X-ray Absorption Fine Structure Method Research Articles

Demonstration of Sensitivity of the Total-Electron-Yield Extended X-ray Absorption Fine Structure Method on Plastic Deformation of the Surface Layer

X-ray Absorption Fine Structure Spectroscopy (XAFS) has proven instrumental for the study of atomic-scale structures across diverse materials. This study conducts a meticulous comparative analysis between total electron yield (TEY) and absorption coefficients at the K absorption edge of polycrystalline Fe and Zr60Cu20Fe20 alloy. Our findings not only highlight differences between TEY and transmission XAFS measurements but also demonstrate the capabilities and limitations inherent in these measurement modes within the context of XAFS. This article provides an experimental exploration of widely used X-ray absorption spectroscopy methods, shedding light on the nuances of TEY and transmission XAFS. Through presenting experimental results, we aim to offer insights crucial to the material science community, guiding experimentalists in optimizing measurements while raising awareness about potential misinterpretations.

Gangue Source Reduction Technology and Process Optimization Based on Underground Coal Gangue Photoelectric Separation

The precise identification of damp, sticky coal gangue; efficient jet nozzle separation; and process layout in a narrow, restricted space are essential technologies for gangue source reduction based on underground gangue photoelectric separation, which is critical for the long-term growth of coal mines. In this paper, the X-ray absorption fine structure (XAFS) method was used to identify the X-ray absorption law of different atoms in coal-based minerals and explore the differences in the microscopic crystal properties of coal gangue; the numerical simulation calculation of four commonly used nozzles—namely, flat, convergent, flat–convergent, and streamline—was carried out using Fluent software for coal gangue jet separation to optimize the nozzle morphology and parameters. The technical characteristics of the underground layout of the photoelectric separation system for coal gangue were expounded, and the technological layout of the separation system was explored. The results showed that the absorption coefficients μ(E) of Al and Si atoms in minerals to X-rays are significantly different, and the XAFS method has the ability to identify coal, gangue, and other minerals. The streamlined nozzle has a long jet core area, slow decay of jet velocity, low gas consumption per unit time, and better performance than the other three types of nozzles. Based on the development and mining system of the Renjiazhuang Coal Mine, three kinds of photoelectric separation system layout schemes of coal gangue were designed, namely centralized layout, distributed layout, and mobile layout. The advantages and disadvantages of each scheme were compared, which enriched the technical means of gangue source reduction.

Tracking the Local Structure Change during the Photoabsorption Processes of Photocatalysts by the Ultrafast Pump-Probe XAFS Method

The birth of synchrotron radiation (SR) facilities and X-ray free electron lasers (XFELs) has led to the development of new characterization tools that use X-rays and opened frontiers in science and technology. Ultrafast X-ray absorption fine structure (XAFS) spectroscopy for photocatalysts is one such significant research technique. Although carrier behavior in photocatalysts has been discussed in terms of the band theory and their energy levels in reciprocal space (k-space) based on optical spectroscopic results, it has rarely been discussed where photocarriers are located in real-space (r-space) based on direct observation of the excited states. XAFS provides information on the local electronic and geometrical structures around an X-ray-absorbing atom and can address photocarrier dynamics in the r-space observed from the X-ray-absorbing atom. In this article, we discuss the time dependent structure change of tungsten trioxide (WO3) and bismuth vanadate (BiVO4) photocatalysts studied by the ultrafast pump-probe XAFS method in the femtosecond to nanosecond time scale with the Photon Factory Advanced Ring (PF-AR) and the SPring-8 Angstrom Compact free-electron LAser (SACLA). WO3 shows a femtosecond decay process of photoexcited electrons followed by a structural change to a metastable state with a hundred picosecond speed, which is relaxed to the ground-state structure with a nanosecond time constant. The Bi L3 edge of BiVO4 shows little contribution of the Bi 6s electron to the photoabsorption process; however, it is sensitive to the structural change induced by the photoexcited electron. Time-resolved XAFS measurements in a wide range time domain and with varied wavelengths of the excitation pump laser facilitate understanding of the overall details regarding the photocarrier dynamics that have a significant influence on the photocatalytic performance.

XAFS Applications on Polymers and Related Materials

polymer materials are a class of materials of great importance for their peculiar chemical-physical properties. The basic principles of X-ray absorption fine structure (XAFS) which is promoted by synchrotron radiation, including extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES) were introduced. Various XAFS methods were reviewed for applications in studies of polymers and related materials, including usual polymers, organometallic polymers, Pd-droped polymers, ionomers, carbon based materials, etc. These mentioned applications have showed the significance and advantage of XAFS in polymers and related materials field. It is confident that the promotion and growth in XAFS would bring more benefits in scientific research of polymers.

Application of X-ray Absorption Fine Structure Method for the Quantitative Analysis of Hexavalent Chromium in Chromate Conversion Coating and Plastic

The X-ray absorption fine structure method was applied for the quantitative analysis of hexavalent Cr in electronic products. The pre-edge peak intensity of the Cr K-edge increased according to the hexavalent Cr amount, and the hexavalent Cr ratio was calculated quantitatively by using the intensity. By combining with inductively coupled plasma atomic emission spectroscopy measurement results that gave the total Cr amount, the absolute amount of hexavalent Cr in chromate conversion coating and plastic samples could be evaluated. The results obtained by this method were in good agreement with those obtained by the chemical analysis method. This method can be successfully applied for the determination of hexavalent Cr amount in electronic products such as chromate conversion coating and plastic.

Local structure in Cu2ZnSnS4 studied by the XAFS method

The local structure in kesterite Cu2ZnSnS4 is studied by the X-ray absorption fine structure (XAFS) method. Absorption at the K-edge of all three cations: Cu, Zn and Sn has been measured and analyzed. Interatomic distances determined from the EXAFS data are in keeping with the existing X-ray diffraction values. Both, the XANES and EXAFS data at the Sn K-edge indicate that tin exists in the +IV oxidation state and predominantly occupies its native sites in Cu2ZnSnS4.

回折法と X 線吸収分光(XAFS)法を用いた地球惑星物質の精密構造解析

Advantage of mineralogical approach in clarifying peculiar physical properties for materials is introduc in the review. Precise structure analyses of the diffraction and X?ray absorption fine structure (XAFS) spectroscopy methods provide the important information on the Earth and planetary materials. The information from both long-range-order structure by diffraction method and local structure by XAFS method is important for the understanding of the correlation between structures and physical properties of minerals. High pressure and high temperature in-situ diffraction and XAFS experiments were performed using a multi-anvil high-pressure device and synchrotron radiation. Both experiments are also useful as a probe of vibration dynamics and disordered structure. The pressure-dependent anharmonic effective potentials and characteristic values can be investigated using the diffraction and XAFS Debye-Waller factors. The ionic conduction mechanism has been proposed based on the effective one-particle potential and effective pair potential. Super ionic conduction of the mantle constituents resulting from anharmonic thermal vibration can produce the high electric and the low thermal conductivities in the Earth's lower mantle. Local structures of atoms in melt and glass of tetrahedrally coordinated materials change rapidly to higher coordinated states with pressure as if first-order phase transition. Unique structures are left in the local structures of the trace elements in minerals and tektite-impactite glass. The application of recently innovated techniques to the characterization of materials under extreme conditions contributes to the advancement of fundamental Earth-scientific knowledge.

Local structure of magnetite and maghemite and chemical shift in Fe K-edge XANES

Local structures around Fe and chemical shifts in X-ray absorption fine structure (XAFS) spectra were investigated for synthetic Fe1-dO, Fe3O4 (magnetite), γ-Fe2O3(maghemite), and SrFeO3-e, as well as natural Fe3O4 and α-Fe2O3 (hematite) specimens. XAFS spectra near the Fe K-edge were measured at BL-9C and BL-12C of the Photon Factory, KEK, Japan. Similar measurements for Fe-N pairs in Fe nitrides (FeN, Fe2N, Fe4N) were obtained for comparison. The X-ray absorption near edge structure (XANES) spectra for various iron compounds, in particular Fe3O4 and γ-Fe2O3, and FexN specimens, showed clear chemical shifts of half-maximum positions with the changing oxidation states of the Fe ions in their structures. The energy at half maximum position should be used for the quantitative discussion of the oxidation and valence states of the Fe ion in Fe compounds rather than the threshold energy E0 found using differentiating XAFS spectra. The δ values in Fe3-δO4 (δ=0.333 for end-member γ-Fe2O3) for magnetite and maghemite were estimated by the extent of the chemical shifts. Decreases in the average Fe-O distances and extended X-ray absorption fine structure (EXAFS) Debye-Waller factor σ2 values for spinel-type Fe3-δO4 solid-solutions were consistent with the estimated δ values. The error in proving the Fe3+/Fetotal ratio in the system by the XAFS method would appear to be less than ±0.10, and higher reliability than this value would be acquired in the comparison of relative values at half-maximum positions.

Investigation on the stability of water-soluble ZnO quantum dots in KB cells by X-ray fluorescence and absorption methods

The structural stability of water-soluble ZnO quantum dots (QDs) in oral epidermoid carcinoma (KB) cells was studied by the External Micro Proton Induced X-ray Emission (External Micro-PIXE) technique and the X-ray absorption fine structure (XAFS) measurement. The External Micro-PIXE and XAFS experiments were respectively performed at the JAEA and the Shanghai Synchrotron Radiation Facility. The elements’ distributions were detected by the External Micro-PIXE technique. The XAFS method was applied to obtain information about zinc (Zn) K-edge spectra. The fits of the XAFS data showed that the Zn–O bond structure of water-soluble ZnO QDs was stable after being absorbed by KB cells. Its local structural parameters were almost identical with those of the standard wurtzite structure. Water-soluble ZnO QDs had good structural stability in KB cells.

Innovations in X-ray-induced electron emission spectroscopy (XIEES)

Currently, a pressing need has arisen for controlling the local atomic and electron structure of materials irrespective of their aggregate state. Efficient approaches to the studies of short-range order are based on phenomena accompanied by interference of secondary electrons excited by primary X-ray radiation. The set of such approaches are commonly referred to as the X-ray absorption fine structure (XAFS) methods. In reality, the XAFS methods are based on the use of synchrotron radiation and applied to structural studies in two modes of measurements, transmission analysis and recording of secondary effects. Only two such effects-specifically, the X-ray fluorescence an d X-ray-induced electron emission effect—are commonly discussed. Access to synchrotron accelerators is problematic for most researchers, so a demand is created for designing laboratory systems that make direct access possible. Since the power of laboratory systems is much lower than that of synchrotrons, it is essential to use much more efficient detectors of secondary electrons. In addition, it is of interest to analyze energy characteristics with a high spatial resolution. Channel multipliers and multichannel boards are incapable of providing such a possibility. For this reason, an improved electron detector has been developed to analyze the photoemission effect in an accelerating field.

Local atomic order in Al-based metallic glasses studied using XAFS method

Abstract Local atomic order in series of Al–(Y, Sm)–TM (TM = transition metal: Co, Ni) amorphous, melt-spun alloys was investigated by Sm L 3 -edge and TM K-edge X-ray absorption fine structure (XAFS) method. The evaluated coordination number of Sm is approximately 16 for all investigated systems and TM coordination ranges form 5 to 6. A slight decrease in TM coordination along with increase of TM content is observed. The interatomic distances between Al and Sm atoms are equal to the sum of their metallic radii within the experimental error, while Al–TM bonds are shortened by 10 % . The structural disorder around Sm atoms is significantly higher then around TM. We have found that only Al atoms are present in the first coordination shell of both Sm and TM species. The XAFS data show that the amorphous network coherency is lost at distances exceeding 4 A. The results are discussed in a framework of Miracle’s structural model of metallic glasses suggesting that the average local structure around Sm atoms consists of 16 efficiently packed Al atoms in the first coordination shell of Sm and the TM atoms occupy the octahedral sites in the closely packed fcc cluster structure.

Polarized total-reflection x-ray absorption fine structure for self-assembled monolayer of zinc porphyrin at air–water interface

A new x-ray absorption fine structure (XAFS) method is applied to the air–solution interface. Under the total reflection condition, the XAFS method becomes surface sensitive, enabling the self-assembled monolayer of a metal complex at the solution surface to analyze in situ. Furthermore the introduction of two types of linearly polarized x rays allows us to determine the selective orientation of a planar metal complex at the surface. We obtain spectra for a square planar complex, 5,10,15,20-tetrakis(4-carboxyphenyl)porphyrinato zinc(II) (ZnTPPC) adsorbed on the aqueous solution surface forming a monolayer with two polarized x rays and compared them with spectra of the same compound in a bulk solution and in solid powder. The polarized XAFS spectra exhibit different features leading to the unambiguous conclusion that the plane of the ZnTPPC molecule is oriented parallel to the air–water interface and that there is no coordination to the axial sites of the zinc atom.

Distribution of trace elements in selected pulverized coals as a function of particle size and density

Trace elements in coal have diverse modes of occurrence that will greatly influence their behavior in many coal utilization processes. Mode of occurrence is important in determining the partitioning during coal cleaning by conventional processes, the susceptibility to oxidation upon exposure to air, as well as the changes in physical properties upon heating. In this study, three complementary methods were used to determine the concentrations and chemical states of trace elements in pulverized samples of four US coals: Pittsburgh, Illinois No. 6, Elkhorn and Hazard, and Wyodak coals. Neutron Activation Analysis (NAA) was used to measure the absolute concentration of elements in the parent coals and in the size- and density-fractionated samples. Chemical leaching and X-ray absorption fine structure (XAFS) spectroscopy were used to provide information on the form of occurrence of an element in the parent coals. The composition differences between size-segregated coal samples of different density mainly reflect the large density difference between minerals, especially pyrite, and the organic portion of the coal. The heavy density fractions are therefore enriched in pyrite and the elements associated with pyrite, as also shown by the leaching and XAFS methods. Nearly all the As is associated with pyrite in the three bituminous coals studied. The sub-bituminous coal has a very low content of pyrite and arsenic; in this coal arsenic appears to be primarily organically associated. Selenium is mainly associated with pyrite in the bituminous coal samples. In two bituminous coal samples, zinc is mostly in the form of ZnS or associated with pyrite, whereas it appears to be associated with other minerals in the other two coals. Zinc is also the only trace element studied that is significantly more concentrated in the smaller (45 to 63 μm) coal particles.