Microbeam diffraction

the diffracted X-rays represent the structure within the top surface layers. A depth profile (z-profile) of the structure can be generated by inverting a sequence of scans at a series of incidence angles (r-profiles) [118]. GID experiments are carried out using an experimental arrangement similar to those of a related technique, reflectometry. Whereas the reflectometry measures the electron density variations normal to the surface from which parameters such as the surface thickness and the arrangement of different layers in multilayered surfaces can be examined [119,120], GID can be used to analyze the atomic and molecular structure near the surface. 

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Mueller, M., B. Murphy, M. Burghammer, C. Riekel, M. Roberts, M. Papiz, D. Clarke, J. Gunneweg, and E. Pantos (2004), Identification of ancient textile fibers from Khirbet Qumran caves using synchrotron radiation microbeam diffraction, Spec-trochimica Acta 59B(10-11), 1669-1674. 

The atomic structure of HOD film surface was investigated using electron microbeam diffraction in Ref. [259]. The substrate used was a 500-nm thick P-SiC(lOO) that had been heteroepitaxially grown on Si(lOO) and was tilted about the [1 lOj-axis by 4° from the exact (100) orientation. The thickness of the HOD film was -20 pm. According to the RHEED pattern, using the electron micro-beam (the spatial resolution as observed by SEM was 0.1 pm), the length of the surface dimer rows was 1.5nm, which was significantly shorter than that of the homoepitaxial layer, 7 to 10 nm. 

FIG. 11 Low-magnification SEM image of the surface of a lead frame coated with a Sn-Cu finish that exhibited several Sn whiskers. The one selected for a microbeam diffraction analysis is circled. (From Ref. 42.)... 

Nakata M, Link DR, Takanishi Y, Takahasi Y, Thisayukta J, Niwano H, Coleman DA, Watanabe J, Iida A, Clark NA, Takezoe H (2005) Electric-field-induced transition between the polarization-modulated and ferroelectric smectic-CgPf liquid crystalline states studied using microbeam X-ray diffraction. Phys Rev E 71 011705... 

Methods were discussed to reveal texture in plant materials in situ by X-ray diffraction. A uniform texture in plant materials is generally confined to areas of microscopic dimensions, and the oriented materials are normally of poor crystallinity. Special methods are therefore needed to obtain fibre diffraction from such areas. They may be distinguished as microbeam techniques, artificial orientation of micro-areas, chemical methods improving crystallinity in oriented but poorly crystalline materials, and combinations of these possibilities. 

The examples of application presented were taken from the authors personal experience. They concerned a microbeam technique in which the collimators and camera are adapted respectively to produce X-ray beams down to about 10 microns diameter and registration of the diffraction on flat film 10 mm diameter at distances down to 1 mm from the specimen (l, 2). This enabled fibre patterns to be obtained from wax coatings on plants (1) and a single starch granule C3) in both instances leading to new insights about the ultrastructure of these objects. 

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. 

Paris O, Loidl D, Muller M, Lichtenegger H, and Peterlik H. Cross-sectional texture of carbon fibers analysed by scanning microbeam x-ray diffraction. J. Appl. Crystallogr., 2001 34 473-479. 

While it may be possible to adapt an ordinary pinhole camera to some microbeam work simply by changing the collimator, better results will be obtained with a specially designed microcamera [6.3, G.39]. Such a camera will usually have a small specimen-to-focal-spot distance (to increase intensity and improve collimation), a small specimen-to-film distance (to reduce exposure time), and some arrangement for accurately positioning the specimen in the beam. Diffraction patterns of specimens amounting to as little as 10 micrograms have been obtained in such cameras. 

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). 

Microbeam X-Ray Diffraction Study 3.1 Two Kinds of Fiber Structures... 

Microbeam X-ray diffraction with beam sizes in the micrometer range is a useful and powerful method to investigate the in situ transition of the crystalline region and the local structure for monofilaments. To reveal the detailed fiber structure and the distribution of the two types of molecular conformations (a- and P-structure crystals) in monofilaments, microbeam X-ray diffraction was performed using synchrotron radiation at SPring-8, Japan. The beam size was focused to 0.5 pm with a Fresnel zone plate (Suzuki et al. 2001) and the monofilament was linearly scanned perpendicularly to the fiber axis with a step of 2 pm. 

Figme 7a shows the microbeam X-ray diffraction patterns for a cold-drawn and two-step-drawn UHMW-P(3HB) monofilament obtained from three marked points in the microscope image (Iwata et al. 2004 Iwata 2005). In the microbeam X-ray fiber diagram of no. 1 (edge part), all the reflections were indexed with only the a-structure crystal. However, in the diagrams of nos. 2 and 3 (center part), the other reflection indexed by the P-structure was observed, together with the a-structure... 

Fig. 7 Microbeam X-ray fiber pattern of drawn monofilaments, recorded from the three marked points in the microscope image, and schematic display, revealed by microbeam X-ray diffraction a cold-drawn and two-step-drawn UHMW-P(3HB) monofilaments with core-sheath structure b one-step-drawn P(3HB-co-3HV) monofilaments after isothermal crysteillization with a uniform structure. The arrows indicate a reflection derived from the p-structure. (Reprinted with permission from Iwata 2005. Copyright 2005, Wiley-VCH Verlag GmbH Co)...

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... 

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