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。     

Synchrotron X-ray techniques for the investigation of structures and dynamics in interfacial systems

This review focuses on recent results obtained by synchrotron X-ray techniques applied to the characterization of interfacial systems, with main emphasis on flat interfaces and on colloidal systems. The techniques covered are, for structural determinations: X-ray reflectivity (XRR), grazing incidence X-ray diffraction (GIXRD) and grazing incidence X-ray excited fluorescence (GIXF), while dynamics are investigated by X-ray photon correlation spectroscopy (XPCS) mainly in the grazing-incidence geometry (GIXPCS).The systems reviewed are, in order of growing complexity, floating Langmuir monolayers, supported films of lipids and proteins, polymeric films, buried interfaces, colloidal systems and gels formed by colloids either in 3D or in the form of 2D interfacial layers. Recent results are critically discussed, and some interesting directions of development are outlined, having also in mind new technical developments such as X-ray free electron laser sources and micro-focused synchrotron beamlines.     

Internal conversion in energy dispersive X-ray analysis of actinide-containing materials.

The use of X-ray elemental analysis tools like energy dispersive X-ray (EDS) is described in the context of the investigation of nuclear materials. These materials contain radioactive elements, particularly alpha-decaying actinides that affect the quantitative EDS measurement by producing interferences in the X-ray spectra. These interferences originating from X-ray emission are the result of internal conversion by the daughter atoms from the alpha-decaying actinides. The strong interferences affect primarily the L X-ray lines from the actinides (in the typical energy range used for EDS analysis) and would require the use of the M lines. However, it is typically at the energy of the actinide's M lines that the interferences are dominant. The artifacts produced in the X-ray analysis are described and illustrated by some typical examples of analysis of actinide-bearing material.     

X-Ray radiometric analysis of the element composition of materials

Methods and equipments developed for X-ray radiometric analysis at the Central Research Institute for Mineral Raw Materials are described. The main advantages of X-ray radiometry compared with X-ray spectral analysis are discussed.     

In-Situ/Operando X-ray Characterization of Metal Hydrides

In this article, the capabilities of soft and hard X-ray techniques, including X-ray absorption (XAS), soft X-ray emission spectroscopy (XES), resonant inelastic soft X-ray scattering (RIXS), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD), and their application to solid-state hydrogen storage materials are presented. These characterization tools are indispensable for interrogating hydrogen storage materials at the relevant length scales of fundamental interest, which range from the micron scale to nanometer dimensions. Since nanostructuring is now well established as an avenue to improve the thermodynamics and kinetics of hydrogen release and uptake, due to properties such as reduced mean free paths of transport and increased surface-to-volume ratio, it becomes of critical importance to explicitly identify structure-property relationships on the nanometer scale. X-ray diffraction and spectroscopy are effective tools for probing size-, shape-, and structure-dependent material properties at the nanoscale. This article also discusses the recent development of in-situ soft X-ray spectroscopy cells, which enable investigation of critical solid/liquid or solid/gas interfaces under more practical conditions. These unique tools are providing a window into the thermodynamics and kinetics of hydrogenation and dehydrogenation reactions and informing a quantitative understanding of the fundamental energetics of hydrogen storage processes at the microscopic level. In particular, in-situ soft X-ray spectroscopies can be utilized to probe the formation of intermediate species, byproducts, as well as the changes in morphology and effect of additives, which all can greatly affect the hydrogen storage capacity, kinetics, thermodynamics, and reversibility. A few examples using soft X-ray spectroscopies to study these materials are discussed to demonstrate how these powerful characterization tools could be helpful to further understand the hydrogen storage systems.     

Applications of synchrotron-based X-ray techniques in environmental science

Synchrotron-based X-ray techniques have been widely applied to the fields of environmental science due to their element-specific and nondestructive properties and unique spectral and spatial resolution advantages. The techniques are capable of in situ investigating chemical speciation, microstructure and mapping of elements in question at the molecular or nanometer scale, and thus provide direct evidence for reaction mechanisms for various environmental processes. In this contribution, the applications of three types of the techniques commonly used in the fields of environmental research are reviewed, namely X-ray absorption spectroscopy (XAS), X-ray fluorescence (XRF) spectroscopy and scanning transmission X-ray microscopy (STXM). In particular, the recent advances of the techniques in China are elaborated, and a selection of the applied examples are provided in the field of environmental science. Finally, the perspectives of synchrotron-based X-ray techniques are discussed. With their great progress and wide application, the techniques have revolutionized our understanding of significant geo- and bio-chemical processes. It is anticipatable that synchrotron-based X-ray techniques will continue to play a significant role in the fields and significant advances will be obtained in decades ahead.     

The application of synchrotron techniques to the study of lithium-ion batteries

This paper gives a brief review of the application of synchrotron X-ray techniques to the study of lithium-ion battery materials. The two main techniques are X-ray absorption spectroscopy (XAS) and high-resolution X-ray diffraction (XRD). Examples are given for in situ XAS and XRD studies of lithium-ion battery cathodes during cycling. This includes time-resolved methods. The paper also discusses the application of soft X-ray XAS to do ex situ studies on battery cathodes. By applying two signal detection methods, it is possible to probe the surface and the bulk of cathode materials simultaneously. Another example is the use of time-resolved XRD studies of the decomposition of reactions of charged cathodes at elevated temperatures. Measurements were done both in the dry state and in the presence of electrolyte. Brief reports are also given on two new synchrotron techniques. One is inelastic X-ray scattering, and the other is synchrotron X-ray reflectometry studies of the surface electrode interface (SEI) on highly oriented single crystal lithium battery cathode surfaces. Dedicated to the 85th birthday of John O’M. Bockris     

Influence of the distance between a spectrometer and sample on the intensity of X-ray fluorescence

Expressions for calculating the extreme point coordinates of focal spots of X-ray tubes and a detector’s sensitive area are found. These coordinates are used in calculations of the sample area. The dependence of the X-ray fluorescence intensity on the distance between a spectrometer and an analyzed sample is studied experimentally. The intensities of the FeK _α spectral lines in iron-containing materials are calculated at different geometric parameters of a spectrometer. It is found that the distance between a sample and detector at which the maximum of the measured intensity is observed depends on the size and position of the detector and X-ray tube collimators, as well as on the relative position of the X-ray tube and detector. Recommendations on how to achieve the maximum intensity of X-ray fluorescence are proposed. The results of the present work can be used for the development of X-ray fluorescence analysis techniques applicable for free-flowing materials directly in technological processes.     

X-ray investigation of monolayers formed at the soft air/water interface

Gibbs or Langmuir monolayers formed at the soft air/liquid interface are easy to handle and versatile model systems for material and life sciences. The phase state of the monolayers can be modified by lateral compression of the film while the layer structural changes are monitored by highly sensitive surface characterization techniques. The use of high brilliant synchrotron light sources for X-ray experiments is essential for the monolayer research. The present review highlights the recent achievements recorded in the monolayer field with a special emphasis on different synchrotron based X-ray characterizing methods as: grazing incidence X-ray diffraction, X-ray reflectivity and total reflection X-ray fluorescence. Some examples of single-chain surfactants, special sugar lipids, and semifluorinated compounds are given. Additionally, thin layers formed by peptides, polymers or nanoparticles are highlighted.     

Determination of the elemental composition of tissues of the cardiovascular system by atomic spectrometry, mass spectrometry and X-ray spectrometry methods

The review discusses the published data on the concentrations of chemical elements in tissues of the cardiovascular system determined by atomic absorption and atomic emission spectrometry, mass spectrometry, and also X-ray fluorescence analysis, proton-induced X-ray emission, and X-ray microanalysis. The main parameters of X-ray spectrometry methods used for the examination of the cardiovascular system are compared, the new trends in the analysis of these samples and the main sample preparation approaches are considered.     

Determination of trace elements in sediment reference materials by monochromatic X-ray excitation X-ray fluorescence spectrometry.

A new reliable analytical method, "Monochromatic X-ray Excitation X-ray Fluorescence Spectrometry", has been proposed. For validating the method, trace elements in sediment certified reference materials were determined. In the method X-ray fluorescence spectra are measured for specimens and pure metals; in addition the mass-attenuation coefficients of the specimens for various X-ray wavelengths are also measured. The data are analyzed by the fundamental parameter method and the uncertainty of the analysis is evaluated. The obtained results were in satisfactory agreement with the certified values within their uncertainties. This method will be applicable to the certification of reference materials, in the field of which reliable results with uncertainty statements are required.     

An indirect method of X-ray spectra measurement by simultaneous attenuations of the scattered beam

Direct and indirect methods of X-ray spectra determination present obstacles to their practical use since they must position either the collimator-detector assembly or the attenuators-ionization chamber, respectively, along the X-ray beam direction. These arrangements require considerable space and in many instances the detectors promptly saturate. An indirect procedure, which overcomes the aforementioned problems, is developed. It consists of the scattering of the X-ray beam from a carbon disk, which is detected simultaneously by several detectors placed away from the beam. The X-ray flux reaching each of these detectors is attenuated in metal sheets of different thicknesses, thus obtaining simultaneously the attenuation curve values. A set of analytical equations are derived to calculate attenuation curves by taking into account all the absorption and elastic and inelastic scattering processes that a beam of photons undergoes when going from the X-ray tube to the detector. Users, even those who are not well acquainted with computer programming, can easily obtain the X-ray spectrum by a least square fitting of a measured attenuation curve to a previously derived analytical expression. A simulated Monte Carlo program of photon transport from the X-ray tube to the detector provided simulated attenuation curves data. Analytically calculated and simulated attenuation curves for the same input spectrum wholly overlap and furthermore, reconstructed spectra from both sets of curves for different kilovoltages are also in full agreement. Finally, in addition to the importance of having the detectors out of the beam direction, the proposed arrangement features other main advantages, namely, only one X-ray tube shot is needed to obtain the required data, the physical processes involved are very well known, analytical equations are easily interpreted, and the measuring apparatuses can be comparatively simple to assemble and operate.     

Standardless quantitation of thin film specimens

This paper reviews the procedures available for the X-ray microanalysis of specimens in the form of thin self-supporting films without the use of standards. Standardless analysis refers to the procedure in which there is no requirement to prepare standards and then measure them during the course of the current analysis. The factors by which the measured X-ray intensities are converted to compositions are calculated for the elements of interest after the experimental measurements have been completed. These calculations are based on published tabulated data for the physical constants required, or evaluated from theoretical or empirical models. The physical parameters which are required to evaluate the characteristic X-ray production in the specimen are the fluorescence yield, the partition function and the X-ray production cross-section. Most analytical procedures ensure that other variables such as the specimen thickness and electron beam current are not required. Of the parameters mentioned, the first two have been examined and extensively tabulated in the literature. This paper focuses primarily on methods of evaluating the X-ray cross-sections for both the characteristic and bremsstrahlung production.The way in which the physical parameters are incorporated into the standardless quantitation methods for materials samples is described. A new standardless version of the continuum normalisation method for quantitative analysis for samples with organic matrices is introduced. Some techniques for making corrections for absorption to the observed intensities are discussed, and formulae are given for X-ray absorption and fluorescence which it may be necessary to use with thicker specimens.     

Application of X-ray spectroscopy in nondestructive photon activation analysis

A survey is given on the use of X-ray spectroscopy for the qualitative and quantitative analysis of samples activated by 30 MeV bremsstrahlung from an electron linear accelerator. Detection limits are calculated from the measured X-ray spectra and compared with those for γ-ray spectroscopy. The advantages and limitations of the method are discussed. Some practical applications of X-ray spectroscopy in nondestructive multielement analysis are quoted.     

Higher-order processes in X-ray photoionization of atoms

There are several fourth-generation X-ray light source projects now underway around the world and it is anticipated that by the end of the decade, one or more of these X-ray free-electron lasers will be operational. In this contribution, we describe recent measurements and future plans to study both multielectron and multiphoton atomic photoionization. Although such higher-order processes are rare with present third-generation sources, they will be commonplace in experimental work with the new sources. The topics we discuss here are double K-shell ionization and two-photon X-ray photoionization.     

High-sensitivity X-ray fluorescence analysis of solutions with the use of a sorption accumulation microsystem

A mass-transfer kinetic model is proposed for an embedded sorption accumulation microsystem based on polycapillary structures to be used in the developed X-ray fluorescence analyzer with preconcentration. The model is used to substantiate a kinetic method for high-sensitivity X-ray fluorescence determination of elements in multicomponent solutions. With the use of this model, experimental data on X-ray fluorescence spectra are analyzed and kinetic and equilibrium parameters are found for the sorption of copper, nickel, manganese, iron, and zinc on the selective DETATA sorbent.     

Picosecond Time Resolved Hard X-Ray Diffraction from Laser Heated Metallic Crystals

We report the development of a novel hard X-ray diffraction system with picosecond time resolution. Picosecond X-ray pulses are produced by excitation of an X-ray diode with picosecond ultraviolet light pulses at a repetition rate of 300 Hz. The X-ray pulses are synchronized to the optical pulses with picosecond accuracy. The system has been utilized in picosecond time resolved X-ray diffraction of laser pulse heated gold and platinum single crystals.     

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.     

Development of a procedure for the determination of X-ray fluorescence of metals in aerosols

The precision of the determination of the of heavy metals in aerosols by X-ray fluorescence after their collection on a paper filter is evaluated depending on the chemical composition and weight of unsaturated samples. Recommendations on the choice of the optimal shape of the calibration function and on the conditions for the determination of its coefficients used for the X-ray analysis of unsaturated samples are formulated. A procedure for the X-ray determination of metals in aerosols collected on paper filters is developed; its performance characteristics are presented.