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Fifth volume of a 40 volume series on nanoscience and nanotechnology, edited by the renowned scientist Challa S.S.R. Kumar. This handbook gives a comprehensive overview about X-ray and Neutron Techniques for Nanomaterials Characterization. Modern applications and state-of-the-art techniques are covered and make this volume an essential reading for research scientists in academia and industry.



1. Synchrotron X-Ray Phase Nanotomography for Bone Tissue Characterization

X-ray phase nano-tomography allows the characterisation of bone ultrastructure: the lacuno-canalicular network, nanoscale mineralisation and the collagen orientation. In this chapter, we review the different X-ray imaging techniques capable of imaging the bone ultrastructure and then describe the work that has been done so far in nanoscale bone tissue characterisation using X-ray phase nano-tomography.
X-ray computed tomography at the micrometric scale is more and more considered as the reference technique in imaging of bone microstructure. The trend has been to push towards higher and higher resolution. Due to the difficulty of realising optics in the hard X-ray regime, the magnification has mainly been due to the use of visible light optics and indirect detection of the X-rays, which limits the attainable resolution with respect to the wavelength of the visible light used in detection. Recent developments in X-ray optics and instrumentation have allowed the implementation of several types of methods that achieve imaging limited in resolution by the X-ray wavelength, thus enabling computed tomography at the nanoscale. We review here the X-ray techniques with 3D imaging capability at the nanoscale: transmission X-ray microscopy, ptychography and in-line holography. Then, we present the experimental methodology for the in-line phase tomography, both at the instrumentation level and the physics behind this imaging technique. Further, we review the different ultrastructural features of bone that have so far been resolved and the applications that have been reported: imaging of the lacuno-canalicular network, direct analysis of collagen orientation, analysis of mineralisation on the nanoscale and the use of 3D images at the nanoscale as the basis of mechanical analyses. Finally, we discuss the issue of going beyond qualitative description to quantification of ultrastructural features.
Peter Varga, Loriane Weber, Bernhard Hesse, Max Langer

2. 3D Chemical Imaging of Nanoscale Biological, Environmental, and Synthetic Materials by Soft X-Ray STXM Spectrotomography

Synchrotron-based soft X-ray scanning transmission X-ray microscopy is applied to 3D chemical imaging using tilt series tomography at multiple photon energies. Instrumentation, methodology and examples from a range of nanoscale biological, environmental and materials science are presented.
Synchrotron-based soft X-ray scanning transmission X-ray microscopy is applied to 3D chemical imaging using tilt series tomography at multiple photon energies (STXM spectro-tomography). Instrumentation, methodology and examples from a range of nanoscale biological, environmental and materials science are presented. Dry and wet samples dealing with biomineralization and the interface of bacteria and minerals are presented. 3D chemical maps are generated from a model system for the perfluorosulfonic acid ionomer in the electrodes of polymer electrode membrane fuel cells. Results for 3D imaging of wet biofilms and wet latex microspheres are presented. Future improvements in the forms of soft X-ray spectro-ptychography, cryo-spectro-tomography, laminography and improved instrumentation for wet samples are discussed.
Gregor Schmid, Martin Obst, Juan Wu, Adam Hitchcock

3. X-Ray Photon Correlation Spectroscopy for the Characterization of Soft and Hard Condensed Matter

X-ray photon correlation spectroscopy (XPCS) allows to access a wide variety of dynamic phenomena at the nanoscale by studying the temporal correlations among photons that are scattered by a material when it is illuminated using a coherent X-ray beam. Here, we describe how XPCS is used to study the dynamics of soft and hard condensed matter, review the recent literature and briefly discuss the future of the technique, especially in the context of the emerging diffraction-limited storage rings and X-ray free electron laser sources.
When a disordered system is illuminated with coherent light, the interference between the scattered waves gives rise to a speckle pattern. The speckle pattern depends on the exact arrangement of the scatterers. Information about the dynamics of the system can be obtained by analysing the temporal correlations of the speckle intensities. This is the basis of the X-ray photon correlation spectroscopy (XPCS) technique, which is the counterpart of photon correlation spectroscopy (PCS) using coherent X-rays instead of laser light. XPCS is one of the main techniques to probe the slow nanoscale fluctuations and dynamics of soft and hard condensed matter systems. If a coherent X-ray beam from a third-generation synchrotron source is used as the illumination probe, then, depending on the sample and the scattering geometry, the dynamics of materials on timescales ranging from microseconds to thousands of seconds and length scales from microns down to nanometres can be accessed. At present, the main limitations of XPCS are the relatively low coherent flux of existing X-ray sources and the limited speed of X-ray area detectors. The upcoming new X-ray sources (diffraction-limited storage rings and X-ray free electron lasers) will enable to measure dynamics at large momentum transfer values with tenths of picoseconds time resolution.
The principles, experimental methodology and recent application of XPCS are reviewed here, followed by a brief discussion about the possibilities that the new X-ray sources will create for future XPCS experiments.
Oier Bikondoa

4. XAFS for Characterization of Nanomaterials

X-ray absorption fine structure (XAFS) spectroscopy studies the modification of the X-ray absorption coefficient, above the absorption edge of a specific element, due to the presence of neighboring atoms and delivers information on materials nano- and electronic structure. The long-range translational symmetry is not a prerequisite, as in the case of diffraction-based techniques, which, along with the atom-specific character of XAFS, renders it a powerful tool for the study of nanomaterials.
In the following the principles of XAFS spectroscopy will be discussed. A brief introduction of the theoretical basis of the spectroscopy will be presented, the emphasis being on the phenomena that affect the spectrum at energies below, near, and far above the absorption edge. In addition to that, the main experimental setups used for the acquisition of the XAFS spectra in the soft and hard X-ray regimes will also be presented. Furthermore, the analysis procedure of the extended part of the XAFS (called extended XAFS, acronym EXAFS) spectrum and the related parameters, as well as methodologies followed in the analyses of the near-edge part of the spectrum (called X-ray absorption near-edge structure or near-edge X-ray absorption fine structure, the corresponding acronyms being XANES and NEXAFS, respectively), will be described. Finally, recently published representative applications of XAFS spectroscopy for the study of various types of nanomaterials, for example, nanocatalysts, carbon-based nanomaterials, semiconductor quantum dots, etc., will be reviewed.
Maria Katsikini, Eleni C. Paloura

5. The Characterization of Atomically Precise Nanoclusters Using X-Ray Absorption Spectroscopy

The XAS toolbox (EXAFS, XANES, theoretical calculations, in situ measurements) is used in a variety of applications to determine the structure and electronic properties of atomically precise nanoclusters (APNCs). The analysis using the EXAFS part of the XAS spectrum involves models that are based on atomic packing (e.g., fcc, icosahedra) or surface effects. Theoretical methods based on DFT can improve the understanding of disorder effects on the EXAFS measurements. In comparative experiments, the effect of solvation and of the ligands (density of ligands, different ligands) is discussed. It was found that the strength of the Au–thiol bonding can lead to relaxation effects that reduce the contraction of Au–Au bonds in the core. Changes in structure could be observed for solvation and catalytic reaction with the application of in situ measurements in specifically designed reactors. Even though EXAFS is a powerful method with a number of advantages, such as that no long-range order is necessary, all kinds of materials can be investigated, nondestructively. The analysis of EXAFS data is quite challenging, however, and effects such as structural disorder, if the sample is a mixture of components (not pure) or if the APNCs have several binding ligands, can distort the results. The use of l-DOS based on theoretical XANES calculations that can give information about electronic properties of APNCs is also challenging. In complement with XPS experiments, however, consistent answers can be found.
Lisa Bovenkamp-Langlois, Martha W. Schaefer

6. X-Ray Absorption Spectroscopic Characterization of Nanomaterial Catalysts in Electrochemistry and Fuel Cells

X-ray absorption spectroscopy is a nondestructive synchrotron-based technique that measures the changes in x-ray absorption coefficient of a material as a function of energy of the x-rays. The technique has an advantage over other spectroscopy techniques as it can resolve the short-range arrangement of atoms. Since many of today’s catalysts for electrochemical systems are in particles of a few nanometers in size (nanoparticles) and the technique can resolve the inner atomic structure of the nanoparticle, XAS quickly became a powerful tool for studying electrochemical catalysts, particularly in the field of fuel cells.
The chapter describes operation principles of x-ray absorption spectroscopy (XAS) technique and its application to atomic arrangement in nanoparticles, with a special interest in electrochemistry.
XAS is a nondestructive technique that measures the changes in x-ray absorption coefficient of a material as a function of energy. X-rays of a narrow energy resolution are shone on the sample, and the incident and transmitted x-ray intensities are recorded as the incident x-ray energy is incremented. When the incident x-ray energy matches the binding energy of an electron of an atom within the sample, the number of x-rays absorbed by the sample increases dramatically, causing a drop in the transmitted x-ray intensity that is referred to as an absorption edge. Each element has a set of unique absorption edges giving XAS element selectivity. Because it requires a tunable x-ray source, XAS spectra are usually collected at synchrotrons. The x-rays are highly penetrating and allow studies of gases, solids, or liquid at concentrations of as low as a few ppm. When applied to nanoparticles, the technique can resolve inner arrangement of atoms within. XAS can be separated into two parts, depending on the range it covers with respect to the absorption edge, i.e., x-ray absorption near-edge spectroscopy and extended x-ray absorption fine structure (XANES and EXAFS).
As it is element specific, XANES can resolve the oxidation state of the element, as well as its coordination environment and subtle changes in it. EXAFS analyzes the local structure of the atoms in all physical states (solid, liquid, and gas), but the unique power of the spectroscopy is found in metal clusters, particularly in nanomaterials. It can resolve the inner structure of the nanoparticle clusters composed of two or more elements, i.e., solid solution, aggregate mixtures, or core–shell particle in which one metal is present mostly in the center of the particle (core) and the other forms a shell around it. These nanoparticle systems are of a special interest in catalytic electrochemical oxidation and/or reduction, as most of these systems require expensive noble metals and minimizing their content is the goal of the present technology development. Since the atoms in the core of the particle are not exposed to the electrochemical environment, they can be substituted by non-noble materials. This chapter deals with electrochemical catalysts composed of two or more metal atoms and shows the basics of the analysis of these systems.
Kotaro Sasaki, Nebojsa Marinkovic

7. In Situ SXS and XAFS Measurements of Electrochemical Interface

In this chapter, we focus on structural studies at electrode/electrolyte solution interfaces by means of surface x-ray scattering (SXS) and x-ray absorption fine structure (XAFS) measurements using synchrotron radiation (SR) light as an x-ray source. After describing the importance of these techniques for structural studies at the electrode/electrolyte interface as an introduction, we explain the fundamental principles and experimental methodologies of these techniques. Finally, we describe trends in the development of these techniques and review the latest topics.
Toshihiro Kondo, Takuya Masuda, Kohei Uosaki

8. Gas-Phase Near-Edge X-Ray Absorption Fine Structure (NEXAFS) Spectroscopy of Nanoparticles, Biopolymers, and Ionic Species

Near-edge X-ray absorption fine structure (NEXAFS) spectroscopy probes directly or indirectly the photoabsorption cross section of a system under study as a function of the photon energy around the core–shell ionization thresholds. When the photon energy matches the difference between the core level and an unoccupied valence level, the photoabsorption cross section increases. The core levels are associated with particular atoms within the system under the study; therefore, NEXAFS spectroscopy appears to be a very sensitive probe of physicochemical and structural properties of molecules and materials. It has been intensively applied to investigate gaseous, liquid, and solid species. In this chapter, we describe methods to perform gas-phase NEXAFS spectroscopy of large systems, such as nanoparticles, clusters, and biopolymers, as well as of ionic species. We also review recent research findings.
The development of third-generation synchrotron radiation (SR) sources, providing extremely bright and energy-resolved X-ray beams, established NEXAFS spectroscopy as a powerful and widely used technique to investigate electronic and structural properties of both organic and inorganic samples of increasing complexity. Particularly, gas-phase NEXAFS studies allow for an investigation of well-defined targets prepared under desired conditions.
Unfortunately, gas-phase NEXAFS spectroscopy of large species such as biopolymers (e.g., proteins and DNA) and nanoparticles, as well as ionic species, is experimentally very challenging due to great difficulties in both bringing large molecules or particles intact into the gas phase and providing high-enough target density, photon flux, and interaction time needed to distinguish K-shell excitation processes. Only recently, the development of new experimental techniques has allowed performing gas-phase NEXAFS of nanoparticles, biopolymers, and ionic species.
Herein, we present the basic principles of NEXAFS spectroscopy and describe the state-of-the-art experimental approaches that allow for NEXAFS spectroscopy of large biopolymers and nanoparticles isolated in the gas phase. Finally, we present some key research finding spanning from relatively small biomolecules to large biopolymers and nanoparticles.
Aleksandar R. Milosavljević, Alexandre Giuliani, Christophe Nicolas

9. In Situ X-Ray Reciprocal Space Mapping for Characterization of Nanomaterials

In this chapter, we will focus on the small-angle X-ray scattering (SAXS) technique performed on planar samples in the grazing-incidence small-angle X-ray scattering (GISAXS) geometry. This particular method of SAXS allows a fast, nondestructive analysis of the near-surface electron density variations on the lateral length scale ranging from several angstroms up to several hundreds of nanometers with adjustable in-depth sensitivity down to several nanometers. Special emphasis will be given to GISAXS experiments with laboratory X-ray sources as these are much more easily accessible as compared to synchrotron facilities.
The steadily growing research field of applied nanomaterials calls for development of advanced analytical methods for rapid and nondestructive structural characterization. A relatively simple grazing-incidence small-angle X-ray scattering (GISAXS) technique is an efficient analytical tool for structural studies of layered nanomaterials and self-assembled nanostructures. The feasibility to obtain statistically relevant parameters that characterize position correlations and size distributions in the surface or embedded nanoparticle assemblies or interface correlations in the layered nanostructures render the GISAXS technique a valuable complementary tool to the standard real-space investigation methods like transmission electron microscopy (TEM), scanning tunneling microscopy (STM), scanning electron microscopy (SEM), atomic force microscopy (AFM), etc. While a sophisticated sample preparation is often required for the real-space imaging techniques, the GISAXS has no special requirements. This technique is especially valuable for a real-time tracking of the nucleation and growth phases of nanomaterials preparation due to the long X-ray attenuation length in air and absence of special requirements for the experimental setup.
In this chapter, we will review applications of GISAXS for in situ studies of nanomaterial formation including the nucleation, agglomeration, self-assembly, and reassembly phenomena. Majority if not all in situ GISAXS experiments of nanomaterial formation have been performed at synchrotron facilities, taking the advantage of their high X-ray photon flux and low beam divergence. Only the advent of new micro-focusing X-ray sources coupled with high-performance reflective X-ray optics has allowed such GISAXS in situ experiments in a laboratory as will be demonstrated on several examples in this chapter.
Peter Siffalovic, Karol Vegso, Martin Hodas, Matej Jergel, Yuriy Halahovets, Marco Pelletta, Dusan Korytar, Zdeno Zaprazny, Eva Majkova

10. X-Ray Powder Diffraction Characterization of Nanomaterials

We discuss here what important knowledge can be gained by X-ray diffraction (of course, more specifically, we talk of X-ray powder diffraction) experiments on nanoparticles and nanomaterials in general. Historically, the uses of X-ray diffraction have been to investigate (a) the crystal structure of materials at the atomic scale and (b) their microstructure, a broad term meaning deviations from perfect crystalline order on a scale that is larger than the atomic one but still microscopic. In fact, macroscopic properties of materials tend to depend on both of those. For nanomaterials, the focus is to understand how the small crystal domain extension and related phenomena influence properties that differ – often in a very useful way – from the parent crystalline material. This means that the focus is on the microstructure, due to the fact that reduced domain extension is a (strong) deviation from crystal order – this is by definition something that extends to infinity. Of course there exist crystalline phases that are stable only at the nanoscale – and in such case, the crystal structure determination still is very important. In this contribution, we shall review all modern experimental methods and especially – as this is the core of the method – the data analysis techniques currently used, from the oldest, based on the Bragg formalism to interpret crystal diffraction, to the newest, relying on atomic-scale modeling.
Antonio Cervellino, Ruggero Frison, Norberto Masciocchi, Antonietta Guagliardi

11. X-Ray Absorption Fine Structure Analysis of Catalytic Nanomaterials

X-ray absorption fine structure (XAFS) is an absorption spectroscopy which provides the material local structure with a bond distance of less than sub-Å precision. It does not require any long-range order nor special environment. Therefore, it is the suitable technique to characterize the catalytic nanomaterials under working conditions. This chapter presents an overview of the principle, emerging technology, and applications of XAFS in characterizing nanomaterials in catalysis.
Catalysts are materials that accelerate the reaction rate. The structure characterizations are difficult using diffraction methods because catalysts are often used as nanoclusters highly dispersed on oxide surfaces. In addition, the structures before, during, and after catalytic reactions are different from each other, and the in situ observation techniques of catalyst structures are highly required. X-ray absorption fine structure (XAFS) method is the most appropriate technique to investigate the catalyst nanomaterial structure under working conditions. We will review the history and principle of XAFS, followed by experimental setup and preparation of the sample. The analysis of XAFS will be briefly described, where the error estimations using Hamilton ratio method are discussed. We will mention its application to nanoparticles – monometallic and bimetallic under reaction conditions. We also describe the two emerging technologies in XAFS, called as ultrafast time-resolved XAFS and polarization-dependent total reflection fluorescence XAFS (PTRF-XAFS), which can provide new structural information we never have had with other characterization methods. Finally, we discuss its future perspective.
Wang-Jae Chun, Satoru Takakusagi, Yohei Uemura, Kyoko Bando, Kiyotaka Asakura

12. Contribution of Small-Angle X-Ray and Neutron Scattering (SAXS and SANS) to the Characterization of Natural Nanomaterials

Small-angle neutron scattering (SANS) and small-angle X-ray scattering (SAXS) are well-established techniques that have been successfully used in nanoscale structure determination of synthetic or manufactured systems used in soft matter or materials domain. In this chapter, we examine the application of such techniques to determine features of natural nano-materials encountered in the petroleum and new energy industry.
Successful implementation of industrial processes depends partly on understanding of systems in use conditions. Hence, for transformation of natural materials, a good knowledge of structure and behavior of these materials in process conditions is desirable. Among natural materials, few of them are nanostructured, and very few techniques are available to characterize these systems in thermodynamic and hydrodynamic conditions close to one encountered in the industrial process.
Small-angle scattering (SAS) techniques, either X-ray or neutrons, has the potential, but its use is sometimes limited to manufactured or synthetic systems. Laboratory SAXS equipments become more popular but remain sparse, especially in industrial environment. Large-scale facilities such as synchrotron or neutron centers have been used for academic research but open now more and more to industrial issues. The aim of this chapter is to discuss the contribution of SAXS and SANS to the characterization of natural nano-materials.
Two different nanostructured materials will be examined here. The first one comes from heavy cuts of petroleum where the largest and most aromatic molecules – the asphaltenes – self-associate. The behavior of such aggregates generally impairs processes. This aggregation behavior will be examined in the bulk as well as at liquid/liquid or liquid/solid interfaces. A special attention will be paid to observation close to use conditions. The second ones are geomaterials, including sedimentary rocks and gas and oil shales. For these materials, the pore size distribution (open versus closed porosity, accessibility of pores to various fluids) is of primary interest leading to a better understanding of gas storage and transport mechanisms and their controls.
We will show, through the study of these two nanostructured materials, how SAS techniques contribute to the characterization of such systems.
Loïc Barré

13. Synchrotron Small-Angle X-Ray Scattering and Small-Angle Neutron Scattering Studies of Nanomaterials

Small-angle scattering is a very powerful technique to probe structures of materials. X-ray, neutron, and light scattering techniques present structural information of materials in a wide range from nanometer to micrometer scale. Chemists, physicists, and engineers have used these techniques to study structures of various systems from hard to soft materials. In this topic, we focus upon soft materials such as polymers, gels, colloids, etc. We present a review of their recent studies with small-angle X-ray scattering (SAXS) and small-angle neutron scattering (SANS).
In a typical experimental setup, synchrotron SAXS and SANS are capable of probing structures of aggregates in the range of 1–100 nm. The use of ultra-small-angle scattering techniques such as ultra-small-angle X-ray scattering (USAXS) and ultra-small-angle neutron scattering (USANS) makes it possible to probe structures of aggregates with larger size on a micrometer scale. Here we review some structural studies on various soft materials, which form a hierarchical organization. Recent development of synchrotron radiation source and neutron facility allows us to obtain scattering data on various length scales. It is shown that combination of various scattering methods provides us with information on hierarchical structures of soft materials from a microscopic to macroscopic level. The structural analysis on each level is also presented in the text. Furthermore, contrast variation and contrast-matching SAXS and SANS methods are very effective for structural investigation of multicomponent nanomaterials, e.g., these methods are very useful to probe internal structures of complex systems such as polymer micelles, polymer–inorganic nanocomposite gels, and rubber-filler systems swollen in an organic solvent.
Hiroyuki Takeno

14. Quasielastic Neutron Scattering: An Advanced Technique for Studying the Relaxation Processes in Condensed Matter

Quasi-elastic neutron scattering (QENS) is a part of more general inelastic neutron scattering and is a very powerful technique to explore the motions in biomolecules, polymers, simple liquids, alloy melts, and soft matter in general. In this chapter, we will discuss basic theoretical aspects of QENS, instrumentation, types of motion in liquids and solids, understanding these motions from the QENS data, and recent studies using QENS.
The QENS is a versatile technique to study the relaxation processes in the condensed materials, particularly in liquids. This technique typically uses cold neutrons as the energy of the cold neutrons is in a similar range with relaxation process in liquids and the wavelength is of the order of the interatomic distance in condensed materials. The QENS techniques can provide much more information on the relaxation process (motions) as compared to other techniques, e.g., dielectric spectroscopy, nuclear magnetic resonance, and tracer diffusion measurements. The QENS technique is particularly helpful for understanding the microscopic dynamics of soft and biomaterials since these materials contain a large number of hydrogen atoms, and the hydrogen atom is very sensitive to neutron scattering due to a large scattering cross section.
Neutron scattering offers not only QENS but also other scattering techniques like diffraction, inelastic, reflectometry, triple axis, small-angle scattering, and neutron imaging. However, facilities available for neutron scattering research are very few in the world. The production of neutrons is very expensive and typically requires either a nuclear reactor or a target-based source and also detection of neutrons need materials like3He, which is rare on earth, are the reason for it. Over the last few decades, few neutron scattering facilities like Spallation Neutron Source, National Institute of Standards and Technology (NIST) Center for Neutron Research (NCNR), Australian Neutron Scattering Facility, Forschungsreaktor Munchen (FRM)-II Germany, ISIS-UK, and JAPARK at Japan have been built. Also, there has been tremendous improvement in neutron scattering instrumentations, particularly building of new backscattering and spin echo spectrometers in the abovementioned facilities. At present relaxation process in a time scale of 0.1 ps–350 ns can be measured using neutron scattering.
In the beginning, QENS was mainly used to study the diffusion in simple liquids and hydrogen diffusion, in metals, etc. At present the QENS technique has been used in many fields of science ranging from colloids, polymers, ionic liquids, hydrogen storage, food processing, biotechnology, and environments. In this chapter we will provide an overview of basic theoretical understanding of QENS, concepts of instrumentation, data analysis, identification of transport mechanism from QENS data, and recent research results using QENS.
Madhusudan Tyagi, Suresh M. Chathoth


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