Recently in Imaging Category

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).

Coherent X-ray diffraction imaging is one of a number of recently developed lens-less microscopic techniques giving 2D real space structure when combined with phase retrieval data processing. A team in Shandong University in China has recently published an interesting observation of intact unstained magnetotactic bacteria. It was confirmed that the reconstructed images give some intercellular structures, such as nucleoid, polyβ-hydroxybutyrate granules, and magnetosomes, which have been identified by electron microscopy. The team was also successful in quantification of the density, i.e., it was found that the average density of magnetotactic bacteria is 1.19 g/cm³ from their data. The experiment was done with 5 keV X-ray photons at BL29XU, SPring-8, Japan. For more information, see the paper, "Quantitative Imaging of Single Unstained Magnetotactic Bacteria by Coherent X.ray Diffraction Microscopy", Jiadong Fan et al., Anal. Chem. 87, 5849 (2015).

At the European Synchrotron Radiation Facility (ESRF) in Grenoble, France, scientists from Italy, Germany and France have succeeded in 'reading' letters inside a papyrus roll found in the ancient library, discovered in Herculaneum. The experiments were done at the beamline ID17, and the X-ray phase contrast tomography technique was employed. The team was successful in extracting words under several papyrus layers in a fragment, and finally found that they are the complete Greek alphabet. For more information, see the paper, "Revealing letters in rolled Herculaneum papyri by X-ray phase-contrast imaging", V. Mocella et al., Nature Communications, 6, 5895 (2015). An interesting movie has also been uploaded to Youtube, https://www.youtube.com/watch?v=d3aWBgNYOCU

X-ray ptychography is known as a promising lensless imaging method. Compared with other similar techniques, it can give a rather wide viewing area with the same high-spatial-resolution in nano scale, by combining multiple coherent diffraction measurements from the illumination of several overlapping regions on the sample. However, this apparently has to assume a highly sophisticated scanning/positioning instrumentation. The method may suffer also from partial-coherence effects and fluctuations. Dr. A. Menzel (Paul Scherrer Institut, Switzerland) and his colleagues have recently published an interesting report on fast measurement. The authors discussed ptychographic on-the-fly scans, i.e., collecting diffraction patterns while the sample is scanned with constant velocity. It was found that such a scan can be used as a model for a state mixture of the probing radiation and helps to achieve reliable image recovery. The feasibility of on-the-fly measurements in traditional scanning transmission X-ray microscopy is already known. This time, the research team was successful in applying these to X-ray ptychography, which usually uses reconstruction algorithms assuming diffraction data from a static sample. Such problems were discussed in detail. For more information, see the paper, "On-the-fly scans for X-ray ptychography", P. M. Pelz et al., Appl. Phys. Lett., 105, 251101 (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).

Dr. F. P. Romano and his colleagues have reported full-field X-ray fluorescence imaging based on the principle of the pin-hole camera. The instrument consists of a low power X-ray source (W anode, 50kV-2mA), a pinhole (50 micron dia) and a CCD camera (back illuminated type, 1024 × 1024 pixels, pixel size 13 micron square). To obtain good energy resolution (133 eV at 5.9 keV), the research team took a number of images in single photon counting mode. The team also obtained a reasonable spatial resolution down to 30 microns. The system can change the magnification ratio from 0.35 to 6, depending on the viewing area of interest and the required spatial resolution. For more information, see the paper, "Macro and Micro Full Field X-Ray Fluorescence with an X-Ray Pinhole Camera Presenting High Energy and High Spatial Resolution", F. P. Romano et al, Anal. Chem., 86, 10892 (2014).

So far, high-resolution microscopic analysis of individual atmospheric particles has been fairly difficult because of problems with the filters used for capturing particles. The research group in the National Institute for Standards and Technologies, United States, is proposing a multiplatform approach for microscopically assessing chemical and optical properties of individual heterogeneous urban dust particles. The procedures described in the paper could also be useful for similar analysis. The method uses 5 steps; (i) particles embedded in fibrous filters are transferred to polished silicon/germanium wafers with electrostatically-assisted high-speed centrifugation, (ii) particles with light absorbing/scattering behavior are identified from bright/dark field light-microscopy, (iii) particles identified from light microscopy are compositionally mapped at high-definition with field-emission scanning electron microscopy and energy-dispersive X-ray spectroscopy, (iv) compositionally-mapped particles are further analyzed with focused ion-beam (FIB) tomography whereby a series of thin slices from a particle are imaged, and the resulting image stack is used to construct a 3-dimensional model of the particle, and (v) particle chemistry is assessed over two distinct regions of a thin FIB slice of a particle with energy-filtered transmission electron microscopy (TEM) and electron energy-loss spectroscopy associated with scanning TEM. For more information, see the paper, "Qualitative Multiplatform Microanalysis of Individual Heterogeneous Atmospheric Particles From High-Volume Air Samples", J. M. Conny et al., Anal. Chem., Just Accepted (DOI: 10.1021/ac5022612 Publication Date (Web): September 14).

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).

At ESRF in Grenoble, France, several very interesting imaging experiments are going on. Some fossils of Archaeopteryx, which were believed to live 150 million years ago, are being imaged by using a pin-hole X-ray camera at synchrotron beamlines BM5 and ID19. The main question is about their wings - whether they could fly or not. So far, the research has encountered a number of challenges. The project is conducted by Germany's Burgermeister-Muller-Museum (the Solnhofen Museum). For more information, see the following Web site, http://www.solnhofen.de/index.php?id=0,49

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).

Professor Y. Takahashi (Osaka University, Japan) and his colleagues have recently reported that coherent X-ray imaging using Bragg diffraction can aid the observation of nanoscale dislocation strain fields in a silicon single crystal. The experiments were done with 11.8 keV micro-focused X-ray photons, around 1 μm in both directions, using KB mirrors at BL-29XUL, SPring-8, Japan. In this research, a 1 μm thick silicon (100) single crystal was placed in the X-ray path so that X-rays could pass through it and the 220 Bragg reflection spot was observed by a CCD camera 2 m behind the sample. The sample was scanned in XY directions as well. The research team found phase singularities, i.e., two pairs of vortices with opposite directions in the phase map, that corresponded to the locally dark positions in the intensity map. It was concluded that this corresponded to the projection of the {111} dislocation loops. For more information, see the paper, "Bragg x-ray ptychography of a silicon crystal: Visualization of the dislocation strain field and the production of a vortex beam", Y. Takahashi et al., Phys. Rev. B87, 121201(R) (2013).

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).

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).

Coherent X-ray diffractive imaging has made remarkable progress over the past 15 years. The technique basically reconstructs real space microscopic images with the spatial resolution of nm without the use of lenses, mainly because of the ability to retrieve phases. However, it relies on the degree of high coherence of the available X-ray photon beam, and, until now, almost all experimental studies have been subject to some limits. It is not very easy to satisfy the ideal conditions, mainly because of the partial coherence of the beam itself and some decoherence caused by imperfect detection as well as the dynamic motions of the sample. Dr. P. Thibaut (Technische Universität München, Germany) and his colleague have recently reported their analytical studies into extending ptychography by formulating it as low-rank mixed states. The procedure is closely related to quantum state tomography and is equally applicable to high-resolution microscopy, wave sensing and fluctuation measurements. They concluded that some of the most stringent experimental conditions in ptychography can be relaxed, and susceptibility to imaging artifacts is reduced even when the coherence conditions are not ideal. For more information, see the paper, "Reconstructing state mixtures from diffraction measurements", P. Thibault et al., Nature, 494, 68 (2013).

In Japan, a research team led by Professor K. Yamauchi (Osaka University) and Professor T. Ishikawa (Riken, Harima, Japan) has recently succeeded in focusing ultra short X-ray laser pulses from the SPring-8 Angstrom Compact free electron LAser (SACLA). With reflective optics comprising elliptically figured mirrors with nm accuracy to preserve a coherent wavefront, they have obtained a focused small beam of 0.95 × 1.20 μm² at 10 keV. The estimated achievable power density at the sample position is 6 × 10¹⁷ W/cm². For more information, see the paper, "Focusing of X-ray free-electron laser pulses with reflective optics", H. Yumoto et al., Nature Photonics, 7, 43 (2013).

Dr. Okamoto (Canon, Japan) and his colleagues have reported X-ray waveguiding based on electromagnetism in photonic crystals, using a waveguide consisting of a pair of claddings sandwiching a core with a periodic structure. For more information, see the paper, "X-ray Waveguide Mode in Resonance with a Periodic Structure", K. Okamoto et al., 109, 233907 (2012).

Coherent X-ray diffraction imaging is a promising new technique to observe samples in material science and biology with a spatial resolution of around 10 nm. However, the range of applications is still not very wide, because the method requires that the X-ray source be highly coherent both laterally and longitudinally. Thus, one of the most important questions for users is the feasibility of the technique when only a partially coherent source is available. A research group led by Professor K. Nugent (University of Melbourne, Australia) has recently reported some quite good news on this issue. So far, it has been often said that the lateral coherence length should be at least twice the greatest spatial extent of the object. The longitudinal coherence length is determined by the bandwidth of the monochromatic X-ray beam. According to the present study, one could relax the minimal criteria by a factor of 2 for both lateral coherence length and longitudinal coherence length, if the coherence properties are known either a priori or through experiment. In other words, more flux could be made available at the sample position for the coherent X-ray diffraction imaging experiments with the use of a partially coherent X-ray source. For more information, see the paper, "Diffraction imaging: The limits of partial coherence", B. Chen et al., Phys. Rev. B86, 235401 (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.

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.

When spatially coherent X-ray beams pass through a sample, edge-enhancement is observed in the transmission X-ray image because of the refraction effect. At Canadian Light Source (Saskatoon, Saskatchewan, Canada), Professor P. C. Johns (Carleton University) and his colleague have recently reported an interesting extension of this type of X-ray refractive imaging. They used multiple pencil beams (up to five) to create both transmission and refractive projection images, simultaneously, during the sample scan crossing the beams. The radial data were extracted from the overlapped image by a Maximum Likelihood-Expectation Maximization (MLEM) algorithm. For more information, see the papers, "Synchrotron-based coherent scatter x-ray projection imaging using an array of monoenergetic pencil beams", K. Landheer et al., Rev. Sci. Instrum., 83, 095114 (2012).

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).

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).

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

One of the key aspects of progress in X-ray microscopy is the advent of coherent diffractive imaging, which basically does not use any lenses. Ptychography is one improved version of a series of techniques using coherent X-ray beams and allows reconstructions of both strongly and weakly scattering samples. A further extension of this method has recently been published by a German group led by Professor T. Salditt (Georg-August-University Göttingen). The research introduced chemical contrasts based on near-edge X-ray absorption fine structures. The group demonstrated that two different molecules in a biological system are distinguished visually by using the contrasts near the oxygen K edge. For more information, see the paper, "Chemical Contrast in Soft X-Ray Ptychography", M. Beckers et al., Phys. Rev. Lett. 107, 208101 (2011).

W. Rontgen took the world's first X-ray photo on November 8, 1895, thereby creating the very famous X-ray image of his wife's fingers. Ker Than has written a short article in National Geographic News on this X-ray photo. For more information, see the article, " 115-Year-Old X-Ray", http://news.nationalgeographic.com/news/2010/11/photogalleries/101108-x-rays-google-doodle-115th-anniversary-years-science-pictures/?now=2010-11-08-00:01

Professor M. D. Ward (New York University, USA) and his colleagues have recently proposed an interesting and effective application of the micro X-ray diffraction technique to anticounterfeit protection of pharmaceutical products. Counterfeit drugs have been a global threat to public health, and they undermine the credibility and the financial success of the producers of genuine products. There have been great demands for some good methods for rapid and nondestructive screening of the products. The research team's idea is the use of barcodes and logos fabricated on drug tablets using soft-lithography stamping of compounds that can be read by X-ray diffraction mapping but are invisible to the naked eye or optical microscopy. The materials used were suspensions of rutile powder mixed with corn syrup in a 1:2.5 (w/w) ratio or zinc oxide powder mixed with corn syrup at a 1:10 (w/w) ratio. It was demonstrated that the technique is feasible for realistic screening, because of its nondestructive, automated, and user-friendly properties. For more information, see the paper, "Anticounterfeit Protection of Pharmaceutical Products with Spatial Mapping of X-ray-Detectable Barcodes and Logos", D. Musumeci et al., Anal. Chem., Articles ASAP (DOI: 10.1021/ac201570r Publication Date (Web): August 30, 2011).

Most living vertebrates are jawed vertebrates (gnathostomes), and only scarce information on the evolutionary origin of jaws is available from living jawless vertebrates (cyclostomes), hagfishes and lampreys. The extinct bony jawless vertebrates, or 'ostracoderms', have been regarded as precursors of jawed vertebrates and provide an insight into this formative episode in vertebrate evolution. Very recently, Chinese scientists employed synchrotron radiation X-ray tomography in an effort to analyze the cranial anatomy of galeaspids, a 370-435-million-year-old 'ostracoderm' group from China and Vietnam. For more information, see the paper, "Fossil jawless fish from China foreshadows early jawed vertebrate anatomy", Z. Gai et al., Nature 476, 324 (2011).

Parametric down-conversion is a quantum-optical process in which a 'pump' photon splits spontaneously into two (the 'signal' and 'idler') in a nonlinear optical medium. Recently, Professor T. Ishikawa (RIKEN, Harima, Japan) and his colleagues reported their experiments with X-ray photons. They have visualized three-dimensionally the local optical response of diamond at wavelengths between 103 and 206 Å with a resolution as fine as 0.54 Å. This corresponds to a resolution from λ/190 to λ/380, an order of magnitude that is the best ever achieved. For more information, see the paper, "Visualizing the local optical response to extreme-ultraviolet radiation with a resolution of λ/380", K. Tamasaku et al., Nature Physics 7, 705 (2011).

The Dead Sea Scrolls are a collection of 972 texts from the Hebrew Bible and extra-biblical documents found between 1947 and 1956 at Khirbet Qumran on the northwest shore of the Dead Sea from which it derives its name, in the British Mandate for Palestine, in what is now named the West Bank. Recently, a research group led by Professor B. Kanngiesser (Technische Universität Berlin, Germany) has investigated the feasibility of merging two X-ray techniques, ordinary micro XRF and confocal 3D micro XRF for optimized analysis of highly inhomogeneous samples such as the Dead Sea Scrolls. Ordinary micro XRF lacks information on the depth, but the measurement is efficient and rather quick. On the other hand, confocal 3D micro XRF has depth resolution, but the measurement takes very long. The authors found that the reliability of the analysis of highly heterogeneous samples can be improved by quantitatively combining both data. For more information, see the paper, "3D Micro-XRF for Cultural Heritage Objects: New Analysis Strategies for the Investigation of the Dead Sea Scrolls", I. Mantouvalou et al., Anal. Chem., Article ASAP (DOI: 10.1021/ac2011262 Publication Date (Web): June 29, 2011).

A research group led by Professor L. Vincze (Ghent University, Belgium) has recently reported the interesting analysis of 1-20 μm sized inclusions in natural diamond crystals from Rio Soriso (Juina area, Mato Grosso State, Brazil). The crystals are called ultra-deep diamond, because they were formed in the astenospheric upper mantle, the transition zone (410-670 km), and even the lower mantle (>670 km) of the Earth. The experiment is basically 3D imaging by confocal X-ray fluorescence suing synchrotron radiation. By scanning X-ray energy near the Mn and Fe K absorption edges, the authors obtained chemical information on the inclusion cloud in the crystal. It was found that the observed Fe-rich inclusions were ferropericlase (Fe,Mg)O, hematite and a mixture of these two minerals. Another finding was that significant overprint of inclusions along pre-existing planar features is possible without changing their outer shape. For more information, see the paper, "Three-Dimensional Fe Speciation of an Inclusion Cloud within an Ultradeep Diamond by Confocal μ-X-ray Absorption Near Edge Structure: Evidence for Late Stage Overprint", G. Silversmit et al., Anal. Chem., Article ASAP (DOI: 10.1021/ac201073s Publication Date (Web): June 27, 2011).

Ptychographic X-ray diffraction microscopy is known as an extension of so-called X-ray diffraction microscopy, which is a lensless X-ray imaging technique based on coherent diffraction measurements and iterative phasing methods. The technique employs sample scanning to see a large viewing area, but so far, the spatial resolution has been rather limited mainly because of positioning errors due to the drift between the sample and illumination optics. Recently, Professor Y. Takahashi (Osaka University, Japan) and his colleagues have published an experimental way to resolve the problem. The research group has developed a method of correcting positioning errors, and made it possible to illuminate a highly focused hard X-ray beam at the exact position on the samples. The spatial resolution achieved is as good as 10 nm or even better in a viewing area of larger than 5 μm. For more information, see the paper, "Towards high-resolution ptychographic X-ray diffraction microscopy", Y. Takahashi et al., Phys. Rev. B83, 214109 (2011).

A Swiss group has recently published many interesting chemical images of trace elements in heterogeneous media. The authors combined several techniques; laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS), synchrotron radiation based micro-X-ray fluorescence and extended X-ray absorption fine structure spectroscopy. The analysis was done for Opalinus clay, which has been proposed as the host rock for high-level radioactive waste repositories. 2D images were shown for the matrix elements Ca, Fe, and Ti, as well as for the trace element, Cs. The synchrotron experiments were performed at Sector 20 (PNC-CAT), Advanced Photon Source (APS), and microXAS beamline at the Swiss Light Source (SLS). The beam size was 4×3 μm² and 3×3 μm², respectively. For more information, see the paper, "Quantitative Chemical Imaging of Element Diffusion into Heterogeneous Media Using Laser Ablation Inductively Coupled Plasma Mass Spectrometry, Synchrotron Micro-X-ray Fluorescence, and Extended X-ray Absorption Fine Structure Spectroscopy", H. A. O. Wang et al., Anal. Chem., Article ASAP (DOI: 10.1021/ac200899x Publication Date (Web): May 31, 2011).

Professor J. N. Anker (Clemson University, South Carolina, United States) and his colleagues have recently reported an interesting application of optical luminescence excited by X-rays. So far, the spatial resolution of conventional florescence microscopy for tissue has been fairly limited. This is mainly due to the spread of the excitation light, which is scattered by the sample itself, particularly in the case of thick tissue. The novel idea is to use X-ray excited optical luminescent light from the scintillator plate placed at the back of the tissue. X-rays are not scattered very much even in thick tissue, and such a small spread leads to high-resolution chemical imaging of the tissue. The authors demonstrated an interesting application as a pH imager using methyl-red dyed paper. For more information, see the paper, "High-Resolution Chemical Imaging through Tissue with an X-ray Scintillator Sensor", H. Chen et al., Anal. Chem., 83, 5045 (2011).

Phase contrast X-ray imaging is a promising method for low Z samples which cannot always be properly imaged by conventional absorption and scattering imaging. Recently Professor R. D. Speller (University College London) and his colleagues reported a novel way using a laboratory X-ray source outfitted with a pair of coded apertures; one in front of the sample for imaging and one behind it. They were offset slightly to remove scattering background. Readers might be aware that the method is quite similar to X-ray Talbot interferometry (for example, see the previous news article, "Micro-structure imaging using visibility contrast", No.5, Vol. 39 (2010)), when a 2D grating is used as a coded-aperture. The technique could open up many interesting opportunities through its application to a wide range of fields, such as nano-bio technologies, because the experiments can be done with an ordinary incoherent X-ray source. For more information, see the paper, "Noninterferometric phase-contrast images obtained with incoherent x-ray sources", A. Olivo et al., Appl. Optics, 50, 1765 (2011).

In most cases, rocks and geomaterials are chemically and structurally inhomogeneous. The use of X-ray absorption spectro-microscopy is one promising solution, but the very long measuring time for scanning large samples with a tiny beam poses a limit for detailed analysis. At the European Synchrotron Radiation Facility (ESRF) in Grenoble, France, scientists recently performed much more efficient and feasible experiments by coupling near-edge X-ray absorption spectroscopy and full-field transmission radiography with a large X-ray beam. The method basically consists of the repeated acquisition of X-ray images as a function of X-ray energy near the absorption edge (in the present case, iron K edge). The research group also combines this with polarization contrast imaging. By looking at the Fe³⁺/Fe(total) image, some redox variations were found in the single mineralogical phase of complex metamorphic rocks. The research group also analyzed bentonite analogue by separating the spectra into those of 5 simple minerals. The material is a candidate for the storage of nuclear waste and CO₂, and the information is helpful in designing such applications. For more information, see the paper, "Submicrometer Hyperspectral X-ray Imaging of Heterogeneous Rocks and Geomaterials: Applications at the Fe K-Edge", V. De Andrade et al., Anal. Chem., Article ASAP (DOI: 10.1021/ac200559r Publication Date (Web) April 18, 2011).

A group led by Professor C. Chang (University of Pennsylvania, USA) has recently reported a quantitative X-ray phase imaging method that can be readily implemented on existing facilities. This technique utilizes Fresnel zone plates both as imaging optical elements for magnification and as second-order grating structures for phase-shifting interferometry. For more information, see the paper, "Quantitative x-ray differential-interference-contrast microscopy with independently adjustable bias and shear", T. Nakamura et al., Phys. Rev. A83, 043808 (2011).

A German group led by Professor U. Panne (Humboldt University, Berlin) has recently reported the successful application of the micro X-ray diffraction technique to the evaluation of the durability of cements against reaction with sodium sulfate. The experiments were done with a Debye-Scherrer camera equipped with a large-size CCD camera (3072×3072) and monochromatic micro beam (11.6 keV, 10 μm). By moving the sample along the X-ray path, it is possible to obtain information at different depths, and the team could therefore eventually reconstruct the profile of each crystalline phase along the depth from the surface. It was found that phase transformations proceeded during damage caused by penetration of sulfates. For more information, see the paper, "Deciphering the Sulfate Attack of Cementitious Materials by High-Resolution Micro-X-ray Diffraction", M. C. Schlegel et al., Anal. Chem., 83, 3744 (2011).

A Japanese group led by Professor K. Tsuji (Osaka City University, Japan) recently reported an interesting application of 3D micro X-ray fluorescence (XRF) imaging. One should note that their research employed low-power laboratory X-ray sources (30-50W, Mo tube) instead of synchrotron X-rays. They also used two polycapillary lenses for both incoming and outgoing directions to limit the viewing volume in 3D. The research group measured some forensic samples such as multilayered automotive paint fragments, leather samples etc., which have different color coatings. They analyzed 3D profiles of many elements (Si, S, Cl, K, Ca, Ti, Mn, Fe, Zn, and Ba) and discussed the relationship with the coating. For more information, see the paper, "Depth Elemental Imaging of Forensic Samples by Confocal micro-XRF Method", K. Nakano et al., Anal. Chem., Article ASAP (DOI: 10.1021/ac1033177 Publication Date (Web): March 25, 2011).

A French-Belgian joint group led by Dr. V. Rouchon (Centre de Recherche sur la Conservation des Collections, MNHN-MCC-CNRS, France) and Professor K. Janssens (Universiteit Antwerpen, Belgium) recently published an interesting paper on the application of X-ray spectrometry to cultural heritage. For many years, in Europe, iron gall inks have been used for writing manuscripts, and they could damage the paper via two major ways: (i) acid hydrolysis, enhanced by humidity, and (ii) oxidative depolymerization provoked by the presence of oxygen and free Fe(II) ions. The present research aimed to give some quantitative evidence for each contribution by studying depolymerization of cellulose under various environmental conditions, with viscometry and related changes in the oxidation state of iron determined by X-ray absorption near-edge spectrometry. It was found that residual amounts of oxygen (less than 0.1%) promote cellulose depolymerization, whereas the level of relative humidity has no impact. For more information, see the paper, "Room-Temperature Study of Iron Gall Ink Impregnated Paper Degradation under Various Oxygen and Humidity Conditions: Time-Dependent Monitoring by Viscosity and X-ray Absorption Near-Edge Spectrometry Measurements", V. Rouchon et al., Anal. Chem., 83, 2589 (2011).

A German group recently developed an X-ray fluorescence imaging system with a pnCCD-based camera. They performed a test using a laboratory 30 μm microfocus X-ray tube and synchrotron radiation at the BAM beamline, BESSY II. It was found that the system simultaneously records ca. 70,000 spectra with an energy resolution of 152 eV (at Mn Kα) with a spatial resolution of 50 μm over a viewing area of 12.7 mm squared. For more information on pnCCD detectors, for example, the following Web page could be useful, http://www.pnsensor.de/Welcome/Detector/pn-CCD/index.html For more information on the whole system for X-ray fluorescence imaging, see the paper, "Compact pnCCD-Based X-ray Camera with High Spatial and Energy Resolution: A Color X-ray Camera", O. Scharf et al., Anal. Chem., 83, 2532 (2011).

Recently, a European international research group led by Professor K. Janssens (Antwerp University, Belgium) has succeeded in solving the scientific mechanism of color darkening in the paintings of Vincent van Gogh. Some readers may remember a previous news article, "Synchrotron XRF revealed Van Gogh's hidden painting", No.5, Vol. 37 (2008), which explained how synchrotron X-ray spectroscopy and imaging are powerful tools in the analysis of such paintings. In the present work, the research group discusses the change in color from yellow to dark brown in two Van Gogh paintings, Bank of the Seine (1887) and View of Arles with Irises (1888). They also systematically studied the aging process of artificial samples using pigments. The chrome yellow pigment is chemically lead chromate (PbCrO₄), which may include some amount of PbSO₄ and/or PbO. During their research based on X-ray micro-spectroscopy, it was found that part of the material is transformed into hydrated chromium oxide (Cr₂O₃・2H₂O), which is known as viridian, i.e., a blue-green pigment under sunlight or UV light irradiation. They also noted the formation of other Cr(III) compounds. Their conclusion was that the color change is due to the reduction from Cr(VI) to Cr(III) on the surface of the paintings, and the formation of a thin layer containing Cr(III). This would be the reason for the brownish color. Most of the experiments were done at beamline ID21 at the European Synchrotron Radiation Facility (ESRF, Grenoble, France). For more information, see the papers, "Degradation Process of Lead Chromate in Paintings by Vincent van Gogh Studied by Means of Synchrotron X-ray Spectromicroscopy and Related Methods. 1. Artificially Aged Model Samples" and "2. Original Paint Layer Samples", L. Monico et al., Anal. Chem., 83 1214-1231 (2011).

Two very exiting experimental reports have been published on the application of an X-ray free electron laser (XFEL) at Linac Coherent Light Source (LCLS, Stanford, USA). An international research team led by Dr. H. Chapman (DESY, Hamburg, Germany) and Professor J. Hajdu (Uppsala University, Sweden) has demonstrated a new advanced stage of protein crystallography, which uses only tiny proteins instead of preparing large-size crystals. This could open up new possibilities for the analysis of proteins that have been difficult or even impossible to prepare so far. The technique has been basically known as coherent X-ray diffraction imaging. The present research is the first experimental application of extremely brilliant femtosecond XFEL pulses. In addition to the demonstration of snapshots of nano-crystalline proteins, they have reported the first single-shot images of intact viruses. For more information, see the papers, "Femtosecond X-ray protein nanocrystallography", H. N. Chapman et al., Nature, 470, 73 (2011) and "Single mimivirus particles intercepted and imaged with an X-ray laser", M. M. Seibert et al., Nature, 470, 78 (2011).

Scientists in Japan have been using two synchrotrons, the SPring-8 and the Photon Factory, to analyze the dust particles collected by the HAYABUSA Asteroid probe, which returned from Asteroid Itokawa on June 13, 2010. HAYABUSA, which means "Falcon" in Japanese, was launched from the Uchinoura Space Center in Japan on May 9, 2003, and arrived at Itokawa in September 2005. The HAYABUSA particles were initially analyzed using electron microscopes, and then forwarded to the above synchrotron facilities in January 2011. Many interesting 3D images were collected at BL20XU, SPring-8, and the structure and chemical compositions were also analyzed at BL-3A, Photon Factory, KEK. For more information on the HAYABUSA project, visit the web page of the Japan Aerospace Exploration Agency (JAXA), http://www.isas.jaxa.jp/e/enterp/missions/hayabusa/index.shtml

A research group led by Professor F. Pfeiffer (Technische Universitat Munchen, Germany) has recently reported an extremely powerful combination of X-ray tomography and ptychographic coherent imaging, which enables quantitative phase-contrast X-ray microscopy without any lenses. A refractive index in the X-ray region is usually expressed as n = 1 - d - iβ, where d and β are real and imaginary parts, and relate to the phase shift and the attenuation, respectively. The researchers developed a new method to give a 3D image of d rather than β, because d can give much higher visibility in samples based on low-Z elements, which are most likely in bio-medical applications. So far, phase-contrast X-ray imaging has had limitations in giving such quantitative information. The use of coherent X-ray diffraction is one of the most promising solutions, and ptychography is a further extension that enhances precision in recovering the phase by introducing scanning of the sample. As the spatial resolution of the computed images is no longer limited by the quality or resolving power of a lens, just a pinhole was used in the present research. By combining such image reconstruction to obtain nano-scale 2D images with other image processing based on a back-filtered projection algorithm, they have succeeded in obtaining 3D images on the 100 nm scale of bone structures such as the osteocyte lacunae and the interconnective canalicular network. The experiments were done at X12SA beamline, Swiss Light Source. For more information, see the paper, "Ptychographic X-ray computed tomography at the nanoscale", M. Dierolf et al., Nature, 467, 436 (2010). In the same issue, there is an instructive account, "A new phase for X-ray imaging", H. N. Chapman, Nature, 467, 409 (2010). For the details of ptychography, see the paper, "The Theory of Super-Resolution Electron Microscopy Via Wigner-Distribution Deconvolution", J. M. Rodenburg and R. H. T. Bates, Phil. Trans. Roy. Soc. (London) A339, 521 (1992).

Dr. B. M. Patterson (Los Alamos National Laboratory, USA) and his colleagues have recently published an interesting paper on analytical problems arising from micro X-ray computer tomography. They discussed the use of a dimensional standard based upon NIST certified glass microspheres dispersed in a low density poly(styrene) matrix. For more information, see the paper, "Dimensional Standard for Micro X-ray Computed Tomography", B. M. Patterson et al., Anal. Chem., Article ASAP (DOI: 10.1021/ac101522q Publication Date (Web): September 16, 2010).

Dr. W. Yashiro (University of Tokyo, Japan) and his colleagues recently reported an interesting application of X-ray Talbot interferometry, which usually gives absorption and differential-phase images. As micro-structures of the sample distort X-ray wave fronts, the research group quantitatively discusses how visibility reduction is caused and influenced. They also experimentally demonstrate that this new type of experimental method using visibility contrast is feasible for imaging micro-structures, which have been studied by ultra small angle X-ray scattering so far. For more information, see the paper, "On the origin of visibility contrast in x-ray Talbot interferometry", W. Yashiro et al., Optics Express, 18, 16890 (2010). For more information on visibility contrast, see the paper, "Hard x-ray dark-field imaging using a grating interferometer", F. Pfeiffer et al., Nature Materials, 7, 134 (2008).

The recent advent of coherent soft and hard X-ray sources has facilitated the development of imaging techniques that are capable of being inverted to the real space information extremely quickly. A research group at the SLAC National Accelerator Laboratory, USA, recently developed a novel technique for soft X-rays, based on differential holographic encoding, termed holography with extended reference by autocorrelation linear differential operation (HERALDO). The technique has achieved superior resolution over other similar lensless techniques, such as X-ray Fourier transform holography, while maintaining the signal-to-noise ratio and algorithmic simplicity. The spatial resolution was 16 nm, and this was obtained by synthesizing images in the Fourier domain from a single diffraction pattern, which allows resolution improvement beyond the reference fabrication limit. In addition to the capability of instant high-resolution reconstruction, the technique is found to be robust against data imperfections. It reduces artifacts arising from the commonly-missing central low-q data. For more information, see the paper, "High-Resolution X-Ray Lensless Imaging by Differential Holographic Encoding", D. Zhu et al., Phys. Rev. Lett. 105, 043901 (2010). For more information on the original idea of HERALDO, see the paper, "Holography with extended reference by autocorrelation linear differential operation", M. Guizar-Sicairos and J. R. Fienup, Optics Express, 15, 17592 (2007).

Scientists led by Dr. N. Awaji (Fujitsu Laboratories, Japan) have recently reported successful large area imaging by Fourier transform holography in both soft and hard X-ray regions. The key was the separation of a holographic mask from the sample, enabling the sample to then be scanned to increase the observation area (~10μm or even more), though the beam size was fairly limited (~1μm) to maintain good coherence. They demonstrated some magnetic domain images of perpendicular magnetized film with soft X-rays (778 eV), and also some patterned samples and the cross-section of the Cu-interconnect-line with hard X-rays (5,500 eV). The spatial resolution for the above energies was 42 and 75 nm, respectively. The experiments were performed at SPring-8 (Harima, Japan). For more information, see the paper, "Large Area Imaging by Fourier Transform Holography Using Soft and Hard X-rays", N. Awaji et al., Appl. Phys. Express 3, 085201 (2010).

X-ray fluorescence has provided new information on the technique known as "sfumato", which Da Vinci and other Renaissance painters used to produce delicate gradations in tones or colors across the canvas. Dr. P. Walter (Laboratoire du Centre de Recherche et de Restauration des Musees de France, CNRS, France) and his colleagues recently performed quantitative chemical analysis on seven paintings from the Louvre Museum (including the Mona Lisa), by synchrotron X-ray fluorescence at the European Synchrotron Radiation Facility (ESRF). They were able to clarify how the painter made shadows on faces by the use of layers of glaze or a very thin paint, and by means of the nature of the pigments or additives. For more information, see the paper, "Revealing the sfumato Technique of Leonardo da Vinci by X-Ray Fluorescence Spectroscopy", L. de Viguerie et al., Angewandte Chemie International Edition (Published Online: Jul 14 2010, DOI: 10.1002/anie.201001116).