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We investigate the electronic structures of hole-doped, La0.7Ca0.3MnO3, and electron-doped, La0.7Ce0.3MnO3, manganites by x-ray absorption near edge structure (XANES) spectroscopy at the O and Mn K-edges. While, the O K-edge XANES results indicate that Ca and Ce doping induce holes in O 2 p derived states, the Mn K-edge XANES do not give any evidence for creation of the Mn4+ (or Mn2+) ions by Ca (or Ce) dopants. Such results further questions the validity of double exchange mechanism in understanding the anomalous properties of manganites. [ABSTRACT FROM AUTHOR]

This work presents N, O K-edge x-ray absorption near-edge structure (XANES) and Ta L3-edge extended x-ray absorption fine structure (EXAFS) studies of amorphous Ta(N,O) films prepared with various flow rate ratios of N2/O2. The N and O K-edge XANES and Ta L3-edge EXAFS spectra demonstrate the presence of N2 molecules. These spectra also show that Ta(N,O) films have similar local atomic structure as that of Ta2O5. No evidence of the formation of Ta–N bond was obtained. The intensities of the π* feature in the N K-edge spectra and the features of O 2p–Ta 5d hybridized states were found to correlate with the residual stress and the refractive index, respectively. [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]

Using x-ray absorption and valence-band photoelectron spectroscopy (PES) we investigated the electronic structures of icosahedral (i)-Al[SUB70]Pd[SUB22.5]Re[SUB7.5] quasicrystals (QCs) with a 4.2 K/300 K resistivity ratio, r, ranging from 8.3 to 107 obtained under various annealing conditions. Our Al K-and Pd L[SUB3]-edge x-ray absorption results show that the density of states, N(E), near the Fermi level, E[SUBF], jumps to a larger value when r decreases down to below about 20.6. The valence-band PES results show that N(E) near E[SUBF] is greatly reduced in i-Al[SUB70]Pd[SUB22.5]Re[SUB7.5] QCs relative to that of the pure metal, which confirms the existence of the pseudogap. The PES spectrum has a sharp cutoff at E[SUBF] for r = 8.3 QC, while it decreases smoothly down to zero at E[SUBF] for larger r's. The combined results suggest the occurrence of metal-insulator transition at an r between 13 and 20.6. [ABSTRACT FROM AUTHOR]

X-ray absorption spectroscopy has been used to investigate the electronic structure of as-deposited and oxidized Ni/Au contacts on p-GaN. The Ni K-, L[sub 2,3]-, and O K-edges x-ray absorption spectra clearly show the formation of NiO in the annealed contacts. Annealing in air increases Ni-site hole concentration and slightly shortens the nearest-neighbor Ni-O bond length, which enhances p-d hybridization and charge transfer from Ni to O. The observed very low specific contact resistance in the oxidized contacts is found to be due to the enhanced hole concentration at the Ni site. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]