O K-, Au, Ag, and Pt L 3-edge X-ray absorption near-edge structure (XANES), X-ray emission spectroscopy, and scanning photoelectron microscopy (SPEM) measurements have been performed to study the correlation between the electronic structures and photocatalytic activities of nanocrystalline (nc)-(Au, Ag, and Pt) particles on the surface of ZnO nanorods (ZnO-NRs). The O K-edge XANES spectra reveal greater occupation of the O 2p orbitals, i.e., a greater negative effective charge of the O ions, in nc-Pt/ZnO-NRs than of nc-(Au, Ag)/ZnO-NRs. This result suggests that nc-Pt particles have weaker photocatalytic activities than those of nc-(Au, Ag) particles on the surface of ZnO-NRs. Well-defined bandgaps of nanoparticle-coated ZnO-NRs increase in the order Au (3.3 eV) → Pt (3.5 eV) → Ag (3.6 eV), which can be correlated with an decreasing Pauling’s electronegativity and a reduction of the screening effect. The valence-band SPEM measurement of nc-(Au, Ag, and Pt)/ZnO-NRs does not support the general argument that the Fermi levels of the (Au, Ag)/semiconductor composites are shifted toward the conduction-band edge relative to that of the Pt/semiconductor composite.

O K- and Zn and Au L3-edge x-ray absorption near-edge structure (XANES), x-ray emission spectroscopy (XES), and scanning photoelectron microscopy (SPEM) are performed to investigate the electronic structure of ZnO nanorods with nanocrystalline (nc)-Au particles grown on the surfaces. The XANES spectra of nc-Au∕ZnO nanorods reveal the decrease of the number of both O 2p and Zn 4s∕3d unoccupied states with the increase of the nc-Au particle size. The number of Au 6s∕5d unoccupied states increases when the size of nc-Au particle decreases, indicating that the deposition of nc-Au particles on the surface of ZnO nanorods promotes charge transfer from the ZnO nanorods to nc-Au particles. Excitation energy dependent XES and SPEM spectra show that the number of electrons in the valence band of O 2p-Zn 4sp hybridized states decreases as the nc-Au particle size increases, revealing that more electrons are excited from the valence band to the conduction band of ZnO nanorods and the storage of electrons in nc-Au particles.

Electronic structures of the nanorods of RuO2 and IrO2 metallic oxides were investigated by x-ray absorption near-edge structure (XANES) and scanning photoelectron microscopy (SPEM). O K-, Ru, and Ir L3-edge XANES results reveal that hybridization between O 2p and metal t2g orbitals is weaker in IrO2 than in RuO2. The enhancement of the tip-region SPEM intensities relative to those in the sidewall regions for both RuO2 and IrO2 nanorods is found to extend over a large energy range in contrast to those of carbon nanotubes and ZnO nanorods, which are confined to deep below and near the Fermi level, respectively.

The electronic and bonding properties of nitrogenated carbon nanotubes ͑N-CNTs͒ exposed to chlorine plasma were investigated using C and N K-edge x-ray absorption near-edge structure ͑XANES͒ and scanning photoelectron microscopy ͑SPEM͒. The C and N K-edge XANES spectra of chlorine-treated N-CNTs consistently reveal the formation of pyridinelike N-CNTs by the observation of 1s → * ͑e 2u ͒ antibonding and 1s → * ͑b 2g ͒ bonding states. The valence-band photoemission spectra obtained from SPEM images indicate that chlorination of the nanotubes enhances the C-N bonding. First-principles calculations of the partial densities of states in conjunction with C K-edge XANES data identify the presence of C-Cl bonding in chlorine treated N-CNTs.

Behind the weak excitonic emission of ZnO quantum dots: ZnO/Zn(OH ) 2 core-shell structure

The electronic structures and bonding properties of oxygen-and chlorine-treated nitrogenated carbon nanotubes ͑N-CNTs͒ were studied using x-ray absorption near-edge structure ͑XANES͒ and scanning photoelectron microscopy. Features in the C K-edge XANES spectra are shifted by ϳ0.3 eV toward higher energies and by ϳ1.1 eV toward lower energies relatively to those of the more symmetrical pyridinelike and graphitelike structured N-CNTs upon chlorination and oxidation, respectively. Increases in N K-edge XANES intensities for both chlorination and oxidation reveal substitution of CC bonds by C-N bonds consistent with the observed valence-band photoemission spectra of the decrease of the C 2s bond and the increase of the N 2s bond.

Nitrogen (N) and metal (Al, Ga, and In) K-edge x-ray absorption near-edge structure (XANES), x-ray emission spectroscopy (XES), and Raman scattering measurements were performed to elucidate the electronic structures of group-III–nitride nanorods and thin films of AlN, GaN, and InN. XANES spectra show slight increase of the numbers of unoccupied N p states in GaN and AlN nanorods, which may be attributed to a slight increase of the degree of localization of conduction band states. The band gaps of AlN, GaN, and InN nanorods are determined by an overlay of XES and XANES spectra to be 6.2, 3.5, and 1.9eV, respectively, which are close to those of AlN and GaN bulk/films and InN polycrystals.

X-ray absorption near-edge structure (XANES) and scanning photoelectron microscopy (SPEM) measurements have been performed for Zn1−xCoxO and Zn1−xMgxO to elucidate the effects of the doping of Co and Mg, which have very different electronegativities, on the electronic structures of ZnO nanorods. The intensities of O K-edge near-edge features in the XANES spectra of Zn1−xCoxO and Zn1−xMgxO nanorods are found to be lower than those of ZnO, which suggests that both Co and Mg substitutions of the Zn ions enhance the effective charge on the O ion. The valence-band SPEM measurements show that Mg doping does not increase the density of near-Fermi-level states, which implies that Mg doping will not improve field emission of ZnO nanorods. It is surprising to find that both Co and Mg substitutions of Zn increase the numbers of O 2p dominated valence-band states, despite that Co and Mg have larger and smaller electronegativities than that of Zn.