Some samples may exist only in very small quantities, e.g. a dusting of a material on the inside of a sample bottle. Under these circumstances it is not possible to fill one of the standard flat-plate sample holders. One solution is to use a silicon crystal cut in such a way that the planes within the crystal never fulfill the Bragg condition. The sample can then be sprinkled onto the surface of the crystal. Some powders simply stick electrostatically to the silicon surface, while for other samples a trace amount of silicon grease should be smeared onto the silicon crystal beforehand. The big advantage of using silicon crystals in this way is that the background scatter from the mount itself is close to zero. | |
The second sample holder is for use on those occasions when you have a moderate quantity of sample, but an insufficient amount to fill a standard sample holder. The trick here is to use a silicon crystal as above, but with a small (0.5 mm deep) well in the middle for the sample. This has the advantage over a similarly-shaped metal sample holder in that the X-ray beam can penetrate through to the base of the sample without giving extra spurious peaks from the holder. |
© Copyright 1997-2006. Birkbeck College, University of London. | Author(s): Jeremy Karl Cockcroft |