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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]

In this study we measured the Fe, Mn, and Ni L[sub 2,3]-edge X-ray absorption near-edge structure (XANES) and K-edge extended X-ray absorption fine structure (EXAFS) of the ferromagnetic (FM) NiFe and antiferromagnetic (AFM) FeMn bilayer films prepared with various annealing temperatures. The branching ratios of the white-line intensities in the Fe, Mn, and Ni L[sub 2,3]-edges XANES spectra and consequently the magnetic properties of these exchange-biased FM NiFe — AFM FeMn bilayers are found to depend strongly on the annealing temperature. We find that the first peak in the Fe, Mn, and Ni K-edge EXAFS Fourier transform spectra are very similar, which suggests that the nearest-neighbor bond lengths among Fe, Mn, and Ni atoms are essentially the same in the NiFe-FeMn bilayers. However, the peaks at distances greater than ∼ 3 Å appear to be sensitive to the annealing temperature especially for the Fe and Mn K-edge spectra, which suggests that annealing alters the atomic structures of the next-nearest-neighbor and more distant shells surrounding the Fe and Mn atoms in the NiFe-FeMn bilayers. [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 and atomic structures of quasi-one-dimensional blue bronze K0.3MoO3 were investigated by polarization-dependent O K-edge x-ray absorption near-edge structure (XANES) and Mo K-edge extended x-ray absorption fine structure (EXAFS) measurements at various temperature and applied voltages. The O K-edge XANES spectra suggest that the number of unoccupied O 2p–Mo 4d hybridized states increases and decreases with temperature, respectively, below and above a critical temperature of 180 K. The along b-axis electric current measurements show a threshold applied voltage, beyond which the current increases rapidly. The Mo K-edge EXAFS measurements show that the Mo–O bond lengths are insensitive to the temperature even beyond 180 K. [ABSTRACT FROM AUTHOR]

This study performs O K- and Ti L[sub 3,2]-edge x-ray absorption near-edge structure (XANES) measurements and first-principles pseudopotential calculations for the electronic structures of ABO[sub 3]-type Pb[sub 1-x]Ca[sub x]TiO[sub 3] (x=0–1) perovskites. The features in the O K-edge XANES spectra are found to be contributed primarily by hybridization between O 2p and Ti 3d, Pb 6p, and Ca 3d orbitals. The O K-edge XANES spectra reveal that partial substitution of A cations, Pb, by Ca not only decreases O 2p–Pb 6p but also O 2p–Ti 3d hybridization. The Ti L[sub 3,2]-edge measurements find that the off-center displacement of Ti, and hence, ferroelectricity persist up to a Ca concentration between 0.3 and 0.4. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

X-ray absorption near edge structure (XANES) and scanning photoelectron microscopy (SPEM) measurements have been employed to obtain information on the electronic structures of the GaN nanowires and thin film. The comparison of the XANES spectra revealed that the nanowires have a smaller (larger) N (Ga) K edge XANES intensity than that of the thin film, which suggests an increase (decrease) of the occupation of N 2p (Ga 4p) orbitals and an increase of the N (Ga) negative (positive) effective charge in the nanowires. The SPEM spectra showed that the Ga 3d band for the nanowires lies about 20.8 eV below the Fermi level and has a chemical shift of about -0.9 eV relative to that of the thin film. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

X-ray absorption near edge structure (XANES) spectra of hard amorphous a-Si–C–N thin films with various compositions were measured at the C and N K-edge using sample drain current and fluorescent modes. The C K-edge XANES spectra of a-Si–C–N contain a relatively large 1s→π[sup *] peak, indicating that a substantial percentage of carbon atoms in the a-Si–C–N films have sp[sup 2] or graphite-like bonding. Both the observed sp[sup 2] intensity and the Young’s modulus decrease with an increase in the carbon content. For N K-edge XANES spectra of the a-Si–C–N films we find the emergence of a sharp peak near the threshold when the carbon content is larger than between 9% and 36%, which indicates that carbon and nitrogen atoms tend to form local graphitic carbon nitride. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Electronic structures of hole-doped and electron hole-doped manganites, La[sub 0.7]Ca[sub 0.3]MnO[sub 3] and La[sub 0.7]Ce[sub 0.3]MnO[sub 3], have been elucidated by X-ray absorption near-edge structure (XANES) spectra of O K- and Mn L[sub 3,2]-edges. In the electron-doped system, La[sub 0.7]Ce[sub 0.3]MnO[sub 3], the spectral features of O K-edge spectra are shifted by ∼ 1 eV towards the higher energy side and reduction of Mn valency from 4[sup +] and 3[sup +] to 3[sup +] and 2[sup +] is expected when compared to hole-doped manganite. The XANES of Ce M[sub 5,4]-edges indicates a tetravalent state for Ce, similar to that in CeO[sub 2]. Ce[sup 4+] is incorporated into the lattice of LaMnO[sub 3], resulting in the modification of MnO[sub 6] octahedra and also indicating strong hybridization of Ce 5d and/or Ce 4f states with O 2p states. [ABSTRACT FROM AUTHOR]

The electronic properties of amorphous carbon nitride were studied by x-ray-absorption near-edge structure (XANES) and valence-band photoelectron spectroscopy (PES). The nitrogen incorporation was found to induce graphitization, as evidenced by an increase of the sp2 cluster in C and N K-edge XANES spectra. The structure is found to be similar to pyridine. Hybridized C–N bond lengths were determined from the position of the σ* resonance of XANES spectra and the obtained results suggest sp2 hybridization. A valence-band PES spectrum showed that the p-π band became more intense than the p-σ band upon higher at. % nitrogen addition, which confirmed the role played by the π bonds in controlling the electronic structure of a-CNx films. [ABSTRACT FROM AUTHOR]

O K-, Zn L3, and K-edges x-ray absorption near-edge structure (XANES) spectra and scanning photoelectron microscopy (SPEM) spectra were obtained for ZnO nanorods with various diameters. The analysis of the XANES spectra revealed increased numbers of O 2p and Zn 4p unoccupied states with the downsizing of the nanorods, which reflects the enhancement of surface states when the diameter is decreased. Valence-band photoemission spectra show a significant narrowing of the valence band for the 45 nm diameter nanorod. The Zn 3d intensities in the Zn 3d SPEM spectra are drastically diminished for all nanorods as compared to the ZnO reference film, which can be interpreted as a reduction in density of itinerant final states or in transition probability. [ABSTRACT FROM AUTHOR]

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. [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]

As-grown and Zn-implanted wurtzite GaN samples have been studied by angle-dependent x-ray absorption near edge structure (XANES) measurements at the N and Ga K-edges and the Ga L[SUB3]-edge. The angle dependence of the XANES spectra shows that the Ga-N bonds lying in the bilayer have lower energies than bonds along the c-axis, which can be attributed to the polar nature of the GaN film. The comparison of the Ga L[SUB3]-edge XANES spectra of as-grown and Zn-doped GaN reveals significant dopant induced enhancement of near-edge Ga d-derived states. [ABSTRACT FROM AUTHOR]