV, between -4 and -5 eV and at ∼-7.5 eV on the (2×1) surface.

Nominally clean diamond surfaces have been shown to contain adsorbed foreign atoms on them. Some of the adsorbed atoms have also been known to lead to various surface modifications, a phenomenon that is important in diamond electronics. Establishing the identity and nature of the adsorbed atoms on these surfaces is therefore key to the successful application of diamond in various technological fields. In this work, X-ray photoelectron spectrometry (XPS) has been used to investigate the three low index diamond surfaces. The results show oxygen as the main foreign atom on these surfaces other than hydrogen, with varying fractions of oxygen monolayer coverage being observed. It is further established that the adsorbed oxygen exists in several bonding configurations, with the energy shifts associated with the various functional groups being determined.

Copper oxides deposited at titania surfaces have a beneficial effect on the photocatalytic activity of TiO2, but their role is not fully understood. In this work, possible nanostructures of copper oxide on TiO2 (101) have been investigated by simulations based on density functional theory. Various stoichiometries, from Cu2O to CuO, and morphologies, from clusters to nanowires, have been considered. Nanowire structures were consistently more stable than isolated clusters. In these structures, a Cu2O stoichiometry was found to be thermodynamically more stable than CuO at room conditions, in contrast to what happens in bulk copper. Occupied Cu 3d and O 2p states extend well into the band gap of titania, whereas the nature of the lowest-lying empty states depend on the stoichiometry: for Cu2O they consist mostly of Ti 3d orbitals, while in CuO unoccupied Cu 3d orbital ∼0.8 eV above the Fermi level are present. Thus, both oxides reduce the band gap of the system with respect to pure titania, but only Cu2O should be effective in separating photogenerated electrons and holes. These results provide insight into the role of copper oxides in the photocatalytic process.

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A high rate capacity, moderate volume expansion and energetically stable alkali ion graphene–HfS2 electrode material.