X-ray microbeam

In the first section will be presented XAS from the physical principles to data analysis and measurements. Then section 2 will be devoted to a discussion of a few examples to illustrate the power and limitations of XAS for gaining structural information. Examples are focused on EXAFS studies on nanocrystalline materials. Detailed reviews for applications on other fields of materials science or for presenting the complementary information available by the study of the X-ray Absorption Near Edge Structure (XANES) part of the X-ray absorption spectrum can be found in a number of books [3-5], A brief overview of the recent development of the technique regarding the use of X-ray microbeams available on the third generation light sources will be finally presented in the last section. 

Muller M, Riekel C, Vuong R, and Chanzy H. Skin/core micro-structure in viscose rayon fibers analysed by x-ray microbeam and electron diffraction mapping. Polymer, 2000 41 2627-2632. 

Muller M, Czihak C, Burghammer M, and Riekel C. Combined x-ray microbeam small-angle scattering and fibre diffraction experiments on single native cellulose fibres. J. Appl. Crystallogr., 2000 33 817-819. 

Fig. 43 Lens array for generation of many hard x-ray microbeams. The insert shows the microbeams generated from a beam-line...

Dhez P, Chevallier P, Lucatorto , Tarrio C (1999) Instrumental aspects of X-ray microbeams in the range above 1 keV. Rev Sci Instr 70 1907-1920... 

Microbeam optics. X-ray microbeams can be produced using techniques that rely on collimation, refraction, diffraction, or reflection (e.g., Ice 1996). The most straightforward devices are collimators, apertures that merely allow a small portion of the synchrotron X-ray beam to be transmitted. The devices are achromatic (i.e., lacking energy dispersion) but the vast majority of the usable beam is absorbed so that beam intensities are low. Hard X-ray beams of a few micrometers in size can be produced in this way (e.g., Sutton et al. 1994). 

Spatial resolution currently achievable with hard X-ray microbeam techniques, down to the 100 nm range, is quite satisfactory. In many cases, spatial resolution at the beam size cannot be realized because of the properties of the sample, notable thickness (because of the penetrating nature of the X-rays, 100 nm resolution can only be achieved in samples <100 nm thick). Improvements in sensitivity can be achieved in two principal ways, increase in incident flux or improvement in detection efficiency. Major increases in incident flux will be impractical in many cases because of the radiation sensitivity of the earth and environmental samples of interest. Improvements in fluorescence detection efficiency will be a more fruitful avenue because current detection schemes use very small solid angles. Energy dispersive detectors that intercept large solid angles would be a major advance in sensitivity enhancement. 

Sutton SR, Rivers ML (1999) Hard X-ray synchrotron microprobe techniques and applications. In Synchrotron Methods in Clay Science. CMS Workshop Lectures Vol. 9. Schulze DG, Stucki JW, Bertsch PM. (eds). The Clay Mineral Society, Boulder CO, p 146-163 Sutton SR, Flynn G, Rivers M, Newville M, Eng P (2000) X-ray fluorescence microtomography of individual interplanetary dust particles. Lunar Planet Sci XXXI 1857 Sutton SR, Rivers ML, Bajt S, Jones KW, Smith JV (1994) Synchrotron X-ray-fluorescence microprobe-a microanalytical instrument for trace element studies in geochemistry, cosmochemistry, and the soil and environmental sciences. Nucl Instrum Methods Phys Res A 347 412-416 Suzuki Y, Awaji M, Kohmura Y, Takeuchi A, Takano H, Kamijo N, Tamura S, Yasumoto M, Handa (2001) X-ray microbeam with sputtered-shced Fresnel zone plate at SPring-8 undulator beamline. Nucl Instrum Methods Phys Res A 467-468 951-953... 

Limiting the flux throughput through pinholes is insufficient for most practical analytical purposes hence, techniques for generating intense X-ray microbeams are based on the use of various types of X-ray optics. Refractive lenses that are extensively used in visible or ultraviolet light optics are more difficult to use for X-rays because the refractive index, n, is very close to and slightly smaller than 1.000 by a factor d. The refractive index can be expressed as... 

Such lenses are cheaply constructed but suffer from the absorption and scattering. Many other techniques for the formation of intense X-ray microbeams are available on the basis of the use of various types of X-ray optics based on refraction, diffraction, or reflection bent mirrors, crystals and multi-layers, linear and tapered glass mono-capillaries, complex polycapillary lens systems, transmission Fresnel zone... 

Punshon, T., Jackson, B. P., Lanzirotti, A., Hopkins, W. A., Bertsch, P. M., Burger, J. (2005) Application of synchrotron X-ray microbeam spectroscopy to the determination of metd distribution and specia-tion in biological tissues. Spectrosc Lett, 38, 343-363. 

Wegrzynek et al. [756] have dealt with the quantitation problem when an X-ray microbeam is used to measure elemental distributions in a low-Z matrix. This /U.XRF technique was developed for the characterisation of sample homogeneity in a polymer matrix. Microhomogeneity studies using /uSR-XRF and LA-ICP-MS on CRM BCR 680 cfr. Chp. 8.3) were reported with satisfactory agreement between the sets of data [757,758]. 

Nolle P, Stierle A, Kasper N, Jin-Phillipp NY, Reichert H, Ruhm A, Okasinski J, Dosch H, Schoder S (2008) Combinatorial high-energy x-ray microbeam study of the size-dependent oxidation of Pd nanoparticles on MgO(lOO). Phys Rev B 77(11) 115444. doi 10.1103/ PhysRevB.77.115444... 

Figure 10.2 Micro XRF imaging for As, K, and Ca at the edges of mature pinna containing the lamina of pinna, pseudo-indusium, sporangium, and spore. X-ray microbeam size, 3.5x5.5pm scan step, 3.5 x 5.5 pm measurement time, IspixeP image size, 180 x 125 pixels, (a) Sample photograph by optical microscopy and the measurement area. Scale bar, pm. Elemental concentrations in each map are scaled to the maximum value for that map. 2006 The Royal Society of Chemistry.

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