XANES

About: XANES is a research topic. Over the lifetime, 7737 publications have been published within this topic receiving 188032 citations.

Room-temperature ferromagnetism in Co-doped CeO2 nanospheres prepared by the polyvinylpyrrolidone-assisted hydrothermal method

Abstract: Nanospheres of pure CeO2 and Co-doped CeO2 (Ce1−xCoxO2, 0.01 ≤ x ≤ 0.07) dilute magnetic oxide were prepared by hydrothermal treatment using cerium (III) nitrate, cobalt (III) nitrate, and polyvinylpyrrolidone (PVP) as a surfactant. The prepared samples were studied using x-ray diffraction (XRD), transmission electron microscopy, field-emission scanning electron microscopy (FE-SEM), and UV-Visible spectroscopy. The valence states of Ce and Co ions were determined by using x-ray absorption near edge spectroscopy. The magnetic properties of the samples were studied using vibrating sample magnetometry. The results from XRD indicated that the synthesized samples had a cubic structure without a change in the structure of CeO2 due to Co substitution. FE-SEM micrographs showed that the samples had a spherical morphology. The Co-doped CeO2 showed a red shift of the band gap energy that originates from defects caused by Co substitution. The samples of both CeO2 and Co-doped CeO2 exhibit room temperature ferromagne...

Electronic structure of TiO2nanotube arrays from X-ray absorption near edge structure studies

Abstract: We report an X-ray absorption near edge structure (XANES) investigation of several TiO2nanotube arrays, including the as-prepared nanotube arrays from electrochemical anodic oxidation of Ti foil (as-prepared ATNTA), as-prepared nanotube arrays after annealing at 580 °C (annealed ATNTA) and annealed ATNTA after electrochemical intercalation with Li (Li-intercalated ATNTA). XANES at the O K-edge and Ti L3,2 and K edges shows distinctly different spectral features for the as-prepared and the annealed ATNTA, characteristic of amorphous and anatase structures, respectively. Intercalation of Li into annealed ATNTA induces a surprising, yet spectroscopically unmistakable, anatase to rutile transition. XANES at the Li K-edge clearly shows ionic features of Li in ATNTA. The charge relocation from Ti 3d to O 2p at the conduction band in TiO2 was also observed when Li ions were intercalated into annealed ATNTA albeit no noticeable reduction of Ti4+ to Ti 3+ was observed. The O K-edge shows a distinctly enhanced feature in the multiple scattering regime, indicating a close to linear O–Li–O arrangement in Li-intercalated ATNTA. These results show bonding changes between Ti and O resulting from the interaction of Li ions in the TiO2 lattices. Such bonding variation has also been supported by X-ray excited optical luminescence (XEOL), which suggests Li+-defect interactions. The implications of these results are discussed.

Spatially resolved electron energy-loss near-edge structure analysis of a near Σ = 11 tilt boundary in sapphire

Abstract: Spatially resolved electron energy-loss spectra have been recorded from the same E = 11 grain boundary of a high purity sapphire (03B1 - Al2O3) bi-crystal that had previously been examined by high resolution electron microscopy. The energy-loss near-edge structure (ELNES) on the aluminium L2,3 edge of the bulk 03B1 - Al2O3 is consistent with previously published X-ray absorption near-edge spectra (XANES). The presence of the grain-boundary introduces additional fine structure on the L2,3 edge, which is extracted from the dominant bulk spectrum using the chemical-standard "difference" method. A comparison with various spectral "fingerprints" suggests that the structural environment of the Al cations within the boundary plane has a reduced point-group symmetry and coordination number. Quantitative analyses of spectral intensities indicate that the equivalent of a full monolayer of Al cations is involved in the structural change at the boundary. These experimental observations are consistent with a recently calculated low energy relaxed grain-boundary structure.

Molecular orientation of terephthalic acid assembly on epitaxial graphene: NEXAFS and XPS study

Abstract: The adsorption of terephthalic acid molecules [C6H4(COOH)2), TPA] on a single layer of graphene grown epitaxially on Ni(111) has been investigated by means of near-edge X-ray absorption fine structure (NEXAFS) spectroscopy and X-ray photoelectron spectroscopy (XPS) at room temperature. The assignment of the NEXAFS resonances was aided by ab initio calculations for the free TPA molecule. For coverages up to a monolayer the molecular plane of TPA adopts a parallel orientation with regard to the epitaxial graphene (EG) layer. Deprotonation of TPA molecules at one monolayer coverage can be excluded. For TPA multilayers, the molecular plane is tilted on average by approximately 45° with respect to the sample surface.

Cobalt valence states and origins of ferromagnetism in Co doped TiO2 rutile thin films

Abstract: Co doped rutile thin films were fabricated on α-Al2O3 (10-12) substrates by laser molecular beam epitaxy. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy indicated that the rutile thin films are (101) oriented and have smooth surfaces with no impurity phases. Co K-edge x-ray absorption near-edge structure, extended x-ray absorption fine structure, and x-ray photoelectron spectroscopy revealed the coexistence of different valence states of Co in the film. Magnetic circular dichroism studies suggest that the observed ferromagnetism is uniform and is related to the electron band structure of TiO2 rutile. Contribution of oxidized (Co2+) and metallic (Co0) cobalt to the ferromagnetism is discussed.