They can be used to form a Parallel Beam XRD instrument geometry which greatly reduces and removes many sources of errors in peak position and intensity inherent to the parafocusing geometry, such as sample position, shape, roughness, flatness, and transparency. Polycapillary collimating optics convert a highly divergent beam into a quasi-parallel beam with low divergence. Polycapillary X-ray optics can be used to overcome many of these drawbacks and constraints to enhance XRD applications. These sources also have large excitation areas, which are often disadvantageous for the diffraction analysis of small samples or small sample features. Additionally, traditional XRD systems are often based on bulky equipment with high power requirements as well as employing high powered X-ray sources to increase X-ray flux on the sample, therefore increasing the detected diffraction signals from the sample. Sample flatness, roughness, and positioning constraints preclude in-line sample measurement. A mis-positioned sample can lead to unacceptable specimen displacement errors. Alignment errors often lead to difficulties in phase identification and improper quantification. Additionally, this geometry requires that the source-to-sample distance be constant and equal to the sample-to-detector distance. This geometry offers the advantages of high resolution and high beam intensity analysis at the cost of very precise alignment requirements and carefully prepared samples. The parafocusing (or Bragg-Brentano) diffractometer is the most common geometry for diffraction instruments. If the experimental angle is systematically changed, all possible diffraction peaks from the powder will be detected. When a powder with randomly oriented crystallites is placed in an X-ray beam, the beam will see all possible interatomic planes. However, most materials are not single crystals, but are composed of many tiny crystallites in all possible orientations called a polycrystalline aggregate or powder. The intensities of the diffracted waves depend on the kind and arrangement of atoms in the crystal structure. The directions of possible diffractions depend on the size and shape of the unit cell of the material. The diffraction of X-rays by crystals is described by Bragg’s Law, n(lambda) = 2d sin(theta). crystalline), the scattered X-rays undergo constructive and destructive interference. In materials with regular structure (i.e. The dominant effect that occurs when an incident beam of monochromatic X-rays interacts with a target material is scattering of those X-rays from atoms within the target material. A primary use of the technique is the identification and characterization of compounds based on their diffraction pattern. X-ray diffraction (XRD) relies on the dual wave/particle nature of X-rays to obtain information about the structure of crystalline materials.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |