同步辐射吸收谱学基础.pptx

1、同步辐射X射线吸收谱学基础,中国农业大学 齐孟文,1.同步辐射synchrotron radiation 速度接近光速的带电粒子在磁场中沿弧形轨道运动时沿切线方向发出的电磁辐射，由于最初是在同步加速器上观察到的，所以被称为同步辐射 。,基本特性 高亮度 辐射功率和功率密度级高功，第三代同步辐射光源的亮度是X光机的上亿倍。 宽波段 覆盖从远红外 、可见光、紫外直到X射线范围内的连续光谱，根据需要可方便获得特定的单色光。 脉冲光 具有优良的脉冲时域结构，脉冲宽度在10-1110-8 秒之间可调，对动态研究特别有利。 高准直 辐射在以电子运动方向为中心的一个很窄的圆锥内，张角非常小，几乎是平行光束。

2、,高偏振：在电子轨道平面内是完全偏振光，轨道上下是椭圆椭偏振光，从特殊设计的插件可以得到任意偏振的光。 精确性 光通量、角分布和能谱等均可精确计算，因此它可以作为辐射计量的标准光源。 其他特性：高度稳定性、高通量、微束径、准相干等。,同步辐射技术和方法,广谱可调 量度极高 相干性好 准直性好,谱学 能量分辨 散射 动量分辨 成像 位置分辨 动态 时间分辨,用于在原子水平研究物质分子结构和性质的有利工具,2.X射线吸收谱学2.1基础知识,X射线吸收宏观现象 其中， 是线性吸收系数，与样品密度（），原子序数（Z），原子质量（A），X射线能量相关（E）： 当元素确定，（E）E ，为一条单调下降的曲线

3、，可用Victoreen公式描述： 值在原子内壳层K,L能级 处，发生突跳，叫作吸收边。,X射线吸收的微观过程,XAFS数据区域的特征及分析,XAFS数据处理的基本流程 充分理解E空间、K空间、R空间三者之间的联系和转换关系是掌握XAFS数据处理的关键。 E-k换公式 这里，E0是吸收边的能量，m是电子的质量，K为波矢量=2/。 Fourier变换公式,E空间,K空间,R空间,(a) X-ray absorption coefficient (E)/ (where is the sample density) as a function of the incident X-ray energy

4、 E, in the 130 keV range, for a selection of elementscommonly found in coordination compounds (E)/ can be approximately expressed as: (E)/ Z4/AE3, where Z the atomic number and A the atomic mass of the elementof interest). In particular, (E)/ is reported for three “light” atoms, i.e. H (Z = 1), O (Z

5、 = 8), and S (Z = 16) and three metals belonging to the 1st, 2nd and 3rd row of the transitionmetal series, i.e. Fe (Z = 26), Ru (Z = 44), and Os (Z = 76). The X-ray absorption edges encountered in the reported range are indicated for each element. Data obtained from NIST:/Phys

6、RefData/XrayMassCoef/tab3.html. Note the logarithmic scale of the ordinate axis. (b) Schematic representation of a typical experimental setup forXAS measurements: I0, I1, and I2are ionization chambers, If indicates a fluorescence detector. (c) Molecular model of the complex Ru(bpy)2(AP)22+(bpy = 2-2

7、-bipyridyne;AP = 4-amminopyridine). Atom colour code: Ru, pink; N, blue; C, grey; H, white. (d) Ru K-edge XAS spectrum (black thick line) for the Ru(bpy)2(AP)22+complex shown in part(c), in water solution (10 mM concentration), collected in transmission mode at the BM29 beamline of the European Sync

8、hrotron Radiation Facility (ESRF, Grenoble, France)396. In the figure are also reported: pre-edge (blue) and post-edge (green) lines (obtained by fitting the experimental data with two polynomial functions in suitable pre-and post-edge energy intervals) required to estimate the edge-jump (E0) for no

9、rmalization of the raw spectrum; atomic-like background 0(E) (pink solid line), employedin the extraction of the EXAFS oscillations, see part (e). (e) Normalized XAS signal for Ru(bpy)2(AP)22+obtained from the raw data reported in part (d). The inset shows theextracted k2-weighted k2(k) EXAFS functi

10、on obtained by subtracting the absorption signal expected for an isolated atom, labelled as 0(E) in part (d), and converting the E-values in k-values using the expression k = (1/h ) 2me(E E0)1/2. (f) R-space EXAFS spectra obtained by calculating the FT of the k2(k) spectrum reported in the inset ofp

11、art (e) in the 216A1 k-range; both modulus (top part) and imaginary part (bottom part) of the FT are reported. Unpublished figure, reporting data published in Ref. 396.,1）Pd-doped perovskite: An effective catalyst for removal of NOx from lean-burn exhausts with high sulfur resistance， acs catal. 201

12、3, 3, 10711075,2.2分析举例,智能型催化剂，Pb掺杂的催化剂La0.7Sr0.3CoO3，在贫/富油活塞燃烧循环过程的种态变化，在贫油燃烧时，不影响其催化剂原有的氧化和吸附NO3-的特性，而在富油燃烧阶段，表层和次表层的金属Pb被碳烃化合物还为零价Pd0，协同催化第一阶段储存的NOX还原为N2，最终无害化减排。,RSFs of the fresh Pd0.03 sample (solid line); the Pd0.03 sample treated upon 500 ppm NO/6.7% O2 at 3250C for 1 h (dashed line); the Pd0

13、.03 sample treated upon 500 ppmNO/0.1% C3H6 at 325 C for 1 h (dotted line); and standard Pd foil(dasheddotted line).,2）X-ray Absorption near Edge Structure and Extended X-ray Absorption Fine Structure Analysis of Fe(II) Aqueous and Acetone Solutions， J. Phys. Chem. A 2011, 115, 1342013424,目的：发现Fe（）的

14、丙酮液较水溶液电镀效果好，因此研究其在两种溶液中的原子邻域结构。 处理： Table 1. Composition of Examined Solutions,Figure 1. Normalized K-edge absorption spectra of Fe(II) in wateracetone solutions. The inset shows enlarged pre-edge region.,Figure 2. Top panels: best fit of EXAFS (k) 3 k spectra at the Fe K-edge of Fe(II) ion in solu

15、tions 13, respectively. Bottom panels: FT of the experimental data (dotted line) and total theoretical signals (full line).,3）Synthesis, Characterization, and Computation of Catalysts at the Center for Atomic-Level Catalyst Design，J. Phys. Chem. C 2014, 118, 2004320069,Figure . Schematic representat

16、ion of the changes in the physical characteristics of catalysts in the course of time keeping in tune with advances made in techniques developed for their synthesis.,EXAFS Combined with a Millifluidic Chip to StudyGold Nanostructure Growth,图解：上图左边多流芯片反应器，右边为为时间分辨TEM影像和XAS进程分析。反应物由各自通道引入，做层流运动，在交互面处发

17、生反应，在驻留17S后形成AuxSy-纳米结构，然后通入NaBH4，结构随时间样见右边图示，比较图中的（e）和（f），发现通入NaBH4，纳米的结构形态不变，但由化学上已有主要的硫化金种态转变为金纳米粒子。,4） Controls on the Valence Species of Arsenic in Tobacco Smoke:XANES Investigation with Implications for Health and Regulation， Environ. Sci. Technol. 2014, 48, 34493456,Figure . XANES spectra for

18、 inorganic reference compounds. Gray bands are centered on the first derivative maxima in As2O3 and As2O5, taken to indicate the edge energies of inorganically bound As(III) and As(V), respectively, Error is typically 0.25 eV,5）Direct Determination of Cadmium Speciation in Municipal Solid WasteFly A

19、shes by Synchrotron Radiation Induced -X-ray Fluorescence and -X-ray Absorption Spectroscopy，Environ. Sci. Technol. 2002, 36, 3165-3169,FIGURE . -XRF maps of various elements obtained from particle 9 (diameter ca. 160 m), showing self-absorption of the light elements.Imagine size: 20 20 pixels, pixe

20、l size: 10 8, spectrum collection time per pixel: 6 s. Darker tones indicate a higher elemental abundance; light tones indicate lower concentrations. -XAS in the 26.65-26.95 keV range was performed on a (HxV) 312 m2 micro-area containing the highest concentration of Cd (“hot spot 9a”).,6）Subcellular

21、 Speciation Analysis of Trace Element Oxidation States Using Synchrotron Radiation Micro-X-ray Absorption Near-Edge Structure，Anal. Chem. 2007, 79, 7353-7359,Figure.The X-ray beam produced by the synchrotron facility is focused down to 1.5 m vertical and 4.0m horizontal sizes over the 6-18 keV range

22、. A video microscope is used to localize the subcellular compartments to be analyzed. An ionization chamber measures incoming radiation intensity (I0), whilea Si(Li) detector measures the emitted X-ray fluorescence (If). X-ray fluorescence is used both to image chemical elements in cells and to perf

23、orm XANES.,Figure 4. (A) XANES spectra of iron(II) reference compound (Fe(II), the cytosol (Dried-C) and the nucleus (Dried-N) of a freeze-dried cell analyzed at room temperature, the cytosol (Cryo-C) and nucleus (Cryo-N) of a frozen hydrated cell analyzed at -100 C, and of iron(III) reference compo

24、und (Fe(III). The dotted lines represent iron(II) and iron(III) first-derivative edge positions, respectively, at 7122.9 and 7128.7 eV. (B) Bright-field microscopy of a freeze-dried cell as observed prior to micro-XANES experiment. The cellular compartments are easily identified; analyzed zones are

25、indicated by an arrow (C, cytosol; N, nucleus). The corresponding spectra are presented in panel A.,3.SR-X射线光电子谱,通过测定同步辐射与物质作用，因光电效应产生的光电子的能谱，对物质特定的原子/分子的电子结构，以及由此产生的几何结构进行分析的谱学。发射的光电子的动能为： 其中，h是入射X射线光子的能量， 是原子第i层轨道电子的结合能。,(a) Performing XPSmeasurements using a variable incident X-ray source such as

26、 a synchrotron provides the additional benefits of being able to access deeper lying core levels and the ability to control the surface sensitivity, or probe depth, of the experiment.,在低能入射光时，如b）200eV以下，因所产生光电子的非弹性碰撞平均自由程较短，其信号主要来自样品的表层；在高能入射光时，如b）600eV，则信号对容积灵敏的。在SiO2中平均自由程对入射能量的关系曲线及相应的光电子动能窗见C）。,

27、A 50 um liquid microjet in operation at the Swiss Light Source. The direction of liquid flow is from top to bottom. The liquid is expanded at a velocity of 50 m/s into the measurement chamber through a micron sized quartz nozzle. The liquid filament is then irradiated with X-rays before being caught

28、 by the catcher and removed from the measurement chamber. (Right) The liquid microjet, incident photons, and the electron detection axis are all normal to one another.,4.SR-X射线荧光分析,基本原理,SR,e-,h,Synchrotron radiation micro-X-ray fluorescence analysis:a tool to increase accuracy in microscopic analysis，Nuclear Instruments and Methods in Physics Research B 199 (2003) 375381,同步辐射与射线微束技术结合，产生的显微X-射线荧光分析，主要用作认证方法或作为其他方法的基准校正手段。由于荧光光子在探测介质中的传输过程，可用