January 2009 Archives

Eu is one of the most interesting lanthanides, compounds of which often exhibit remarkable optical, electrical, and magnetic properties. Therefore, it is extremely important to develop a technique for chemical state analysis. The X-ray emission spectra of Eu had not been thought to exhibit significant chemical effects. A research group led by Professor H. Hayashi (Japan Women's Univ) firstly found a large chemical shift (~5 eV) in Eu Lγ₄ emission line, depending on the valence state. They discussed the feasibility of using this as a probe for spin- and valence-selective X-ray absorption fine structure spectroscopy. For more information, see the paper, "Probe for spin- and valence-selective X-ray absorption fine structure spectroscopy: EuLγ₄ emission", H. Hayashi et al., Anal. Chem., 81, 1522 (2009).

X-ray absorption spectroscopy is one of the most powerful probes of molecular structures. So far, applications have been limited to the steady state and/or quite slowly changing systems. Recently, Professor M. Chergui (Ecole Polytechnique Federale de Lausanne, (EPFL), Switzerland) and his colleagues reported a very impressive ultrafast X-ray absorption experiment. There is a large class of Fe(II)-based molecular complexes that show two electronic states closely spaced in energy: a low-spin (LS) singlet and a high-spin (HS) quintet state. They therefore exhibit spin crossover (SCO) behavior, wherein conversion from a LS ground state to a HS excited state (or the reverse) can be induced by small changes in temperature and pressure or by light absorption. The studies were done for an aqueous solution of [Fe^II(bpy)₃]²⁺, which serves as a model system for the family of Fe(II)-based SCO complexes. A 100-mm-thick free-flowing liquid jet of an aqueous solution of 50 mM [Fe^II(bpy)₃]²⁺ was excited by an intense 400-nm laser pulse (115-fs pulse width, repetition rate 1 kHz), and a tunable femtosecond hard X-ray pulse from the slicing source was used to probe the system in transmission mode at 2 kHz. The X-ray flux was about 10 photons/pulse at 7 keV. The time resolution was under 250 fs. By recording the intensity of a characteristic near edge absorption spectral feature as a function of laser pump/X-ray probe time delay, the very early stages of photo excitation in Fe(II)-based complexes were clarified. For more information, see the paper, "Femtosecond XANES Study of the Light-Induced Spin Crossover Dynamics in an Iron(II) Complex", Ch. Bressler et al., Science, 323, 489 (2009).

The Science and Technology Foundation of Japan has announced that two US scientists have been named as laureates of the 2009 (25th) Japan Prize. Dr. Dennis L. Meadows, 66, Professor Emeritus of Systems Policy, University of New Hampshire and one of the authors of the report, "The Limits to Growth," for the Club of Rome in 1972, has received the prize in this year's category of "Transformation towards a sustainable society in harmony with nature". Dr. David E. Kuhl, 79, Professor of Radiology, University of Michigan Medical School, was selected in the other prize category of "Technological integration of medical science and engineering". They will receive certificates of merit, and commemorative medals. There is also a cash award of fifty million Japanese yen for each prize category. The presentation ceremony is scheduled to be held in Tokyo at the National Theatre on Wednesday 23rd April, 2009. The prize categories for the 2010 (26th) Japan Prize will be "Industrial Production and Production Technology" and "Biological Production and Environment". For further information, visit the Web page, http://www.japanprize.jp/en/index.html

The U.S. Department of Energy (DOE) has granted "Critical Decision 3" (CD-3) status to the National Synchrotron Light Source II (NSLS-II) at Brookhaven National Laboratory, approving the start of construction in fiscal year (FY) 2009 and scheduling completion in FY 2015. A total project cost for NSLS-II of $912 million has been approved. NSLS-II is expected to be the world's first storage-ring-based synchrotron light source that combines nanometer spatial resolution with high brightness, coherence, and beam stability, enabling nanometer-scale characterization of materials, with powerful applications in nanotechnology and biotechnology. For more information about the NSLS-II project, visit the website at http://www.bnl.gov/nsls2/

Laser generation in the X-ray region has become realistic because of the construction of free electron laser facilities, which will be available in the near future (Linac Coherent Light Source (LCLS) at Stanford in 2009; European XFEL in 2014). Another significant route is the extension of existing laser technologies such as high-order harmonic generation (HOHG), particularly from relativistically oscillating plasma mirror-like surfaces. Professor M. Zepf (Queens University Belfast, UK) and his colleagues recently published an interesting paper showing that it is possible to achieve a near-diffraction-limited focal spot size that is also controllable. For more information, see the paper, "Diffraction-limited performance and focusing of high harmonics from relativistic plasmas", B. Drome et al., Nature Physics, advanced online publication doi:10.1038/nphys1158

Professor T. Rayment (School of Chemistry, University of Birmingham, UK) and his colleagues have developed a channel-flow cell to study electrochemical reactions on electrodes by time-resolved X-ray absorption spectroscopy. During the studies with the model system, it was found that a flowing solution is essential to remove any products of beam damage. For more information, see the paper, "Channel-Flow Cell for X-ray Absorption Spectroelectrochemistry", R. J. K. Wiltshire et al., J. Phys. Chem., C 113, 308 (2009)

Lyncean Technologies, Inc., which was founded in Palo Alto, California, in 2001 by Stanford Professor Ronald Ruth's group, recently announced that its Compact Light Source (CLS) successfully performed hard X-ray phase contrast imaging. Some results appear on the cover of the January 2009 issue of the Journal of Synchrotron Radiation. The CLS is a miniature synchrotron which uses inverse Compton scattering to produce high-intensity, tunable, quasi-monochromatic X-ray beams. For more information, visit the Web page, http://www.lynceantech.com Their first scientific results are published in the paper, "Hard X-ray phase-contrast imaging with the Compact Light Source based on inverse Compton X-rays", M. Bech et al., J. Synchrotron Rad. 16, 43 (2009).