Quick-scanning X-ray absorption fine structure beamline at SSRF

The layout and characteristics of the hard X-ray spectroscopy beamline(BL11B)at the Shanghai synchrotron radiation facility are described herein.BL11B is a bending-magnet beamline dedicated to conventional and millisecond-scale quick-scanning X-ray absorption fine structures.It is equipped with a cylindrical collimating mirror,a double-crystal monochromator comprising Si(111)and Si(311),a channel-cut quick-scanning Si(111)monochromator,a toroidal focusing mirror,and a high harmonics rejection mirror.It can provide 5-30 keV of X-rays with a photon flux of~5×10^(11)photons/s and an energy resolution of~1.31×10^(-4)at 10 keV.The performance of the beamline can satisfy the demands of users in the fields of catalysis,materials,and environmental science.This paper presents an overview of the beamline design and a detailed description of its performance and capabilities.

Extended X-ray absorption fine structure (EXAFS) of FAPbI_(3) for understanding local structure-stability relation in perovskite solar cells

Perovskite solar cells (PSCs) employing formamidinium lead iodide (FAPbI_(3)) have shown high efficiency.However,operational stability has been issued due to phase instability of α phase FAPbI_(3) at ambient temperature.Excess precursors in the perovskite precursor solution has been proposed to improve not only power conversion efficiency (PCE) but also device stability.Nevertheless,there is a controversial issue on the beneficial effect on PCE and/or stability between excess FAI and excess PbI_(2).We report here extended X-ray absorption fine structure (EXAFS) of FAPbI_(3) to study local structural change and explain the effect of excess precursors on photovoltaic performance and stability.Perovskite films prepared from the precursor solution with excess PbI_(2)shows better stability than those from the one with excess FAI,despite similar PCE.A rapid phase transition from α phase to non-perovskite δ phase is observed from the perovskite film formed by excess FAI.Furthermore,the (Pb-I) bond distance evaluated by the Pb L_(III)-edge EXAFS study is increased by excess FAI,which is responsible for the phase transition and poor device stability.This work can provide important insight into local structure-stability relation in the FAPbI_(3)-based PSCs.

时间分辨热化学原位XAFS方法

为了利用X射线吸收精细结构(X-ray absorption fine structure,XAFS)谱学技术开展热化学反应动力学研究,在上海光源X射线吸收精细结构谱学线站(BL14W1)开展了时间分辨热化学原位XAFS方法的研究。采用自主研制的数据采集设备解决了时间分辨XAFS技术中不同类型信号同步触发和同步采集的问题,实现了数据间的精准匹配。在单色器转速为720"/s、数据采集设备采样率为2MS/s、数据长度为1200eV的条件下,获得了一个9.6s的Cu标样的数据谱,通过与常规XAFS数据和标准XAFS数据进行对比,结果表明本文得到的时间分辨XAFS实验系统具有良好的准确性、分辨率和信噪比。在此基础上,进一步结合线站自主研制的原位装置开展了时间分辨热化学原位XAFS方法,并利用高温常压原位装置开展了CuO还原为金属Cu的验证性实验。在230℃恒温氢气气氛下30min内观测到Cu吸收边能量逐渐向低能量处偏移,同时它位于8998eV的主峰强度逐渐减弱并且劈裂为双峰结构,出现明显的金属Cu的特征。实验结果表明此方法达到了捕获物质动态演化过程的预期目的,在拓展XAFS谱学实验平台的同时,为热化学反应的动力学过程研究提供了一种强大的实验手段。

XAFS Study of Coordination Structure of Cu（L-His）2 in Solution

Multiple coordination modes are present copper coordination environment varies in the CuII-histidine complex in solution and the with pH. In this work, we have investigated the coordination geometry of Cu（His）2 complex using X-ray absorption fine structure （XAFS） analysis. Copper K-edge XAFS spectra were acquired on aqueous Cu2＋ samples with his- tidine at different pH values. The coordination environments were further confirmed by chemically modified histidine. Results show that the caboxylate groups coordinate at acidic condition, while amino and imidazole nitrogens get coordinated at higher pH. For the co- ordination geometry of Cu（His）2 in solution at physiological pH, the sixfold coordination is preferentially formed, while the fivefold coordination can co-exist in equilibrium.

Theoretical characterization of the adsorption configuration of pyrrole on Si(100)surface by x-ray spectroscopy

The possible configurations of pyrrole absorbed on a Si(100)surface have been investigated by x-ray photoelectron spectroscopy(XPS)and near-edge x-ray absorption fine structure(NEXAFS)spectra.The C-1s XPS and NEXAFS spectra of these adsorption configurations have been calculated by using the density functional theory(DFT)method and fullcore hole(FCH)approximation to investigate the relationship between the adsorption configurations and the spectra.The result shows that the XPS and NEXAFS spectra are structurally dependent on the configurations of pyrrole absorbed on the Si(100)surface.Compared with the XPS,the NEXAFS spectra are relatively sensitive to the adsorption configurations and can accurately identify them.The NEXAFS decomposition spectra produced by non-equivalent carbon atoms have also been calculated and show that the spectral features vary with the diverse types of carbon atoms and their structural environments.

XAFS在凝聚态物质研究中的应用

详细介绍了X射线吸收精细结构谱学(XAFS)的理论、数据分析及实验等基本原理,以及XAFS在薄膜、纳米结构和体相材料(包括半导体、合金以及复杂氧化物)等凝聚态物质研究中的应用;同时,还介绍了原位XAFS、微区XAFS和时间分辨XAFS等新的实验方法,并对该方法的应用前景进行了展望.

老化过程中铜形态变化的X射线吸收精细结构谱的(XAFS)初步研究

利用X射线吸收精细结构谱(XAFS)对老化过程中土壤中铜的分子形态进行初步表征。以硫酸铜、氧化铜和硫化铜的X射线吸收扩展边结构(EXAFS)谱为参比,对土壤样品中Cu的EXAFS谱进行拟合,得到不同老化阶段与参比物质相对应的结合态Cu的百分含量,并与连续提取法表征进行比较。XAFS分析结果表明,老化阶段土壤样品中铜的主要结合形态是CuSO_4,同时还有部分CuS,基本不含有CuO。随着时间的推移,土壤中CuSO_4百分含量呈现出下降的趋势,CuS百分含量呈现出上升的趋势。这与连续提取法研究结果中其可交换态的百分比下降,残渣态上升的趋势相似。

Al_(70)Cu_(20)Fe_(10)合金微结构的XRD和XAFS研究

采用机械合金化MA(mechanical alloying)方法成功地制备了Al70Cu20Fe10纳米合金。在结构分析中,联合使用传统的XRD(X-ray diffraction)方法与新兴的XAFS(X-ray absorption fine structures)技术,使XRD的长程有序结构和XAFS的特定原子近邻环境两个方面的信息相互补充、互为印证,有效地克服了高度无序体系结构分析的困难。结果表明,机械合金化Al70Cu20Fe10(MA-10 h)合金中的化合物成分是体心四方结构的Al2Cu,Al70Cu20Fe10(MA-20 h和MA-40 h)合金中的化合物成分是简单立方结构的Cu9Al4。

Oxidation of antimony (Ⅲ) in soil by manganese (Ⅳ) oxide using X-ray absorption fine structure

The oxidation of antimony （Ⅲ） in soils was studied using X-ray absorption fine structure （XAFS） spectra. An andosol soft sample and artificial soil samples （SiO2 blended with iron （Ⅲ） hydroxide and manganese （Ⅳ） oxide） were used herein. After adding antimony （Ⅲ） oxide to all soil samples, the oxidation process was observed by recording the XAFS spectra of Sb K-edge, Fe Kedge, and Mn K-edge. The results indicated that manganese （Ⅳ） oxide played an important role in the oxidation of Sb（Ⅲ）; however iron （Ⅲ） hydroxide was not directly related to the reaction. During a 2-hr continuous Sb K-edge X-ray absorption near edge structure （XANES） measurement with an interval of I rain of one of the artificial soil samples （SiO2 ＋ MnO2 ＋ Sb2O3）, a pseudo-first-order reaction was determined with an average estimated rate of 0.52 ±0.04 hr-1. Compared to the lower oxidation rate of andosol, it is suggested that because of the low concentration of Mn（Ⅳ） in natural soils, the oxidation process of Sb（Ⅲ） might be relatively slow and require more time to convert Sb（Ⅲ） to Sb（V）.

Synthesis, characterization and extended X-ray absorption fine structure of novel polynuclear copper complexes with new eighteen-membered macrocycle ligands

Macrocycle compounds have great importance in host-guest chemistry and moleculeidentifications. 4-acetyl-bispyrazolones are a new type of polydentate ligands. Whenthey react with diamine compounds, new compounds or complexes containing C=O andC=N groups can be obtained. These compounds can be used to study the relationship ofcoordination structure and its properties, energy transferring processes between metal

Structure and chemical valence study of Sr_(n+1)Ru_nO_(3n+1)(n= 1, 2, ∞) series

Effect of structure parameter n and its coupling with the connection mode among RuO6 octahedra of Srn＋1RUnO3n＋1 （n = 1, 2, ∞） are investigated. The gradually enhanced rotation and tilting effect with increasing n are observed in Srn＋1RUnO3n＋1. Besides, the chemical valence of Ru is not changed, while the one of Sr gradually varies with increasing n, which highlights the great contribution of connection mode to the chemical environment. Our results show a strong n dependence on the connection mode between octahedra in Srn＋1RUnO3n＋1 （n = 1, 2, ∞）.

XAFS applications in semiconductors

X-ray absorption fine structure (XAFS) has experienced a rapid development in the last three decades and has proven to be a powerful structural characterization technique nowadays. In this review, the XAFS basic principles including the theory, the data analysis, and the experiments have been introduced in detail. To show its strength as a local structure probe, the XAFS applications in semiconductors are summarized comprehensively, that is, thin films, quantum wells and dots, dilute magnetic semiconductors, and so on. In addition, certain new XAFS-related techniques, such as in-situ XAFS, micro-XAFS, and time-resolved XAFS are also shown.

Relating atomic local structures and Curie temperature of NdFeB permanent magnets:an X-ray absorption spectroscopic study

Relationship between atomic local structures and Curie temperature of NdFeB permanent magnets was investigated semi-quantitatively using synchrotron radiation technique. Fe K-edge X-ray absorption spectroscopy(XAS) was employed to study the local structure of Fe atoms for samples before and after doping Dy, Tb or Gd. It is found that the bond lengths and coordination numbers are changed. Thus, the exchange interaction between Fe atoms increases with Dy, Tb or Gd doping, resulting in the improvement of Curie temperature of NdFeB permanent magnets. The doping effect is proven by experimental measurement of the magnetic properties. Microstructural characterization using scanning electron microscopy(SEM) was also used to further analyze the effect of different rare earth elements doping on Curie temperature of NdFeB permanent magnets.

Research Article Local structure and magnetic properties of a nanocrystalline Mnrich Cantor alloy thin film down to the atomic scale

The huge atomic heterogeneity of high-entropy materials along with a possibility to unravel the behavior of individual components at the atomic scale suggests a great promise in designing new compositionally complex systems with the desired multifunctionality.Herein,we apply multi-edge X-ray absorption spectroscopy(extended X-ray absorption fine structure(EXAFS),Xray absorption near edge structure(XANES),and X-ray magnetic circular dichroism(XMCD))to probe the structural,electronic,and magnetic properties of all individual constituents in the single-phase face-centered cubic(fcc)-structured nanocrystalline thin film of Cr_(20)Mn_(26)Fe_(18)Co_(19)Ni_(17)(at.%)high-entropy alloy on the local scale.The local crystallographic ordering and componentdependent lattice displacements were explored within the reverse Monte Carlo approach applied to EXAFS spectra collected at the K absorption edges of several constituents at room temperature.A homogeneous short-range fcc atomic environment around the absorbers of each type with very similar statistically averaged interatomic distances(2.54-2.55Å)to their nearest-neighbors and enlarged structural relaxations of Cr atoms were revealed.XANES and XMCD spectra collected at the L2,3 absorption edges of all principal components at low temperature from the oxidized and in situ cleaned surfaces were used to probe the oxidation states,the changes in the electronic structure,and magnetic behavior of all constituents at the surface and in the sub-surface volume of the film.The spin and orbital magnetic moments of Fe,Co,and Ni components were quantitatively evaluated.The presence of magnetic phase transitions and the co-existence of different magnetic phases were uncovered by conventional magnetometry in a broad temperature range.

钛硅复合氧化物局域结构的研究

用 XAFS(X-ray absorption fine structure)分析了由溶胶-凝胶、液相浸渍和化学气相沉积等三种方法制备的二氧化钛和二氧化硅复合氧化物的 Ti K 边结构．结果表明：溶胶-凝胶法制得的复合氯化物中的钛分散很好，液相浸渍法次之，而化学气相沉积法最差，不论哪种方法，随钛含量(或钛硅原子比)的增加，边前特征峰 A2降低，钛的第一配位层 Ti-O 的配位数和键长增加；在复合载体中既有钛中心对称的八面体6配位 TiO_6的结构也有钛中心对称性差的四面体4配位 TiO_4或五面体5配位结构，并且随钛含量增加，钛的局域结构越来越接近锐钛矿型二氧化钛，根据 XAFS、XRD、IR 表征结果，提出了钛硅复合氧化物模型。

X射线吸收精细结构光谱在土壤中的应用

由于X射线吸收精细结构（X—rayabsorption fine structure，XAFS）可以原位探测吸收原子的2～3个邻近配位壳层，获得目标元素的电子结构信息和化学结构信息，所以XAFS已成为微观领域最重要的结构分析工具，丰富了我们对元素的重要化学性质和反应过程的认识。本文简述了XAFS的基本原理，探讨了样品制备、测试及数据分析等过程需关注的问题，重点综述了应用XAFS研究土壤重金属和营养元素的形态、土壤固一液界面的反应过程和机理，并指出其应用的局限性和未来发展的前景，旨在推动我国XAFS在土壤科学中的应用。由于土壤中界面反应的复杂性，XAFS应结合其他结构分析技术，结构分析技术应结合宏观数据和计算机模拟，土壤学应与其他学科交叉、融合，只有这样，才有可能在时间和空间尺度上阐明土壤组分在环境界面上的复杂反应过程和机理。

机械合金化Fe_(0.6)Ni_(0.4)体系的结构研究

利用XAFS(X射线吸收精细结构)和XRD(X射线衍射)方法研究了机械合金化Fe_(0.6)Ni_(0.4)系统在制备过程中的晶体结构和Fe原子的局域配位环境。结果表明,球磨5h,样品中Fe、Ni原子开始产生合金化,但仍然为bcc和fcc混合的两种物相;球磨10h后,bcc结构Fe的特征配位峰消失,转化为fcc结构,随着球磨时间的增加,配位无序度逐渐增大;球磨40h后,Fe原子的近邻结构又有新的变化,是由多种物态组成的混合物。

高能球磨对纳米Fe_(60)Ni_(40)系统微结构的影响

利用XRD(X射线衍射)和XAFS(X射线吸收精细结构),研究了机械合金化Fe60Ni40二元金属合金的微结构随球磨时间的变化情况.结果表明:球磨5h,αFe和金属Ni的混合物开始形成合金,样品保持原来的bcc和fcc结构;球磨20h,αFe的特征配位峰完全消失,样品为比较均匀的fcc结构的固溶体;球磨时间增至40h时,Fe原子的近邻结构又有了新的变化,是由多种物态组成的复相固溶体.用柯西公式计算的结果表明:随着球磨时间的增加,晶粒不断细化,晶格畸变加剧,Ni相的晶格常数与Fe60Ni40合金的物相同步变化.这说明机械合金化过程中,晶格畸变引起的晶格常数的变化是相变的重要因素.

共掺杂(Cr,Cu,Li)调控Co原子在Co掺杂的ZnO磁性半导体中的分布

利用X射线吸收谱(XAFS)和X射线光电子能谱(XPS)等技术研究了共掺杂原子(Li,Cu,Cr)对Co原子在Co掺杂ZnO薄膜中分布形式的影响.在共掺杂前,Co原子以替代Zn原子的替代位和金属Co团簇两种形式存在.共掺杂Cr原子后,样品中的Co团簇消失,掺杂的Co原子只以替代位的形式分布在ZnO基体中.与之相反,共掺杂Cu(Li)原子后,样品中的Co团簇含量显著增加.进一步分析表明,共掺杂的Cr原子与Cu(Li)对Co原子分布形式具有截然不同的调控作用是与共掺杂原子在ZnO基体中的空间占位特点密切相关.

X射线吸收谱精细结构分析的理论探讨(英文)

EXAFS是研究多元物质中任一组元临近结构的有效手段。本文在分析EXAFS的物理机制的基础上 ,对X射线吸收精细结构分析的方法和手段进行了深入的理论上的研究及探讨 。