When studying nanocrystalline materials, it is crucial to get quantitative information on a local scale, e.g. on grain and domain size or on the order parameter. This is not possible using X-ray, but in the TEM quanitative analysis can be obtained from an electron diffraction pattern (SAD) taken from the area of interest. This is done by analysing parameters obtained using profile analysis of SAD (PASAD).
The PASAD-tools provide a Digital Micrograph™ Plugin with Graphical interface for full-automatic and fast determination of quantitative data from a SAD.
For quantitative analysis, the SAD have to be transformed in an electron diffraction profile by azimuthal integration. As deviations from the correct center of integration can cause artificial peak broadening and even double peaks, the center is refined to sub-pixel pecission by the program. Furthermore elliptic distortions are corrected. The background of the diffraction profile is subtracted using a spline fit. To ensure reproducibility the location of the splinepoints is determined automatically by detecting and prefitting the peaks. Peak parameters are determined by fitting a combined model of all peaks using pseudo Voigt peak-functions. This peak parameters can then be used for the quantitative local scale analysis e.g. by evaluating grain sizes using the peak broadening.
PASAD 2.0 contains a lot of additional features, e.g. the possibility to calculate the radial distribution function. Further information can be found in the documentation page .
The software can be used free of charge under the condition a reference is made to the following publication (or any newer PASAD related publication)
C. Gammer, C. Mangler, C. Rentenberger and H.P. Karnthaler. Quantitative local profile analysis of nanomaterials by electron diffraction. Scripta Materialia 63 (2010) pp. 312-315.
Recent applications of PASAD include:
Three-Dimensional Analysis by Electron Diffraction Methods of Nanocrystalline Materials.
Growth of nanosized chemically ordered domains in intermetallic FeAl made nanocrystalline by severe plastic deformation.
Feel free to contact me for any questions, bug reports or feature requests!
Christoph Gammer
Physics of Nanostructured Material, University of Vienna
present address: Erich Schmid Institute of Materials Science, Austrian Academy of Sciences, Leoben, Austria.
christoph.gammer(o)oeaw.ac.at
