X-Ray Absorption and X-Ray Emission Spectroscopy: Theory and Applications

List of Contributors

Roberto Alonso-Mori LCLS, SLAC National Accelerator Laboratory, Menlo Park, CA, USA

Kiyotaka Asakura Catalysis Research Center, Hokkaido University, Sapporo, Japan

Simon R. Bare UOP LLC, Des Plaines, IL, USA

François Baudelet Synchrotron SOLEIL, St Aubin, France

Javier Blasco Instituto de Ciencia de Materiales de Aragón (ICMA), CSIC-Universidad de Zaragoza, Zaragoza, Spain

Elisa Borfecchia Department of Chemistry and INSTM Reference Center, University of Turin, Italy; NIS Centre, University of Turin, Italy

Federico Boscherini Department of Physics and Astronomy, University of Bologna, Bologna, Italy

Lin X. Chen Chemical Sciences and Engineering Division, Argonne National Laboratory, Lemont, IL, USA; Department of Chemistry, Northwestern University, Evanston, IL, USA

Marine Cotte European Synchrotron Radiation Laboratory, Grenoble, France; Laboratoire d'archéologie Moléculaire et Structurale, LAMS, Paris, France

Jeffrey Cutler Canadian Light Source Inc., Saskatoon, Canada

Paola D'Angelo Department of Chemistry, University of Rome La Sapienza, Rome, Italy

Melissa A. Denecke Dalton Nuclear Institute, The University of Manchester, Manchester, UK

François Farges Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie (IMPMC), Muséum national d'Histoire naturelle and UMR CNRS 7590, Paris, France

Marcos Fernández-García Instituto de Catálisis y Petroleoquímica (CSIC), Madrid, Spain

Adriano Filipponi Dipartimento di Scienze Fisiche e Chimiche, Universit` degli Studi dell'Aquila, L'Aquila, Italy

Ronald Frahm Department of Physics, University of Wuppertal, Wuppertal, Germany

Joaquín García Instituto de Ciencia de Materiales de Aragón (ICMA), CSIC-Universidad de Zaragoza, Zaragoza, Spain

Bruce C. Gates Department of Chemical Engineering and Materials Science, University of California, Davis, CA, USA

Wojciech Gawelda European XFEL GmbH, Hamburg, Germany

Diego Gianolio Diamond Light Source Ltd, Didcot, UK

Pieter Glatzel European Synchrotron Radiation Facility, Grenoble, France

Stéphane Grenier Univ Grenoble Alpes, Inst NEEL, F-38042 Grenoble, France; CNRS, Inst NEEL, F-38042 Grenoble, France

Jean-Paul Itié Synchrotron SOLEIL, St Aubin, France

Yves Joly Univ Grenoble Alpes, Inst NEEL, F-38042 Grenoble, France; CNRS, Inst NEEL, F-38042 Grenoble, France

Kevin Jorissen Department of Physics, University of Washington, Seattle, WA, USA

Innokenty Kantor European Synchrotron Radiation Facility, Grenoble, France

Joshua J. Kas Department of Physics, University of Washington, Seattle, WA, USA

Joseph D. Kistler Department of Chemical Engineering and Materials Science, University of California, Davis, CA, USA

Christian König General Energy Department, Paul Scherrer Institute, Villigen, Switzerland

Thomas Kroll SLAC National Accelerator Laboratory, Stanford University, Menlo Park, CA, USA

Carlo Lamberti Department of Chemistry, University of Turin, Italy; Southern Federal University, Rostov-on-Don, Russia

Kirill A. Lomachenko Southern Federal University, Rostov-on-Don, Russia; Department of Chemistry, University of Turin, Turin, Italy

Marcus Lundberg Department of Chemistry, Uppsala University, Uppsala, Sweden

Giorgio Margaritondo Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland

Olivier Mathon European Synchrotron Radiation Facility, Grenoble, France

Christopher J. Milne SwissFEL, Paul Scherrer Institute, Villigen, Switzerland

Oliver Müller Department of Physics, University of Wuppertal, Wuppertal, Germany

Maarten Nachtegaal General Energy Department, Paul Scherrer Institute, Villigen, Switzerland

Katharina Ollefs European Synchrotron Radiation Facility, Grenoble, France

Sakura Pascarelli European Synchrotron Radiation Facility, Grenoble, France

David E. Ramaker Department of Chemistry, George Washington University, Washington, USA

Bruce Ravel National Institute of Standards and Technology, Gaithersburg, MD, USA

John J. Rehr Department of Physics, University of Washington, Seattle, WA, USA

Andrei Rogalev European Synchrotron Radiation Facility, Grenoble, France

Jean-Pascal Rueff Synchrotron SOLEIL, St Aubin, France

Pedro Serna Instituto de Tecnología Química, Universidad Politécnica de Valencia–Consejo Superior de Investigaciones Científicas, Valencia, Spain

Dimosthenis Sokaras SSRL, SLAC National Accelerator Laboratory, Menlo Park, CA, USA

Alexander V. Soldatov Southern Federal University, Rostov-on-Don, Russia

Edward I. Solomon Department of Chemistry, Stanford University, Stanford, CA, USA

Gloria Subías Instituto de Ciencia de Materiales de Aragón (ICMA), CSIC-Universidad de Zaragoza, Zaragoza, Spain

Yoshio Suzuki Japan Synchrotron Radiation Research Institute, SPring-8, Kouto, Sayo, Japan

Jakub Szlachetko SwissFEL, Paul Scherrer Institute, Villigen, Switzerland; Institute of Physics, Jan Kochanowski University, Kielce, Poland

Yasuko Terada Japan Synchrotron Radiation Research Institute, SPring-8, Kouto, Sayo, Japan

Jeroen A. van Bokhoven Swiss Light Source, Paul Scherrer Institute, Switzerland; Institute for Chemical and Bioengineering, ETH Zurich, Switzerland

Fabrice Wilhelm European Synchrotron Radiation Facility, Grenoble, France

Max Wilke Deutsches GeoForschungsZentrum, GFZ, Potsdam, Germany

Foreword

With pleasure we accepted the invitation of the editors to write a Foreword for the book XAS and XES: Theory and Applications. This book is a follow-up to X-Ray Absorption: Principles, Applications and Techniques of EXAFS, SEXAFS and XANES, Wiley, 1987, which we edited.

X-ray absorption spectroscopy has changed considerably since the 1980s when EXAFS and XANES were relatively new techniques, synchrotrons were not dedicated and almost no user facilities were available. Night-time collection of data during a parasitic mode at the Stanford synchrotron was an adventure, to say the least. We survived it by listening to Bach's cantatas, as rendered by one of our PhD students.

When we began working with EXAFS spectroscopy in the 1980s, adsorbate-induced structural changes and metal-support interactions were hot topics in catalytic research. At that time we were interested in the change in morphology that CO adsorption induced on a γ-Al2O3-supported Rh catalyst and in the structure of the interface between rhodium metal particles and the catalyst support. To study the morphology change and metal-support interface in situ, we applied EXAFS, but at that time it was necessary to make the long trip to the Stanford Synchrotron in the USA where we were grateful for the measuring time allotted to us by our American colleagues Dale Sayers and Jim Katzer. Our first results were published in 1983 [1] and 1985 [2]. These studies demonstrated the exciting potential of EXAFS. We were, of course, not the only scientists interested in EXAFS. There was a need in the scientific community for a basic tutorial on X-Ray Absorption Fine structure present in the near edge region (XANES) and beyond (EXAFS). Inspired by stimulating contacts with scientific colleagues from around the world and the constant but positive pressure of the publisher (Wiley), we decided to edit a book that would provide information to students and scientists as a reference book to conduct XAS studies and, more advanced, to measure and interpret data. Information about a visit to a synchrotron was even more important in those days of parasitic measuring than today, so the physics of a synchrotron was included. We were fortunate enough to receive contributions from the most qualified and renowned scientists. Since then, the book has been used by many researchers, and more than 1,400 copies have been sold.

The field of x-ray absorption has developed considerably since 1987. On average, about 2000 papers on XAS are published yearly in scientific journals. More sophisticated instrumentation with extremely high resolution has enabled the development of new tools and techniques, such as x-ray emission spectroscopy. Promising applications of this technique have been developed in the past 20 years, making this book an essential reference work in this field.

It is a great pleasure that our student and collaborator, Jeroen A. van Bokhoven, and his colleague, Carlo Lamberti, have taken the initiative to edit a new volume, with Wiley as the enthusiastic publisher. Twenty-eight years after the appearance of our book, we are pleased that highly qualified scientists have made contributions to XAS and XES: Theory and Applications, which also includes x-ray emission spectroscopy. These contributions and the work of the enthusiastic and well-known editors have resulted in a book, which not only provides an essential introduction to the field of XAS and XES, but also demonstrates the enormous potential of these techniques for the study of structural and electronic properties of many types of matter.

The book has 27 chapters, divided into two volumes. The 12 chapters in Volume I describe the experimental and theoretical aspects of XAS and XES. The 15 chapters in Volume II focus on the enormous potential of both spectroscopic techniques with many important applications. The first volume contains an introduction by the editors. They start with a detailed historical overview of the past 100 years of x-ray absorption, mentioning many important scientific contributions. At this point we would like to refer to the monumental papers in 1971 [3] and in 1974 [4] by our friends Dale Sayers, Ed Stern and Farrel Lytle. Their contributions were crucial in developing EXAFS from a scientific curiosity to an extremely important analytical tool. Both Ed Stern and Dale Sayers made important contributions to our book, published in 1987.

Jeroen A. van Bokhoven and Carlo Lamberti have performed a heroic task in completing the new book in such a short time. Experts in the various subfields reviewed the chapters. The book will be of great importance for beginners in the fields of XAS and XES. They will find all the information necessary to become experts. Also experienced users active in particular subfields of both spectroscopies will learn in this book about the enormous potential of both XAS and XES for other applications. This will lead to more and better experiments and thus to better science. We are confident that the new book will find at least as great a readership as our book.

Diek C. Koningsberger (Professor emeritus)

Group of Inorganic Chemistry and Catalysis

Utrecht University, The Netherlands

Roel Prins

Professor emeritus Catalysis

ETH Zurich, Switzerland

References

H. F. J. van ‘t Blik, J. B. D. A. van Zon, T. Huizinga, J. C. Vis, D. C. Koningsberger, R. Prins (1983) An extended x-ray absorption fine structure spectroscopy study of a highly dispersed rhodium/aluminum oxide catalyst: the influence of carbon monoxide chemisorption on the topology of rhodium, J. Phys. Chem., 87, 2264–2267.

J. B. D. A. van Zon, D. C. Koningsberger, H. F. J. van ‘t Blik, R. Prins, D. E. Sayers (1984) On the detection with EXAFS of metal-support oxygen bonds in a highly dispersed rhodium on alumina catalyst, J. Chem. Phys., 80, 3914–3915.

D.E. Sayers, E.A. Stern, and F.W. Lytle (1971) New technique for investigating noncrystalline structures: Fourier analysis of the extended x-ray absorption fine structure, Phys. Rev. Lett., 27, 1204–1207.

E.A. Stern, D.E. Sayers, and F.W. Lytle (1975) Extended x-ray-absorption fine-structure technique. III. Determination of physical parameters, Phys. Rev. B, 11, 4836–4846.

Part I

Introduction: History, XAS, XES, and Their Impact on Science

CHAPTER 1

Introduction: Historical Perspective on XAS

Carlo Lamberti¹,² and Jeroen A. van Bokhoven³,⁴

¹Department of Chemistry, University of Turin, Italy

²Southern Federal University, Rostov-on-Don, Russia

³Swiss Light Source, Paul Scherrer Institute, Switzerland

⁴Institute for Chemical and Bioengineering, ETH Zurich, Switzerland

1.1 Historical Overview of 100 Years of X-Ray Absorption: A Focus on the Pioneering 1913−1971 Period

The x-ray absorption spectroscopy (XAS) adventure started about one hundred years ago and has come a long way since. The technique remained a curiosity for much of this time, representing a minor branch of science, developed by only a few highly motivated and enthusiastic scientists. without any apparent possibility of practical application and without a solid and comprehensive theory able to describe and predict the experimental observations done, on gases, liquids and solid (crystalline and amorphous) systems. In 1971, Sayers, Stern and Lytle made ground-breaking progress when they applied Fourier analysis to the point-scattering theory of x-ray absorption fine structure, so as to formally invert the experimental data (primarily collected in the photoelectron wave-vector space) into a radial distribution function. For the first time, they were able to quantitatively determine structural parameters, such as the bond distance, coordination number, as well as the thermal and disorder parameters [1]. In the 44 years following that key publication, the field developed exponentially. Nowadays it is impossible to imagine frontier research in materials science, solid state physics and chemistry, catalysis, chemistry, biology, medicine, earth science, environmental science, cultural heritage, nanoscience, etc. without the contribution of XAS and related techniques. In this introductory chapter we provide a brief sketch of the main events that have established XAS and related techniques as leading scientific characterization tools.

After the discovery of x-rays in 1895 by Röntgen [2, 3], it took a while before the first x-ray absorption spectrum was observed by de Broglie in 1913 [4]. De Broglie mounted a single crystal on the cylinder of a recording barometer, using a clockwork mechanism to rotate the crystal around its vertical axis at a constant angular speed. As the crystal rotated, the x-rays scattered at all angles between the incident beam and the diffraction planes hence, according to the Bragg law (2dhkl sin θ = λ = hc/E, with c being the speed of light, c = 2.9979 10+8 m/s, and h being the Planck constant, h = 6.626 × 10−34 J s [5], so that hc = 12.3984 Å keV) [6–8], changing the x-ray energy E. X-rays of varying intensities were recorded on a photographic plate. Two distinct discontinuities were observed on the film, which were found to be independent of the setting of the x-ray tube. These proved to be the K-edge absorption spectra of silver and bromine atoms contained in the photographic emulsion. As the spectrographic dispersion was poor at these short wavelengths, the spectra were of low energy resolution and the fine structure was not resolved. Successive work by de Broglie in this field proved remarkable [9, 10]. A posteriori, it is curious to note that de Broglie's famous intuition concerning the association of a wavelength (λ) to any massive particle with momentum (p): λ = h/p [11], is actually the key to understanding the phenomenon related to the fine structure of the x-ray absorption spectra.

In 1913, Moseley published his empirical law describing the frequencies (energies, E = hν) of certain characteristic x-rays emitted from pure elements, named Kα and Lα lines according to the successive Siegbahn notation. Emission energies were found to be approximately proportional to the square of the element atomic number Z [12]. This finding supported Bohr's model of the atom [13–15] in which the atomic number corresponds to the positive charge of the nucleus of the atom measured in |e| units: |e| =1.602 10−19 C. Almost 50 years after Mendeleev's milestone work, Moseley's findings suggested that the atomic weight A was not a deciding player in the periodicity of physical and chemical properties of the elements within the periodic table. In contrast, the properties of the elements varied periodically with the atomic number Z. This x-ray emission study is historically important because it quantitatively justifies the nuclear model of the atom, where the atom's positive charge is located in the nucleus and associated on an integer basis with the atomic number. Until Moseley's work, the term atomic number was merely a label to identify the place of each element in the periodic table, and it was not known to be associated with any measurable physical quantity.

In 1916, in Lund in Sweden, Siegbahn and Stenström [16–18] developed the first vacuum x-ray spectrometer [19, 20] (Figure 1.1(a)), thereby taking a fundamental technological step in the progress of x-ray spectroscopy. With this kind of innovative technology, the fine structure beyond the absorption edges of selected atoms was – for the first time – experimentally observed by Fricke in 1920 [21] and by Hertz in 1921 [22]. Fricke detected the K-edges for the elements from magnesium (Z = 12, E0 = 1.3 keV) up to chromium (Z = 24, E0 = 6.0 keV) [21], whereas Hertz canvassed the L-edges of cesium (Z = 55, E0 = 5.0 keV) up to neodymium (Z = 60, E0 = 6.2 keV) [22]. In the period before World War II, other authors reported analogous behavior on several different absorption edges [20, 23–37].

Figure 1.1 (a) Scheme of the vapor cell and x-ray spectrometer used by Hanawalt [20] to measure the fine structures in K-edge x-ray absorption spectra of molecules in the vapor phase. The cell was composed of: two furnaces (B and A), the former to host the solid phase and control the vapor pressure via the temperature, the latter to prevent re-condensation of the evaporated phase; a long quartz tube hosting the vapor phase (V) equipped at the end with two concave windows (W) as thin as 3 μm so as to maintain a vacuum and remain sufficiently transparent to x-rays. The spectrometer consists of: an x-ray tube of the Siegbahn type (X); slits used to collimate the incoming x-rays (S); a calcite (CaCO3) crystal used as a monochromator (C); a quartz tube fluxed with H2 (H) and equipped with biological x-ray transparent membranes (G) acting as windows; and a photographic plate used as a detector (P). This spectrometer was able to cover the 4.9−12.4 keV spectral region, corresponding to 2.5 Å > λ > 1.0 Å and represents the historical prototype of a dispersive spectrometer (see [38], Chapter 8 in this volume). Depending on the absorbing gas, the length of time ranging from 4 to 30 h is needed to impress the photographic plate as shown in (b), where the energy increases from top to bottom. The absorption edge and the successive modulations are clearly visible in (b). The photographic images were then converted into absorption-energy plots such as those reported in (c) and (d) for AsCl3 (as K-edge at 11.8 keV) and Zn (K-edge at 9.6 keV), respectively. Because only I1 is measured in the set-up, the spectra appear inverted. The first resonance after the edge, representing a maximum in the absorption, was called the white line while the successive minimum in the absorption spectrum was called the black line. The former term is retained in the current terminology, whereas the latter has been lost. Adapted from Hanawalt, 1931, [20], with permission American Physical Society.

Hanawalt made remarkable observations in 1931 [20], observing that the chemical and physical state of the sample affects the fine structure of the corresponding XAS spectra. Using the experimental set-up reported in Figure 1.1(a), consisting of a quartz cell allowing the XAFS spectra of different molecules sublimated in the vapor phase to be acquired, and collecting XAFS spectra on a photographic plate (Figure 1.1(b)), he was able to make two empirical observations of fundamental importance. First, he proved that substances sublimating in the molecular form, such as arsenic (4Assolid → (As4)gas) and AsCl3 (Figure 1.1(c)), are characterized by XAFS spectra exhibiting different fine structures above the edge when measured in the solid or in the vapor phase. Second, he observed that the monatomic vapors of zinc (Figure 1.1(d)), mercury, xenon and krypton elements exhibit no secondary structure. These incredibly advanced experiments already at this stage captured the main messages of EXAFS spectroscopy, but it took several years for the correct interpretation and decades before quantitative data could be extracted and the full potential of EXAFS exploited [1].

The first theoretical attempt to explain the fine structure in the XAS spectra was proposed in 1931 and 1932 by Kronig [39, 40], who developed a model based on the presence of long-range order in the probed system. The Kronig long-range order theory can be summarized in the following equation:

(1.1)

where Wn are the energy positions corresponding to the zone boundaries (i.e., not the absorption maxima or minima, but the first rise in each fine structure maximum); h is the Planck's constant; m is the electron mass (m = 9.1094 10− 31 kg); α, β, γ are the Miller indices; d is the lattice parameter and θ is the angle between the electron direction and the reciprocal lattice direction. The Kronig long-range order equation (1.1) was fundamentally simple to apply and interpret, and experimental spectra presented an approximate agreement with the theory. For any observed absorption features, there was always some (α, β, γ) triplet able to match the experiment with the prediction of the Kronig's model. However, the stronger Bragg reflections of the lattice did not always correlate with the most intense absorption features of the EXAFS spectra, as intuitively expected. However, agreement was tantalizingly close and the equation was uniformly implemented as a check for measured data to obtain a Kronig structure.

As we now know, this theory is intrinsically incorrect owing to its baseline assumptions, which do not accurately explain the EXAFS signals observed in gases, liquids, solutions and amorphous solids. Stimulated by the experiments of Hanawalt [20] (see Figure 1.1), Kronig himself presented a new theory in 1932 based on the fundamental role of short-range order to explain the fine structure observed in the spectra of diatomic molecules in the gas phase [41]. The new approach explained the XAFS features in terms of modulation of the wave function of the final state of a photoelectron upon its scattering from the potentials of neighboring atoms. Implemented successively by Petersen [42–44] and by many other authors in the 1930s through to the 1960s [45–61], this approach represents the basis of the modern concept of XAFS, though it was still unable to provide quantitative information on the local structure of the absorbing atom in the investigated samples. At that stage, XAFS was still just a spectroscopic curiosity and not yet a powerful characterization tool. In most reported cases [20, 21, 25, 30, 34, 50, 60, 62], the discussion was limited to a table containing a list of the observed maxima and minima of the fine structure of a given material, and a comparison of these values alongside those predicted by the other theories of the time, vide supra. No quantitative information was extracted and only qualitative conclusions could be reached: (1) several authors observed that the amplitude of the XAFS oscillations decreases with increasing temperature [31, 57, 59, 61]; (2) it was observed that metals with the same crystal structure had similar fine structures [24, 30, 33, 34]; and (3) in 1957, Shiraiwa et al. [54] measured the x-ray absorption spectra of crystalline and amorphous germanium, observing that the shape of the fine structure was the same on the two materials though oscillations were less intense and disappeared at lower energies in the amorphous phase than in the crystalline phase. Similar conclusions were reached in 1962 by Nelson et al. [58] who measured germanium (IV) oxide in the amorphous state and in both hexagonal and tetragonal crystalline forms.

From an experimental point of view, a fundamental improvement in the instrumentation was achieved in the 1960s when commercial diffractometers were modified so that absorption spectra of much better quality could be obtained, though still using conventional x-ray tubes as a source [62–64]. A silicon crystal, acting as a single-crystal monochromator, was positioned on a goniometer configured to allow step scaling. Diffraction experiments carried out using this assembly allowed scientists to scan the energy through the desired absorption edge. By mounting and dismounting the sample in the beam path, both I1 and I0 could be detected, thereby allowing a precise determination of the absorption coefficient μ(E) = (1/x) ln[I0(E)/I1(E)], being x the sample thickness. With this experimental set-up, Van Nordstrand [63, 64] performed a systematic study on many transition metal compounds and classified their XANES spectra according to the atomic structure and valence of the metal element in the compound, also noting the chemical shift with valence. This fingerprint classification was used to identify the structural/valence form of elements of interest in catalysts, which are usually so highly dispersed that their diffraction patterns cannot be measured. This work by Van Nordstrand was the first example of the application of XANES in catalysis.

The crucial advance in the interpretation of the post-edge oscillations (now referred to as EXAFS) occurred in 1971 [1], when it was shown by Sayers, Stern and Lytle that a Fourier transform of the background-subtracted oscillations (Figure 1.2(a)) gives a pattern in R-space close to the function of radial distribution of atomic density (Figure 1.2(b)). From the EXAFS spectra collected on crystalline and amorphous germanium, they were able to extract the following quantitative structural information: (1) the crystalline distance to first and second neighbors in amorphous germanium within 1% accuracy; and (2) by comparing the relative second-shell-peak intensities of the crystalline and amorphous samples, the authors were able to conclude that the Debye-Waller factor is six times larger in the amorphous phase; from this they deduced that the tetrahedral bonds are distorted by about 5° in the amorphous phase [1]. To achieve these insights must have been extremely exciting. It is remarkable that such accurate conclusions were obtained while working with experimental spectra collected using an x-ray tube as a source.

Figure 1.2 (a) Smoothed experimental EXAFS data for crystalline (top) and amorphous (bottom) germanium, plotted as a function of the photoelectron energy E. (b) Fourier transform of the EXAFS functions reported in (a). The numbers above the peaks indicate the measured distances in Å. Adapted from Sayers, et al., 1971, [1] with permission from American Physical Society; E.A. Stern and F.W. Lytle.

This work represented the milestone for EXAFS spectroscopy and was supported and further implemented in more formal derivations based on Green's function and generalization to muffin-tin scattering potentials. This development was performed through successive works by Sayers, Stern and Lytle and their co-authors [65–69] and by other independent groups [70–74].

Starting in the 1970s, the cumulative availability of several and progressively more brilliant and broadband synchrotron radiation sources [75–79] established EXAFS and XANES spectroscopies (and successively XES) as a reliable tool to determine and understand the structural and electronic configuration of unknown systems. During the 1980s and 1990s in particular, the development and the distribution of codes for data analysis saw a rapid expansion of EXAFS and XANES spectroscopies into the broader scientific community for the purposes of structural characterization of materials. Among the many data processing packages available, we only mention: GNXAS [80–84], developed by Natoli, Filipponi, and Di Cicco; EXCURVE [85–88] by Binsted et al., and FEFF [89–101] developed by Rehr et al. A plethora of codes developed in the past two decades were conceived with the intention of using theoretical phases and amplitudes generated by the different releases of FEFF. This is particularly relevant because packages, such as FEFFIT [102, 103], had a huge impact in making the EXAFS data analysis more user-friendly and thus accessible. FEFFIT is developed by Newville, and the ATHENA, ARTEMIS, HEPHAESTUS packages are developed by Ravel and Newville [104]. For a more complete overview of the codes developed for EXAFS data analysis, see the recent review by Bordiga et al. [105].

Overall, the impact of XAS on a variety of scientific disciplines has been boosted by: (1) the existence of a solid theory allowing a quantitative analysis of the XAS spectra [1]; (2) the increased availability of beamlines at synchrotron radiation facilities allowing high quality XAS spectra to be collected; and (3) the development of reliable codes allowing data analysis to be performed in a safe, reproducible, and controllable way. The improved usability of XAS is self-evident on the ISI Web of Science in the period between 1971 and December 2014 (Figure 1.3). The milestone of one hundred papers per year was reached and passed in the year 1981. At that stage, the community was sufficiently mature to organize the first XAFS conference (XAFS I) at Daresbury in the United Kingdom, with a total of 27 papers published in the proceedings. The community progressively grew, reaching 1000 published papers in 1995 and more than 1500 from 2005 onwards. Statistics concerning papers published in the proceedings of the XAFS conferences from XAFS I to XAFS XIV, in Camerino, Italy, were reported in Table 1 of [105]; the XAFS XV conference in Beijing, China, published 136 papers in its proceedings in J. Phys.: Conf. Ser., 430 (2013). Strong correlations are observed between the date of the conference proceedings and the number of papers published by the XAFS community (the years labeled with a Roman numeral are those where the proceedings of the corresponding XAFS conference were published). Notwithstanding this fact, the trend is clear – the community publishes more than 2000 papers per year. When x-ray emission is included in the tally, this number is in excess of 2000 (see inset in Figure 1.3). We believe that the number of possible publications is limited by access to synchrotron radiation. At synchrotrons, x-ray absorption beamlines are among those with the highest oversubscription. High oversubscriptions clearly indicate the high demand of XAS experiments from the overall scientific community and suggest that a higher number of papers per year would be published if more beam time were available.

Figure 1.3 Number of papers published per year found using (XAFS OR EXAFS OR XANES OR x ray absorption spectroscopy OR x-ray absorption spectroscopy OR x ray absorption fine structure OR x-ray fine structure) as the search key. Spanned period 1971−December 2014; total number of papers >35,000. Roman numerals mark the years where the proceedings of the XAFS conference were published in journals indexed by ISI Web of Science. Inset: number of papers published per year found using (XES OR RIXS OR x ray emission spectroscopy OR x-ray emission spectroscopy) as the search key. Spanned period 1985−2014; total number of papers 1910–1934 (1987–2011 in the 1971−2014 period). Source: ISI Web of Science service.

The inset in Figure 1.3 describes an analogous bibliographic research for the papers related to XES in the 1985–2014 time span. The number of papers is much lower but a similar upward trend is observed. This community has passed the threshold of 50 papers per year in 1988, doubling in volume since 2010. In this case, the number of papers per year is even more severely limited by the accessibility to high flux beamlines equipped with sophisticated crystal analyzers that are described in [106], Chapter 6 in this volume. More and more beamlines are installing crystal analyzers, heralding the rapid development of this technique in the near future.

If we consider the birth of x-ray spectroscopy in 1913 on a continuum with the appearance of the paper by de Broglie [4], as discussed above, then the 1971 milestone paper by Sayers, Stern and Lytle [1] appears roughly in the middle of the XAS history (1913–present). Partial and more complete reviews of the pioneering 1913–1971 (58 years) period of x-ray absorption spectroscopy can be found in the literature [60, 95, 105, 107–114], from which the present section has drawn inspiration. The remaining 26 chapters in this volume provide a detailed account of the progress made by x-ray absorption and x-ray emission spectroscopy in almost all scientific directions in the period 1971−2014 (43 years), while providing perspectives for the following years.

1.2 About the Book: A Few Curiosities, Some Statistics, and a Brief Overview

The idea and the ambition to compile a book that updates the famous book edited by Koningsberger and Prins [115] in 1988 was born in the summer of 2013, at a dinner between van Bokhoven and Lamberti in the typical Piedmont restaurant, Le tre galline (literally The Three Hens) in downtown Torino. Catalyzed by excellent food and wine, that evening produced the very first list of chapters and prospective authors. The project was then pitched to Wiley, who accepted it with rapid enthusiasm, and the invitation letters were then sent to the authors. We are proud that most of the names on that list are now authors of chapters in this book.

With respect to the outline of the book as it stood after consultation with the anonymous reviewers of the proposed plan, only three chapters are missing. These three chapters were supposed to cover the following aspects: (1) theoretical methods of XES spectra simulation; (2) combined techniques: XAFS and XES experiments performed simultaneously with other data collections (XRD, SAXS, IR, Raman, UV-vis, etc.); and (3) the biological and medical applications of XAS. Point (1) has been partially covered by Rehr and co-workers (Sections 3.3.3, 3.3.5 and 3.3.6 in Chapter 3) [101] and by Glatzel and co-authors [106] (Section 6.2 in Chapter 6). Point (2) was largely covered by Fernández García [116] (Section 12.6 in Chapter 12) while point (3) remains unfortunately absent. We recommend that interested readers refer to the literature for more information on this topic [117–173]. Overall, we are very happy to deliver 29 out of the initial 30 subjects, and especially proud to present the outstanding work of so many prestigious researchers.

The author selection was the fundamental initial stage of this project. In all cases, an accurate bibliographic analysis was made with a view to inviting the most authoritative scientists in each specific sub-field. Of course, in many cases where the potential authors enjoyed comparable prestige, our choice was most likely biased by our personal networks and relationships. Notwithstanding this systematic bias, this book comprises the contributions of 57 authors from 11 countries (Canada, France, Germany, Italy, Japan, Poland, Russia, Spain, Switzerland, the United Kingdom, and the United States), on three different continents (Figure 1.4). Most of the authors are affiliated to universities or to synchrotron radiation sources, but public and private research centers are also fractionally represented (inset of Figure 1.4).

Figure 1.4 Number of contributions to the book from the different countries, from left to right, in alphabetical order. The indicated country reflects the affiliation of the authors, not their citizenship. Inset: number of contributions to the book from the types of institution of the authors. In both cases, authors contributing to more than one chapter have been counted more than once.

Academic contributions came from Bologna (Italy), Davis (California, USA), Hokkaido (Japan), Kielce (Poland), L'Aquila (Italy), Madrid (Spain), Manchester (UK), Paris (France), Potsdam (Germany), Rome La Sapienza (Italy), Stanford (California, USA), Turin (Italy), Wuppertal (Germany) and Zaragoza (Spain) and from EPFL Lausanne (Switzerland), ETH Zürich (Switzerland), Northwestern University (Illinois, USA), Southern Federal University (Russia), and Universidad Politécnica de Valencia (Spain).

We are also pleased to present contributions from many of the world's most important synchrotron radiation facilities: the Argonne National Laboratory (USA), the Canadian Light Source Inc. (Canada), the Diamond Light Source (UK), the European Synchrotron Radiation Facility (France), European XFEL Hamburg (Germany), the Japan Synchrotron Radiation Research Institute (Japan), the SLAC National Accelerator Laboratory (USA), SPring-8 (Japan), the Swiss Light Source (Switzerland), SwissFEL (Switzerland), and Synchrotron SOLEIL (France). We are confident that the DESY Hamburg (Germany), the Advanced Photon Source (Argonne, USA) and the BNL (USA) institutions are represented by the respective contributions of Professor R. Frahm in Chapter 7, L. X. Chen in Chapter 9 and B. Ravel in Chapter 11, because these authors spent an important portion of their scientific careers working at these establishments. As for the contribution coming from research centers, we have authors from the French CNRS, the Institut NÉEL in Grenoble, the IMPMC in Paris, the Muséum National d'Histoire Naturelle de Paris, the National Institute of Standards and Technology in the USA, and UOP LLC (a Honeywell company in Des Plaines, IL). We consider Chapter 24 on industrial use to be a unique addition to the book and a clear illustration of the maturity and value of x-ray spectroscopy.

The book is divided into two volumes. Volume I comprises Chapters 1–12 and mainly deals with the experimental and theoretical aspects of x-ray absorption and emission spectroscopies. After this Introduction, it continues with Margaritondo's Chapter 2 [174], where the physics of photon emission by accelerated charged particles in bending magnets, wigglers, undulators, and free electron lasers is described in a pedagogic and rigorous way. The concepts of photon flux and source brightness are introduced, as well as the time structure of synchrotron radiation so important for pump and probe experiments [175]. Elements of beamline optics such as mirrors, monochromators, and focusing elements, as well as x-ray detectors, are included. In Chapter 3, the Rehr group reviews the progress made in recent years towards both theory and ab initio codes in calculating XAS spectra, with a particular emphasis on the EXAFS part [101]. The Real-Space Multiple Scattering Approach is discussed in detail, as well as its close connection with the excited state electronic structure. In Chapter 4, Joly and Grenier [176] discuss the general equations used to describe the x-ray absorption process by matter in the XANES region. They describe the primary codes used to compute XANES spectra and explain how the Finite Difference Method allows researchers to avoid the muffin-tin approximation.

In Chapter 5, Gianolio provides a concise and efficient guide to direct experimenters in all the practical aspects that have to be faced prior to and during an XAS experiment in pursuit of optimal data collection [177]. All the stages in planning, preparing, and executing XAS experiments are described, revealing the common pitfalls that should be avoided. This chapter is highly recommended for inexperienced users though it may also be useful for the more experienced ones.

Glatzel, Alonso-Mori, and Sokaras describe XES instrumentation in Chapter 6, including the theory and some applications of hard x-ray photon-in/photon-out spectroscopy [106]. In this chapter the authors discuss the first decay of the XAS excited state back to the ground state, and describe XES as a second-order optical process which includes resonant inelastic x-ray scattering (RIXS) and high energy resolution fluorescence detected (HERFD) and partial fluorescence yield (PFY) XAS. Standard XAS is contrasted with XES, which provides considerably more detailed information about electronic structure. The critical problem related to experimental artefacts that may occur as a consequence of non-negligible self-absorption processes is also discussed.

The next three chapters describe the domain of time-resolved XAS experiments at progressively more demanding time scales. In Chapter 7, Nachtegaal, Frahm et al. give an overview of the QEXAFS set-ups at several synchrotron radiation sources worldwide and describe the capabilities of the different technical realizations. Some historical aspects and the technical requirements for detectors, angular encoders, and hardware and software for fast data acquisition are also discussed. A selection of significant examples illustrates the current state of the art. The energy dispersive XAS technique is detailed in Chapter 8 by Mathon, Kantor, and Pascarelli [38]. After a brief historical introduction, they enter into the technical details of the essential x-ray source, dispersive optics, and beam detection. Selections of relevant examples at progressively faster time resolutions are reported. Chapter 9, authored by Chen, is devoted to the description of laser pump-x-ray probe experiments [175]. The basic theory and the basic experimental set-up of x-ray transient absorption (XTA) spectroscopy at synchrotrons and at free electron lasers are described. These aspects are supported by a selection of relevant examples. Taken together with chapters 13, 18, 19, 22, 24 and 26 in Volume II, these three chapters illustrate the enormous progress that has been achieved in realizing the time resolution of XAS experiments in the past two decades.

With Chapter 10, authored by Suzuki and Terada, we enter the domain of space-resolved experiments [178]. The focusing optics of x-rays are reviewed in detail, followed by a selection of relevant examples and a perspective section for future development of the technique.

In Chapter 11, Ravel considers the delicate problem of quantitative EXAFS data analysis [179]. A brief historical overview of EXAFS theory from 1971 to the present is outlined. The author provides a description of the muffin-tin potential, of Fermi's golden rule, and of Green's function expansion. The most commonly used codes for EXAFS data analysis are reviewed, underlying their peculiarities: the n-body decomposition in GNXAS, the exact curved wave theory in EXCURVE, and the path expansion in FEFF. The relevant aspects of the fitting statistics are treated in detail. Also addressed are: problems arising from the limitation of the total number of optimized parameters, the adoption of constraints in the fits, as well as the multiple data set analysis approaches. These concepts are illustrated by various practical examples of EXAFS analysis.

In Chapter 12, Fernández García et al. [116] emphasize the proper use of the so-called related techniques in unlocking the full potential of EXAFS. They stress the importance of combining information at long (XRD), medium (PDF) and local range (XAS, DAFS) to achieve a complete structural view of the investigated materials. They show how it is possible to obtain EXAFS-like information from low Z elements (PDF, EXELFS, XRS), how local-range contributions coming from amorphous and crystalline phases present in the same sample can be disentangled (DAFS), and how EXAFS-like contributions coming from the same element hosted in different crystallographic sites can be separated (DAFS). Finally, the relevance, advantages, and criticalities of simultaneous data collection with different techniques are discussed.

Volume II covers most of the current applications of x-ray absorption and emission spectroscopies. In Chapter 13, van Bokhoven and Lamberti review applications in catalysis [180]. The authors introduce the basic principles of catalysis and discuss the use of simple vacuum cleaved single crystals as models for studying systems under high pressure on more complex, high surface area catalysts. The concepts physisorption, chemisorption, catalytic conversion, and reaction are discussed in conjunction with their effect on structure-performing relations. The significance of space-resolved and time-resolved experiments in understanding the catalyst operation is thoroughly discussed, with the support of relevant examples.

Physics and chemistry under high pressure are reviewed by Itié et al. in Chapter 14 [181], in association with XAS, XMCD, and IXS techniques. Examples of pressure-induced phase transitions and amorphization are discussed in detail. Chapter 15, written by Solomon et al. [182], reviews the use of XAS and XES in structural and electronic characterization of coordination complexes. The authors first discuss the data available from XAS experiments at the K-edges of transition metals, and then that accessed through L-edges studies. In both cases, they begin by describing simple complexes containing transition metal ions with a single hole in the 3d level, such as Cu(II). Subsequently they move on to more complex ions comprising multiple 3d holes, such as Fe(III) and Fe(II).

Applications of XAS to semiconductor physics are reported by Boscherini in Chapter 16 [183]. Various experimental acquisition modes of XAS spectroscopy (transmission, fluorescence, total, partial and conversion electron yields, and photoluminescence yield) are reviewed initially. Determination of the local environment of dopants in semiconductors is then discussed, followed by determination of the bond-length strain in thin films and heterostructures, and by a summary of dilute magnetic semiconductors. The physics and chemistry of mixed valence oxides are reviewed by García et al. in Chapter 17 [184]. After a brief introduction to XAS, XES and x-ray resonant scattering techniques, the authors provide examples relevant to different classes of mixed-valence oxides, such as high critical temperature superconductors, manganites, and perovskites.

Chapter 18, authored by Ramaker [185], reports on the application of XAS in the electrochemistry field, with a special emphasis on fuel cells and batteries. In this discipline the advantages of emerging techniques, such as high-energy resolution fluorescence detection and off-resonant spectroscopy, are underlined and compared with the traditional full-yield XAS technique that analyzes the XANES using the differential Δμ approach. Applications related to materials involved in nuclear energy production processes are reviewed by Denecke in Chapter 19 [186]. The overall cycle of nuclear fuel is described, underlying the relevance of XAS experiments in characterizing radioactive materials. Besides the present and future fuel types, this chapter also discusses different reactor components and studies related to nuclear fuel recycling and lanthanide/actinide separation, as well as studies concerning nuclear waste disposal.

The impact of XAS and XES spectroscopies in the fields of planetary, geological, and environmental sciences is reviewed in Chapter 20 by Farges and Wilke [187], who report an overview of planetary materials and meteorites, crystalline deep earth materials, nuclear materials with natural origin, magmatic and volcanic materials processes, element complexation in aqueous fluids, mechanisms and reactivity at the mineral–water interfaces, biomineralization, and atmospheric interactions. Chapter 21, written by Farges and Cotte, deals with the application of XAS spectroscopy in the field of cultural heritage [188]. The chapter starts with an overview of the instrumentation needed for space-resolved experiments using both hard and soft x-rays, and discusses the spectral resolution of XRF detectors. A large class of materials relevant in the field is presented, including glasses, ceramics, vitro-ceramics, metallic clusters, pigments and paintings, inks, woods, fossils, bones, ivory, metals, and rock-forming monuments.

The present and future applications of XAS and XES experiments in x-ray free electron lasers (XFELs) are reviewed by Gawelda, Szlachetko and Milne in Chapter 22 [189], making a critical comparison with third-generation synchrotron radiation sources. They report a worldwide overview of the operational and under-construction XFEL facilities, before describing the properties of x-ray pulses from XFELs in terms of number of photon per pulse and pulse duration in time. New, unprecedented, potentialities in terms of time-resolved experiments are described, complementing the chapters dealing with time-resolution that appear in Volume I of this book [175]. The implementation of single-shot dispersive XAS, high energy resolution off-resonant spectroscopy, and XES techniques at XFELs are presented. Finally, this chapter presents several cutting-edge experiments. Rogalev et al. review the applications of x-ray magnetic circular dichroism (XMCD) in Chapter 23. The chapter begins with an in-depth historical perspective, followed by a description of the fundamental sum rules of Carra et al. in 1993. Subsequently, experimental considerations and data analysis are described, concluding with a selection of relevant examples.

The industrial applications of XAFS are discussed in Chapter 24 by Bare and Cutler, considering both patents and the open literature. In this chapter, the authors start with a review of the patent literature with a particular insight into how XAFS has been used to support patent claims. The following topics, relevant to industry, are treated in detail: semiconductors, thin films, electronic materials, fuel cells, batteries, electrocatalysts, metallurgy, tribology, and homogeneous and heterogeneous catalysts. The industrial science at light sources is discussed, taking the Canadian Light Source, the SOLEIL synchrotron in France, the National Synchrotron Light Source (NSLS), and the Swiss Light Source (SLS) as examples. The following companies are presented as examples of industrial users of synchrotron radiation: Haldor Topsøe A/S, UOP LLC, General Electric, and IBM.

In Chapter 25, Filipponi and D'Angelo review the applications of XAS in liquid systems [190]. The chapter starts with some thermodynamic considerations, followed by a rigorous definition of the concept of pair and higher-order distribution functions. The different computational approaches to model liquid structures are introduced, including classical Born-Oppenheimer and Car-Parrinello molecular dynamics simulations, as well as Monte Carlo simulation approaches. Subsequently, the role of XAFS in understanding liquids (and generally in disordered systems) is outlined. XAFS signal decomposition is described and the XAFS signal from the pair distribution is rigorously defined. Selected examples illustrate this concept.

Gates et al. [191] review on-surface metal complexes and their applications in Chapter 26. The chapter begins with an introduction to mononuclear (single-metal-atom) complexes on different supports. Several relevant examples are reported and discussed thoroughly. Finally, in Chapter 27, Soldatov and Lomachenko review applications of x-ray absorption and emission spectroscopies to nanomaterials [192]. They discuss nanoclusters, metal and bimetallic nanoparticles and nanostructures, monoatomic -O-Ti-O-Ti-O- quantum wires embedded in siliceous microporous matrices, as well as defects in solids.

Understandably, the review process for this book has been quite time-consuming, as all the chapters have been reviewed by at least two independent referees (with the exception of three of the chapters for which only one referee comment was available within the scheduled deadline). This process involved more than 50 referees; in some cases, double-duty by referees reviewing two chapters, and in several instances a second or third review of one chapter by the same referees. In adopting such a rigorous review process, it is our intention to present the highest quality publication possible. The editors are deeply indebted to all the referees, who worked diligently and anonymously towards this goal. Together with the authors, they significantly contributed to the high quality of the chapters. We are extremely grateful for all the work done by the authors, which has resulted in this extensive book in two volumes. To prevent publication in three volumes, rigorous limits were set on the length of each chapter. In the early stages of this project, we were strongly encouraged by the very positive and often enthusiastic replies we received from the authors after requesting them to contribute to the book. During the processing and reading of the chapters and observing their development, it has become even clearer that XAS and XES are scientifically mature and extremely widely applied. Evidently, maturity has done little to suppress rapid and global technique development. The new and exciting opportunities and applications described in this book illustrate the tremendous development during the past decades. This leads to the exciting conclusion that the future for XAS and XES is bright. We are proud that this book appears in 2015, the International Year of Light (Anno Lucis) as recognized by the United Nations (UNESCO Executive Board).

Jeroen A. van Bokhoven and Carlo Lamberti

Zurich and Torino, December 2014

Contributions versus countries bar graph shows number of contributions of books by various countries out of which France contributes the highest and least contributors are Canada and Poland.

Acknowledgement

C. Lamberti and J.A. van Bokhoven thank the MaMaSELF consortium (http://www.mamaself.eu/) for the financial support that has allowed us to finalize this joint work. C. Lamberti acknowledges the Mega-grant of the Russian Federation Government to support scientific research at Southern Federal University, No. 14.Y26.31.0001.

References

D.E. Sayers, E.A. Stern and F.W. Lytle (1971) New Technique for Investigating Noncrystalline Structures: Fourier Analysis of the Extended X-Ray Absorption Fine Structure, Phys. Rev. Lett., 27, 1204–1207.

W.C. Röntgen (1895) Über eine neue Art von Strahlen, Sitzungsberichte der Würzburger Physik.-medic. Gesellschaft, 9, 132–141.

W.C. Röntgen (1896) Eine neue Art von Strahlen. II, Sitzungsberichte der Würzburger Physik.-medic. Gesellschaft, 1, 11–19.

M. de Broglie (1913) Sur une nouveau procédé permettant d'obtenir la photographie des spectres de raies des rayons Röntgen, C. R. Acad. Sci., 157, 924–926.

M. Planck (1901) Über das Gesetz der Energieverteilung im Normalspektrum, Annal. Phys., 4, 553–563.

W.L. Bragg (1913) The Diffraction of Short Electromagnetic Waves by a Crystal, Proc. Cambridge Phil. Soc., 17, 43–57.

W.H. Bragg and W.L. Bragg (1913) The Reflection of X-rays by Crystals, Proc. R. Soc. Lond. A, 88, 428–438.

W.H. Bragg (1913) The Reflection of X-rays by Crystals. (II.), Proc. R. Soc. Lond. A, 89, 246–248.

L. de Broglie (1920) Sur le calcul de fréquences limites d'absorption K et L des éléments lourds, C. R. Acad. Sci., 170, 585.

L. de Broglie (1920) Sur l'absorption des rayons Röntgen par la matière, C. R. Acad. Sci., 171, 1137.

L. de Broglie (1923) Waves and Quanta, Nature, 112, 540.

H.G.J. Moseley (1913) The High Frequency Spectra of the Elements, Phil. Mag., 26, 1024–1034.

N. Bohr (1913) On the Constitution of Atoms and Molecules, Phil. Mag., 26, 1–24.

N. Bohr (1913) On the Constitution of Atoms and Molecules. II Systems Containing Only a Single Nucleus, Phil. Mag., 26, 476–502.

N. Bohr (1913) On the Constitution of Atoms and Molecules. III Systems Containing Several Nuclei, Phil. Mag., 26, 857–875.

W. Stenström (1918) Experimentelle Untersuchungen der Röntgenspektra. M-Reihe, Ann. Phys., 362, 347–375.

M. Siegbahn (1919) Röntgenspektroskopische Präzisionsmessungen, Ann. Phys., 364, 56–72.

M. Siegbahn (1919) Precision-measurements in the X-ray spectra, Phil. Mag., 37, 601–612.

M. Siegbahn (1931) Spektroskopie der Röntgenstrahlen, Springer, Berlin.

J.D. Hanawalt (1931) The Dependence of X-ray Absorption Spectra upon Chemical and Physical State, Phys. Rev., 37, 715–726.

H. Fricke (1920) The K-Characteristic Absorption Frequencies for the Chemical Elements Magnesium to Chromium, Phys. Rev., 16, 202–215.

G. Hertz (1920) Über die Absorptionsgrenzen in der L-Serie Z. Phys., 3, 19–25.

A.E. Lindh (1921) Zur Kenntnis des Röntgenabsorptionsspektrums von Chlor, Z. Phys., 6, 303–310.

D. Coster (1924) Über die Absorptionsspektren im Röntgengebiet, Z. Phys., 25, 83–98.

K. Chamberlain (1925) The Fine Structure of Certain X-Ray Absorption Edges, Phys. Rev., 26, 525–536.

A.E. Lindh (1925) Über die K-Röntgenabsorptionsspektra der Elemente Si, Ti, V, Cr, Mn und Fe, Z. Phys., 31, 210–218.

B.B. Ray (1929) Mehrfachabsorption und sekundäre K-Absorptionsgrenze im Röntgengebiet, Z. Phys., 55, 119–126.

D.M. Yost (1929) The K-Absorption Discontinuities of Manganous and Chromate Ions, Phil. Mag., 8, 845–847.

A.E. Lindh (1930) Zur Kenntnis des K-Röntgenabsorptionsspektrums der Elemente Ni, Cu und Zn, Z. Phys., 63, 106–113.

B. Kievit and G.A. Lindsay (1930) Fine Structure in the X-Ray Absorption Spectra of the K Series of the Elements Calcium to Gallium, Phys. Rev., 36, 648–664.

J.D. Hanawalt (1931) Der Einfluß der Temperatur auf die K-Absorption des Eisens, Z. Phys., 70, 293–305.

A.J. O'Leary (1931) Interaction of X-rays with Bound Electrons, Phys. Rev., 37, 873–883.

D. Coster and J. Veldkamp (1931) Bestimmung des Absorptionskoeffizienten für Röntgenstrahlen in der Nähe der K-Absorptionskante der Elemente Cu und Zn, Z. Phys., 70, 306–316.

G.A. Lindsay (1931) Über die Feinstruktur in der K-Absorptionskante von Kalium, Z. Phys., 71, 735–738.

D. Coster and J. Veldkamp (1932) Über die Feinstruktur der Röntgenabsorptionskanten, Z. Phys., 74, 191–208.

F.R. Hirsh, Jr. and F.K. Richtmyer (1933) The Relative Intensities of Certain L-Series X-Ray Satellites in Cathode-Ray and in Fluorescence Excitation, Phys. Rev., 44, 955–960.

A.S. Rao and K.R. Rao (1934) The Spectra of Br V, Br VI and Br VII, Proc. Phys. Soc., 46, 163.

O. Mathon, I. Kantor and S. Pascarelli (2015) Time-resolved XAS using an energy dispersive spectrometer: techniques and applications, in XAS and XES: Theory and Applications, vol. 1 (eds J.A. van Bokhoven and C. Lamberti), John Wiley & Sons, Ltd., pp. 185–212.

R.d.L. Kronig (1931) Zur Theorie der Feinstruktur in den Röntgenabsorptionsspektren, Z. Phys., 70, 317–323.

R.d.L. Kronig (1932) Zur Theorie der Feinstruktur in den Röntgenabsorptionsspektren. II, Z. Phys., 75, 191–210.

R.d.L. Kronig (1932) Zur Theorie der Feinstruktur in den Röntgenabsorptionsspektren. III, Z. Phys., 75, 468–475.

H. Petersen (1932) Zur Theorie der Röntgenabsorption molekularer Gase, Z. Phys., 76, 768–776.

H. Petersen (1933) Zur Theorie der Röntgenabsorption molekularer Gase. II, Z. Phys., 80, 258–266.

H. Petersen (1936) Zur Theorie der Röntgenabsorption molekularer Gase. III, Z. Phys., 98, 569–575.

T.M. Snyder and C.H. Shaw (1940) The Fine Structure of the X-Ray Absorption Limits of Bromine and Chlorine, Phys. Rev., 57, 881–886.

A.I. Kostarev (1941) Teoрия тонкой структуры полос поглощения рентгено-спектра твёрдого тела; [Theory of the Fine Structure of Absorption Bands in X-Ray Spectra of Solids], Zh. Éksp. Teor. Fiz., 11, 60–73.

C.H. Shaw (1946) Secondary Structure in the K Absorption Limit of Germanium Tetrachloride, Phys. Rev., 70, 643–645.

A.I. Kostarev (1949) Истолкование сверхтонкой структуры рентгеновых спектров поглощения твёрдых телл [Interpretation of Ultrafine Structure of X-Ray Absorption Spectra of Solids], Zh. Éksp. Teor. Fiz., 19, 413–420.

Y. Cauchois and N.F. Mott (1949) The Interpretation of X-ray Absorption Spectra of Solids, Phil. Mag., 40, 1260–1269.

N. Amar Nath (1955) The Origin of Fine Structures in X-Ray Absorption Spectra of Ionic Solutions, Proc. Phys. Soc. B, 68, 472–473.

M. Sawada, K. Tsutsumi, T. Shiraiwa and M. Obashi (1955) On the Fine Structures of X-ray Absorption Spectra of Amorphous Substances: The Amorphous State of the Binary System of Nickel-Sulfur. II., J. Phys. Soc. Jpn., 10, 464–468.

M. Sawada, K. Tsutsumi and A. Hayase (1957) Fine Structures of X-ray Absorption Spectra of Cobalt in the Face Centered Cubic Lattice and Close-packed Hexagonal Lattice, J. Phys. Soc. Jpn., 12, 628–636.

K. Tsutsumi, A. Hayase and M. Sawada (1957) Fine Structures of X-ray K Absorption Spectra of Copper in Various Copper Compounds, J. Phys. Soc. Jpn., 12, 793–801.

T. Shiraiwa, T. Ishimura and M. Sawada (1957) Fine Structures of X-ray Absorption Spectra of Crystalline and Amorphous Germanium, J. Phys. Soc. Jpn., 12, 788–792.

T. Shiraiwa, T. Ishimura and M. Sawada (1958) The Theory of the Fine Structure of the X-ray Absorption Spectrum, J. Phys. Soc. Jpn., 13, 847–859.

T. Shiraiwa (1960) The Theory of the Fine Structure of the X-ray Absorption Spectrum, II, J. Phys. Soc. Jpn., 15, 240–250.

V.V. Shmidt (1961) К теории температурной зависимости тонкой структуры рентгеновских спектров поглощения [On the Theory of the Temperature Dependence of the Fine Structure in X-Ray Absorption Spectra], Izv. Akad. Nauk. SSSR, Ser. Fiz., 25, 977–982.

W.F. Nelson, I. Siegel and R.W. Wagner (1962) K X-Ray Absorption Spectra of Germanium in Crystalline and in Amorphous GeO2, Phys. Rev., 127, 2025–2027.

V.V. Shmidt (1963) К теории температурной зависимости тонкой структуры рентгеновских спектров поглощения. Случай высоких температур [On the Theory Of Temperature Dependence of the Fine Structure in X-Ray Absorption Spectra: High Temperature Regime], Izv. Akad. Nauk. SSSR, Ser. Fiz., 27, 384–389.

L.V. Azaroff (1963) Theory of Extended Fine Structure of X-Ray Absorption Edges, Rev. Mod. Phys., 35, 1012–1021.

F.W. Lytle (1963) X-Ray Absorption Fine-Structure Investigations at Cryogenic Temperatures, in Developments in Applied Spectroscopy, vol. 2 (eds J.R. Ferraro and J.S. Ziomek), Plenum, New York, pp. 285–296.

F. Lytle (1966) Determination of Interatomic Distances from X-ray Absorption Fine Structure, Adv. X-ray Anal., 9, 398–409.

R.A. Van Nordstrand (1960) The Use of X-Ray K-Absorption Edges in the Study of Catalytically Active Solids, Adv. Catal., 12, 149–187.

R. Van Nordstrand (1967) in Handbook of X-Rays (ed. E. Kaelble), McGraw-Hill, London, pp. 41–48.

E.A. Stern (1974) Theory of the Extended X-Ray-Absorption Fine Structure, Phys. Rev. B, 10, 3027–3037.

F.W. Lytle, D.E. Sayers and E.A. Stern (1975) Extended X-Ray-Absorption Fine-Structure Technique. II. Experimental Practice and Selected Results, Phys. Rev. B, 11, 4825–4835.

E.A. Stern, D.E. Sayers and F.W. Lytle (1975) Extended X-Ray-Absorption Fine-Structure Technique. III. Determination of Physical Parameters, Phys. Rev. B, 11, 4836–4846.

J.J. Rehr, E.A. Stern, R.L. Martin and E.R. Davidson (1978) Extended X-Ray-Absorption Fine-Structure Amplitudes, Wave-Function Relaxation and Chemical Effects, Phys. Rev. B, 17, 560–565.

D.R. Sandstrom and F.W. Lytle (1979) Developments in Extended X-Ray Absorption Fine Structure Applied to Chemical Systems, Ann. Rev. Phys. Chem., 30, 215–238.

W.L. Schaich (1973) Comment on the Theory of Extended X-Ray-Absorption Fine Structure, Phys. Rev. B, 8, 4028–4032.

C.A. Ashley and S. Doniach (1975) Theory of Extended X-Ray Absorption Edge Fine Structure (EXAFS) in Crystalline Solids, Phys. Rev. B, 11, 1279–1288.

P.A. Lee and J.B. Pendry (1975) Theory of the Extended X-Ray Absorption Fine Structure, Phys. Rev. B, 11, 2795–2811.

G. Beni and P.M. Platzman (1976) Temperature and Polarization Dependence of Extended X-Ray Absorption Fine-Structure Spectra, Phys. Rev. B, 14, 1514–1518.

E. Sevillano, H. Meuth and J.J. Rehr (1979) Extended X-Ray Absorption Fine Structure Debye-Waller Factors. I. Monatomic Crystals, Phys. Rev. B, 20, 4908–4911.

I. Munro (1997) Synchrotron Radiation Research in the UK, J. Synchrotron Rad., 4, 344–358.

T. Sasaki (1997) A Prospect and Retrospect: The Japanese Case, J. Synchrotron Rad., 4, 359–365.

S. Doniach, K. Hodgson, I. Lindau, P. Pianetta and H. Winick (1997) Early Work with Synchrotron Radiation at Stanford, J. Synchrotron Rad., 4, 380–395.

O. Hallonsten (2009) Small Science on Big Machines: Politics and Practices of Synchrotron Radiation Laboratories, Research Policy Institute, Lund.

A.L. Robinson (2009) X-ray Data Booklet: Section 2.2. History of Synchrotron Radiation, Center for X-ray Optics and Advanced Light Source, Berkeley, CA.

A. Filipponi, A. Di Cicco, T.A. Tyson and C.R. Natoli (1991) Ab Initio Modeling of X-Ray Absorption-Spectra, Solid State Commun., 78, 265–268.

A. Filipponi, A. Di Cicco and C.R. Natoli (1995) X-Ray-Absorption Spectroscopy and N-Body Distribution Functions in Condensed Matter.1. Theory, Phys. Rev. B, 52, 15122–15134.

A. Filipponi and A. Di Cicco (1995) X-Ray-Absorption Spectroscopy and N-Body Distribution Functions in Condensed Matter. 2. Data Analysis and Applications, Phys. Rev. B, 52, 15135–15149.

T.E. Westre, A. Dicicco, A. Filipponi, C.R. et al. (1995) GNXAS, A Multiple-Scattering Approach to EXAFS Analysis: Methodology and Applications to Iron Complexes, J. Am. Chem. Soc., 117, 1566–1583.

H.H. Zhang, A. Filipponi, A. DiCicco et al. (1996) Multiple-Edge XAS Studies of Synthetic Iron-Copper Bridged Molecular Assemblies Relevant to Cytochrome C Oxidase. Structure Determination Using Multiple-Scattering Analysis with Statistical Evaluation of Errors, Inorg. Chem., 35, 4819–4828.

S.J. Gurman, N. Binsted and I. Ross (1984) A Rapid, Exact Curved-Wave Theory for EXAFS Calculations, J. Phys. C: Solid State Phys., 17, 143.

S.J. Gurman, N. Binsted and I. Ross (1986) A Rapid, Exact, Curved-Wave Theory for EXAFS Calculations. 2. The Multiple-Scattering Contributions, J. Phys. C: Solid State Phys., 19, 1845–1861.

N. Binsted, S.L. Cook, J. Evans et al. (1987) EXAFS and Near-Edge Structure in the Cobalt K-Edge Absorption Spectra of Metal Carbonyl Complexes, J. Am. Chem. Soc., 109, 3669–3676.

N. Binsted and S.S. Hasnain (1996) State-of-the-Art Analysis of Whole X-Ray Absorption Spectra, J. Synchrot. Radiat., 3, 185–196.

J.M. de Leon, J.J. Rehr, S.I. Zabinsky and R.C. Albers (1991) Ab Initio Curved-Wave X-Ray-Absorption Fine-Structure, Phys. Rev. B, 44, 4146–4156.

J.J. Rehr, J.M. Deleon, S.I. Zabinsky and R.C. Albers (1991) Theoretical X-Ray Absorption Fine-Structure Standards, J. Am. Chem. Soc., 113, 5135–5140.

J.J. Rehr, R.C. Albers and S.I. Zabinsky (1992) High-Order Multiple-Scattering Calculations of X-Ray-Absorption Fine-Structure, Phys. Rev. Lett., 69, 3397–3400.

S.I. Zabinsky, J.J. Rehr, A. Ankudinov et al. (1995) Multiple-Scattering Calculations of X-Ray-Absorption Spectra, Phys. Rev. B, 52, 2995–3009.

A.L. Ankudinov, B. Ravel,