As of January 24, 2013

for international journal X-Ray Spectrometry (John Wiley & Sons Ltd.)

Ti Kβ and X-ray Raman spectra from BaTiO₃ nano particles (December 28, 2012)

Recently a research group led by Okayama University in Japan has reported the successful application of resonant X-ray emission spectroscopy (RXES) to BaTiO₃ nanoparticles of various sizes ranging from a bulk-like 200 nm to a paraelectric 50 nm.  While it is well known that the crystal structure changes from tetragonal to cubic as the particle size decreases, some recent reports indicated that a very large enhancement of the dielectric constant was observed at a specific particle size of around 70 nm.  The research was done to clarify the above problem.  In the X-ray emission spectra measured with monochromatic excitation near the sharp peak of the Ti-K absorption edge, two small Raman peaks were observed between Kβ_2,5 (4962.6 eV) and elastic scattering of (for example, 4983.6 eV) peaks.  It was found that the higher energy Raman peak (5.3 eV lower than incident X-ray energy) still exists at a size of 85 nm, even though the intensity basically diminishes for the small particle size BaTiO₃, which corresponds to the extraordinary large crystal structure change.  The results suggest that Raman peak intensity is correlated to the large enhancement of the dielectric constant.  For more information, see the paper, "Enhancement of dielectric constant of BaTiO₃ nanoparticles studied by resonant x-ray emission spectroscopy", N. Nakajima et al., Phy. Rev. B86, 224114 (2012).

Focusing XFEL pulses with mirrors (December 16, 2012)

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).

Aluminum Kα spectra obtained by extremely strong photons with the energy below the K absorption edge (December 13, 2012)

At Linac Coherent Light Source (LCLS), Stanford, USA, a series of experimental works has been carried out based on the core-level excitation and relaxation process.  One recently published paper from Stanford reports the resonant generation of Kα emission from aluminum foil (1μm thick) in a solid-plasma state created by irradiating very strong X-ray free-electron laser pulses (less than 80 fs time width, 1.6×10¹² photons/pulse).  In the experiment, quasimonochromatic (0.5% bandwidth) X-ray pulses in the energy range of 1480-1580 eV (below and slightly above the K edge of ground state Al) were focused onto a 3μm diameter spot on the sample, with a corresponding peak intensity in excess of 10¹⁷ W/cm².  To analyze the X-ray spectra, the research group employed a wavelength-dispersive X-ray spectrometer with a flat ADP (101) crystal and an X-ray CCD camera. Since the same atom can absorb multiple photons contained in the single pulse time width, with L-shell holes being created and leading to the excitation of a K-shell electron into one of these L-holes, the Kα X-rays are produced. The research group studied many such emission spectra produced by tuning the XFEL energy to the K-L transitions of those highly charged ions that have transition energies below the K edge of the cold material.  It was also found that resonance emission peaks broaden significantly, and this was explained as opacity effects.  Because of the intensity-dependent optical depth, the transparent sample at low intensity thickens optically with an intense XFEL pulse.  For more information, see the paper, "Resonant Kα Spectroscopy of Solid-Density Aluminum Plasmas", B. I. Cho et al., Phys. Rev. Lett., 109, 245003 (2012).
 

Theoretical mechanism of inner-shell resonant absorption effects (December 11, 2012)

A Chinese group recently published a paper proposing a new interpretation of neon’s absorption of extremely strong X-ray photons from an X-ray free electron laser, which was experimentally studied at Stanford in 2010 (see, L. Young et al., Nature, 466, 56 (2010)).  Although the ordinary absorption edge of neon is around 867 eV, the energy becomes higher than usual because of multiple ionization.  Therefore, detailed studies were done between 800 eV and 2000 eV at Stanford at that time. The main discussion here is the large discrepancies between theory and experiment found at 1050 eV, where the rates of K-shell absorption 1s → 4p of Ne⁶⁺ and 1s → 3p of Ne⁷⁺ are larger than the direct single-photon ionization rates by more than one order of magnitude.  The authors of this paper propose that the inner-shell resonant absorption (IRA) effects be considered as the mechanism.  They showed that resonant photopumping of K-shell electrons to the L, M, or even higher bound orbitals can provide an interaction strength that is two or three orders of magnitude larger than that in the continuum level.  Only when the IRA effects were taken into account were the observed charge state distributions explained well.  For more information, see the paper, "Inner-shell resonant absorption effects on evolution dynamics of the charge state distribution in a neon atom interacting with ultraintense x-ray pulses", W. Xiang et al., Phys. Rev. A86, 061401(R) (2012).
 

Simulation of X-ray laser by means of dissociative core-excited states (December 7, 2012)

The recent advent of the X-ray free-electron laser (XFEL) based on self-amplified spontaneous emission (SASE) has brought new opportunities in X-ray physics and many scientific applications.  On the other hand, the shot-noise start-up in the SASE mechanism lends an inherent stochastic character to X-ray pulses, leading to rather large variations both in wavelength and intensity.  One strategy to solve the problem is to use an XFEL pulse to create a population inversion in a medium which then lases in the X-ray region (See, N. Rohringer et al., Nature, 481, 488 (2012)).  Alternatively, resonant core excitation can be used as well.  Recently, a theoretical chemistry group led by Professor F. Gel’mukhanov (Royal Institute of Technology, Sweden) has published a prediction of X-ray lasing based on resonant core excitation of a molecule to a state which is subject to ultrafast dissociation, i.e., a state in which dissociation precedes the femtosecond core hole decay. As an example, Cl 2p_1/2 → 6σ excitation of the HCl molecule by an XFEL pulse and the subsequent ultrafast dissociation were studied.  For more information, see the paper, "Dissociative X-ray Lasing", Q. Miao et al., Phys. Rev. Lett., 109, 233905 (2012).
 

Periodicity-resonant X-ray waveguide (December 5, 2012)

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).
 

Use of partial coherence in coherent X-ray diffraction imaging experiments (December 3, 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).
 

Grazing-incidence X-ray analysis to see buried structures (November 22, 2012)

Dr. B. Beckhoff (Physikalisch-Technische Bundesanstalt, Germany) and his colleagues have recently published some successful applications of grazing-incidence X-ray fluorescence and near-edge X-ray absorption fine structure to nano-scale thin layers of chemically vapor deposited B_xC_yN_z on metallic Ni.  For more information, see the paper, "Nondestructive and Nonpreparative Chemical Nanometrology of Internal Material Interfaces at Tunable High Information Depths", B. Pollakowski et al., Anal. Chem., 85, 193 (2013).
 

Realtime X-ray phase and stress analysis (November 5, 2012)

A German group at Karlsruhe Institute of Technology has recently reported a quick X-ray diffraction experiment during laser surface hardening of materials.  They employed a single exposure setup with two fast silicon strip line detectors (Mythen 1K, Dectris Ltd.), allowing for stress analysis according to the sin²ψ profile, and the measurements were done at beamline P05, PETRA III, DESY, Hamburg in Germany.  A 6 kW diode laser was used for hardening of the material at a heating/cooling rate of 1000 K/s.  In the paper, they described how they can perform high-resolution strain analysis by separating elastic and thermal strains.  For more information, see the paper, "Fast in situ phase and stress analysis during laser surface treatment: A synchrotron x-ray diffraction approach", V. Kostov et al., Rev. Sci. Instrum., 83, 115101 (2012).
 

EXAFS analysis of negative expansion (February 23, 2012)

An interesting paper has been published showing the extended X-ray absorption fine structure (EXAFS) as evidence of negative expansion of CdTe crystal.  Measurements were done for both the K edges of cadmium and tellurium, from 4.2 K to room temperature.  For more information, see the papers, "Negative thermal expansion in crystals with the zincblende structure: an EXAFS study of CdTe", N Abd el All et al., J. Phys.: Condens. Matter 24, 115403 (2012).
 

2013 International Symposia jointly organized by American MRS and Japanese Applied Physics Society (January 15, 2013)

The Japan Society of Applied Physics (JSAP) and the Materials Research Society (MRS) have announced the 2013 JSAP-MRS Joint Symposia, which will be held in Doshisha University, Kyoto, Japan on September 16-20, 2013.  This meeting features 23 joint symposia from A to W, and readers should note that Symposium G concerns X-rays; "Exploring the Science of Exposed and Buried Interfaces with Advanced X-ray Techniques".  For more information, see the Web page,
https://www.gakkai-web.net/gakkai/jsap/jsap_mrs/hp/index.html
 

Canadian Light Source’s scientists help the Middle East (January 14, 2013)

The Synchrotron-light for Experimental Science and Applications in the Middle East (SESAME) is the largest science project in the region and the only collaborative project involving several Arab nations, as well as Jordan, Turkey, Cyprus, Iran and Israel.  Recently the Canadian Light Source has announced that their staff scientists are helping the project by providing experimental skills and knowledge.  Experiments at the SESAME synchrotron are expected to begin in 2015.  For more information, see the Web page,
http://www.lightsource.ca/media/media_release_20130115.php
 

Fujifilm’s new digital X-ray imaging system (January 17, 2013)

Fujifilm Corporation has launched FCR Dynamix System for non-destructive testing.  For further information, visit the web page, http://www.fujifilm.com/news/n130117.html
 

New application package for SPECTRO xSORT handheld XRF spectrometer (December 18, 2012)

SPECTRO has equipped the SPECTRO xSORT handheld XRF spectrometer with a new application package for the analysis of precious metals such as gold and silver.  For further information, visit the web page, http://www.spectro.com/
 

Hitachi acquires SII Nano Tech (January 1, 2013)

Hitachi High-Technologies Corporation (TOKYO: 8036, Hitachi High-Tech) has announced the acquisition of all shares of SII NanoTechnology Inc. from Seiko Instruments Inc. (SII).  The new company name is Hitachi High-Tech Science Corporation.  For further information, visit the web page, http://www.hitachi-hitec-science.com/en/index.shtml
 

Spectris acquires Analytical Spectral Devices Inc. (November 26, 2012)

Spectris plc (LSE: SXS) has announced that it has signed an agreement to acquire Analytical Spectral Devices Inc. for a debt and cash-free net consideration of $14 million.  For further information, visit the web page, http://www.panalytical.com/

SpectroscopyNow.com

For additional news about X-ray analysis and other spectroscopy sciences, browse the Wiley website.

Kenji Sakurai
Director, X-Ray Physics Group, National Institute for
Materials Science (NIMS)
and Professor, Doctoral Program in Materials Science and
Engineering, Graduate School of Pure and Applied Sciences,
 University of Tsukuba
1-2-1, Sengen, Tsukuba, Ibaraki 305-0047 Japan
Phone : +81-29-859-2821, Fax : +81-29-859-2801
sakurai@yuhgiri.nims.go.jp
http://www.nims.go.jp/xray/lab/