Experimental Techniques

    When using an x-ray microbeam, rotation of the sample relative to the microbeam is to be avoided.  There are two critical problems associated with rotations and microbeams:

    This is topically a drawback when studying single crystals or materials that are polycrystalline but made with crystalline grains which are larger than the beam size (i.e. the beam will see each individual grain as a single crystal). To avoid rotations, polychromatic radiation can be use instead of monochromatic radiation to have the Bragg conditions satisfied for a number of reflections at the same time. A 2D diffraction pattern collected using a broad bandpass (polychromatic, "pink", "white") radiation is called a Laue pattern.


In the scanning X-ray microdiffraction technique, the sample is scanned beneath the incident x-ray microbeam within the focal plane.  At each step in the scan, diffraction data can be collected via an area detector such as a X-ray CCD detector.

    Either polychromatic beam or monochromatic beam can be used to perform a microdiffraction scan.  Polychromatic beam is used when the grain size of the material is greater than or about equal to the x-ray beam size.  With white beam, data is collected as Laue patterns from any crystallites within the diffracting volume.  Monochromatic beam is used when the grain size is much less than beam size.  In this case, the sample can be viewed as a powder.  Data is collected in the form of diffraction rings.