August 2011 Archives

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).

A research team led by Professor I. Tsuyumoto (Kanazawa Institute of Technology, Japan) has recently studied chromium Kβ spectra and found that the intensity of Kβ" satellite, which is observed at the higher energy side of the main Kβ_1,3 peak, is strongly correlated with the pre-edge peak of the X-ray absorption near edge structure specific for chromium (VI) compounds, such as CrO₃, Na₂CrO₇・2H₂O, Na₂CrO₄・4H₂O, K₂Cr₂O₇, K₂CrO₄, Zn₂CrO₄(OH)₂・2H₂O, PbCrO₄, and BaCrO₄. For more information, see the paper, "X-ray Fluorescence Analysis of Hexavalent Chromium Using Kβ Satellite Peak Observed as Counterpart of X-ray Absorption Near-Edge Structure Pre-Edge Peak", I. Tsuyumoto et al., Anal. Chem., Articles ASAP (DOI: 10.1021/ac201606c Publication Date (Web): August 26, 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).

Professor J. R. Engstrom (Cornell University) and his colleagues have recently published a detailed comparative study on surface morphology obtained from in-situ, time-resolved X-ray reflectivity, which is extremely feasible as a tool for investigating surface and interfaces during thin film growth, but requires some modeling of the growth process for the interpretation. The research group prepared two sets of organic thin films, pentacene/SiO₂ and diindenoperylene SiO₂; for each system, giving a total of four films, grown to different thicknesses, under nominally identical conditions. The X-ray reflectivity data were analyzed based on three different models, and the obtained parameters were directly compared with AFM data. It was found that all models employed can give good agreement between the surface morphology obtained from fits with the actual morphology at early times. On the other hand, this agreement deteriorates at later times, once the root-mean squared (rms) film roughness exceeds about 1 monolayer. It was also found that the best fits to reflectivity data, corresponding to the lowest values of χ², do not necessarily yield the best agreement between simulated and measured surface morphologies, simply because the model reproduces all local extrema in the data. For more information, see the paper, "Quantitative modeling of in situ x-ray reflectivity during organic molecule thin film growth", A. R. Woll et al., Phys. Rev. B84, 075479 (2011).

The research team led by Professors V. Holý (Charles University, Czech Republic) and T. Baumbach (ANKA-Institute for Synchrotron radiation, Germany) have recently performed some extension of coherent X-ray diffractive imaging for high-resolution strain analysis in crystalline nanostructured devices such as layered nanowires and/or dots. Their research successfully determined the strain distribution in (Ga,Mn)As/GaAs nanowires. The key was their improvement of the phase-retrieval algorithm, i.e., separation of diffraction signals in reciprocal spaces. It was found that individual parts of the device can be reconstructed independently by this inversion procedure. The method is effective even for strongly inhomogeneously strained objects. For more information, see the paper, "Selective coherent x-ray diffractive imaging of displacement fields in (Ga,Mn)As/GaAs periodic wires", A. A. Minkevich et al., Phys. Rev. B84, 054113 (2011).

X-ray fluorescence spectra can give information on various chemical states, including spin states such as high-spin and low-spin. Recently, Dr. G. Venko (KFKI Research Institute for Particle and Nuclear Physics, Hungary) and his colleagues published their research on light-induced spin crossover transition. They studied the spin state of aqueous [Fe(bpy)3]²⁺ (bpy=2,2'-bipyridine) molecules, 60 ps after an ultrashort laser pulse excitation by time-resolved X-ray fluorescence. The laser induces a low-spin to high-spin conversion, and then the system goes back to the low-spin state on a 0.1 ns timescale. For more information, see the paper, "Picosecond Time-Resolved X-Ray Emission Spectroscopy: Ultrafast Spin-State Determination in an Iron Complex", G. Vanko et al., Angew. Chem. Int. Ed. 49, 5910 (2010).

The following awards were presented during the plenary session of the 60th Annual Denver X-Ray Conference: The 2011 Barrett Award was presented to Dr. Juan Rodriques-Carvajal, Institute Laue-Langevin, Grenoble, France to honor his exceptional contributions to the field of X-ray diffraction, in particular for his work on characterization of the structural and magnetic properties of strongly correlated oxides using diffraction techniques and for writing and freely disseminating FULLPROF, the most widely used Rietveld refinement program for analysis of crystallographic and magnetic structures. The 2011 Jenkins Award was given to Dr. Paul K. Predecki to honor his contributions to the development of X-ray methods for a wide variety of materials, and his generosity in teaching and inspiring others in X-ray materials analysis both at the University of Denver and through organization and management of the Denver X-ray Conference. The 2011 Jerome B. Cohen Student Award was given to Vallerie Ann Innis-Samson, University of Tsukuba, Ibaraki, Japan, for her work, X-ray Reflection Tomography: A New Tool for Surface Imaging. For further information, visit the Web page, http://www.dxcicdd.com/

X-ray spectroscopy is an extremely strong tool for metal speciation at the molecular level in biological and environmental samples, especially for metalloproteins. When samples are quite easily influenced by photoreduction, however, analysis has not been straightforward. Recently, a Chinese group has studied in detail soft X-ray induced photoreduction in organic Cu(II) compounds. The research team measured XANES spectra at Cu-LIII, O-K, and C-K edges to see how the valence state of Cu changes. A scanning transmission X-ray microscopy was also employed to look at specific radiation damages. It was found that reducing the radiation dose to 0.1 MGy effectively prevented the photoreduction of organic Cu(II) compounds. For more information, see the paper, "Soft X-ray Induced Photoreduction of Organic Cu(II) Compounds Probed by X-ray Absorption Near-Edge (XANES) Spectroscopy", J. Yang et al., Anal. Chem., Article ASAP (DOI: 10.1021/ac201622g Publication Date (Web): August 1, 2011).