XANES

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

Electronic and Chemical Properties of Ce0.8Zr0.2O2(111) Surfaces: Photoemission, XANES, Density-Functional, and NO2 Adsorption Studies

Abstract: Synchrotron-based high-resolution photoemission, conventional X-ray (Mg Kα) photoemission (XPS), X-ray absorption near-edge spectroscopy (XANES), and first-principles density-functional calculations have been used to study the electronic properties of a Ce0.8Zr0.2O2 mixed-metal oxide. The results of density-functional calculations show that the band gap in bulk Ce0.8Zr0.2O2 is ∼0.6 eV smaller than that in bulk CeO2, with the Zr atoms in the mixed-metal oxide showing smaller positive charges than the cations in ZrO2 or CeO2. When present in a lattice of CeO2, the Zr atoms are forced to adopt larger metal−O distances than in ZrO2, leading to a reduction in the oxidation state of this element. Due to nonequivalent Zr−O distances, at least three different types of oxygen atoms are found in the Ce0.8Zr0.2O2 system. O K-edge XANES spectra for a series of Ce1-xZrxO2 (x = 0, 0.1, 0.2, 0.3, and 1) compounds show a distinctive line shape for the mixed-metal oxides that cannot be attributed to a sum of CeO2 and ZrO2...

Blue photoluminescence and local structure of Si nanostructures embedded in SiO2 matrices

Abstract: Strong and stable blue photoluminescence (PL), visible to the naked eye under 0.4 μW of 300 nm and 2.7 μW of 370 nm excitation, has been observed for samples of Si clusters embedded in SiO2 matrices, prepared by rf co‐sputtering followed by N2 annealing at 800 °C. Si K‐edge extended x‐ray absorption fine structure (EXAFS) and near‐edge x‐ray absorption fine structure (NEXAFS) strongly suggest the existence of Si nanoclusters with crystalline cores in the efficient emitting material. The PL excitation dependence is explained by an increase in the conduction band density of states deep in the band, and the formation of a band tail.

Highly Oriented, Self-Assembled Alkanephosphate Monolayers on Tantalum(V) Oxide Surfaces

Abstract: Octadecyl phosphoric acid ester has been found to produce oriented, well-ordered monolayers on a flat tantalum(V) oxide surface, via self-assembly from a heptane/propan-2-ol solution. By means of contact angle, optical waveguide lightmode spectroscopy (OWLS), near-edge X-ray absorption fine structure spectroscopy (NEXAFS), and X-ray photoelectron spectroscopy (XPS) measurements, it has been shown that these layers closely resemble those formed by the corresponding thiol−gold system, with respect to packing density, inclination, and order. The system shows promise as an approach to functionalizing oxide surfaces with well-ordered organic monolayers, with potential applications in the fields of biochemical analysis and sensors.

Nucleation and Growth of Fe Nanoparticles in SiO2: A TEM, XPS, and Fe L-Edge XANES Investigation

Abstract: Magnetic iron nanoparticles embedded in insulating oxides matrices are prized targets for “on chip” magnetic sensors, nano fluxgates and nano hard magnets. In this study, the nucleation and growth of iron nanoparticles in the near surface region of 400 nm silica thin films (on silicon substrates) during ion implantation and post- implantation electron beam annealing was systematically investigated by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Fe L-edge X-ray absorption near edge spectroscopy (XANES). Results show the presence of Fe oxides after low-fluence low-energy ion implantation in SiO2, suggesting that initially Fe substitutes for Si in the silica matrix. Larger Fe fluences lead to the formation of sub-2 nm metallic Fe nuclei. Postimplantation annealing transformed the dispersed cationic Fe species into metallic Fe nanoclusters (diameter 1–10 nm) that are stabilized by a thin passivating surface oxide film. The versatility of ion implantation and electron bea...

Influence of synthesis method on structural and magnetic properties of cobalt ferrite nanoparticles

Abstract: The Co–ferrite nanoparticles having a relatively uniform size distribution around 8 nm were synthesized by three different methods. A simple co-precipitation from aqueous solutions and a co-precipitation in an environment of microemulsions are low temperature methods (50 °C), whereas a thermal decomposition of organo-metallic complexes was performed at elevated temperature of 290 °C. The X-ray diffractometry (XRD) showed spinel structure, and the high-resolution transmission electron microscopy (HRTEM) a good crystallinity of all the nanoparticles. Energy-dispersive X-ray spectroscopy (EDS) showed the composition close to stoichiometric (~CoFe2O4) for both co-precipitated nanoparticles, whereas the nanoparticles prepared by the thermal decomposition were Co-deficient (~Co0.6Fe2.4O4). The X-ray absorption near-edge structure (XANES) analysis showed Co valence of 2+ in all the samples, Fe valence 3+ in both co-precipitated samples, but average Fe valence of 2.7+ in the sample synthesized by thermal decomposition. The variations in cation distribution within the spinel lattice were observed by structural refinement of X-ray absorption fine structure (EXAFS). Like the bulk CoFe2O4, the nanoparticles synthesized at elevated temperature using thermal decomposition displayed inverse spinel structure with the Co ions occupying predominantly octahedral lattice sites, whereas co-precipitated samples showed considerable proportion of cobalt ions occupying tetrahedral sites (nearly 1/3 for the nanoparticles synthesized by co-precipitation from aqueous solutions and almost 1/4 for the nanoparticles synthesized in microemulsions). Magnetic measurements performed at room temperature and at 10 K were in good agreement with the nanoparticles’ composition and the cation distribution in their structure. The presented study clearly shows that the distribution of the cations within the spinel lattice of the ferrite nanoparticles, and consequently their magnetic properties are strongly affected by the synthesis method used.