The conduction and valence band edges for electronic band gaps and Fermi levels are determined for Ta2O5, TaON, and Ta3N5 by ultraviolet photoelectron spectroscopy (UPS) and electrochemical analyses. Reasonable agreement between the results of the two methods is obtained at the pH at which the ζ potentials of the particles are zero. The tops of the valence bands are found to be shifted to higher potential energies on the order Ta2O5 < TaON < Ta3N5, whereas the bottoms of the conduction bands are very similar in the range −0.3 to −0.5 V (vs NHE at pH = 0). From the results, it is concluded that TaON and Ta3N5 are promixing catalysts for the reduction and oxidation of water using visible light in the ranges λ < 520 nm and λ < 600 nm, respectively. It is also demonstrated that the proposed UPS technique is a reliable alternative to electrochemical analyses for determining the absolute band gap positions for materials in aqueous solutions that would otherwise be difficult to measure using electrochemical methods.

The structure of silicene, the two-dimensional honeycomb sheet of Si, grown on Ag(111) was investigated by scanning tunneling microscopy (STM) and low-energy electron diffraction (LEED) combined with density functional theory (DFT) calculation. Two atomic arrangements of honeycomb configuration were found by STM, which are confirmed by LEED and DFT calculations; one is 4×4 and the other is √13×√13 R13.9°. In the 4×4 structure, the honeycomb lattice remains with six atoms displaced vertically, whereas the √13×√13 R13.9° takes the regularly buckled honeycomb geometry.

We demonstrate that silicene, a 2D honeycomb lattice consisting of Si atoms, loses its Dirac fermion characteristics due to substrate-induced symmetry breaking when synthesized on the Ag(111) surface. No Landau level sequences appear in the tunneling spectra under a magnetic field, and density functional theory calculations show that the band structure is drastically modified by the hybridization between the Si and Ag atoms. This is the first direct example demonstrating the lack of Dirac fermions in a single layer honeycomb lattice due to significant symmetry breaking.

We examined the zero-field splitting of an iron(II) phthalocyanine (FePc) attached to clean and oxidized Cu(110) surfaces and the dependence on an applied magnetic field by inelastic electron tunneling spectroscopy with STM. The symmetry of the ligand field surrounding the Fe atom is lowered on the oxidized surface, switching the magnetic anisotropy from the easy plane of the bulk to the easy axis. The zero-field splitting was not observed for FePc on a clean Cu(110) surface, and the spin state converts from triplet to singlet due to the strong coupling of Fe d states with the Cu substrate, as is also confirmed by photoelectron spectroscopy. These findings demonstrate the importance of coupling at the molecule-substrate interface for manipulating the magnetic properties of adsorbates.

With its exceptional charge mobility, graphene holds great promise for applications in next-generation electronics. In an effort to tailor its properties and interfacial characteristics, the chemical functionalization of graphene is being actively pursued. The oxidation of graphene via the Hummers method is most widely used in current studies, although the chemical inhomogeneity and irreversibility of the resulting graphene oxide compromises its use in high-performance devices. Here, we present an alternative approach for oxidizing epitaxial graphene using atomic oxygen in ultrahigh vacuum. Atomic-resolution characterization with scanning tunnelling microscopy is quantitatively compared to density functional theory, showing that ultrahigh-vacuum oxidization results in uniform epoxy functionalization. Furthermore, this oxidation is shown to be fully reversible at temperatures as low as 260 °C using scanning tunnelling microscopy and spectroscopic techniques. In this manner, ultrahigh-vacuum oxidation overcomes the limitations of Hummers-method graphene oxide, thus creating new opportunities for the study and application of chemically functionalized graphene.

We demonstrate electron-stimulated migration for carbon monoxide (CO) molecules adsorbed on the Pd(110) surface, which is initiated by the excitation of a high-frequency (HF) vibrational mode (C-O stretching mode) with inelastic tunneling electrons from the tip of scanning tunneling microscopy. The hopping phenomenon, however, cannot be detected for CO/Cu(110), even though the hopping barrier is lower than in the CO/Pd(110) case. A theoretical model, which is based on the anharmonic coupling between low-frequency modes (the hindered-translational mode related to the lateral hopping) and the HF mode combined with electron-hole pair excitation, can explain why the hopping of CO is observed on Pd(110) but not on Cu(110).

Introducing a charge into a solid such as a metal oxide through chemical, electrical, or optical means can dramatically change its chemical or physical properties. To minimize its free energy, a lattice will distort in a material specific way to accommodate (screen) the Coulomb and exchange interactions presented by the excess charge. The carrier-lattice correlation in response to these interactions defines the spatial extent of the perturbing charge and can impart extraordinary physical and chemical properties such as superconductivity and catalytic activity. Here we investigate by experiment and theory the atomically resolved distribution of the excess charge created by a single oxygen atom vacancy and a hydroxyl (OH) impurity defects on rutile TiO(2)(110) surface. Contrary to the conventional model where the charge remains localized at the defect, scanning tunneling microscopy and density functional theory show it to be delocalized over multiple surrounding titanium atoms. The characteristic charge distribution controls the chemical, photocatalytic, and electronic properties of TiO(2) surfaces.

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