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171.
172.
The molybdenum purple bronze KMo6O17 is quasi two-dimensional (2D) metallic oxide that shows a Peierls transition towards a metallic charge density wave state. Since this specific transition is directly related to the electron properties of the normal state, we have investigated the electronic structure of this bronze at room temperature. The shape of the MoK1s absorption edge reveals the presence of distorted MoO6 octahedra in the crystallographic structure. Photoemission experiments evidence a large conduction band, with a bandwidth of 800 meV and confirm the metallic character of this bronze. A wide depleted zone separates the conduction band from the valence band that exhibits a fourfold structure, directly connected to the octahedral symmetry of the Mo sites. The band structure is determined by ARUPS in two main directions of the (0 0 1) Brillouin zone. It exhibits some unpredicted features but corroborates the earlier theoretical band structure and Fermi surface. It confirms the hidden one-dimensionality of KMo6O17 that has been proposed to explain the origin of the Peierls transition in this 2D compound. 相似文献
173.
V. Yu. Aristov O. V. Molodtsova V. M. Zhilin Yu. A. Ossipyan D. V. Vyalikh B. P. Doyle S. Nannarone M. Knupfer 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,57(4):379-384
A detailed investigation of the chemistry and electronic structure during the formation of the interfaces between thin films
of the archetypal organic molecular semiconductor copper phthalocyanine (CuPc) and Ag or Sn deposited on it was performed
using photoemission and near-edge X-ray absorption
spectroscopies with synchrotron light. Our study demonstrates the formation
of sharp, abrupt interfaces, a behavior which is of particular importance
for applications in organic devices. Moreover, for Ag on CuPc we demonstrate
that this interface is free from any reaction, whereas there is slight
interface reaction for Sn/CuPc. 相似文献
174.
用XANES实验方法研究Cr的价态 总被引:2,自引:0,他引:2
用改进的XANES(X射线吸收近边结构谱)方法对不同比例Cr(Ⅲ)和Cr(Ⅵ)的酵母制剂进行Cr价态研究,该方法与传统方法的区别是用一个电离室同时进行透射和荧光XANES实验.此实验方法简单,快捷,特别适用于在相同的实验条件下,以一个已知标样为标准,对一系列未知价态样品进行的比较分析.实验结果表明酵母对Cr有很强的还原能力,它几乎能将所有的Cr(Ⅵ)还原成Cr(Ⅲ).Cr的K边XANES谱在掺入酵母剂前后有所变化,说明不同样品中的Cr原子近邻结构有所不同 相似文献
175.
Molybdenum Carbide as Alternative Catalysts to Precious Metals for Highly Selective Reduction of CO2 to CO 下载免费PDF全文
Marc D. Porosoff Dr. Xiaofang Yang Dr. J. Anibal Boscoboinik Prof. Dr. Jingguang G. Chen 《Angewandte Chemie (International ed. in English)》2014,53(26):6705-6709
Rising atmospheric CO2 is expected to have negative effects on the global environment from its role in climate change and ocean acidification. Utilizing CO2 as a feedstock to make valuable chemicals is potentially more desirable than sequestration. A substantial reduction of CO2 levels requires a large‐scale CO2 catalytic conversion process, which in turn requires the discovery of low‐cost catalysts. Results from the current study demonstrate the feasibility of using the non‐precious metal material molybdenum carbide (Mo2C) as an active and selective catalyst for CO2 conversion by H2. 相似文献
176.
XAS analysis of iron and palladium bonded to a polysaccharide produced anaerobically by a strain of Klebsiella oxytoca 下载免费PDF全文
Iztok Arčon Stefano Paganelli Oreste Piccolo Michele Gallo Katarina Vogel‐Mikuš Franco Baldi 《Journal of synchrotron radiation》2015,22(5):1215-1226
Klebsiella oxytoca BAS‐10 ferments citrate to acetic acid and CO2, and secretes a specific exopolysaccharide (EPS), which is able to bind different metallic species. These biomaterials may be used for different biotechnological purposes, including applications as innovative green biogenerated catalysts. In production of biogenerated Pd species, the Fe(III) as ferric citrate is added to anaerobic culture of K. oxytoca BAS‐10, in the presence of palladium species, to increase the EPS secretion and improve Pd‐EPS yield. In this process, bi‐metallic (FePd‐EPS) biomaterials were produced for the first time. The morphology of bi‐metallic EPS, and the chemical state of the two metals in the FePd‐EPS, are investigated by transmission electron microscopy, Fourier transform infra‐red spectroscopy, micro‐X‐ray fluorescence, and X‐ray absorption spectroscopy methods (XANES and EXAFS), and compared with mono‐metallic Pd‐EPS and Fe‐EPS complexes. Iron in FePd‐EPS is in the mineralized form of iron oxides/hydroxides, predominantly in the form of Fe3+, with a small amount of Fe2+ in the structure, most probably a mixture of different nano‐crystalline iron oxides and hydroxides, as in mono‐metallic Fe‐EPS. Palladium is found as Pd(0) in the form of metallic nanoparticles with face‐centred cubic structure in both bi‐metallic (FePd‐EPS) and mono‐metallic (Pd‐EPS) species. In bi‐metallic species, Pd and Fe nanoparticles agglomerate in larger clusters, but they remain spatially separated. The catalytic ability of bi‐metallic species (FePd‐EPS) in a hydrodechlorination reaction is improved in comparison with mono‐metallic Pd‐EPS. 相似文献
177.
Ab initio X-ray absorption near edge structure (XANES) calculations for FeSexTe1−x, using a structural model that combines FeSe and FeTe phases at the nanoscale, are compared with Fe K-edge XANES measurements in the “pre-edge” region. The important aspects of this model are (i) magnetic order in the FeTe phase; (ii) Se and Te atoms placed randomly in both FeSe and FeTe crystallographic positions and; (iii) the two distinct distances for Fe–Se and Fe–Te of the bulk phases. The calculated spectra reproduce the observed increase of spectral weight in the experiments on FeSexTe1−x with Se concentration. This is consistent with an inhomogeneous local electronic structure of FeSexTe1−x. Additionally, we have calculated projected electronic density of d-states for the Fe atom, revealing increased spectral weight in the “pre-edge” region of the XANES spectra, which correlates with the increase in Se concentration. The decrease of calculated Fe d-density of states for the Fermi level, N(εF), for high Te content is consistent with the suppression of superconductivity in the title system. 相似文献
178.
X-ray absorption spectroscopy (XAS) is one of the best techniques to obtain the information on the electronic and local structures of materials. In the last few decades, XAS becomes a common analytical technique for the investigation of solid oxide fuel cells and proton-conducting ceramic fuel cells. In particular, operando and/or advanced XAS measurements can be recently available with the increased accessibility of synchrotron radiation. In this article, recent trends of solid oxide fuel cell and proton-conducting ceramic fuel cell researches using XAS are overviewed. 相似文献
179.
Simon Trudel E. Daryl Crozier Peter S. Budnik 《Journal of solid state chemistry》2011,184(5):1025-19128
The oxidation state and local geometry of the metal centers in amorphous thin films of Fe2O3 (Fe3+ oxidation state), CoFe2O4 (Co2+/Fe3+ oxidation states), and Cr2O3 (Cr3+ oxidation state) are determined using K edge X-ray absorption near-edge structure (XANES) spectroscopy and extended X-ray absorption fine structure (EXAFS) spectroscopy. The metal oxide thin films were prepared by the solid-state photochemical decomposition of the relevant metal 2-ethylhexanoates, spin cast as thin films. No peaks are observed in the X-ray diffraction patterns, indicating the metal oxides are X-ray amorphous. The oxidation state of the metals is determined from the edge position of the K absorption edges, and in the case of iron-containing samples, an analysis of the pre-edge peaks. In all cases, the EXAFS analysis indicates the first coordination shell consists of oxygen atoms in an octahedral geometry, with a second shell consisting of metals. No higher shells are observed beyond 3.5 Å for all samples, indicating the metal oxides are truly amorphous, consistent with X-ray diffraction results. 相似文献
180.
Nikolay Smolentsev Grigory Smolentsev Shiqiang WeiAlexander V. Soldatov 《Physica B: Condensed Matter》2011,406(14):2843-2846
GaN:Mn dilute magnetic semiconductors with zinc-blende type of lattice and room temperature ferromagnetism were investigated by the X-ray absorption near edge structure (XANES) with a high accuracy approach of the multidimensional interpolation, which makes it possible to determine the nanoscale local atomic structure around Mn impurities. It is found that Mn atoms are substantially incorporated into the GaN lattice and Jahn-Teller distortion around Mn atom is observed. Our results show that symmetry changes around Mn atom influence on XANES spectrum significantly. Furthermore, the possible impact of local distortions on the magnetic properties is discussed. 相似文献