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We have studied the electronic structure of Fe-doped ZnO nanoparticles, which have been reported to show ferromagnetism at room temperature, by x-ray photoemission spectroscopy, resonant photoemission spectroscopy, x-ray absorption spectroscopy, and x-ray magnetic circular dichroism (XMCD). From the experimental and cluster-model calculation results, we find that Fe atoms are predominantly in the Fe3+ ionic state with mixture of a small amount of Fe2+ and that Fe3+ ions are dominant in the surface region of the nanoparticles. It is shown that the room temperature ferromagnetism in the Fe-doped ZnO nanoparticles primarily originated from the antiferromagnetic coupling between unequal amounts of Fe3+ ions occupying two sets of nonequivalent positions in the region of the XMCD probing depth of ∼2–3 nm. [ABSTRACT FROM AUTHOR]

We have investigated the electronic structure of GdBaCo2O5.5 across the metal--insulator transition (MIT) using soft x-ray absorption and photoelectron spectroscopy. For the low-temperature insulating phase, we find that half of the Co3+ ions at the octahedral sites are in the low spin (LS) and the other half in the high spin (HS) state, while the Co3+ ions at the pyramidal sites are in the HS configuration. Upon increasing the temperature across the MIT, part of the LS octahedral Co3+ undergoes a spin-state transition into the HS configuration. We infer that this destroys the spin-state ordering and thus explains the decrease in resistivity. We observed that the band gap is reduced but not closed in the high-temperature phase. [ABSTRACT FROM AUTHOR]

The electronic structure of the Cr ions in Zn1− x Cr x Te ( x=0.03 and 0.15) has been investigated using X-ray magnetic circular dichroism (XMCD) and photoemission spectroscopy. Magnetic-field ( H) and temperature ( T) dependences of the Cr L 2,3 XMCD spectra well corresponded to the behavior of the magnetization measured by a SQUID magnetometer. The line shape of the Cr L 2,3 XMCD spectra was independent of H, T, and x, indicating that the ferromagnetism was originated from the same Cr electronic states independent of Cr concentration. The Cr 3 d partial density of states (DOS) showed a peak at the top of the valence band but there was no DOS at the Fermi level, corresponding to their insulating behaviors. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 1.9 eV, respectively, which are close to those of AlN and GaN bulk/films and InN polycrystals. [ABSTRACT FROM AUTHOR]

The electronic structure and magnetic properties of Al-doped Fe3O4 films at various Al concentrations were investigated by Al and O K-edge x-ray absorption near-edge structure (XANES) and Fe L3,2-edge magnetic circular dichroism (MCD) measurements. The O K-edge XANES spectra reveal that the intensity of O 2p–Fe 3d hybridized states decreases linearly as the Al concentration increases, suggesting that nonmagnetic Al substitution reduces couplings of the O 2p with Fe 3d orbitals. The Fe L3-edge MCD spectra show that the intensities of MCD features decrease as the Al concentration increases, which suggests that Al substitution reduces the magnetic moments of Fe ions. The Fe L3,2 XANES spectra suggest the absence of mixed valence states in agreement with previous x-ray resonance scattering measurements. [ABSTRACT FROM AUTHOR]

We explored the orbital structure of FeTiO3 with polarization-dependent x-ray absorption spectra complemented with electronic structure calculations. The electronic structure, near the bottom of conduction band, is composed of O 2p and Ti 3d orbitals. Ti 3d/4p hybridization dominantly lies on the ab plane. The highly delocalized Ti 4p orbital might hybridize with O 2p orbital and even extend to the next-neighbor Fe atom whereby establishing a linear orbital combination of Ti-O-Fe. A clear picture of the orbital construction in FeTiO3 will help to elucidate the paths of pressure-induced charge transfer and other physical or magnetic characteristics. [ABSTRACT FROM AUTHOR]

We have investigated the electronic structure of CaCu3Ru4O12 and LaCu3Ru4O12 using soft x-ray photoelectron and absorption spectroscopy together with band structure and cluster configuration interaction calculations. We found the Cu to be in a robust divalent ionic state while the Ru is more itinerant in character and stabilizes the metallic state. Substitution of Ca by La predominantly affects the Ru states. We observed strong correlation effects in the Cu 3d states affecting the valence band line shape considerably. Using resonant photoelectron spectroscopy at the Cu L3 edge we were able to unveil the position of the Zhang-Rice singlet states in the one-electron removal spectrum of the Cu with respect to the Ru-derived metallic bands in the vicinity of the chemical potential. [ABSTRACT FROM AUTHOR]

The correlation between the p-type hole conduction and the electronic structures of Cr-deficient CuCr1-xO2 (x = 0-0.1) compounds was investigated using O K-, Cu, and Cr L3.2-edge x-ray absorption near-edge structure (XANES), scanning photoelectron microscopy, and x-ray emission spectroscopy measurements. XANES spectra reveal a gradual increase in the Cu valence from Cu1+ to Cu2+ with increasing Cr deficiency x, whereas, the valence of Cr remains constant as Cr3+. These results indicate that the p-type conductivity in the CuCr1-xO2 samples is enhanced by a Cu1+-O-Cu2+ rather than a Cr3+Cr4+ or direct Cu1+-Cu2+ hole mechanism. Remarkable Cr-deficiency-induced changes in the densities of Cu 3d, Cu 3d-O 2p, and O 2p states at or near the valence-band maximum or the Fermi level were also observed. In addition, a crossover of conduction mechanism from thermally activated (TA) hopping to a combination of TA and Mott's three-dimensional variable range hopping occurs around 250 K. [ABSTRACT FROM AUTHOR]

Local electronic structures of ruthenocuprate RuSr2EuCu2O8 (RuEu-1212) were investigated by using x-ray absorption near-edge structure (XANES) and valence-band photoemission (VB-PES) measurements at room temperature. 80 K, and 25 K. The XANES results indicate that when RuEu-1212 is below Curie temperature, TM, electrons are transferred not only from Cu 3d states, but also from Ru 4 d states, to O 2p orbitals. Additionally, the partial spectral weight distributions derived from VB-PES measurements provide evidence of a weak overlapping between Ru 4 d states and strongly Cu 3d--O 2p hybridized states below the Fermi level, which results in a weak coupling between the CuO2 and RuO2 layers. The analysis of extended x-ray absorption fine structure shows that the appearance of weak ferromagnetism and superconductivity is accompanied by a significant decrease of dynamic local lattice distortions of high-shell Cu-Sr and Ru-Sr bonding in RuEu-1212. [ABSTRACT FROM AUTHOR]

Abstract: The yield of secondary electrons emitted from an epitaxial three monolayer (3ML) NiO(100)/Ag(100) film excited by soft X-ray linearly polarized synchrotron radiation at the Ni L 2,3 absorption threshold has been measured for different values of the thickness of a MgO(100) capping layer. Compared with the as grown 3ML NiO(100)/Ag(100) film, we observe a significant enhancement by about a factor 1.2 of the secondary electron emission for the capped 8ML MgO(100)/3ML NiO(100)/Ag(100) sample. A further substantial yield enhancement by a factor 1.6 with respect to the uncapped NiO sample is observed after deposition of an additional 8ML MgO(100) film, for a total capping layer thickness of 16ML. The observed secondary electron yield enhancement is discussed in terms of modified electronic structure, surface work function changes, and characteristic electron propagation lengths. [Copyright &y& Elsevier]

We report O K-, Ca K- and L3,2-, and Ti L3,2-edge X-ray absorption near edge structure (XANES) spectra of Ba1-xCaxTiO3 (x=0, 0.01, 0.08, and 1) and the electronic properties inferred from these XANES spectra. The spectra of O K-, Ca L3,2- and Ti L3,2-edges show characteristic spectral features attributable to the t2g and eg bands. The Ti and Ca L3,2-edge spectra contain two sets of L3 and L2 features with a L3–L2 separation of about 5.5 and 3.4 eV, respectively. We also observe a pre-edge feature in the Ca K-edge spectra and drastically reduced t2g features in the Ca L3,2-edge spectra. Our XANES spectra reveal that the Ca 3d bands are low-lying and the Ca 3d t2g bands are partially occupied. [Copyright &y& Elsevier]