Synchrotron microfocus

Buleon A., Gerard C., Riekel C., Vuong R., Chanzy H., DetaUs of the crystaUine ultrastructure of C-starch granules revealed by synchrotron microfocus mapping. Macromolecules, 31, 1998,6605-6610. 

A continuous lipidic cubic phase is obtained by mixing a long-chain lipid such as monoolein with a small amount of water. The result is a highly viscous state where the lipids are packed in curved continuous bilayers extending in three dimensions and which are interpenetrated by communicating aqueous channels. Crystallization of incorporated proteins starts inside the lipid phase and growth is achieved by lateral diffusion of the protein molecules to the nucleation sites. This system has recently been used to obtain three-dimensional crystals 20 x 20 x 8 pm in size of the membrane protein bacteriorhodopsin, which diffracted to 2 A resolution using a microfocus beam at the European Synchrotron Radiation Facility. 

Temperatures as high as 2,500 K have been achieved by laser heating (LH). For such LHDAC experiments, the sample size was around 50-100 pm, the laser beam was focused to about 40 pm, and the synchrotron beam was microfocused to about 10 pm in diameter [70]. The photon-flux for the 14.4 keV ( Fe) synchrotron radiation at the focusing spot was about 10 photons s with a 1 meV energy bandwidth. This flux was reduced by a 5 mm path through diamond, via photo absorption, to 25% of its original value. For comparison the flux of the 21.5 keV radiation of Eu would be reduced to only 60%. 

In summary, the NLE technique offers a concepmally new approach to observe NFS. Existing limits for time resolution could be overcome by a microfocused synchrotron beam (as planned for PETRA III) and by detectors with high spatial resolution and background from SAXS could be suppressed by employing high-energy transitions and crystalline sapphire as rotor material. 

Archaeological Soils and Sediments Application of Microfocus Synchrotron X-ray Scattering, Diffraction, and Fluorescence Analyses in Thin-... 

Figure I. Schematic illustrations of microfocus synchrotron X-ray analysis methods (a) small-angle X-ray scattering (SAXS) (b) microfocus X-ray diffraction (XRD) and (c) microfocus X-ray fluorescence (XRF).

Figure 4. Microfocus synchrotron SAXS measurements Thickness T (nm) and Shape (rj) parameters ofcalcium-iron-phosphate features from the midden profile at Vollen, Langenesvceret, Norway. (Reproducedfrom Reference 32. Copyright 2004 Elsevier)...

For the future, even smaller-scale sample areas can be considered for analysis as can isotope ratios. It could be envisaged that multiscale prospection analyses could proceed from optical methods to microfocus synchrotron X-ray fluorescence and SAXS and, finally, to destructive isotopic studies with LA-ICP-MS or to finer resolutions with SIMS. 

The illustrative studies show the advantages of utilizing combined optical and microfocus synchrotron X-ray based analyses in investigations of... 

The scattering experiments were carried out at the Microfocus Beamline (ED 13) in the European Synchrotron Radiation Facility (ESRF) in Grenoble, France. The most remarkable characteristics of this beamline are ... 

Rux is much less of a problem at X-ray sources indeed sometimes it needs to be reduced to avoid detector saturation. The whole field of protein crystallography is heavily dependent on the use of synchrotron sources, an enormous area of application which has made a spectacular impact - and no doubt will continue to do so. The high flux additionally means that the application of real time studies is much further advanced for both the wide and small angle regimes. Additionally, X-rays are much more easily focussed, and can therefore be used at high spatial resolution to produce microfocus data. For biological systems this has already led to some interesting studies, e.g. on starch " and flax. ... 

Beam instability. The use of EXAFS on heterogeneous samples, especially with a microfocused beam, tends to exacerbate certain problems that are well known from other systems. One simple example of such a problem is the sensitivity to beam motion, which results from putting a small beam on an equally small particle. The beam tends to move on the sample during data acquisition, for a variety of reasons. These motions can cause artifacts in the data. For example, during the course of a synchrotron fill, the source point may move, and the decreasing power incident on the optics may also cause position shifts. Vibrations either of the sample or the optics result in increased noise and an increased effective spot size. If the position drifts on a time scale comparable to the length of time required to scan over an EXAFS oscillation, one could get artifacts, which are indistinguishable from EXAFS, except that they do not repeat from scan to scan. If... 

Nobumichi Tamura (left) obtained his Ph.D. in 1993 at the Institut National Polytechnique de Grenoble (INPG) for his work on the structure of quasicrystals and crystalline approximant phases. In 1998 he moved to Oak Ridge National Laboratory to contribute to the development of a new synchrotron-based X-ray microfocus technique capable of resolving strain and texture in thin films with submicrometer spatial resolution. He applied this technique in the field of microelectronics. He is currently staff scientist at the Lawrence Berkeley National Laboratory, where he leads the X-ray microdiffraction project at the Advanced Light Source. His research interest is presently focused on the study of mechanical properties of thin films at mesoscopic scale using synchrotron radiation. 

The same spatial coherence available at synchrotrons can also be obtained with a microfocus X-ray tube with a very small source size similar to the projection microscope but with a significant source-sample distance (Li lm). It was shown that a monochromatic beam is not necessary and the polychromatic output of the X-ray tube can be used. 

This increase in X-ray intensity, together with the development of synchrotron laboratories with facilities dedicated to measurement of XAS, has allowed XAS to develop into a relatively routine analytical tool. It is straightforward to measure XAS spectra for transition metal solutions with concentrations greater than 1 mM (ca. 50 ppm) and it is possible, using the most intense synchrotron sources and the most sensitive detectors, to measure high-quality XAS spectra for samples containing less than 1 ng of the metal of interest. Typical sample volumes range from one mL to one pL and with microfocused X-ray beams (see below) even smaller volumes can be studied. 

Figure 2 Experimental setup of (a) SAXS with point-focusing optics (conventional X-ray and synchrotron sources) and of (b) microfocus SAXS (synchrotron sources).

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