Extinction correction and synchrotron radiation

The primary extinction factor y_p is defined as the ratio of the integrated reflection from a coherently diffracting domain to the integrated kinematical reflection from the same domain. When y_p is larger than 0.5 it may be approximated by y_p = exp{−(αδ)2}, where α is about 0.5 andδ the average size of the coherent domain when measured in units of the extinction length A,δ = D/λ. Transfer equations are applied to symmetrical Laue diffraction, and the reflectivity per unit length, Σ(ε) is solved from the measured reflecting ratio as a function of the rocking angleε =θ− θ_B. Measurements with conventional x-ray sources are made on single crystal slabs of Be and Si using AgKΒ, MoKα₁ and CuKα radiation. The primary extinction factor y_p(ε) is solved from a point-by-point comparison of two measurements where the extinction length λ is changed by varying the polarization and/or wavelength of the x-ray beam. The results show that primary and secondary extinction are strongly correlated, and that the customary assumption of independent size and orientation distributions of crystal mosaics is unjustified. The structure factors for Be and Si show close agreement with other recent measurements and calculations. The limitations of the method are discussed in length, particularly the effects of beam divergences and incoherence of the rays in the crystal. It is concluded that under typical experimental conditions the requirements of the theory are met. Practical limitations arising from the use of characteristic wavelengths and unpolarized radiation prohibit the use of the full potential of the method. The properties of a synchrotron radiation source are compared with a conventional x-ray source, and it is demonstrated that the experimental limitations can be removed by the use of synchrotron radiation. A diffraction experiment with synchrotron radiation is outlined, as well as generalization of the method to small spherical crystals.     

Applications of synchrotron radiation in forensic trace evidence analysis

Synchrotron radiation sources have proven to be highly beneficial in many fields of research for the characterization of materials. However, only a very limited proportion of studies have been conducted by the forensic science community. This is an area in which the analytical benefits provided by synchrotron sources could prove to be very important. This review summarises the applications found for synchrotron radiation in a forensic trace evidence context as well as other areas of research that strive for similar analytical scrutiny and/or are applied to similar sample materials. The benefits of synchrotron radiation are discussed in relation to common infrared, X-ray fluorescence, tomographic and briefly, X-ray diffraction and scattering techniques. In addition, X-ray absorption fine structure analysis (incorporating XANES and EXAFS) is highlighted as an area in which significant contributions into the characterization of materials can be obtained. The implications of increased spatial resolution on microheterogeneity are also considered and discussed.     

Non-destructive depth profile analysis using synchrotron radiation excited XPS

We have used synchrotron radiation as excitation source in an X-ray photoelectron spectroscopy (XPS) experiment to analyse surface-near element depth profiles non-dectructively. By tuning the photon energy one can vary the kinetic energy of the photoelectrons and in turn the information depth of the measurement. To quantify the sample geometry (e.g. layer thicknesses) model calculations similar as for angle-resolved XPS (ARXPS) measurements are necessary. We have successfully applied this technique to several samples. We will show how to calculate the relative intensities of the peaks, using photoionization cross sections and an experimentally determined analyzer transmission function and the procedure to quantify the geometry for a model sample: natively oxidized Ta covered by carbon contamination. At Sn-doped indium oxide samples we found a sub-monolayer of segregated Sn at the surface which was expected from previous investigations.     

Applications of synchrotron radiation micro-focus techniques to the study of polymer and biopolymer fibers

Micro-X-ray diffraction using synchrotron radiation has been developed in recent years as a tool for the local analysis of bulk polymer and biopolymer samples. Developments in X-ray optics associated with the introduction of third generation synchrotron radiation sources now allow routine experiments at the 1 μm scale. Several experiments at the 100 nm scale have also been reported with future developments aiming for the 50 nm scale and smaller. In this review, the current state of experimental possibilities have been summarised with an emphasis on in-situ fiber scanning and deformation studies. Examples of unconventional in-situ studies such as microhardness testing or hydration by inkjet printing systems demonstrate the largely unexplored potential of micro-X-ray diffraction techniques.     

Local structural analysis of In-doped Bi2Se3 topological insulator using X-ray fluorescence holography

We performed X-ray fluorescence holography measurements on an In-doped Bi₂Se₃ topological insulator and obtained an in-plane atomic image in the vicinity of In. We found that atomic images at the positions of the first nearest neighbors (NNs) are very weak whereas those at the positions of the second and the third NNs are relatively strong. On the basis of the fact that In is half of the atomic number of Bi, we attributed the origin of this feature to the clustering of the In atoms in the Bi plane. We calculated the intensity of the atomic images and confirmed that the formation of In cluster results in a decrease by 30% in the first NN atomic image intensity. However, the decrease in the magnitude is not enough to explain the experimental results, suggesting another contribution such as the lattice distortions. The effect of the lattice distortion on the atomic image intensity is discussed on the basis of the simulation including the positional fluctuation of In atoms.     

Analysis of low Z elements on Si wafer surfaces with synchrotron radiation induced total reflection X-ray fluorescence at SSRL, Beamline 3-3: comparison of droplets with spin coated wafers

The unique properties of synchrotron radiation, such as high incident flux combined with low divergence, its linear polarization and energy tunability, make it an ideal excitation source for total reflection X-ray fluorescence (TXRF) spectroscopy in order to non-destructively detect trace impurities of transition metals on Si wafer surfaces. When used with a detector suitable for the determination of low energy radiation this technique can be extended to the detection of low-Z elements, such as Al, Na and Mg. Experiments have been performed at SSRL Beamline 3-3, a bending magnet beamline using monochromatic radiation from a double multilayer monochromator. The wafer was mounted vertically in front of the detector, which was aligned along the linear polarization vector of the incoming synchrotron radiation. This configuration allows the detector to accept a large solid angle as well as to take advantage of the reduced scattered X-ray intensity emitted in the direction of the linear polarization vector. A comparison between droplet samples and spin coated samples was done, in order to compare the capabilities of vapor phase decomposition (VPD-TXRF) with conventional SR-straight-TXRF. Detection limits in the range of 50 fg corresponding to 2E10 atoms/cm² have been obtained for Na. The spin coated samples, prepared from solutions containing an equal amount of Na, Mg and Al showed an unexpected result when performing a scan of the angle of incidence of the incoming X-rays suggesting a different adsorption behavior of the elements in a multielement solution on the wafer surface. The observation of this behavior is important because the spin coating technique is the standard method for the preparation of surface standards in semiconductor quality control. This effect could be characteristic of the Na, Mg, Al solution used, but the angle dependence of the fluorescence signal of a standard should always be investigated before using the standard for calibration of the apparatus and quantification.     

Trace elements in human cancerous and healthy tissues: A comparative study by EDXRF,TXRF, synchrotron radiation and PIXE

It is known that trace elements play an important role in a number of biological processes. These include the activation or inhibition of enzymatic reactions, competition between elements and metal proteins for binding positions and modifications in the permeability of cellular membranes. These elements may also influence carcinogenic processes, thus the knowledge of trace element concentrations in healthy and neoplastic tissues might help in diagnostic and in the etiology and development of cancer.     

Evaluation of zirconium as a permanent chemical modifier using synchrotron radiation and imaging techniques for lithium determination in sediment slurry samples by ET AAS

In the present paper, lithium was determined in river sediment using slurry sampling and electrothermal atomic absorption spectrometry (ET AAS) after L’vov platform coating with zirconium (as a permanent chemical modifier). The performance of this modifier and its distribution on the L’vov platform after different heating cycles were evaluated using synchrotron radiation X-ray fluorescence (SRXRF) and imaging scanning electron microscopy (SEM) techniques. The analytical conditions for lithium determination in river sediment slurries were also investigated and the best conditions were obtained employing 1300 and 2300 °C for pyrolysis and atomization temperatures, respectively. In addition, 100 mg of sediment samples were prepared using 4.0 mol l⁻¹ HNO₃. The Zr-coating permitted lithium determination with good precision and accuracy after 480 heating cycles using the same platform for slurry samples. The sediment samples were collected from five different points of the Cachoeira river, São Paulo, Brazil. The detection and quantification limits were, respectively, 0.07 and 0.23 μg l⁻¹.     

Structural study of perovskite-type fine particles by synchrotron radiation powder diffraction

The crystal structures of BaTiO₃ and PbTiO₃ fine particles have been investigated by powder diffraction using synchrotron radiation high energy X-rays. It is revealed that a BaTiO₃ fine particle essentially consists of tetragonal and cubic structure components at 300 K, whereas a PbTiO₃ fine particle consists of a tetragonal structure. Adopting a structure model for the BaTiO₃ particle that a cubic shell covers a tetragonal core, the thickness of cubic BaTiO₃ shell is estimated at almost constant irrespective of particle sizes. Successive phase transitions are detected in 100 nm particles of BaTiO₃ near the phase-transition temperatures of a bulk crystal. The changes in diffraction profiles are small, but they are apparent for a most up-to-date powder diffractometry. This revised version was published online in August 2006 with corrections to the Cover Date.     

High-temperature studies of La1−x SrxFeO3−δ solid solutions using synchrotron radiation

A series of La_1?x Sr_xFeO_3?δ samples with a perovskite structure were investigated by high-temperature X-ray analysis using synchrotron radiation. In this series, one can observe a morphotropic phase transition (0.3 ? x ? 0.4) from the orthorhombic (0 ? x < 0.3) to cubic (0.4 < x ? 0.75) modification. The samples from the morphotropic transition region (MTR) at room temperature have a highly disordered microblock structure related to their phase heterogeneity; according to high-temperature X-ray analysis data, this is the result of particle stratification of the high-temperature homogeneous solid solution formed at the temperature of the synthesis (1200°C) in the course of cooling.     

Measurement of K-line transition rates for Ti, V, Cr, Mn, Fe and Co using synchrotron radiation

Transition rates were obtained from spectra for pure metallic samples of atomic number ranging from 22 to 27, measured with monochromatic incident X-ray beams from a synchrotron source. The experimental setup for this consisted of an energy dispersive spectrometer in a conventional 45–45° geometry, mounted in an evacuated chamber. Absorption, detector efficiency and multiple scattering were taken into account. The results obtained are compared with recent theoretical and experimental data as well as with the well-known theoretical predictions from Scofield.     

The interaction between atoms of Au and Cu with clean Si(1 1 1) surface: A study combining synchrotron radiation grazing incidence X-ray fluorescence analysis and theoretical calculations

In order to evaluate the interactions between Au/Cu atoms and clean Si(1 1 1) surface, we used synchrotron radiation grazing incidence X-ray fluorescence analysis and theoretical calculations. Optimized geometries and energies on different adsorption sites indicate that the binding energies at different adsorption sites are high, suggesting a strong interaction between metal atom and silicon surface. The Au atom showed higher interaction than Cu atom. The theoretical and experimental data showed good agreement.     

CH3I同步辐射光电离及生成焓、键能和质子亲合势的测定

在超声射流冷却条件下用VUV同步辐射研究了CH3I分子的光电离过程。测定了CH3I光电离及解离电离产生的CH3I^+, CH3^+和I^+的出现势, 结合已确认的热力学数据, 估算出体系中有关离子的标准生成焓、分子和分子离子的键能、自由基的质子亲合势及母体离子的解离能等数据。对CH3I分子VUV光解离电离通道进行了分析。     

Concept for a single-shot mid-infrared spectrometer using synchrotron radiation

Several attempts have been made to extend time-resolved mid infrared spectroscopy to higher time resolution. Such methods are either limited to specific samples that are cyclic and therefore allow the reaction under investigation to be repeated multiple times in the same manner, or they lack spectral resolution or sufficient signal-to noise ratio. Here, we report on a single-shot spectrometer concept which overcomes the aforementioned limitations utilizing fast linear detector arrays and highly brilliant infrared synchrotron radiation. The spectrometer may find applications, beside others, for the investigation of irreversible cascades of structural alterations in proteins.     

Experimental study on synchrotron radiation photoionization of secondary organic aerosol derived from styrene ozonolysis

Secondary organic aerosol (SOA) produced by ozonolysis of styrene and other alkene compounds is a major part of fine particles in urban atmospheres. The atmospheric ozonolysis process of styrene is simulated in a smog chamber, and the formed SOA particles are detected on-line by a synchronous radiation vacuum ultraviolet photoionization mass spectrometer (VUV-PIMS) in this study. Through molecular ion peaks in the photonionization mass spectra of SOA and the corresponding photoionization efficiency curve, combined with off-line measurement verification of ultraviolet visible and infrared absorption spectra, it is determined that formaldehyde, formic acid, benzene, phenol, benzaldehyde, and benzoic acid are the main constituents of styrene SOA. These provide new information for studying the atmospheric ozonolysis oxidation mechanism of styrene. VUV-PIMS can get over complicated sample preparation procedures, secondary pollution, and other shortcomings of the off-line method and is a useful instrument to measure constituents and unveil the formation process of SOA particles.     

Taking snapshots of photoexcited molecules in disordered media by using pulsed synchrotron X-rays

Photoexcited molecules are quintessential reactants in photochemistry. Structures of these photoexcited molecules in disordered media in which a majority of photochemical reactions take place remained elusive for decades owing to a lack of suitable X-ray sources, despite their importance in understanding fundamental aspects in photochemistry. As new pulsed X-ray sources become available, short-lived excited-state molecular structures in disordered media can now be captured by using laser-pulse pump, X-ray pulse-probe techniques of third-generation synchrotron sources with time resolutions of 30-100 ps, as demonstrated by examples in this review. These studies provide unprecedented information on structural origins of molecular properties in the excited states. By using other ultrafast X-ray facilities that will be completed in the near future, time-resolution for the excited-state structure measurements should reach the femtosecond time scales, which will make "molecular movies" of bond breaking or formation, and vibrational relaxation, a reality.     

偶氮苯的同步辐射光电离及光解离

芳香族偶氮化合物(通式为Ar-N=N-Ar)是品种最多、应用最广的一类合成染料。由于偶氮苯类化合物容易发生感光异构[1],近年来已引起材料学家对它们的光子模式信息存储性能方面的广泛关注[2,3]。本文报道同步辐射光电离质谱法研究偶氮苯获得了该类物质的IP、AP、D0等重要参数。1　实验采用光束线编号为U10A同步辐射光源[4],工作波段35-300nm,分辨λ/△λ>500,波长精度±0 1nm,样品处光通量在1011光子/秒,样品处光斑大小3(水平)×1(垂直)mm。实验样品为固体,所以在光电离室电离区的正下方安装了一个加热炉,将固态样品放在炉内,通过调节…     

基于同步辐射X射线荧光光谱与机器学习的非靶标金属组学预测PVC纳米塑料对水稻毒性的浓度依赖性

环境中的微/纳米塑料污染引起了人们极大关注。土壤中的微/纳米塑料不可避免对植物产生影响,因此预测微/纳米塑料的植物毒性可为土壤中微/纳米塑料治理提供抓手。本文以水稻为研究对象,发展了基于同步辐射X射线荧光 (SRXRF) 光谱与机器学习的非靶标金属组学方法,以预测聚氯乙烯纳米塑料(nPVC) 对水稻的毒性。首先将水稻暴露于不同浓度(500 ppb与500 ppm) nPVC,培养35天后,收集水稻叶;其次,利用SRXRF研究暴露nPVC后水稻叶中金属组的变化;然后,利用机器学习方法区分暴露不同浓度nPVC水稻样品。对SRXRF光谱进行主成分分析 (PCA) 非监督聚类,发现500 ppm组能够良好聚类,而500 ppb组与对照组无明显差异,表明500 ppb的nPVC暴露对植物的毒性远低于500 ppm nPVC。对SRXRF全光谱,利用线性模型K近邻算法(KNN)和非线性模型支持向量机(SVM)建立预测模型,区分不同组别的准确率可达94.12%。为了提升运算速度,减少模型计算量,使用竞争性自适应加权重采样算法(CARS)挑选特征光谱建立预测模型,区分不同组别的准确率为89.51%。相对全光谱模型,特征光谱预测模型虽然预测准确率下降了4.61%,但模型输入参数减少了99.38%,因此同样具有良好潜力。本研究表明基于SRXRF和机器学习的非靶标金属组学可准确预测不同浓度nPVC对水稻金属组的干扰程度,从而反映nPVC对水稻毒性的浓度依赖性。该方法同样可用于预测其它微/纳米塑料毒性的浓度依赖性。     

TiO2 distribution in aged and injected isotactic polypropylene parts by synchrotron radiation X‐ray microfluorescence

We studied the TiO₂ pigment distribution along cross sections of injected isotactic polypropylene samples after they were aged by light exposure for 515 and 3000 h in accelerated test equipment. The TiO₂ pigment distribution was studied so that we could understand the whitening process occurring in this type of plastic. For these studies, we used a 20‐μm X‐ray microbeam from a synchrotron light source. We observed that the aged and nonaged samples had almost homogeneous distributions of Ti in the cross sections; therefore, pigment migration could not have been responsible for the surface whitening process. There were maxima of Ti intensities that were not in the same region for all samples. This behavior could be explained by the heterogeneity of the extrusion and injection‐molding processes. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 657–662, 2002; DOI 10.1002/polb.10127