September 2010 Archives

The Cornell High Energy Synchrotron Source (CHESS), at Cornell University (USA) has been granted a total of $109 million. The National Science Foundation (NSF) has received $77 million to continue its existing operation of the facility through 2014 and $32 million for research and development of prototypes for the Energy Recovery Linac (ERL). For further information, visit the web page, http://www.news.cornell.edu/stories/Sept10/ERLCHESS.html

A research group at Lawrence Berkeley National Laboratory, USA, has recently published an interesting report on an automated data analysis method for submicrometer atmospheric particles containing organic and inorganic material. The main idea is the use of X-ray spectral features in the energy range from 278 to 320 eV, which is near the carbon K-edge and potassium LII and LIII edges. The method provides quantitative mapping of the spatial distribution of elemental carbon, organic carbon, potassium, and noncarbonaceous elements in particles of mixed composition. It was recently applied to analyze differences in over 1000 particles collected at various times and locations in Mexico City to examine the effects of atmospheric aging on internally mixed atmospheric aerosol particles. For more information, see the paper, "Automated Chemical Analysis of Internally Mixed Aerosol Particles Using X-ray Spectromicroscopy at the Carbon K-Edge", R. C. Moffet et al., Anal. Chem. 82, 7906 (2010).

Professor M. P. Fontana (University of Parma, Italy) and his colleagues have recently reported X-ray photon correlation spectroscopy (XPCS) studies on poly[[4-pentiloxy-3'-methyl-4'-(6-acryloxyexyloxy)]azobenzene], which is a kind of photosensitive azo-polymer and is softened by photoisomerization. XPCS uses coherent X-rays to measure small angle scattering, called a speckle pattern, which is caused by some inhomogeneities. It gives information on the slow dynamics of various equilibrium and non-equilibrium processes in condensed matter systems. The main advantage of using X-rays instead of other direct methods such as scanning probe microscopy is that it provides statistical information averaged over the whole sample as a function of the momentum transfer. This is essential for the analysis of dynamical heterogeneity and of nonequilibrium and aging effects in the observed dynamics. The research group measured the time correlation functions at different temperatures and momentum transfers (q) and under different illumination conditions (dark, UV or blue light). It was found that the correlation functions are well described by the so-called stretched exponential function with relaxation times that are proportional to the inverse of q. They were able to determine the scaling laws for equilibrium and nonequilibrium fluctuations on local space scales. For more information, see the paper, "Slow dynamics in an azopolymer molecular layer studied by x-ray photon correlation spectroscopy", D. Orsi et al., Phys. Rev. E82, 031804 (2010).

A research group led by Professor F. Pfeiffer (Technische Universitat Munchen, Germany) has recently reported an extremely powerful combination of X-ray tomography and ptychographic coherent imaging, which enables quantitative phase-contrast X-ray microscopy without any lenses. A refractive index in the X-ray region is usually expressed as n = 1 - d - iβ, where d and β are real and imaginary parts, and relate to the phase shift and the attenuation, respectively. The researchers developed a new method to give a 3D image of d rather than β, because d can give much higher visibility in samples based on low-Z elements, which are most likely in bio-medical applications. So far, phase-contrast X-ray imaging has had limitations in giving such quantitative information. The use of coherent X-ray diffraction is one of the most promising solutions, and ptychography is a further extension that enhances precision in recovering the phase by introducing scanning of the sample. As the spatial resolution of the computed images is no longer limited by the quality or resolving power of a lens, just a pinhole was used in the present research. By combining such image reconstruction to obtain nano-scale 2D images with other image processing based on a back-filtered projection algorithm, they have succeeded in obtaining 3D images on the 100 nm scale of bone structures such as the osteocyte lacunae and the interconnective canalicular network. The experiments were done at X12SA beamline, Swiss Light Source. For more information, see the paper, "Ptychographic X-ray computed tomography at the nanoscale", M. Dierolf et al., Nature, 467, 436 (2010). In the same issue, there is an instructive account, "A new phase for X-ray imaging", H. N. Chapman, Nature, 467, 409 (2010). For the details of ptychography, see the paper, "The Theory of Super-Resolution Electron Microscopy Via Wigner-Distribution Deconvolution", J. M. Rodenburg and R. H. T. Bates, Phil. Trans. Roy. Soc. (London) A339, 521 (1992).

X-ray reflectivity is one of the most power analytical tools for observing the layered structures of thin films. So far, many calculations have been done by combining Parratt's recursive formalism with Nevot-Croce corrections on the Fresnel coefficients. The technique basically provides detailed information on the roughness of the surface and interfaces, in addition to the precise thickness values of each layer. However, the analysis of the roughness has not been always straightforward, because it is also necessary to consider multiple diffuse scattering. Recently, Dr. A. M. Polyakov (National University of Science and Technology 'MISiS', Russia) and his colleague published an interesting paper describing a novel approach to the calculation of X-ray reflectivity. Their method is based on the Green function formalism using Kirchhoff's integral equation for describing the X-ray wavefield propagation through a random rough surface separating vacuum and medium. Readers would find it interesting that the influence of multiple diffuse scattering effects upon grazing X-ray specular scattering is essential for the correlation lengths that are of the order of, and/or less than, the X-ray absorption length. Although the present calculation is only valid for the random surface heights described in the frame of Gaussian statistics, the present approach can be further extended in the future. For more information, see the papers, "X-ray specular scattering from statistically rough surfaces: a novel theoretical approach based on the Green function formalism", F. N. Chukhovskii et al., Acta Cryst., A66, 640 (2010).

Some readers might remember the news article, "A new technique with coherent X-rays to determine non-crystalline structures", in X-ray Spectrometry, Vol. 38, No.5 (2009). The technique called X-ray cross correlation analysis (XCCA) is an extension of X-ray photon correlation spectroscopy, and is promising with respect to solving the atomic-scale structures of complicated disordered systems, which have for many years presented difficulties in terms of reaching a clear understanding of the structures. Recently, Dr. M. Altarelli (European X-ray Free-Electron Laser Facility, Hamburg, Germany) and his colleagues published a paper on the theoretical treatment of XCCA. They gave a general theory for the cross correlation function, and tried to interpret the experimental XCCA results for colloidal glass. The authors plan further publications to present the results of various simulations as well. For more information, see the paper, "X-ray cross-correlation analysis and local symmetries of disordered systems: General theory", M. Altarelli et al., Phys. Rev. B82, 104207 (2010).

A geoscientists group at the European Synchrotron Radiation Facility (ESRF, Grenoble, France), has recently found that a natural fertile peridotite, which is a characteristic material of the Earth's mantle, can be partially molten at a pressure of 140 GPa, when the temperature reaches 4,200 K. This could reinforce the hypothesis of the presence of a deep magma ocean. The experiments showed that the liquid produced during this partial fusion is dense and that it can hold multiple chemical elements, among which are important markers of the dynamics of the mantle. For more information, see the paper, "Melting of Peridotite to 140 Gigapascals", G. Fiquet et al., Science, 329, 1516 (2010).

Argentinian scientists have recently published a paper on the emission of X-ray satellite lines in the Kα region of Mg, Si, Sc, Ti, Cr, Fe, Ni, and Zn induced by an electron beam. They studied Kα', Kα₃, Kα₄, Kα₅, Kα₆, and two transitions denoted here as Kα₂₂ and Kα₁₂. The work is a continuation of their previous work (see, the previous article, "Kβ satellites in EPMA", in X-ray Spectrometry, Vol. 39, No.2 (2010).) For more information, see the paper, "Kα satellite transitions in elements with 12 ≤Z≤30 produced by electron incidence", S. P. Limandri et al., Phys. Rev., A82, 032505 (2010).

Dr. B. M. Patterson (Los Alamos National Laboratory, USA) and his colleagues have recently published an interesting paper on analytical problems arising from micro X-ray computer tomography. They discussed the use of a dimensional standard based upon NIST certified glass microspheres dispersed in a low density poly(styrene) matrix. For more information, see the paper, "Dimensional Standard for Micro X-ray Computed Tomography", B. M. Patterson et al., Anal. Chem., Article ASAP (DOI: 10.1021/ac101522q Publication Date (Web): September 16, 2010).