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[交流] 【讨论】关于energy dispersive X-ray diffraction(EDXRD)，能说多少说多少

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1楼 2010-11-18 14:03:01

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The fundamental idea of using in situ EDXRD with a polychromatic X-ray source and an energy-discriminating detector for rapid obtention of diffractograms was first suggested over 35 years ago (Giessen and Gordon, 1968), and the potential for utilisation of synchrotron radiation in EDXRD studies was noted not long afterwards (Buras et al., 1976). However, it is only with more recent improvements in synchrotron X-ray sources and detectors, providing greatly improved signal-to-noise ratios and therefore time and d-spacing resolution (Walton and O’Hare,2000), that EDXRD has become a technique of real importance. Where standard (angle-dispersive) XRD uses a monochromatic beam with a detector scanning over a range of angles, the polychromatic(‘white’) X-ray beam used in EDXRD allows the use Bragg’s Law, Eq. (1), the diffracted beams from structures with different d-spacings are distinguished by different values of for a fixed , rather than via variation in as in regular XRD:n = 2d sin . (1)EDXRD is of particular use in the investigation of hydrothermal reaction processes, which require sample vessels capable of withstanding relatively aggressive chemical environments (Heet al., 1992; Evans et al., 1995). The much greater penetrating power of the polychromatic wiggler-source X-ray beamused here compared to a monochromated bending-magnet beam enables the use of ‘laboratory-sized’ sample cells in transmission geometry, thereby greatly simplifying experimental design and expanding the available parameter space. The removal of the need to scan the detector across a range of angles also decreases the collection time required to obtain a diffractogram, and is not subject to several of the difficulties inherent in the use of an image plate detector, which is the other common way of avoiding this problem when rapid diffractogram acquisition is required (Chupas et al., 2003). Some spatial resolution is sacrificed by use of the energy-discriminating detector when compared to angle-dispersive synchrotron XRD, but this is quite
acceptable in the context of the current investigation, which is dealing with X-ray amorphous materials meaning that all peaks observed are very broad regardless of the detector used. of an energy-discriminating detector fixed at a given angle.