May 2011 Archives

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).

As reported in the previous news article, "Influence of the M9 class earthquake on synchrotron facilities in Japan", No.3, Vol. 40 (2011)), the Photon Factory, located to the north of Tsukuba city in Ibaraki prefecture, had to cancel all beamtime allocated in the term from May to September 2011. However, scientists have devoted a great deal of time and effort to recovery work, and on May 16, the ring became capable of storing electron beams, and generating synchrotron radiation. Recovery commissioning at each beamline started in the 4^th week of May. Many users are involved in test experiments with their own samples. Some readers may be interested in the status of BL-4A, which is the beamline for X-ray fluorescence spectroscopic analysis. Recovery at the beamline appears more or less complete. Some data taken on March 10, one day before the earthquake, were reproduced almost perfectly. Commissioning will continue until early July. For further information, visit the Web page, http://www.kek.jp/ja/news/highlights/2011/PF_recovery.html (only in Japanese language).

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).

Inelastic X-ray scattering is a powerful modern tool to study lattice dynamics of condensed matter. Recently an international team led by Dr. J. Serrano (Polytechnic University of Catalonia, Spain) has tried to extend the technique to several micron-thick systems by introducing grazing-incidence geometry. Their sample is indium nitride grown on a sapphire substrate with a gallium nitride buffer layer inbetween, but X-rays only probe the surface, and not the substrate underneath. The analysis was combined with ab initio calculations to determine the complete elastic stiffness tensor, the acoustic and low-energy optic phonon dispersion relations. This finding could be a help in developing new types of solar cells. For more information, see the paper, "InN Thin Film Lattice Dynamics by Grazing Incidence Inelastic X-Ray Scattering", J. Serrano et al., Phys. Rev. Lett. 106, 205501 (2011).

An interesting theoretical paper on the calculation of K edge resonant X-ray emission spectroscopy has been published recently. The crystalline band structure was calculated using a quasiparticle self-consistent GW implementation, and then coherent spectra were obtained in the Kramers-Heisenberg formalism. The calculated results for ZnO were compared with experiments. For more information, see the paper, "First-principles calculation of resonant x-ray emission spectra applied to ZnO", A. R. H. Preston et al., Phys. Rev. B83, 205106 (2011).

A research team led by Professor J. Stohr (SLAC National Accelerator Laboratory, Stanford, USA) has recently performed time-resolved scanning transmission X-ray microscopy measurements to study the current-induced magnetization switching mechanism in nanopillars exhibiting strong perpendicular magnetic anisotropy. Because of both the short-time (70 ps) and high-spatial (25 nm) resolutions of this imaging technique, the detailed mechanism has become clear as follows; after an incubation time of ~1.3 ns, a 100×300nm² ellipsoidal device switches in ~1 ns via a central domain nucleation and opposite propagation of two domain walls toward the edges. For further understanding, micromagnetic simulations were done and shown as being in good agreement with experiments. For more information, see the paper, "Nonuniform switching of the perpendicular magnetization in a spin-torque-driven magnetic nanopillar", D. P. Bernstein et al., Phys. Rev. B83, 180410(R) (2011).

A research team led by Dr. L. Robinet (Synchrotron Soleil, Saint Aubin, France) has recently published an interesting paper describing how the blue pigment, smalt, has faded in many famous paintings such as "The Heavenly and Earthly Trinities (The Pedroso Murillo)" by Bartolome Esteban Perez Murillo. The experiment was basically X-ray absorption spectroscopy near the Co K edge. The samples were tiny pieces taken from the original paintings archived in the National Gallery, London and the Louvre Museum, Paris. It was found that in intense blue particles the cobalt is predominantly present as Co²⁺ in tetrahedral coordination, while in colorless altered smalt the Co²⁺ coordination number in the glass structure is increased, and there is a transformation from tetrahedral towards octahedral coordination. This change correlates with the alkali content as well, indicating that it is caused by leaching of potassium cations, which act as charge-compensators and stabilize the tetrahedral coordination of the cobalt ions that is responsible for the blue color. For more information, see the paper, "Investigation of the discoloration of smalt pigment in historic paintings by Co K-edge micro X-ray absorption spectroscopy", L. Robinet et al., Anal. Chem., Article ASAP (DOI: 10.1021/ac200184f Publication Date (Web) May 9, 2011).

In the presence of German President Christian Wulff and Brazilian President Dilma Rousseff, the three directors of DESY, the European XFEL, and LNLS have signed a cooperation agreement in Brasilia. For further information, visit the Web page, http://www.xfel.eu/news/2011/brasilian_german_agreement/

Optical tweezers are widely used because they are capable of trapping small materials by highly-focused laser beams. They are highly useful for manipulating single fragile objects. Recently compact optical tweezers have been designed and developed specifically for synchrotron X-ray diffraction experiments. Samples of a few micrometers up to a few tens of micrometers size can be trapped easily. The selection and positioning of single objects out of a batch of many can be performed semi-automatically by software routines. For more information, see the paper, "Optical Tweezers for Synchrotron Radiation Probing of Trapped Biological and Soft Matter Objects in Aqueous Environments", S. C. Santucci et al., Anal. Chem., Article ASAP (DOI: 10.1021/ac200515x Publication Date (Web) May 4, 2011).