Synchrotron X-ray and Neutron Diffraction Studies in Solid-State Chemistry

Neutron diffraction studies, especially with powders, play an important role in structural solid-state chemistry, making possible the precise determination of the location of light atoms, particularly hydrogen, and enabling a distinction to be made between certain neighboring elements in the periodic table that are difficult to distinguish in experiments with X-rays. Neutron diffraction investigations also make a unique contribution in the area of magnetic structure determination. The availability of intense synchrotron X-rays sources, however, is opening up new opportunities to the structural chemist, many of them complementary to the “traditional” strengths of neutron methods. The key features of synchrotron radiation in relation to structural studies are the wavelength tunability, which facilitates the use of resonant diffraction methods, and the high brightness and excellent vertical collimation of the source, which make possible the construction of diffractometers with unparalleled angular and spatial resolution. The following types of experiments are now possible with synchrotron X-ray diffraction: (1) The ab initio determination of structures from powder diffraction data. (2) The differentiation between different oxidation states of an element (valence contrast experiments) based upon the sensitivity of an absorption edge to the valence of the element in question. (3) The differentiation of elements adjacent to each other in the periodic table, which is now feasible with synchrotron X-rays for all elements beyond chromium. (4) Site-selective X-ray absorption spectroscopy. (5) The study of cation occupancies in materials where more than one element occupies a site that is, or may be, partially occupied. (Such problems are important in zeolite chemistry and high-temperature superconductors.) (6) The determination of crystal structures from microcrystals. (7) In situ and rapid, time-resolved diffraction studies. This review examines the roles played by X-ray and neutron diffraction studies in modern solid-state chemistry, and describes some recent examples in which the use of neutron radiation or synchrotron X-rays has been advantageous.     

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.     

Development of micro X-ray fluorescence spectrometer with multi excitation sources

X-ray fluorescence analysis (XRF) is a suitable technique for elemental analysis in nondestructive measurement. Recently, small area analysis by using the XRF technique has gained popularity. The synchrotron radiation source is responsible for the increase in the popularity of micro-XRF analysis. However, most people find it difficult to gain access to the synchrotron radiation facility. In this study, a micro-XRF system is developed for use in laboratories. To enable the use of this system, it is necessary to satisfy the following two conditions: (1) the excitation source must be optional for efficient excitation of the sample and (2) the X-rays must be focused. An X-ray tube with multi excitation sources has also been developed. In this tube, there are three targets, namely Cr, W, and Pd, on the anode, and each target can be excited sequentially. A doubly curved crystal (DCC) developed using a Si(111) crystal is used as the optics for focusing the X-rays into a beam with a diameter of less than 100 μm. A system composed of the X-ray tube and DCC optics is used to perform the small particle analysis of a Si wafer. The lower limit of detection (LLD) of the sample particle is estimated as 1.6 μm in diameter.     

Monte-Carlo based background reduction and shielding optimisation for a large hyper-pure germanium detector

The performance of a radiation shielding system for a hyper-pure germanium detector has been characterised for Terrestrial radiation sources, Cosmic muons, X-ray fluorescence and the Compton scattering of source photons. Several methods to reduce the background seen are quantified, including increasing the inner radius of the Pb cave, and increasing the thickness of the shielding. Substantial improvements in the reduction of fluorescence X-rays are found to be achievable by modifying the liner thicknesses used. Increasing the Sn liner from 1.5 to 2.5 mm will increase the shielding of Pb X-rays from 95 to 99.5 %. Reducing the Cu liner from 1.0 to 0.5 mm maintains a 99.5 % level of shielding for Sn/Cd X-rays, however it greatly reduces the amount of Compton scattering of source photons into the detector (a process that is shown to cause an order of magnitude more events in the background than X-ray fluorescence). Cosmic muons were found to increase the amount of background radiation seen, both through direct interaction and the production of secondary radiation. The Cosmic muon contribution, however, was found to produce a much smaller effect than that caused by Terrestrial radiation and Compton scattered photons/fluorescence from the source. The total level of background radiation entering the detector chamber was found to decrease up to the full 200 mm of Pb shielding simulated.     

Confocal microscopic X-ray fluorescence at the HASYLAB microfocus beamline: characteristics and possibilities

The possibilities of performing non-destructive elemental analysis in three dimensions on a variety of heterogeneous materials by means of an innovative variation of the microscopic X-ray fluorescence analysis (μ-XRF) method are described. Next to employing focusing optics for concentration of the primary beam of X-rays, a second optical element between the sample and the energy-dispersive detector is used in confocal μ-XRF. Thus, only X-ray fluorescence signals from a cube-like volume (within certain limits imposed by the absorption of the radiation in the sample) can be arbitrarily positioned within the sample. The distribution of major, minor and trace elements (down to the sub-ppm concentration level in some matrices) along lines and planes within the sample can be visualized with a spatial resolution of the order of 15–40 μm. The lowest detectable amounts in confocal mode using pink-beam excitation are situated at the sub-femtogram level.     

Structure analysis of exfoliated unilamellar crystallites of manganese oxide nanosheets

Structure analysis of unilamellar manganese oxide nanosheets obtained via exfoliation of layered manganese oxides was carried out utilizing synchrotron radiation (SR) X-ray in-plane diffraction and polarization-dependent total reflection fluorescence X-ray absorption fine structure (PTRF-XAFS) analyses. A combination of SR excitation and the total reflection of incoming X-rays provides signals strong enough for both analyses even from a monolayer of the MnO(2) nanosheets having a concentration of 0.7 microg cm(-2). In addition, the mean oxidation state of constituent manganese ions in the MnO(2) sheets was estimated on the basis of XANES spectra, and bond valence sum calculations with the bond length obtained from the present EXAFS analyses. The obtained structural data revealed that the two-dimensional lattice of the MnO(2) sheets underwent a slight elongation upon delamination. These changes correspond to approximately 1% expansion of sheet area and 1-2% expansion of thickness, which can be understood by reduction of the mean oxidation number of manganese ions in the sheet through the exfoliation process.     

Über die berücksichtigung von streuanteilen bei der messung von röntgenfluoreszenzintensitäten

A theoretical treatment of the contributions of scattered X-rays to the intensity of fluorescent radiation is given. These contributions are caused as well by scattering of white X-rays as by scattering of characteristic X-rays. The amount is calculated for different elements and thin films. From these considerations follows an increase of the X-ray fluorescence intensity of approximately 1 per cent for bulk materials and up to 30 per cent for thin films.

Since for a quantitative analysis reference samples are needed, values of the concentration or mass per unit area are found, which are higher or lower as compared with the true value, depending on the amount of fluorescent X-rays caused by scattering.     

Method for improving the accuracy of continuous X-ray fluorescence analysis of iron ore mixtures

The dependence of the intensity of X-ray fluorescence on the distance between the spectrometer and the test sample is studied. Changes in the intensity of primary X-radiation, absorption of X-rays by the air, and surface area of the analyzed material are calculated. An efficient method is proposed for improving the accuracy of continuous X-ray fluorescence analysis of iron ore mixtures on the conveyor belt through the exclusion of incorrect results by the dead time of the detection unit. The proposed method is universal and can be used for various loose materials.     

Concentration-data of elements in liquid fuel oils as obtained by neutron activation analysis

The selection of exciting source both from the point of view of excitation efficiency and elimination of matrix effects using incoherently scattered radiation from the analyzed sample is discussed. Samples of materials from the flotation process of copper ore have been used and copper, iron and lead were the elements sought. For the excitation of fluorescence X-rays, sealed radioisotopic sources of²³⁸Pu,²⁴¹Am,²⁴⁴Cm,¹⁰⁹Cd and a molybdenum X-ray tube were used. For X-ray analysis a Si(Li) spectrometer was applied. The processing of X-ray spectra based on the application of the Gaussian peak representation gives results equivalent to the total peak area method. From the intensities of fluorescence and scattered radiation, the contents of elements were calculated using empirical formulae and the results were compared with those of the Heinrich-Rasberry method. A statistical analysis of the results has been carried out and the criteria of optimal regression formula selection are given.     

Synchrotron radiation for structure analysis—EXAFS and XANES

In this paper, a newly developed technique for the structure analysis of materials by the use of the X-rays emitted from storage ring of synchrotron is introduced. Principle, applications and limitations of the extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES) are discussed.     

X射线成像技术在能源材料研究中的应用

随着人类对可持续能源的需求不断增长,先进的表征方法在能源材料研究等领域变得越来越重要。借助X射线成像技术,我们可以从二维和三维角度实时获取能源材料的形貌、结构和应力变化信息。此外,借助高穿透性X射线和高亮度同步辐射源,设计原位实验,可以获取充放电过程中样品的定性和定量变化信息。本文综述了基于同步加速器的X射线成像技术及其相关应用,讨论了包括X射线投影成像、透射式X射线显微成像、扫描透射X射线显微成像、X射线荧光显微成像以及相干衍射成像等几种主要的X射线成像技术在能源材料研究领域的应用,展望了未来X射线成像的应用前景及发展方向。     

X-ray measurements from the cathode surface of glow discharge tube used as a compact X-ray fluorescence instrument

As previously reported, when a high-voltage is applied to a Grimm glow discharge tube, high-energy electrons emitted from the cathode surface bombard the glass window, leading to X-ray emissions from the window. In this study, we have applied an energy-dispersive X-ray analysis to detect X-rays from the cathode which are excited by X-rays emitted from the glass window. Thus, we have proposed to utilize this glow discharge tube as a compact X-ray fluorescence instrument, to which both the X-ray emission source and the sample are directly attached. This compact X-ray fluorescence instrument has the same advantages of easy maintenance, exchangeable target and sample, and simple construction. The quantitative determination of Si, Ti, and Mn in Fe–Si, Fe–Ti, and Fe–Mn alloys was demonstrated with the detection limits of 21, 150 and 420 ppm, respectively. The X-ray measurement form the cathode is a useful method to directly monitor the cathode surface during the glow discharge process. This would be applied to understand and control the glow discharge processes. Moreover, the X-ray diffraction peaks as well as the fluorescent X-ray peaks were observed, indicating that the structure analysis of the cathode material would also be possible.     

Beyond crystallography: the study of disorder, nanocrystallinity and crystallographically challenged materials with pair distribution functions

Studying the structure of disordered and partially ordered materials is notoriously difficult. Recently, significant advances have been made using the atomic pair distribution function (PDF) analysis of powder diffraction data coupled with the use of advanced X-ray and neutron sources and fast computers. Here we summarize some of the more spectacular successes of this technique in studying the structure of complex materials and compounds. Our purpose is to make the PDF analysis technique familiar to the chemical community by describing its methodologies and highlighting its potential in solving structural characterization problems that are intractable by any other technique available to this community e.g. single crystal diffraction, Rietveld refinement of powder diffraction data and extended X-ray absorption fine structure analysis (EXAFS).     

Hard and soft X-ray microscopy and tomography in catalysis: bridging the different time and length scales

X-ray microscopic techniques are excellent and presently emerging techniques for chemical imaging of heterogeneous catalysts. Spatially resolved studies in heterogeneous catalysis require the understanding of both the macro and the microstructure, since both have decisive influence on the final performance of the industrially applied catalysts. A particularly important aspect is the study of the catalysts during their preparation, activation and under operating conditions, where X-rays have an inherent advantage due to their good penetration length especially in the hard X-ray regime. Whereas reaction cell design for hard X-rays is straightforward, recently smart in situ cells have also been reported for the soft X-ray regime. In the first part of the tutorial review, the constraints from a catalysis view are outlined, then the scanning and full-field X-ray microscopy as well as coherent X-ray diffraction imaging techniques are described together with the challenging design of suitable environmental cells. Selected examples demonstrate the application of X-ray microscopy and tomography to monitor structural gradients in catalytic reactors and catalyst preparation with micrometre resolution but also the possibility to follow structural changes in the sub-100 nm regime. Moreover, the potential of the new synchrotron radiation sources with higher brilliance, recent milestones in focusing of hard X-rays as well as spatiotemporal studies are highlighted. The tutorial review concludes with a view on future developments in the field of X-ray microscopy that will have strong impact on the understanding of catalysts in the future and should be combined with in situ electron microscopic studies on the nanoscale and other spectroscopic studies like microRaman, microIR and microUV-vis on the macroscale.     

Photoemission and absorption spectroscopy of carbon nanotube interfacial interaction

Element-specific techniques including near edge X-ray absorption fine structure, extended X-ray absorption fine structure and X-ray photoemission spectroscopy for the characterization of the carbon nanotube interfacial interactions are reviewed. These techniques involve soft and hard X-rays from the laboratory-based and synchrotron radiation facilities. The results provided information of how the nano-particles of catalysts are involved in the initial stage of nanotube growth, the nanotube chemical properties after purification, functionalization, doping and composite formation.     

X-ray diffraction of protein crystal grown in a nano-liter scale droplet in a microchannel and evaluation of its applicability

We describe the technical aspects of the in-situ X-ray diffraction of a protein crystal prepared by a nanodroplet-based crystallization method. We were able to obtain diffraction patterns from a crystal grown in a capillary without any manipulation. Especially in our experimental approach, the crystals that moved to the nanodroplet interface were fixed strongly enough to carry out X-ray diffraction measurements that could be attributed to the high surface tension of the nanodroplet. The crystal was damaged by an indirect action of the X-rays because our in-situ X-ray diffraction measurement was carried out in the liquid phase without freezing the crystal; however, the obtained several diffraction patterns were of sufficiently fine quality for the crystal structure factors to be generated. We consider the technical examination presented in this paper to represent a seamless coupling of crystallization to X-ray analysis.     

EDXRF imaging of Pb in glazed ceramics using a micropattern gas detector

A new system for energy-resolved X-ray fluorescence imaging using a microhole and strip plate (MHSP), a new type of micropattern gas detector (MPGD), is proposed. It works as a single photon counting detector with position and energy detection capability. The interaction of X-rays with the gas medium produces electrons via the photoelectric effect, and the number of electrons is proportional to the absorbed X-ray energy. These electrons are further multiplied in the MHSP. Position detection is achieved using the charge division method. The detector has an active area of 28?×?28 mm² and shows good position resolution, about σ?=?125 μm, an intrinsic energy resolution of about 14% FWHM for 5.9 keV X-rays, and a counting rate capability of up to 0.5 MHz. The system has shown good properties for energy-dispersive X-ray fluorescence (EDXRF) applications, since it allows efficient energy and position detection of fluorescence X-rays from multielemental samples. In this work, the system was used to study lead depth distributions in eighteenth-century Portuguese faiences from the Santa Clara-a-Velha monastery. The fluorescence images were obtained by irradiating the samples, with a pinhole placed between the sample and the detector to focus the radiation into the detector. The results are presented here, including the elemental map distributions for different samples.     

Applications of synchrotron radiation in materials analysis

The synchrotron radiation (SR) emitted by circulating high-energy electrons has extraordinary properties: The light is intensive and bright, it is tunable and highly collimated, and finally, it is linearly polarized. These exceptional properties have initiated a unique revival of many spectroscopies using electromagnetic radiation. The techniques of special concern for materials analysis which are treated in this article are: X-ray absorption, reflection, fluorescence, diffraction and topography. A number of examples will be given in order to illustrate the possibilities of these techniques when SR is used.On leave of absence from Institut für Festkörperforschung, KFA Jülich, D-5170 Jülich, Federal Republic of Germany     

Poly-capillary X-ray and neutron optics (Kumakhov optics)

Poly-capillary X-ray optics (Kumakhov optics) are based on multiple total external reflections of radiation in small-diameter hollow capillary tubes. Such tubes can be made to form different kinds of lens and make it possible to focus and control X-rays and neutrons over broad angular and energy ranges. Thus, as instances, X-rays can be focused for medical therapy and material sciences, and intense quasi-parallel X-ray and neutron beams can be produced from divergent sources for medical diagnosis and X-ray lithography. This new form of optical control offers improved efficiency and effectiveness in almost all uses of X-rays or slow neutrons, and makes possible many new applications.     

Hard X-ray phase imaging and tomography using a grating interferometer

An interferometric technique for hard X-rays is presented. It is based on two transmission gratings and a phase-stepping technique, and it provides separate radiographs of the phase and absorption profiles of bulk samples. Tomographic reconstruction yields quantitative three-dimensional maps of the X-ray refractive index and of the attenuation coefficient, with a spatial resolution down to a few microns. The method is mechanically robust, it requires little monochromaticity, and can be scaled up to large fields of view. These are important prerequisites for use with laboratory X-ray sources. Numerous applications ranging from wave front sensing to medical radiography are presently under investigation.