Microdiffraction is X-ray diffraction analysis performed on small samples or small areas of large samples. Microdiffraction is considered the technique of choice when samples are too small for the optics and accuracy of conventional diffraction instrumentation. The microbeam is used as an X-ray probe so that diffraction characteristics can be mapped as a function of sample position. With the ability to accurately and precisely position the X-ray beam on a sample surface, the information can be plotted as a diffraction function map (DFM). Diffraction data can contain information about compound identification, crystallite orientation (texture), stress, crystallinity, and crystallite size. The field of microdiffraction is rapidly growing in materials research and fabrication because smaller domains now affect product yield and reliability. Applications for microdiffraction analysis include:
- Test pads on patterned wafers
- Compound libraries formed by combinatorial chemistry
- Small specks and inclusions on geological specimens
- Failure analysis of metal or plastic components
- Quality control in manufacturing or fabrication environments where uniformity is important
The limit on the size of the sample is dependent upon the accuracy of the instrumentation, which is measured by such variables as the diameter of the incident X-ray beam and the accuracy of the actual sample positioning. If the sample area of interest is part of a multiphase material, it is necessary for the diameter of the incident X-ray beam to be smaller than the sample area to assure that the diffraction pattern produced is from the sample area of interest only. Recently developed instrumentation and techniques can perform microdiffraction on samples as small as 20 μm in diameter. Incident beam collimators and a high magnification video camera are used to accurately and precisely position the sample area of interest in the X-ray beam. A two-dimensional detector (RAPID II imaging plate) is used to collect the entire diffraction cone while reducing the number of moving axes and associated uncertainty.