For many years, substantial effort has been devoted to developing a good mirror for preparing a small X-ray beam. Professor K. Yamauchi (
Recently in Imaging Category
So far, X-ray microscopy with many types of lens has achieved great success in the observation of biological cells. In order to extend the limits of spatial resolution and efficiency, X-ray diffraction microscopy (also called coherent X-ray diffraction imaging), which uses coherent X-rays and some image reconstruction algorithms instead of an optical lens system, is now considered as a promising procedure to see whole cells at once and pick out much smaller features, down to around 10 nm or even less. A research group led by Professor C. Jacobsen (
Nanometer scale dipole moments in the polarization clusters in BaTiO3 are believed to be thermally excited and thermally relaxed within a picosecond time scale. However, so far, there have been no reports on the direct observation of the dynamics of these dipole moments in such a very short time scale. The limitation here is mainly due to the low spatial coherence of the X-ray beam, in particular when synchrotron radiation is used as a light source. Professor K. Namikawa (Tokyo Gakugei Univ, Japan
X-ray absorption microscopy is simple, but has low sensitivity in biological samples that are made of light elements. X-ray phase contrast imaging can provide contrast that is 3 orders of magnitude greater than X-ray absorption. However, phase contrast imaging has not been that widely used so far mainly because of the unusual requirements of the experimental setup. Dr. W. Yashiro (The University of Tokyo, Japan) and his colleagues have recently proposed a novel setup that is feasible. The research group simply added a transmission grating to the setup for conventional X-ray absorption microscopy with a Fresnel Zone Plate (FZP) objective lens. Because of the self-imaging phenomenon in Talbot effects, a phase difference image can be produced by the transmission grating placed at the downstream of the back focus of the FZP. The experiment was done at beamline BL20XU, SPring-8. For more information, see the paper, "Hard-X-Ray Phase-Difference Microscopy Using a Fresnel Zone Plate and a Transmission Grating", W. Yashiro et al., Phys. Rev. Lett. 103, 180801 (2009).
X-ray phase-contrast imaging is extremely powerful for visualizing internal structures with low-Z matrices, which are most likely in bio-medical specimens. The use of an X-ray interferometer is one of the most promising ways forward for this imaging technology, but resolution has been limited to the micrometer scale so far. A research group led by Dr. A. Snigirev (European Synchrotron Radiation Facility,
A recent edition of Nature News featured the successful application of a carbon nanotube (CNT)-based X-ray source to medical imaging. A group led by Professor O. Zhou (
In January 2006, NASA's Stardust spacecraft brought comet coma particles and interstellar grains from Comet 81P/Wild2. Synchrotron facilities all over the world have been used for extensive analysis of the chemical composition and crystal structures of the matter. Recently, Professor L. Vincze (X-ray Microspectroscopy and Imaging Group,
Xradia, Inc., a developer and manufacturer of ultra-high-resolution 3D X-ray imaging systems, has announced that its scanner was used by researchers at The University of Texas at Austin in the examination of fossil Lucy, the world's most famous ancient human ancestor fossil that dates back 3.2 million years. The company's Xradia MicroXCTTM scanner, a 3D X-ray computed tomography system with sub-micron resolution, was used to scan selected pieces of the fossil, and the resulting data will assist in their studies to learn how Lucy's skeleton supported her movement and posture, and how it compares to modern humans and apes. Lucy is currently on loan from the Ethiopian Government and on tour in the
In Issue 4, vol. 8 (2009) of Nature Materials, the Insight section features a compilation of articles on recent electron and X-ray microscopy. The aim is to illustrate what are the most outstanding capabilities of modern imaging techniques based on electrons and X-ray photons, which have been often treated separately. The 6 articles in the compilation are as follows: "Is science prepared for atomic-resolution electron microscopy?", Knut W. Urban (p.260-262); "Structure and bonding at the atomic scale by scanning transmission electron microscopy", David A. Muller (p.263-270); "Electron tomography and holography in materials science", Paul A. Midgley & Rafal E. Dunin-Borkowski (p.271-280); "Near-edge X-ray absorption fine-structure microscopy of organic and magnetic materials", Harald Ade & Herman Stoll (p.281-290); "Coherent X-ray diffraction imaging of strain at the nanoscale" Ian Robinson & Ross Harder (p.291-298); "X-ray imaging beyond the limits", Henry N. Chapman (p.299-301). Visit the Web page to download the full Insight as PDF file (4.77MB), http://www.nature.com/nmat/journal/v8/n4/pdf/nmat-insight-microscopy.pdf
At the Photon Factory, KEK, Japan , Dr. T. Okuda (University of Tokyo
A research team from the National Natural History Museum in Paris and the American Museum of Natural History in New York Kansas
A method for realizing sub-angstrom spatial resolution in diffractive imaging of single nanocrystals
Diffractive imaging is a technique for so-called lens-less microscopy, and uses diffraction intensity (image) and phase retrieval calculations rather than focusing systems such as lenses, which are not free from aberrations. The spatial resolution is basically limited only by the amount of high-angle scattering. Therefore, the technique has been considered as having the potential to achieve atomic resolution for hard X-rays or other short-wavelength particle beams. However, so far, the reported results have been still at the level of several nanometers. Recently, a research group at the
Neuromeranin (NM) is a dark colored pigment synthesized within specific catecholamine-producing neurons in the human brain. It is of uncertain origin and exists as amorphous granules with a heterogeneous structure called NM granules. At the European Synchrotron Radiation Facility (ESRF) in Grenoble, the microchemical environment of NM in whole neurons from formalin-fixed and paraffin-embedded human substantia nigra sections was recently analyzed. It was found that concentrations of NM-associated elements increase in the developing brain, and that iron-rich microdomains colocalized with other elements within the pigment. Furthermore, intracellular speciation of sulfur in NM has revealed the presence of reduced sulfur compounds and various forms of oxidized sulfur compounds which have not previously been reported. For more information, see the paper, "Intracellular Chemical Imaging of the Developmental Phases of Human Neuromelanin Using Synchrotron X-ray Microspectroscopy", S. Bohic et al., Anal. Chem., Article ASAP, DOI: 10.1021/ac801817k
Recent progress in synchrotron X-ray microscopy has opened up extremely attractive applications. A group led by Professor B. M. Weckhuysen (Utrecht University, The Netherlands) recently watched heterogeneous catalysts in action at high temperature. Solid catalysts have been widely used in the chemical industry, and accelerate the production of many important compounds. They are typically composed of nanometre-sized metal or metal oxide particles attached to a solid support with a high surface area. As complex structural and chemical changes take place during catalytic reactions, direct observation of the reacting catalyst is extremely important. The team employed X-ray microscopy at the Advanced Light Source, Berkeley, United States, to study the catalytic Fischer-Tropsch reaction where a solid catalyst of iron oxide particles mounted on silica is used to convert carbon monoxide and hydrogen into liquid hydrocarbons that can be used as fuels. By the use of Fe LII, III and C K absorption edges, scanning transmission X-ray imaging has revealed that during the reaction the iron oxide underwent several transformations; the initial iron oxide (Fe2O3) is converted into another oxide (Fe3O4), before iron silicates (Fe2SiO4) and metallic iron begin to form. Iron carbides (FexCy) appear in the final stage. For more information, see the paper, "Nanoscale chemical imaging of a working catalyst by scanning transmission X-ray microscopy", E. de Smit et al., Nature 456, 222-225 (2008).
X-ray microscopy is continuing to make significant progress in two directions, through the use of advanced X-ray optical elements and through the combined use of coherent X-rays and image analysis. Currently, the typical spatial resolution available at major synchrotron radiation facilities is the order of tens of nm. Professor C. Schroer (Technische Universität Dresden, Germany
A French research group has reported the application of X-ray fluorescence microscopy to the analysis of macrophages exposed to unpurified and purified single-walled (SW) and multiwalled (MW) carbon nanotubes (CNT). During this research, elemental mapping at cell level was performed for P, Cl, K, Ca and Fe. For more information, see the paper, "Carbon Nanotubes in Macrophages: Imaging and Chemical Analysis by X-ray Fluorescence Microscopy", C. Bussy et al., Nano Lett., 8, 2659-2663 (2008).
It is well-known that Vincent van Gogh (1853-1890) often reused canvases and painted over his older works. Specialists estimate that about one third of his early paintings conceal other compositions under them. Recently, an international team led by Professor K. Janssens (University of Antwerp, Belgium) and Dr J. Dik (Delft University of Technology, The Netherlands) successfully applied synchrotron radiation induced X-ray fluorescence spectroscopy to the painting entitled Patch of Grass (painted by Van Gogh in Paris in 1887 and owned by the Kroller-Muller Museum). The research group recorded X-ray fluorescence intensity maps of several tens of square cm and, in particular, the distribution of Hg and Sb, which corresponds to red and light tones, respectively. In this way, it could analyze an approximate color reconstruction of the flesh tones. Accordingly, a portrait of a woman was discovered behind the painting. The measurement was done at DESY in Hamburg, Germany. For more information, visit the Website, http://www.vangogh.ua.ac.be/, and see the paper, "Visualization of a Lost Painting by Vincent van Gogh Using Synchrotron Radiation Based X-ray Fluorescence Elemental Mapping", J. Dik et al., Anal. Chem., ASAP Article, 10.1021/ac800965g (2008).
Aerogel is a form of nanofoam, an engineered material designed for its high strength-to-weight ratio for application wherever lightness and strength are needed. Now, the internal structure is within the scope of X-ray analysis. Lawrence Livermore and Lawrence Berkeley scientists have successfully applied the coherent X-ray diffraction technique to Ta2O5 nanofoam, the density of which is 1.2 % to the bulk, and have reconstructed 3D images to determine its strength and potential new applications. Combining the obtained structural information with detailed simulations, the research team showed that the blob-and-beam network structure explains why the materials are weaker than expected. For more information, see the paper, "Three-Dimensional Coherent X-Ray Diffraction Imaging of a Ceramic Nanofoam: Determination of Structural Deformation Mechanisms", A. Barty et al., Phys. Rev. Lett., 101, 055501 (2008).
Scanning diffraction microscopy, or ptychography, was first developed for the scanning transmission electron microscope (STEM). In the same way, by using an X-ray nano beam, one can use a STXM. The X-ray beam is focused onto the sample via a lens, and the transmission is measured. The image is obtained by plotting the transmission as a function of the sample position, as it is rastered across the beam. The analysis is straightforward, but its resolution is limited by the beam size. On the other hand, coherent diffractive imaging (CDI) now reaches resolutions below 10 nm, but the reconstruction procedures are not always easy due to the influences of data quality, sample conditions etc. A Swiss research group led by Drs. C. David and F. Pfeiffer (Paul Scherrer Institut) recently demonstrated a ptychographic imaging method that bridges the gap between STXM and CDI by measuring complete diffraction patterns at each point of a STXM scan. The group employed an advanced large-area pixel detector, Pilatus, to obtain the diffraction pattern efficiently. These diffraction data were then treated with an image reconstruction algorithm developed by the team. Several tens of thousands of diffraction images were processed to obtain one super-resolution X-ray image. The algorithm not only reconstructs the sample but also the exact shape of the light probe resulting from the X-ray beam. The 6.8 keV X-ray beam was focused using a zone plate, and the beam size was 300 nm. The spatial resolution achieved was about five times higher. For more information, see the paper, "High-Resolution Scanning X-ray Diffraction Microscopy", P. Thibault et al., Science, 321, 379 - 382 (2008).
The corrosion of steel-based mechanical components is said to be responsible for the loss of about 3% of annual global GDP. Cracks can appear in stainless steel components when stress or strain is combined with a corrosive environment that attacks sensitive grain boundaries. In nuclear power plants, certain grain boundaries can become sensitive during heat treatments or during fast neutron irradiation. It is important to observe how these cracks grow in detail, because they have been identified as the primary cause of several critical system failures. At the European Synchrotron Radiation Facility (ESRF), Grenoble, France, Dr. A. King and his colleagues recently revealed how growing cracks interact with the 3D crystal structure of stainless steel. The sample was a wire of 0.4 mm in diameter, and 40 keV X-rays were employed. By using diffraction contrast tomography, the research group could observe the shapes, positions, and orientations of 362 different grains with some 1600 grain boundaries without destroying the sample. They put the wire into a corrosive liquid, K2S4O6, and applied a load to cause microcracks to grow between the grains. As the cracks grew, 3D tomographic scans (of 30 minutes each) were made at intervals of between several minutes and two hours to follow the progress of the cracks. It was found that the cracks grew along the boundaries between the grains. The technique has enabled visualization of the cracks as they grow and of certain special boundaries that resist cracking. Information on this method is given in the following papers; "X-ray diffraction contrast tomography: a novel technique for three-dimensional grain mapping of polycrystals. I. Direct beam case", W. Ludwig et al., J. Appl. Crystallogr. 41, 302 (2008) and "II. The combined case", G. Johnson et al., J. Appl. Crystallogr. 41, 310 (2008). For more information on the present research, see the paper, "Observations of Intergranular Stress Corrosion Cracking in a Grain-Mapped Polycrystal", A. King et al., Science, 321, 382 - 385 (2008).
Spintronics is now one of the most important keywords in modern sciences and technologies. The currently employed method for magnetic recording uses electrical current pulses, and there appear to be limitations for extremely high density devices (e.g., G-bit level MRAM). One of the most promising solutions is the use of spin polarized current in a ferromagnetic medium, which can provide a spin-transfer torque to the magnetization, resulting in its motion. To develop high-density and very fast devices, it is indispensable to obtain a fundamental understanding of what really takes place there. Recently, a research group led by Dr. G. Meier (Hamburg University, Germany) succeeded in visualizing spin-torque-induced vortex gyration in micrometer-sized permalloy squares using a 30nm-resolution X-ray microscope at the Advanced Light Source (ALS), Berkeley, United States. The phases of the gyration in structures with different chirality have been analyzed considering alternating spin-polarized currents and the current's Oersted field. For more information on the present experiments, see the paper, "Time-Resolved X-Ray Microscopy of Spin-Torque-Induced Magnetic Vortex Gyration", M. Bolte et al., Phys. Rev. Lett., 100, 1701 (2008).
Progress in nano sciences requires further development of local structural probes, particularly for the study of non-uniform materials. As material functions are often concerned with heterogeneity and some hierarchical orders of the structures, some kind of zooming from low to high resolution will become crucial in the future. Furthermore, in addition to two-dimensional (2D) imaging of an object with a lateral resolution determined by the beam size, some depth resolution is important for a better understanding of materials. So far, X-ray techniques have had several limitations with respect to such points. Recently, French scientists led by Professor J-L. Hodeau (CNRS, Grenoble, France) have reported an interesting development. They are trying to combine pencil-beam tomography with X-ray diffraction to examine unidentified phases in nanomaterials and polycrystalline materials. The experiments were for a high-pressure pellet containing several carbon phases and a heterogeneous powder containing chalcedony and iron pigments. For more information, see the paper, "Probing the structure of heterogeneous diluted materials by diffraction tomography", P. Bleuet et al., Nature Materials, 7, 468 (2008).
Recently, some very interesting research on magnetic noise from antiferromagnets has been published. Unlike ferromagnets, the characteristics of which have been studied for many years, antiferromagnets have remained a mystery because their internal structure was too fine to be measured. Their internal order is on the same scale as the wavelength of X-rays, and therefore, X-ray photon correlation spectroscopy, which measures 'speckle' patterns, can give a unique 'fingerprint' of a particular magnetic domain configuration. It was found that the domain wall motion is thermally activated at temperatures above 100 K, but not so at lower temperatures. For more information, see the paper, "Direct measurement of antiferromagnetic domain fluctuations", O. G. Shpyrko, et al., Nature 447, 68 (2007).
It has long been believed that birds can in some way use the natural magnetism of the earth to navigate. Recently, scientists from the University of Frankfurt employed micro X-ray fluorescence as well as micro XAFS spectroscopy to analyze the skin of the upper beak of homing pigeons. Within the skin lining, they established the existence of tiny maghemite (g-Fe2O3) and magnetite (Fe3O4) particles (with a ratio of around 9:1) in the dendritic nerve branches that were arranged in a 3D pattern. According to the research team, this strongly supports the theory that the upper beak of pigeons houses a highly sensitive magneto-receptor that can be used for navigation. The experiments were done with synchrotron X-rays at HASYLAB in Hamburg, Germany. For more information, see the paper, "A novel concept of Fe-mineral-based magnetoreception: histological and physicochemical data from the upper beak of homing pigeons", G. Fleissner et al., Naturwissenschaften, published online in mid-March, 2007.
Professor J. Rodenburg and his colleagues from the University of Sheffield, UK and the Paul Scherrer Institute, Switzerland recently developed a novel X-ray microscope, which is very different from conventional microscopes developed so far, because it does not employ any optics to focus the beams. The lensless technique collects diffraction patterns from several overlapping areas in space, which provides information about how the rays interfere with each other after they have been diffracted through the object. This interference can then be calculated backwards to what the rays' previous phase changes must have been, giving a complete picture of the structure. Since this innovative technique relies on a special type of computation (called ptychographical iterative engine (PIE), for details, see H. M. L. Faulkner and J. M. Rodenburg, Phys. Rev. Lett. 93, 023903 (2004)), rather than specific equipment, it could also be used to boost the power of optical and even electron microscopes. For more information, see the paper, "Hard-X-Ray Lensless Imaging of Extended Objects", J. M. Rodenburg et al., Phys. Rev. Lett. 98, 034801 (2007)
In January 2006, the Stardust spacecraft brought back a number of tiny particles from comet Wild 2, which is believed to have originated within a cloud of comets just beyond the orbit of Neptune called the Kuiper Belt. The particles have been analyzed by X-rays at six synchrotron radiation facilities around the world, ESRF (France), APS (Argonne, USA), SSRL(Stanford, USA), ALS (Berkeley, USA), NSLS (Brookhaven, USA) and SPring-8 (Japan). The particles from this comet are important because they are believed to be close to the starting material of the solar system, which is now about 4.5 billion years old. The particles were found to contain a wide variety of minerals and organic materials that look similar to those seen in primitive meteorites found on earth, but the samples also revealed the presence of new materials not previously found in meteorites. It was also discovered that the samples contained minerals similar to Calcium Aluminum-rich inclusions (CAIs), which can be formed at high temperatures, i.e., in the innermost part of the solar nebula, well inside the orbit of Mercury. For more information on the Stardust mission, visit http://stardust.jpl.nasa.gov/home/index.html. Some interesting results have been published as part of a special series of papers in the Dec. 15, 2006, edition of the journal Science.
By combining coherent X-ray scattering with a method of direct phase recovery called over-sampling, lens-free microscopy in the X-ray region becomes a realistic technique. The latest hot topic is the extension of the technique from two to three dimensions. One of the most promising ways of applying this technique is the recently reported combination of (i) ab initio phase retrieval of 2D coherent diffraction patterns with a guided hybrid input-output algorithm and (ii) 3D image reconstruction with equally sloped tomography. The scheme was applied to quantitative 3D imaging of a heat-treated GaN particle with each voxel corresponding to 17×17×17 nm3. The internal GaN-Ga2O3 core shell structure was successfully captured in three dimensions. For more information about the analysis, see the paper, "Three-Dimensional GaN-Ga2O3 Core Shell Structure Revealed by X-Ray Diffraction Microscopy", J. Miao et al., Phys. Rev. Lett. 97, 215503 (2006).
A group of biologists led by Professor Guerinot (Dartmouth College, USA) has recently clarified that iron is stored in the developing vascular system of the seed of a plant called Arabidopsis. The group also found that this localization depends on a protein called VIT1, shown to transport iron to the vacuole. The experiments combined traditional mutant analysis (turning on and off the VIT1 protein) with an X-ray fluorescence micro tomography technique to obtain a map of where iron is stored in the seed. The results could help in the development of nutrient-rich seed, benefiting both human health and agricultural productivity, because iron deficiency is an area of concern in the issue of human nutrition. The experiments were done at Beamline X26A, National Synchrotron Light Source (NSLS), Brookhaven, USA. For more information, see the paper, "Localization of Iron in Arabidopsis Seed Requires the Vacuolar Membrane Transporter VIT1 ", S. A. Kim et al., Science, 314, 1295-1298 (2006).
Neanderthals were a species of the Homo genus who inhabited Europe and parts of western Asia approximately 24,000 ~ 350,000 years ago. It has even been suggested that Neanderthals achieved adulthood faster than modern humans do today. At the European Synchrotron Radiation Facility (ESRF), Grenoble, France, the enamel dentine junction of both a deciduous and a permanent Neanderthal molar tooth (about 130,000 years old) was studied recently by using high-resolution tomography. It was found that the dental development of Neanderthals was very similar to modern humans. The permanent molar tooth studied had completed its root growth at about 8.7 years of age, which is typical of many modern human children today. For more information on the experimental results, see the paper, "How Neanderthal molar teeth grew", R. Macchiarelli et al., Nature, published online 22 November 2006. For other recent interesting data on Neanderthals, see the paper, "Palaeoanthropology: Return of the last Neanderthal", E. Delson1et al., Nature, 443, 762-763 (2006).
At the FLASH free-electron laser facility at DESY in Hamburg, an international team of scientists recently published the first data on diffraction imaging of a non-crystalline sample. Theoretically, a single X-ray pulse, if it is extremely bright and perfectly coherent, can produce a diffraction pattern from a large macromolecule, a virus or a cell (for example, see, "Potential for biomolecular imaging with femtosecond X-ray pulses", R. Neutze et al., Nature, 406, 752-757 (2000)). In the present experiment, the team tested a laser pulse with 25 fs, 41013 W/cm2/pulse, containing 1012 photons at 32 nm wavelength, and obtained a coherent diffraction pattern from a nanostructured non-periodic object before this exploded into a plasma at ca. 60,000 K. They employed a novel X-ray camera assured of single-photon detection sensitivity by filtering out parasitic scattering and plasma radiation. For more information, see the paper, "Femtosecond diffractive imaging with a soft-X-ray free-electron laser", H. N. Chapman et al., Nature Physics, published online 12 November 2006.
Argonne National Laboratory researchers in collaboration with Xradia, Inc. have developed a novel X-ray surface topography technique by combining X-ray reflection, which is sensitive to height or depth on a sub nanometer scale, and full-field X-ray microscopy with condenser and objective Fresnel zone plates. Recent rapid progress in X-ray microscopy now allows scientists to obtain X-ray images with ca. 10 nm spatial resolution. However, so far, almost all full-filed imaging has employed transmission geometry. The present research has extended the technique to reflection geometry. It has become possible to image the distribution of molecular-scale interfacial features directly and non-invasively with full-field imaging. Interfacial phase contrast from elementary defect structures allows direct observation of 0.6-nm-high monomolecular steps at a solid surface. For more information, see the paper, "Observation of subnanometre-high surface topography with X-ray reflection phase-contrast microscopy", P. Fenter et al., Nature Physics, 2, 700-704 (2006).
Artists in ancient Pompeii painted the town red 2,000 years ago with a brilliant crimson pigment made of cinnabar (HgS) that dominated many of the doomed city's wall paintings. The eruption of the volcano Vesuvius showered the neighbouring towns in pumice and ash, and the Villa Sora, in Torre del Greco, remained buried until just 20 years ago, which is when excavation work started. In the remains of the house, the distinctive red colour of the wall frescoes has turned black in many places. The origins of this darkening degradation have not been clearly identified yet and remain a major issue for curators. At ESRF, by aid of micro X-ray fluorescence and absorption spectroscopy, scientists analyzed red cinnabar paintings coated on a sparry calcite (CaCO3) mortar exhibiting different levels of degradation. The results indicate two possible degradation mechanisms; formation of HgCl2 and CaSO4 through reaction with NaCl and SO2 from the environment, respectively. For more information, see the paper, "Blackening of Pompeian Cinnabar Paintings: X-ray Microspectroscopy Analysis", M. Cotte et al., Anal. Chem., 78, 7484-7492, (2006).
Scientists from CNRS at the University J. Fourier of Grenoble and from the European Synchrotron Radiation Facility (ESRF) have recently succeeded in constructing 3D pictures of a living plant seed using the holotomography technique with synchrotron light. This revealed the presence of a network of voids between the cells that may be used for storing the oxygen needed for efficient germination. For more information, see the paper, "Quantitative phase tomography of Arabidopsis seeds reveals intercellular void network", P. Cloetens et al., Proceedings of the National Academy of Sciences, published online before print September 14, 2006.
The appearance of the ultimate X-ray microscope, with atomic-scale resolution and capable of seeing deep inside objects, has long been awaited. Professor I. Robinson (University College London, UK) and his team recently made a significant step towards realizing this dream, using the technique of coherent X-ray diffraction imaging, the possibility of which was first pointed out by Sayre (Acta Crystallogr. 5, 843 (1952)) but not demonstrated until 1999 by Miao et al (Nature 400, 342 (1999)). They observed the growth of nanometer-sized Pb crystals inside the vacuum chamber. The results showed that asymmetries in the diffraction pattern can be mapped to deformities, providing a detailed 3-D map of their location in the crystal. This new method shows that the interior structure of atomic displacements within single nanocrystals can be obtained by direct inversion of the diffraction pattern. The technique is an attractive alternative to electron microscopy because of the superior penetration of materials of interest by the electromagnetic waves, which are often less damaging to the sample than electrons. The experiments were done at beamline 34-ID-C at the Advanced Photon Source (APS) in the United States. For more information, see the paper, "Three-dimensional mapping of a deformation field inside a nanocrystal", Mark A. Pfeifer et al., Nature 442, 63 (2006).
Extremely sharp focusing of hard X-rays has been achieved with a device called a Multilayer Laue Lens (MLL), recently developed at Argonne National Laboratory in the United States. The device consists of a stack of alternating layers of metal and silicon, made by depositing progressively thicker layers. The main idea is that the structure can work as a linear zone plate for X-rays. The device has an ability to focus the X-rays with an energy level of 19.5 keV to 30 nm, which is almost the smallest beam size for hard X-rays. Promising applications for a better X-ray lens would be in full-field and/or scanning probe microscopy. For more information, see the paper, "Nanometer Linear Focusing of Hard X Rays by a Multilayer Laue Lens", H. C. Kang et al., Phys. Rev. Lett. 96, 127401 (2006)
Imaging with coherent X-rays at high spatial resolution is a promising technique for obtaining information on the internal structures of non-crystalline specimens. Researchers at Cornell High Energy Synchrotron Source (CHESS, Cornell University, USA) recently succeeded in extending the Fresnel theory to retrieve phase information needed for a full image reconstruction. The algorithm gives 3D full field imaging with X-rays. This new scheme has been developed for coherent X-rays, but the distorted-object concept can be applied to other diffraction and imaging fields such as using visible light, electrons, and neutrons. The method is particularly important with respect to the utilization of future X-ray sources that have fully coherent photon beams. Part of their work was published in Phys. Rev. B 72, 033103 (2005). For more information, visit http://news.chess.cornell.edu/index.html
For many years, great efforts have been made around the world to develop soft and hard X-ray microscopes. Very recently, scientists at Lawrence Berkeley Laboratory, California, USA, have succeeded in fabricating an extremely high-performance objective lens, i.e., a micro zone plate, which projects a full-field image of the sample. The spatial resolution is 15 nm or even smaller for synchrotron soft X-rays (150~1800 eV). The key point is the improvement in electron beam lithography, since the spread due to electron scattering has previously been a big problem when patterning. The Berkeley team separately drew two different zone-plate patterns and then overlaid them very accurately. For more information, see the paper, "Soft X-ray microscopy at a spatial resolution better than 15 nm", W. Chao et al., Nature, 435, 1210-1213 (2005).
A team of scientists from the Technical University in Vienna, the Technical University in Berlin and the ESRF have combined tomography and diffraction using 80 keV X-rays to observe creep void evolution and the correlation to texture and microstructure development, which are important parameters for understanding the lifetime of components subjected to high temperature loading. The studies were carried out for a brass alloy, CuZn40Pb2, which contains three phases: -brass, s-brass, and Pb. They developed a specifically designed creep device in order to avoid artifacts during the tomography, and therefore the path of the incoming and the emerging X-rays over a complete 360 deg turn of the sample is identical. A tensile load of 25 MPa was applied by using a spring in order to avoid vibrations, and the sample was heated to 375 ºC by an induction-heated loop around the bottom of the sample. The results reveal that void growth versus time follows an exponential growth law and that the formation of large void volumes coincides with texture evolution and a steady state in the development of dislocation density. The in-situ determination of void evolution in bulk samples opens up new ways toward the assessment of creep damage to the strength of materials and subsequently towards lifetime predictions of samples and components subject to high temperature loading. For more information, see the paper, "Simultaneous Tomography and Diffraction Analysis of Creep Damage", A. Pyzalla et al., Science, 308, 92-95 (2005).
Los Alamos National Laboratory scientists, C. Worley, S. S. Wiltshire, T. C. Miller, G. J. Havrilla and V. Majidi, have developed a novel method for detecting fingerprints on surfaces that typically render such prints invisible. The technique uses micro-X-ray fluorescence (MXRF) and can therefore determine the elements in a fingerprint and obtain a pattern at the same time. Salts such as sodium chloride and potassium chloride that are excreted in sweat are sometimes present in detectable quantities in human fingerprints. As the new method might also be able to tell if the person that left the fingerprints also handled something like bomb-making materials, it could potentially be used as a tool in forensic investigation. For more information, contact Todd Hanson, Phone +1-505-65-2085, tahanson@lanl.gov, http://www.lanl.gov/.
Scientists at German and American synchrotron facilities have recently reported the significance of lensless imaging in achieving extremely high-spatial resolution. Although lenses are generally good at obtaining a magnified image of a sample, they also unfortunately introduce aberrations in the image, which ultimately limit the spatial resolution obtainable. In principle, one can form an image without a lens, by means of a coherent scattering experiment. The challenge is to solve the so-called phase problem. The team recently developed a new approach to X-ray holography, realizing a Fourier transform holography geometry by use of a micro- and nanostructured mask. Special contrast mechanisms can be exploited by resonant soft x-ray scattering and, in the experiment at BESSY, they recorded an image revealing the randomly organized "north" and "south" magnetic regions of a cobalt-platinum film to a spatial resolution of 50 nm, which is 10 times better than that achievable with conventional X-ray focusing optics. In the future, the technique will be used as a method for ultra-fast stroboscopic imaging on a femtosecond time scale using an X-ray free electron laser such as the Linac Coherent Light Source (LCLS), for example, which is expected to open at Stanford in 2009. For more information, see the paper, "Lensless imaging of magnetic nanostructures by X-ray spectro-holography", S. Eisebitt et al., Nature, 432, 885-888 (2004).
The ultra-fast X-ray diffraction technique has now become widely used. Many experiments using this technique are, in principle, a so-called pump-probe measurement, using a Ti:sapphire laser system (wavelength 800 nm, 1-kHz repetition rate with 5-mJ pulse energy and 45-fs duration) and, for example, a moving, 20-mm-thick Cu band to generate characteristic X-ray pulses. Recently, a German group reported the successful imaging of coherent atomic motions in a GaAs/AlGaAs superlattice. The motions are of great interest and are due to the excitation of electron-hole pairs in the GaAs subband. Both expansion of the GaAs layers and contrast of the AlGaAs layers were observed, mainly because bonding in the GaAs layers was affected by the excitation. For more information, see the paper, "Coherent Atomic Motions in a Nanostructure Studied by Femtosecond X-ray Diffraction", M. Bargheer et al., Science, 306, 1771-1773 (2004).
Zahi Hawass and his co-workers plan to conduct X-ray analysis of the mummy of King Tutankhamen who ruled Egypt about 3,300 years ago and died while still a teenager. They will move the mummy from the tomb in the Valley of the Kings in Luxor, where it was discovered in 1922, to the Egyptian Museum in central Cairo by the end of November. Earlier X-ray tests in 1968 revealed bone fragments inside the skull, prompting speculation that the young king was murdered by a blow to the head. However, other evidence suggests death due to illness. This year's experiment is intended to put to rest this mystery by employing a much more powerful X-ray machine donated by Siemens and National Geographic. The main news source is Reuters (http://www.reuters.com/). For more information about the mummy, see for example, http://www.thebritishmuseum.ac.uk/mummy/
Argonne research group recently published details of their successful application of high-spatial-resolution XRF and XAFS measurements, which they performed in order to make elemental maps and qualitative chemical analyses of single free-floating, or planktonic, and surface-adhered, or biofilm, cells of Pseudomonas fluorescens. The results revealed differences between the planktonic and biofilm cells in terms of morphology, elemental composition and sensitivity to hexavalent chromium, a heavy-metal contaminant and a known carcinogen. The biofilm cells were more tolerant of the contaminant, which damaged or killed the planktonic cells. The experiments were performed with a 150 nm X-ray beam produced by phase zone plate at the beamline XOR 2-ID, at the Advanced Photon Source (APS), Argonne, USA. For more information, see the paper, "Elemental and Redox Analysis of Single Bacterial Cells by X-ray Microbeam Analysis", K. M. Kemner et al., Science, 306, 686-687 (2004).
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