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关键词： X-ray absorption near edge spectroscopy   Vesicles   Oxides   Scattering   Extended X-ray absorption fine structure  

摘要： We have used grazing incidence X-ray absorption fine structure spectroscopy at the cobalt K-edge to characterize monolayer CoO films on Pt(111) under ambient pressure exposure to CO and O-2, with the aim of identifying the Co phases present and their transformations under oxidizing and reducing conditions. X-ray absorption near edge structure (XANES) spectra show clear changes in the chemical state of Co, with the 2+ state predominant under CO exposure and the 3+ state predominant under O-2-rich conditions. Extended X-ray absorption fine structure spectroscopy (EXAFS) analysis shows that the CoO bilayer characterized in ultrahigh vacuum is not formed under the conditions used in this study. Instead, the spectra acquired at low temperatures suggest formation of cobalt hydroxide and oxyhydroxide. At higher temperatures, the spectra indicate dewetting of the film and suggest formation of bulklike Co3O4 under oxidizing conditions. The experiments demonstrate the power of hard X-ray spectroscopy to probe the structures of well-defined oxide monolayers on metal single crystals under realistic catalytic conditions.

关键词： Solar cell efficiency  

摘要： In this work, scattering properties of a metal-dielectric structure are carried out in the optical range. In the proposed structure design, the absorption coefficient reaches more than 80% and has an almost constant character in the entire visible spectrum. Based on the obtained simulation results, such structures can be utilized in the field of solar energy storage applications. A review of works in the field of plasmonic solar cells is given, where the efficiency is usually increased due to the confinement of incident radiation in the active region of photoelectric conversion using localized modes, which are concentrated at the surface of conducting nanoparticles. That is, such batteries are operated in narrow wavelength intervals. However, in this article, the assumed solar cell efficiency enhancement can be achieved by incorporating the entire optical range due to the proposed metamaterial structure.

关键词： 面肌痉挛   扩散张量成像   脑白质   痉挛评分  

摘要： 目的 探讨面肌痉挛(H FS)患者全脑白质结构的异常以及与临床特征的相关性.方法 26例H FS患者(患者组)和29例健康志愿者(对照组)纳入本研究.应用基于纤维束的空间统计方法(TBSS)分析患者组与对照组各项扩散张量成像(DTI)参数的差异,并与患者的面部肌肉痉挛程度进行相关分析.结果 与对照组相比,患者组胼胝体膝部和体部、双侧下纵束和下额枕束、左侧上纵束、放射冠前部、后部及上部、双侧内囊后肢以及左侧丘脑后辐射等白质纤维束存在广泛异常.进一步分析发现,患者组部分各向异性分数(FA)值降低伴有径向扩散系数(RD)值和平均扩散系数(MD)值升高的脑区仅局限于右侧下纵束和下额枕束,同时,该区的RD值与患者的痉挛评分呈正相关性.结论 H FS患者脑白质完整性存在一定缺陷,尤其表现在右侧下纵束和下额枕束的RD值异常,这为评估该病的病理生理特征提供了影像学依据.

关键词： Copper   Oxidation state   Electronic structure   Ligands   Energy  

摘要： A series of organometallic copper complexes in formal oxidation states ranging from +1 to +3 have been characterized by a combination of Cu K-edge X-ray absorption (XAS) and Cu K beta valence-to-core X-ray emission spectroscopies (VtC XES). Each formal oxidation state exhibits distinctly different XAS and VtC XES transition energies due to the differences in the Cu Z(eff), concomitant with changes in physical oxidation state from +1 to +2 to +3. Herein, we demonstrate the sensitivity of XAS and VtC XES to the physical oxidation states of a series of N-heterocyclic carbene (NHC) ligated organocopper complexes. We then extend these methods to the study of the [Cu(CF3)(4)](-) ion. Complemented by computational methods, the observed spectral transitions are correlated with the electronic structure of the complexes and the Cu Z(eff). These calculations demonstrate that a contraction of the Cu 1s orbitals to deeper binding energy upon oxidation of the Cu center manifests spectroscopically as a stepped increase in the energy of both XAS and K beta(2,5) emission features with increasing formal oxidation state within the [Cun+(NHC2)](n+) series. The newly synthesized Cu(III) cation [Cu-III(NHC4)](3+) exhibits spectroscopic features and an electronic structure remarkably similar to [Cu(CF3)(4)](-), supporting a physical oxidation state assignment of low-spin d(8) Cu(III) for [Cu(CF3)(4)](-). Combining XAS and VtC XES further demonstrates the necessity of combining multiple spectroscopies when investigating the electronic structures of highly covalent copper complexes, providing a template for future investigations into both synthetic and biological metal centers.

关键词： BiFeO3   Bandgap   Magnetic properties   First principle calculations   Reflection loss  

摘要： Tunable microwave absorption characteristics are highly desirable for industrial applications such as antenna, absorber, and biomedical diagnostics. Here, we report BiNdxCrxFe1-2xO3 (x = 0, 0.05, 0.10, 0.15) nanoparticles (NPs) with electromagnetic matching, which exhibit tunable magneto-optical and feasible microwave absorption characteristics for microwave absorber applications. The experimental results and theoretical calculations demonstrate the original bismuth ferrite (BFO) crystal structure, while Nd and Cr injection in the BFO structure may cause to minimize dielectric losses and enhance magnetization by producing interfacial defects in the spinel structure. Nd and Cr co-doping plays a key role in ordering the BFO crystal structure, resulting in improved microwave absorption characteristics. The BiNd0.10Cr0.10Fe1.8O3 (BNCF2) sample exhibits a remarkable reflection loss (RL) of -37.7 dB with a 3-mm thickness in the 10.15 GHz-10.30 GHz frequency region. Therefore, Nd and Cr doping in BFO nanoparticles opens a newpathway to construct highly efficient BFO-based materials for tunable frequency, stealth, and microwave absorber applications. (c) 2021 Elsevier Inc. All rights reserved.

关键词： Redox reactions   Reaction mechanisms   Oligomers   Energy   Selenium  

摘要： Selenium X-ray absorption spectroscopy (XAS) has found widespread use in investigations of Se-containing materials, geochemical processes, and biologically active sites. In contrast to sulfur K beta X-ray emission spectroscopy (XES), which has been found to contain electronic and structural information complementary to S XAS, Se K beta XES remains comparatively underexplored. Herein, we present the first Se Valence-to-Core (VtC) XES studies of reduced Se-containing compounds and FeSe dimers. Se VtC XES is found to be sensitive to changes in covalent Se bonding interactions (Se-Se/Se-C/Se-H bonding) while being relatively insensitive to changes in Fe oxidation states as selenide bridges in FeSe dimers ([Fe2Se2](2+) vs [Fe2Se2](+)). In contrast, Se K beta HERFD XAS is demonstrated to be quite sensitive to changes in the Fe oxidation state with Se K beta HERFD XAS demonstrating experimental resolution equivalent to K alpha HERFD XAS. Additionally, computational studies reveal both Se VtC XES and XAS to be sensitive to selenium protonation in FeSe complexes.

关键词： Absorption spectroscopy   Diode lasers   Distributed feedback lasers   Optical feedback   Optical testing   Tunable diode laser absorption spectroscopy  

摘要： A novel technique for performing fiber pigtailed DFB laser and linear Fabry-Perot cavity based optical feedback cavity enhanced absorption spectroscopy (OF-CEAS) is proposed. A fiber-coupled electro-optic modulator (f-EOM) with x-cut y-propagation LiNbO3 waveguide is employed, instead of PZT used in traditional OF-CEAS, to correct the feedback phase, which improves the compactness and applicability of OF-CEAS. Through the efficient and real-time control of the feedback phase by actively changing the input voltage of the f-EOM, a good long-term stability of the signal has been achieved. Consequently, a detection sensitivity down to 7.8x10(-10) cm(-1), better than the previous by PZT based OF-CEAS, has been achieved over the integration time of 200 s, even by use of a cavity with moderate finesse of 2850. (C) 2022 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

关键词： photoelectrocatalysis   defect analysis   Raman spectroscopy   X-ray absorption spectroscopy   hematite   oxygen evolution reaction  

摘要： A high degree of variability in behavior and performance of hematite as photoanodes for the oxygen evolution reaction signifies a need to improve our understanding of the interplay between defects and photoelectrochemical performance. We approach this problem by applying structure-property analysis to a series of hematite samples synthesized under either O-2 or N-2 environments such that they exhibit highly variable performance for photoelectrocatalytic oxygen evolution. X-ray absorption fine-structure spectroscopy and Raman spectroscopy provide parameters describing the structure of samples across the series. Systematic comparisons of these parameters to those describing photoelectrochemical performance reveal different defects in samples prepared under N-2 or O-2. Distinct correlations between both the iron oxidation state and charge carrier density with photoelectrocatalytic performance lead to assignment of the primary defects as oxygen vacancies (N-2) and iron vacancies (O-2). Differences in the structural distortions caused by these defects are seen in correlations between short-range structural parameters and photoelectrochemical behavior. These distortions are readily observed by Raman spectroscopy, suggesting that it may be possible to calibrate the width, energy, and intensity of peaks in Raman spectra to enable direct analysis of defects in hematite photoanodes.

关键词： Excited states  

摘要： In photosynthetic systems employing multiple transition metal centers, the properties of charge-transfer states are tuned by the coupling between metal centers. Here, we use ultrafast optical and X-ray spectroscopies to elucidate the effects of metal-metal interactions in a bimetallic tetrapyridophenazine-bridged Os(ii)/Cu(i) complex. Despite having an appropriate driving force for Os-to-Cu hole transfer in the Os(ii) moiety excited state, no such charge transfer was observed. However, excited-state coupling between the metal centers is present, evidenced by variations in the Os MLCT lifetime depending on the identity of the opposite metal center. This coupling results in concerted coherent vibrations appearing in the relaxation kinetics of the MLCT states for both Cu and Os centers. These vibrations are dominated by metal-ligand contraction at the Cu/Os centers, which are in-phase and linked through the conjugated bridging ligand. This study shows how vibronic coupling between transition metal centers affects the ultrafast dynamics in bridged, multi-metallic systems from the earliest times after photoexcitation to excited-state decay, presenting avenues for tuning charge-transfer states through judicious choice of metal/ligand groups.

关键词： Epsilon iron oxide   Sol-gel Method   Glycerol as a steric agent   X-ray absorption spectroscopy   Confocal Raman microscopy   Magnetism  

摘要： Epsilon iron oxide (epsilon-Fe2O3) coatings on Si(100) substrates are obtained by an easy one-pot sol-gel recipe assisted by glycerol in an acid medium. Glycerol, given its small dimensions, enables the formation of epsilon-Fe2O3 nanoparticles with a size of a few nanometers and the highest purity is reached in coatings after a densification treatment at 960 degrees C. The structural and compositional evolution up to 1200 degrees C is studied by confocal Raman microscopy and X-ray absorption spectroscopy techniques, correlating the existing magnetic properties. We report a novel characterization method, which allows monitoring the evolution of the precursor micelles as well as the intermediate and final phases formed. Furthermore, the inherent industrial technology transfer of the sol-gel process is also demonstrated with the epsilon-Fe2O3 polymorph, impelling its application in the coatings form. (C) 2021 The Author(s). Published by Elsevier ***_BY_NC_ND_4.0