Recently in Spectroscopy Category

The three free XRF posters offered by Professor James P Willis (James Willis Consultants cc, South Africa) have become one of the most popular, high-impact topics in the XRF-L mailing list. His posters are as follows: (i) The WDXRF spectrometer, illustrated with appropriate wavelength scans and pulse height distributions, (ii) Some factors affecting XRF sensitivity (Kα lines Sn to Na), and (iii) Theoretical intensities for Sn, Cu, Ti, K and S K lines excited by an end-window Rh tube operating at 60, 50, 40, 30 and 25 kV and 4kW. Information for downloading the PDF files is available at the Web site, http://xrfguidelines.co.za/

Reaching the milestone of X-ray lasers is something that X-ray physicists have dreamed of for many years. Recently developed X-ray free-electron lasers (XFEL) based on self-amplified spontaneous emission (SASE) constitute a very promising tool for future X-ray laser technologies. A team led by Professor H. Yoneda (University of Electro-Communications, Tokyo, Japan) has recently carried out very impressive experiments at Japanese XFEL facility, SACLA, on the same campus as SPring-8. Similar to an X-ray tube, the researchers employed a solid copper target to generate X-rays. However, their experiment is very unique in that two colors were employed by tuning undulator gaps; one energy is around 9 keV, i.e., above the Cu-K absorption edge, and the other energy is almost the same energy as Cu Kα₁ or Kα₂. While 9 keV photons ionize copper atoms and generate Cu K X-ray fluorescence spectra, the lower energy photons can amplify the X-ray fluorescence because of their temporal coherence. Their Cu Kα spectra are impressive, because Kα₁/Kα₂ can be controlled by tuning the second energy of XFEL pulses. The reason for the limited amplification is probably due to the energy band width of incoming temporary coherent X-ray photons. The researchers did not use any monochromators, but controlled only the undulator gaps. They have two different X-ray energies, but unfortunately monochromaticy has some limits and the band width is still quite wide. The present work could be a very important step toward achieving X-ray lasers by using atomic energy levels. For more information, see the paper, "Atomic inner-shell laser at 1.5-angstrom wavelength pumped by an X-ray free-electron laser", H. Yoneda et al., Nature 524, 446 (2015).

Dr. F. Dorchies (Universite Bordeaux, CNRS-CELIA, France) and his colleagues have recently developed a laser-base X-ray absorption spectrometer covering 0.5-4.0 keV with a time resolution of around 3.3 pico second. The spectrometer uses bremsstrahlung caused by the extremely high impact of laser pulses on the metallic target. To perform time-resolved X-ray spectroscopic studies, there have been quite a few challenges. For most research, it is crucial to avoid damaging/destroying samples, and the measuring time should not be very long. In addition, scientists don't like to compromise the signal-to-background ratio of spectral data taken at each time point, even though the quality is not the same as that of ordinary X-ray absorption spectra. The authors seem to believe that they are getting some breakthroughs. Their setup is a combination of a table-top laser (Ti: Sapphire, 800nm, 150mJ, 10Hz) and a Johan spectrometer equipped with a CCD camera. A set of polycapillary optics were employed as a beamline transport between the X-ray source and the sample (1 m distance) to maintain a clean, independent and flexible environment for the sample. The X-ray intensity near the Al K edge and Cu L edges is 1.3 × 10⁶ photons/eV/pulse. For more information, see the paper, "Experimental station for laser-based picosecond time-resolved x-ray absorption near-edge spectroscopy", F. Dorchies et al., Rev. Sci. Instrum. 86, 073106 (2015).

Since the development of EPMA (electron probe micro analysis) by Castaing's PhD thesis in 1951, great efforts have been made to improve the technique. It was believed that the use of standard samples is absolutely indispensable to the determination of the concentration of each element. This can be a limit for some fields, such as nuclear materials application, where the quantification of minor actinides in fresh or spent fuel is demanded with no availability of any standard samples. In France, Dr. A Moy (Universite de Montpellier) and his colleague have recently reported successful standardless analysis of Pb and U in PbS, PbTe, PbCl₂, Pb₅(VO₄)₃Cl (vanadinite), and UO₂, by measuring absolute Mα and Mβ X-ray intensity by a wavelength dispersive spectrometer. Experimentally obtained X-ray intensity was converted into absolute X-ray yields by evaluating the detector efficiency and then compared with calculated background X-ray intensity based on Monte Carlo simulations. For more information, see the paper, "Standardless quantification of heavy elements by electron probe microanalysis", A. Moy et al., Anal. Chem. 114, 255501 (2015).

A team led by Dr. M. Minitti (SLAC National Accelerator Laboratory, USA) has recently succeeded in recording the time evolution of a structural change of ring-type 1,3-cyclohexadiene gas molecule to linear 1,3,5-hexatriene. The employment of the X-ray free-electron laser at LCLS (Linac coherent light source), Stanford allowed them to do ultra fast snapshots of X-ray scattering in several tens of fs (femtosecond) scale. The study is based on pump-and-probe measurement; i.e., X-ray data were collected as a function of the controlled delay time between the UV pump pulse (267 nm, 65 fs, 4-8 μJ, 100 μm size) and X-ray probe pulse (8.3 keV, around 30 fs, 10¹² photons/pulse, 30 μm square size). The team established that some signals caused by structural change are found as early as 30 fs, and the reaction finishes at 200 fs. For more information, see the paper, "Imaging Molecular Motion: Femtosecond X-Ray Scattering of an Electrocyclic Chemical Reaction", M. P. Minitti et al., Phys. Rev. Lett. 114, 255501 (2015).

Ms. Laura Bush, who is an editorial director of Spectroscopy, has recently published an article on the present and future of X-ray fluorescence on the occasion of Spectroscopy's celebration of 30 years. It is a summary of her interviews with experts. For more information, see the article, "Analysis of the State of the Art: XRF", Laura Bush, Spectroscopy, 30 (6) 86-94 (2015), which can be found online at http://www.spectroscopyonline.com/analysis-state-art-xrf A PDF file can also be downloaded from iTunes.

A Slovenian group has recently reported the Kα and Kβ emission spectra of phosphorus, measured by monochromatic synchrotron X-rays (3 keV, at ID26, ESRF) and a 2 MeV proton beam. They also compared them with a Density Functional Theory calculation using StoBe-deMon code (Stockholm-Berlin version of demon). For more information, see the paper, "Chemical State Analysis of Phosphorus Performed by X.ray Emission Spectroscopy", M. Petric et al., Anal. Chem. 87, 5632 (2015).

Readers may remember that electrochemical X-ray fluorescence developed by Prof. Julie V. Macpherson's group at Warwick University, England can analyze sub-ppb level heavy elements in solution (See, News in No.5, Vol.43 (2014)). Recently the research team published their successful extension of the technique to in situ time-evolution analysis. Their electrode is a freestanding film of boron-doped diamond, and it can work also as an X-ray window. Primary X-rays pass through the back side of the electrode and excite the heavy elements in the electrodeposit on the electrode. In addition to quantitative analysis of a mixed solution of Hg²⁺, Pb²⁺, Cu²⁺, Ni²⁺, Zn²⁺, and Fe³⁺(all at 10 μM concentration), time-evolution analysis of electrodeposition can be a very promising application of this unique method. For more information, see the paper, "Direct Identification and Analysis of Heavy Metals in Solution (Hg, Cu, Pb, Zn, Ni) by Use of in Situ Electrochemical X.ray Fluorescence", G. D. O'Neil et al., Anal. Chem. 87, 4933 (2015).

Scientists at Los Alamos National Laboratory have recently reported the X-ray analysis of uranium oxideα-U₃O₈ samples under controlled temperatures and humidities. They found that the combined use of powder X-ray diffraction and U L-III EXAFS can help in identifying temporal changes of uranium oxide stored for a number of years. For more information, see the paper, "Oxidation and Hydration of U₃O₈ Materials Following Controlled Exposure to Temperature and Humidity", A. L. Tamasi et al., Anal. Chem. 87, 4210 (2015).

A team led by Dr. T. Jach (NIST, USA) and Dr. W. T. Elam (University of Washington, USA) has recently published an interesting theoretical paper discussing the broadening of N K absorption and emission spectra of NH₄NO₃ and NH₄Cl. The authors studied many-body lifetime effects in valence-band X-ray emission. For more information, see the paper, "Origins of extreme broadening mechanisms in near-edge x-ray spectra of nitrogen compounds", J. Vinson et al., Phys. Rev. B90, 205207 (2014).

Professor A. Adriaens (Ghent University, Belgium) and her colleagues have recently reported on an X-ray-excited optical luminescence microscope using synchrotron light and its applications. The experiments were done at beamlines BM28 and BM26A at the ESRF in Grenoble, France. A broad X-ray beam is used to illuminate large areas of ~4 mm² of the sample, and the resulting optical emission is observed by a specifically designed optical microscope equipped with a CCD camera. By scanning the X-ray energy near the absorption edge, the image can obtain the sensitivity of chemical states. The authors studied copper surfaces with well-defined patterns of different corrosion products (cuprite Cu₂O and nantokite CuCl). For more information, see the paper, "Evaluation of an X-ray Excited Optical Microscope for Chemical Imaging of Metal and Other Surfaces", P-J. Sabbe et al., Anal. Chem., 86, 11789 (2014).

So far, monochromatic X-rays have been used for 3D micro X-ray fluorescence analysis based on confocal geometry. Dr. P. Wrobel (AGH University of Science and Technology, Poland) and his colleagues have recently discussed the feasibility of polychromatic excitation. The research group described the full theoretical expression of matrix effects and geometrical effects for polychromatic X-ray photons in confocal arrangement. It was demonstrated that the introduction of effective energy approximation works well. For more information, see the paper, "Depth Profiling of Element Concentrations in Stratified Materials by Confocal Microbeam X-ray Fluorescence Spectrometry with Polychromatic Excitation", P. Wrobel et al., Anal. Chem., 86, 11275 (2014).

Professor L. Vincze (Ghent University, Belgium) and his colleagues have reported on the latest fluorescence mode XANES imaging using the SLcam, which is an energy dispersive pnCCD detector. At BM26A, ESRF, the measurements were done for iron foil with some oxides and geological standard samples. The typical detection limit and measuring time were 0.5 wt% and 15 h, respectively. Readers might think that energy-resolution can be sacrificed near the absorption edges of interest in order to shorten the measuring time in the same way as ordinary XANES measurement by means of X-ray fluorescence. Although the use of ordinary X-ray CCD in accumulation mode for a very similar experiment was published 10 years ago (for example, M. Mizusawa et al, J. Synchrotron Rad. 11, 209 (2004)), the present system has the advantage of being able to reduce the background from the major light elements contained in the sample. For more information, see the paper, "Full-Field Fluorescence Mode Micro-XANES Imaging Using a Unique Energy Dispersive CCD Detector", P. Tack et al, Anal. Chem., 86, 8791(2014).

Most X-ray experiments can be done at high quality with ease in an ordinary laboratory. Some experiments, however, have to be done in the field. It is hard to imagine a more extreme definition of "in the field" than the planet of Mars, which is why exciting times have come about since NASA's Mars rover "Curiosity" landed on Mars in August 2012. It has since recorded and sent back a large number of datasets including X-ray fluorescence (XRF) and X-ray diffraction (XRD) data. Naturally, the scientists involved with the projects have been speaking globally since. During EXRS 2014 (June, Bologna, Italy), Professor J. L. Campbell (University of Guelph, Canada) gave a keynote lecture entitled "XRF and PIXE on the Mars Science LAB Curiosity Rover". At the Denver X-ray conference (July, Big Sky, Montana), the Plenary Session was "X-rays on Mars", and 3 scientists gave lectures. Professor D. L. Bish (Indiana University) gave a talk entitled "The First X-ray Diffraction Results From Mars". Professor J. L. Campbell's talk on "XRF Combines with PIXE in Curiosity's Alpha Particle X-ray Spectrometer" was the extension on his talk at EXRS 2014, and further detailed and specific discussion was done there. Professor S.M. Clegg talked about "Exploring Mars with ChemCam on the Curiosity Rover" (ChemCam enables quick element determination by the laser-induced plasma emission spectroscopy). In August, at Montreal, during the International Union of Crystallography's congress, Professor D. L. Bish gave a talk entitled "The First X-ray Powder Diffraction Measurements on Mars". These talks highlighted many interesting technological aspects of the measurements: XRF analysis is done first by the same CCD camera, which works as an energy-dispersive 2D X-ray detector, even when the main aim of the measurement is obtaining the XRD pattern. In the analysis of unknown samples, generally both chemical composition and the crystal structure are indispensable. Another reason is that XRF helps the systematic use of single photon counting mode of the CCD camera to get a good quality XRD pattern. Secondly, the samples are vibrated all the time to ensure a smooth and continuous Debye ring. The rover furthermore contains a series of standard samples to check the reliability and reproducibility of the measurements. The readers might be interested in such a compact X-ray analyzer, which combined both XRD and XRF machine. Very similar system is now commercially available. For further information on the scientific activity on Mars, visit the Web page, http://mars.jpl.nasa.gov/msl/

Professor J. Wang (University of California San Diego, USA) and his colleagues have applied X-ray fluorescence to the analysis of gunshot residue, which has been usually detected based on the analysis trace amounts of metallic and organic species deposited on the hands, face, hair, and clothing of the shooter. The researchers tried to couple square-wave stripping voltammetry (SWSV) and scanning electron microscopy (SEM) plus energy dispersive X-ray spectroscopy (EDX). The former method can be used as a rapid screening tool, while the latter contributes to confirmation of the presence of the characteristic morphology and metal composition of gunshot residue particles. For more information, see the paper, "Orthogonal Identification of Gunshot Residue with Complementary Detection Principles of Voltammetry, Scanning Electron Microscopy, and Energy-Dispersive X-ray Spectroscopy: Sample, Screen, and Confirm", A. M. O'Mahony et al., Anal. Chem., 86, 8031 (2014).

A research team led by Professor I. Nakai (Tokyo University of Science, Japan) has recently clarified the detailed chemical nature of radioactive aerosol microparticles emitted during the Fukushima Daiichi Nuclear Power Plant accident. They collected three fine particles of 2 microns in dia, containing radioactive cesium, on March 14th and 15th, 2011, in Tsukuba, 172 km away from the power plant. In addition to Fe, Zn, Rb, Zr, Mo, Sn, Sb, Te, Cs, and Ba, U was detected in two particles. The oxidation states of the heavy elements were also studied by X-ray absorption spectra. The experiments were done at BL37XU, SPring-8, Japan. For more information, see the paper, "Detection of Uranium and Chemical State Analysis of Individual Radioactive Microparticles Emitted from the Fukushima Nuclear Accident Using Multiple Synchrotron Radiation X-ray Analyses", Y. Abe et al., Anal. Chem., 86, 8521 (2014).

Professor T. M. Cahill (Arizona State University) and his colleagues have recently compared the performance of the different excitation modes of synchrotron radiation X-ray fluorescence. The research team evaluated four different beamline configurations for the analysis of three representative environmental samples; a thin aerosol sample, an intermediate thickness biological sample, and a thick rare earth mineral specimen. They found that white beam excitation is optimal for the analysis of thin samples with little mass, and that filtered white beam excitation (removing lower energy X-rays by absorber) gives better sensitivity for elements emitting more energetic X-rays. In their study, monochromatic excitation, which tends to be the standard mode of operation, did not give good results in terms of sensitivity. For more information, see the paper, "Evaluation of Different Synchrotron Beamline Configurations for X.ray Fluorescence Analysis of Environmental Samples", S. R. Barberie et al., Anal. Chem., 86, 8253 (2014).

A Spanish group has recently published a very interesting application of total-reflection X-ray fluorescence (TXRF). The research team has evaluated the bioaccumulation kinetics of gold nanorods (GNRs) in various tissues upon intravenous administration in mice. It was found that the main achievement was clearly differentiating two kinds of behaviors; gold nano rods were quickly bioaccumulated by highly vascular filtration organs such as the liver and spleen, while they do not show bioaccumulation rates in the brain and lung for the period of time investigated. For more information, see the paper, "Evaluation of Bioaccumulation Kinetics of Gold Nanorods in Vital Mammalian Organs by Means of Total Reflection X-Ray Fluorescence Spectrometry", R. Fernandez-Ruiz et al., Anal. Chem., 86, 7383 (2014).

Dr. V-D. Hodoroaba (BAM, Berlin, Germany) and his colleague have published a report on the feasibility of quantitative X-ray fluorescence (XRF) analysis using coherent (Rayleigh) and incoherent (Compton) X-ray scattering. They have evaluated the ratio of the Compton-to-Rayleigh intensity observed in XRF spectra and also have discussed its relation to the average atomic number. In so-called reference-free XRF analysis, which uses only fundamental parameters and a theoretical formula and does not rely on the calibration curve, there still exist many difficulties, particularly for matrices of lower mean atomic numbers. The analysis presented in this research has sufficiently high sensitivity to distinguish the average atomic number of specimens even within the 0.1 difference. For more information, see the paper, "Gaining Improved Chemical Composition by Exploitation of Compton-to-Rayleigh Intensity Ratio in XRF Analysis", V-D. Hodoroaba et al., Anal. Chem., 86, 6858 (2014).

Dr. B. Kanngießer (Technische Universität Berlin, Germany) and her colleagues have recently reported an interesting archaeological application of 3D chemical analysis based on confocal X-ray absorption near edge spectroscopy. This is highly significant for clarifying the technological background of the decorated black- and red-figured Athenian vases (6^th and 5^th century BC) and the plain black glaze. The research team discussed the correlation of the iron oxidation state in the black glaze layer with the manufacturing process. The 3-stage firing process, which was used in the modern reproduction, was retraced by correlating selected attic black glazed (BG) specimens from different periods (Archaic, Classical, Hellenistic). For more information, see the paper, "Confocal XANES and the Attic Black Glaze: The Three Stage Firing Process through Modern Reproduction", L. Luhl et al., Anal. Chem., Article ASAP (DOI: 10.1021/ac500990k).

The use of X-ray free-electrons has enabled plenty of fascinating science, such as watching non-equilibrium excited-state dynamics in complexes of 3d transition metals. Scientists at LCLS, Stanford have performed femtosecond resolution X-ray fluorescence spectroscopy, with its sensitivity to spin state, elucidating the spin crossover dynamics of [Fe(2, 2ˈ-bipyridine)₃]²⁺ on photoinduced metal-to-ligand charge transfer excitation. For more information, see the paper, "Tracking excited-state charge and spin dynamics in iron coordination complexes", W. Zhang et al., Nature, 509, 345 (2014).

A group led by Prof. Julie V. Macpherson (Warwick University, England) has reported electrochemical X-ray fluorescence, which can quantitatively detect heavy metals in solution. In this technique, electrochemical preconcentration of a species of interest onto the target electrode is achieved by cathodic electro-deposition. X-ray fluorescence can then help unambiguous elemental identification and quantification of metal concentration. The key is that the electrochemical preconcentration step improves the detection limit by over 4 orders of magnitude, and it can reach the sub-ppb level. For more information, see the paper, "Electrochemical X-ray Fluorescence Spectroscopy for Trace Heavy Metal Analysis: Enhancing X-ray Fluorescence Detection Capabilities by Four Orders of Magnitude", L. A. Hutton et al., Anal. Chem., 86, 4566 (2014).

Prof. K. Binnemans (KU Leuven, Heverlee, Belgium) and his colleagues have published several papers on the application of TXRF to the determination and quantification of halide impurities in liquid. So far, the detection of halide ions in solution has been problematic because volatile hydrogen halide compounds are formed when the sample is mixed with the acidic metal standard solution. The loss of hydrogen halide during the drying step of the sample preparation procedure gives imprecise and inaccurate results. To avoid this, the research group is proposing to introduce an alkaline copper standard Cu(NH₃)₄(NO₃)₂. For more information, see the papers, "Determination of Halide Impurities in Ionic Liquids by Total Reflection X-ray Fluorescence Spectrometry", T. V. Hoogerstraete et al., Anal. Chem., 86, 3931 (2014), and "Determination of Halide Ions in Solution by Total Reflection X-ray Fluorescence (TXRF) Spectrometry", T. V. Hoogerstraete et al., Anal. Chem., 86, 1391 (2014).

An interesting and useful tutorial on X-ray analytical methods for newcomers is now available in the Materials Today Podcast. Dr. Ravi Yellepeddi (Thermo Fisher Scientific) explains the principle of X-ray fluorescence, recent progress in instruments, and the variety of applications in industry and research laboratories. The talk is around 30 min. Visit the following Web site,

http://www.materialstoday.com/characterization/podcasts/wavelength-dispersive-xray-fluorescence/

An interesting application of confocal micro-X-ray fluorescence has been reported by Dr. Tianxi Sun (Beijing Normal University, China) and his colleagues. The technique employs a polycapillary focusing X-ray lens and a polycapillary parallel X-ray lens, as well as the laboratory X-ray source (Mo tube). In the present research, the scan of the confocal point can give the Cu²⁺ ion distribution near the surface of the electrode in a steady-state diffusion in an electrolytic tank. The research group studied the effects of the concentration of the electrolyte and the bath voltage on the shape of the layer on the nonuniform distribution of the Cu²⁺ ions. For more information, see the paper, "Spatially Resolved In Situ Measurements of the Ion Distribution Near the Surface of Electrode in a Steady-State Diffusion in an Electrolytic Tank with Confocal Micro X-ray Fluorescence", S. Peng et al., Anal. Chem., 86, 362 (2014).

Dr. P. Korecki (Jagiellonian University, Poland) and his colleagues have recently published a fairly impressive, successful 3D analysis of Cu₃Au (001) single crystal by white-beam X-ray fluorescence holograms measured using a 50W tungsten X-ray tube (50 kV, 1 mA, with 0.8mm Al filter). Primary X-ray photons at the aperture, which is placed at 340 mm from the source, are around 2×10⁸ counts/sec. The sample was positioned 610 mm from the sample, and was rotated relative to the incident beam around two axes (θ, φ). The X-ray fluorescence intensity of Cu K and Au L lines was measured by a Si drift detector (SDD) with a 25 mm² effective area, placed at a distance of 12 mm from the sample. The typical counting rate was around 10⁵ counts/sec, and the total acquisition time was ~90 h, i.e., 4 days. It was demonstrated that a 3D image of the sample was reconstructed from the recorded holograms. Readers might be surprised to know that such a non-efficient experiment can be done even with a low power source. As the authors claim at the end of this paper, the measuring time can be reasonably shortened by the use of more powerful laboratory X-ray sources. For more information, see the paper, "Element sensitive holographic imaging of atomic structures using white x rays", K. M. Da.browski et al., Phys. Rev. B87, 064111 (2013).

A team led by Professor C. T. Chantler (University of Melbourne, Australia) has published vanadium Kβ spectra from metallic foil, measured with medium energy resolution but with high accuracy. For more information, see the paper, "Characterization of the Kβ spectral profile for vanadium", L. F. Smale et al., Phys. Rev. A87, 022512 (2013).

The extremely high peak power of an X-ray free electron laser pulse can be an attractive tool for clarifying the core-level excitation and relaxation process. Recently, Dr. B. Rudek and his colleagues have reported their time-of-flight ion spectroscopy studies on sequential inner-shell multiple ionization of krypton at photon energies at 2 keV and 1.5 keV, which are higher than the LI (~1.92 keV) and lower than the LIII (~1.67 keV) edges for ordinary neutral krypton, respectively. The experiments were done with two X-ray pulse widths (5 and 80 fs) and various pulse energies (from 0.07 to 2.6 mJ), at the Linac Coherent Light Source (LCLS), Stanford, USA. The highest charge state observed at 1.5 keV photon energy (below the LI edge) is Kr¹⁷⁺; at 2 keV photon energy (above the LIII edge), it is Kr²¹⁺. It was found that theoretical calculations based on a rate-equation model can explain the obtained experimental data for 1.5 keV, but fails to do so at 2 keV, where the experimental spectrum shows higher charge states. They discussed that this enhancement is due to a resonance-enhanced X-ray multiple ionization mechanism, i.e., resonant excitations followed by autoionization at charge states higher than Kr¹²⁺, where direct L-shell photoionization at 2 keV is energetically closed. For more information, see the paper, "Resonance-enhanced multiple ionization of krypton at an x-ray free-electron laser", B. I. Cho et al., Phys. Rev. A87, 023413 (2013).

Dr. B. Kanngießer (Technische Universität Berlin, Germany) and her colleagues have recently reported further advances in 3D chemical mapping using a confocal X-ray fluorescence setup. The research group has obtained nondestructive reconstruction of stratified systems with constant elemental composition but with varying chemical compounds. For more information, see the paper, "Three-Dimensional Chemical Mapping with a Confocal XRF Setup", L. Luhl et al., Anal. Chem., Article ASAP (DOI: 10.1021/ac303749b).

In spite of the recent advent of few fs pulse X-ray free-electron laser sources, so far, synchronization between optical lasers and X-ray pulses has been challenging, and the jitter, typically, 100~200 fs r.m.s., has limited the time-resolution of the measurement. At the Linac Coherent Light Source (LCLS), Stanford, scientists have recently solved this problem by introducing a "measure-and-sort" approach, which records all single-shot data with time information to ensure resorting of the data. In the beamline, the same optical laser beam is split into three beams: with the first, the relative delay between laser and X-ray is encoded into wavelength by using a broadband chirped supercontinuum; in the second, the temporal delay is spatially encoded; in the third, pump-probe experiments are performed with time-sorting tools. It was concluded that the error in the delay time between optical and X-ray pulses can be substantially improved to 6 fs r.m.s., leading to time-resolved measurement with only a few fs resolution. For more information, see the paper, "Achieving few-femtosecond time-sorting at hard X-ray free-electron lasers", M. Harmand et al., Nature Photonics, doi:10.1038/nphoton.2013.11; published online, February 17, 2013.

One promising application of laser-matter interactions is generating hot suprathermal electrons with keV-MeV energy, which enables excitation of the K shell of the target material. Recently, Dr. G. Cristoforetti (Intense Laser Irradiation Laboratory, Italy) and his colleagues have reported some interesting experiments on the laser pulse polarization effect on the Kα yield and line shape. The research group studied the interaction of an ultrashort laser pulse (λ = 800 nm, τ = 40 fs) with a Ti foil under intense irradiation. The K X-ray emission was analyzed by a quartz crystal and a CCD camera, and it was found that the energy of Kα lines shift a few eV up to around 15 eV, depending on the pulse polarization. Such dependence can be discussed by considering the efficiency of hot electron generation. For more information, see the paper, "Spatially resolved analysis of Kα x-ray emission from plasmas induced by a femtosecond weakly relativistic laser pulse at various polarizations", G. Cristoforetti et al., Phy. Rev. E87, 023103 (2013).

Recently a research group led by Okayama University in Japan has reported the successful application of resonant X-ray emission spectroscopy (RXES) to BaTiO₃ nanoparticles of various sizes ranging from a bulk-like 200 nm to a paraelectric 50 nm. While it is well known that the crystal structure changes from tetragonal to cubic as the particle size decreases, some recent reports indicated that a very large enhancement of the dielectric constant was observed at a specific particle size of around 70 nm. The research was done to clarify the above problem. In the X-ray emission spectra measured with monochromatic excitation near the sharp peak of the Ti-K absorption edge, two small Raman peaks were observed between Kβ_2,5 (4962.6 eV) and elastic scattering of (for example, 4983.6 eV) peaks. It was found that the higher energy Raman peak (5.3 eV lower than incident X-ray energy) still exists at a size of 85 nm, even though the intensity basically diminishes for the small particle size BaTiO₃, which corresponds to the extraordinary large crystal structure change. The results suggest that Raman peak intensity is correlated to the large enhancement of the dielectric constant. For more information, see the paper, "Enhancement of dielectric constant of BaTiO₃ nanoparticles studied by resonant x-ray emission spectroscopy", N. Nakajima et al., Phy. Rev. B86, 224114 (2012).

At Linac Coherent Light Source (LCLS), Stanford, USA, a series of experimental works has been carried out based on the core-level excitation and relaxation process. One recently published paper from Stanford reports the resonant generation of Kα emission from aluminum foil (1μm thick) in a solid-plasma state created by irradiating very strong X-ray free-electron laser pulses (less than 80 fs time width, 1.6×10¹² photons/pulse). In the experiment, quasimonochromatic (0.5% bandwidth) X-ray pulses in the energy range of 1480-1580 eV (below and slightly above the K edge of ground state Al) were focused onto a 3μm diameter spot on the sample, with a corresponding peak intensity in excess of 10¹⁷ W/cm². To analyze the X-ray spectra, the research group employed a wavelength-dispersive X-ray spectrometer with a flat ADP (101) crystal and an X-ray CCD camera. Since the same atom can absorb multiple photons contained in the single pulse time width, with L-shell holes being created and leading to the excitation of a K-shell electron into one of these L-holes, the Kα X-rays are produced. The research group studied many such emission spectra produced by tuning the XFEL energy to the K-L transitions of those highly charged ions that have transition energies below the K edge of the cold material. It was also found that resonance emission peaks broaden significantly, and this was explained as opacity effects. Because of the intensity-dependent optical depth, the transparent sample at low intensity thickens optically with an intense XFEL pulse. For more information, see the paper, "Resonant Kα Spectroscopy of Solid-Density Aluminum Plasmas", B. I. Cho et al., Phys. Rev. Lett., 109, 245003 (2012).

A Chinese group recently published a paper proposing a new interpretation of neon's absorption of extremely strong X-ray photons from an X-ray free electron laser, which was experimentally studied at Stanford in 2010 (see, L. Young et al., Nature, 466, 56 (2010)). Although the ordinary absorption edge of neon is around 867 eV, the energy becomes higher than usual because of multiple ionization. Therefore, detailed studies were done between 800 eV and 2000 eV at Stanford at that time. The main discussion here is the large discrepancies between theory and experiment found at 1050 eV, where the rates of K-shell absorption 1s → 4p of Ne⁶⁺ and 1s → 3p of Ne⁷⁺ are larger than the direct single-photon ionization rates by more than one order of magnitude. The authors of this paper propose that the inner-shell resonant absorption (IRA) effects be considered as the mechanism. They showed that resonant photopumping of K-shell electrons to the L, M, or even higher bound orbitals can provide an interaction strength that is two or three orders of magnitude larger than that in the continuum level. Only when the IRA effects were taken into account were the observed charge state distributions explained well. For more information, see the paper, "Inner-shell resonant absorption effects on evolution dynamics of the charge state distribution in a neon atom interacting with ultraintense x-ray pulses", W. Xiang et al., Phys. Rev. A86, 061401(R) (2012).

A French group has recently published an interesting report on the analysis of cirrhotic liver tissue. At the Synchrotron Soleil, near Paris in France, scientists combined synchrotron Fourier transform infrared (FTIR) microspectroscopy and synchrotron micro-X-ray fluorescence (XRF) on the same tissue section. They found from FTIR that hepatocytes within cirrhotic nodules have quite highly concentrated esters and sugars, and in the same area, phosphorus and iron were detected by XRF. Also the research team studied their inhomogeneity. For more information, see the paper, "In situ chemical composition analysis of cirrhosis by combining synchrotron-FTIR and synchrotron X-ray fluorescence microspectroscopies on the same tissue section", F. Le Naour et al., Anal. Chem., Just Accepted Manuscipt. Publication Date (Web): 3 Nov 2012.

Scientists at the National Institute of Standards and Technology, USA, have recently discussed some fundamental problems in quantitative electron probe X-ray micro analysis (EPMA). The main arguments center on two significant sources of uncertainty in the quantitative matrix correction models; the mass absorption coefficient and the backscatter coefficient. For more information, see the paper, "Uncertainty Estimates for Electron Probe X.ray Microanalysis Measurements", N. W. M. Ritchie et al., Anal. Chem., Article ASAP, Publication Date (Web): 22 Oct 2012.

A research team led by Professor K. Janssens (Antwerp University, Belgium) has published several interesting results from their series of analytical work on Van Gogh's paintings. They were able to give more detailed insights on the chemical forms of cadmium yellow and chromium yellow, as well as the role of lead in the pigment. For more information, see the following 3 papers, "Combined use of Synchrotron Radiation Based Micro-X-ray Fluorescence, Micro-X-ray Diffraction, Micro-X-ray Absorption Near-Edge, and Micro-Fourier Transform Infrared Spectroscopies for Revealing an Alternative Degradation Pathway of the Pigment Cadmium Yellow in a Painting by Van Gogh", G. Van der Snickt et al., Anal. Chem., Article ASAP, Publication Date (Web): 30 Aug 2012., "The Degradation Process of Lead Chromate in paintings by Vincent van Gogh studied by means of Spectromicroscopic methods. Part III: Synthesis, characterization and detection of different crystal forms of the chrome yellow pigment", L. Monico et al., Anal. Chem., Just Accepted Manuscript. Publication Date (Web): 10 Oct 2012, and "The Degradation Process of Lead Chromate in paintings by Vincent van Gogh studied by means of Spectromicroscopic methods. Part IV: Artificial ageing of model samples of co-precipitates of lead chromate and lead sulfate", L. Monico et al., Anal. Chem., Just Accepted Manuscript. Publication Date (Web): 10 Oct 2012.

One of the remarkable instances of progress in soft-X-ray spectroscopy recently is the successful high-resolution measurement of O-K edge absorption spectra of liquid water and ice, which have some disordered hydrogen-bonds. Professor R. Car (Princeton University) and his colleagues have recently reported their theoretical studies into the quantum dynamics of the nuclei and inhomogeneous screening effects. They found that the inclusion of quantum disorder is essential to bring the calculated spectra in close agreement with the experiment. In particular, the intensity of the pre-edge feature, a spectral signature of broken and distorted hydrogen bonds, is accurately reproduced, in water and hexagonal ice, only when quantum nuclei are considered. The effect of the inhomogeneous screening is less important but non-negligible, particularly in ice. For more information, see the paper, "Roles of quantum nuclei and inhomogeneous screening in the x-ray absorption spectra of water and ice", L. Kong et al., Phys. Rev. B86, 134203 (2012).

An Argentinean group has reported the experimental determination of cross sections for K-shell ionization by electron impact for Al, Si, and Ti and their oxides deposited on carbon substrates, for incident energies between 2.5 and 25 keV. For more information, see the paper, "Experimental determination of cross sections for K-shell ionization by electron impact for C, O, Al, Si, and Ti", S. P. Limandri et al., Phys. Rev. A86, 042701 (2012).

In time-resolved X-ray analysis based on the pump-probe scheme, an increase in the repetition rate is crucial for improving efficiency. At the same time, it is crucial to maintain or improve pulse to pulse stability. Recently a Swiss research team developed a fast multichannel detection system for pump-probe spectroscopy, capable of detecting single shot super-continuum spectra at the repetition rate (10-50 kHz) of an amplified femtosecond laser system. The setup is not for synchrotron X-rays, but many points discussed in the report will be useful. For more information, see the papers, "Femtosecond pump/supercontinuum-probe setup with 20 kHz repetition rate", G. Aubock et al., Rev. Sci. Instrum., 83, 093105 (2012).

Readers might recall several previous news articles on X-ray spectra of neon excited by ultra-short, high-intensity pulses from an X-ray free electron laser source at LCLS, Stanford ("Observation of non-linear resonances of inner-shell electrons by X-ray free electron laser", No.1, Vol. 41 (2012), "Calculation of X-ray emission from doubly ionized neon", No.1, Vol. 40 (2011), ""Hollow" neon atom created by X-ray laser excitation", No.5, Vol. 39 (2010) and "Removing all electrons from neon by X-ray laser", No.6, Vol. 38 (2009) ). Recently, a research team led by Professor C. H. Keitel (Max-Planck-Institut für Kernphysik, Germany) has published its calculation of the resonance X-ray fluorescence spectra of neon, based on a so-called two-level model, which is used to study the transition of 1s2p_z^-1→1s^-12p_z in Ne⁺ at an energy of 848 eV. As X-rays induce Rabi oscillations so fast, they compete with Ne 1s-hole decay. The research group discusses resonance X-ray fluorescence spectra for two different cases; the first is chaotic pulses, which are most likely based on the SASE principle employed in the present XFEL facilities, and the second is Gaussian pulses available from the more ideal types of X-ray lasers expected in the future. For more information, see the paper, "Resonance fluorescence in ultrafast and intense x-ray free-electron-laser pulses", S. M. Cavaletto et al., Phys. Rev. A86, 033402 (2012).

The 15th international conference on X-ray absorption fine structure was recently held in Beijing, China, from July 22 to 28, 2012. In addition to many applications of the XAFS technique in a variety of scientific fields, reports and discussions were held on progress in theory and software, as well as some advanced experiments such as time-resolved XAFS. The next conference will take place at Karlsruhe, Germany in summer 2015. For further information, visit the web page, http://www.ixasportal.net/ixas/index.php?option=com_content&view=article&id=90&Itemid=134

Resonant X-ray scattering is powerful technique for the study of electronic structure at the nanoscale. However, the optical properties of the constituent components of a material must be known prior to modeling of the scattered intensity. Professor J. B. Kortright (Lawrence Berkeley National Laboratory, USA) and his collaborator have recently proposed a method of refining electronic structure, in the form of optical properties, simultaneously with physical structure, in a Kramers-Kronig (K-K) consistent manner. This technique has been applied to specular reflectivity from a SrTiO₃ single crystal, and both a nonresonant surface contaminant layer and a modified SrTiO₃ surface region have been evidenced. For more information, see the paper, "Kramers-Kronig constrained modeling of soft x-ray reflectivity spectra: Obtaining depth resolution of electronic and chemical structure", K. H Stone et al., Phys. Rev. B86, 024102 (2012).

Several electron-microscopist groups have recently reported that a Si drift detector with a 60~100 mm² effective area can be used to detect characteristic X-rays from a single atom in nanomaterials such as silicon and platinum in monolayer and multilayer grapheme, as well as erbium in a C₈₂ fullerene cage supported in a single-walled carbon nanotube. They employed a tiny electron beam of 0.1 nm in the aberration-corrected scanning transmission electron microscope. As will be clear for readers of X-ray Spectroscopy journal, the discussion is a kind of major and/or minor component analysis of extremely small volume rather than so-called ultra trace element analysis. The signal intensity was apparently very weak, but was in the order of some counts/sec according to the reports. Such high sensitivity points to the significant potential of the energy dispersive detector system. On the other hand, further detailed analysis including the estimation of parasitic background will be necessary. For more information, see the papers, "Single atom identification by energy dispersive x-ray spectroscopy", T. C. Lovejoy et al., Appl. Phys. Lett., 100, 154101 (2012), and "Detection of photons emitted from single erbium atoms in energy-dispersive X-ray spectroscopy", K. Suenaga et al., Nature Photonics, advanced online publication doi:10.1038/nphoton.2012.148.

One very interesting outcome at LCLS (Linac Coherent Light Source), Stanford, USA has recently been published. The experiment was single-shot imaging of ferromagnetic, nanoscale spin order taken with femtosecond X-ray free electron laser pulses. For more information, see the paper, "Femtosecond Single-Shot Imaging of Nanoscale Ferromagnetic Order in Co/Pd Multilayers Using Resonant X-Ray Holography", T. Wang et al., Phys. Rev. Lett. 108, 267403 (2012).

A Swiss group has reported on the design and performance of a novel high-temperature and high-pressure continuous-flow reactor, which allows for X-ray absorption spectroscopy or diffraction in supercritical water and other fluids under high pressure (up to 30 MPa) and temperature (up to 500 ^oC). For more information, see the paper,"Design of a continuous-flow reactor for in situ x-ray absorption spectroscopy of solids in supercritical fluids", M. Dreher et al., Rev. Sci. Instrum. 83, 054101 (2012).

An Australian team has reported on its study of a historical self-portrait by Sir Arthur Streeton (1867-1943) with fast-scanning X-ray fluorescence microscopy using synchrotron radiation. They employed the event-mode Maia X-ray detector, which has the capability to record elemental maps at megapixels per hour with the full X-ray fluorescence spectrum collected per pixel. The 25 megapixel elemental maps were obtained across the 200 × 300 mm² scan area. The size of the beam used was 10 × 10 μm². As heavy brushstrokes of lead white overpaint conceal the portrait, the excitation energy was chosen as 12.6 keV in order to avoid the influence of extremely strong Pb L fluorescence as well as Raman inelastic scattering. For more information, see the paper, "High-Definition X-ray Fluorescence Elemental Mapping of Paintings", D. L. Howard et al., Anal. Chem. 84, 3278 (2012).

An interesting paper has been published showing the extended X-ray absorption fine structure (EXAFS) as evidence of negative expansion of CdTe crystal. Measurements were done for both the K edges of cadmium and tellurium, from 4.2 K to room temperature. For more information, see the papers, "Negative thermal expansion in crystals with the zincblende structure: an EXAFS study of CdTe", N Abd el All et al., J. Phys.: Condens. Matter 24, 115403 (2012).

A research group led by Professor B. Kanngießer (Technische Universität Berlin, Germany) has reported on a new approach for chemical speciation in stratified systems using 3D Micro-XAFS spectroscopy. As X-ray fluorescence mode in XAFS measurement generally leads to distorted spectra due to absorption effects, they developed a reliable reconstruction algorithm. For more information, see the paper, "Reconstruction Procedure for 3D Micro X-ray Absorption Fine Structure", L. Lühl et al., Anal. Chem. 84, 1907 (2012).

On Friday 2 December 2011, an unknown painting by Rembrandt was presented in the Rembrandt House Museum (Amsterdam). The small panel, Old Man with a Beard, was painted by Rembrandt around 1630, at the end of his time in Leiden. A research group led by Professor K. Janssens (University of Antwerp) and Professor J. Dik (Delft University of Technology) has performed experimental studies on this painting with a synchrotron beam at the European Synchrotron Radiation Facility (ESRF) and the Brookhaven National Laboratory (BNL), and has unveiled a hidden, unfinished self-portrait below the painting. For further information, visit the web page, http://webh01.ua.ac.be/mitac4/rembrandt/index_301111.html