Stavros Nicolopoulos, Ph.D.
Precession electron diffraction (PED) in a TEM is an emerging technique using electron diffraction patterns collection very close to kinematical condition (like in x-ray diffraction) useful to solve ab-initio crystal structures of nanocrystals.
TEM based 3-D diffraction tomography technique consists in a collection of a series of randomly oriented diffraction patterns in precession mode of the same crystal through the whole TEM angular range, usually from -45º to +45º, at 1º angular intervals. The resulting 3D PED set of reflections can be visualized as clear 3D picture of the reciprocal cell of the crystal and enable direct cell determination and structure determination by measuring reflections intensities. More than 60 structures have been solved using 3D diffraction tomography the last few years dealing with nm size crystals of complex minerals, complex zeolites, MOFs, organic and pharmaceutical compounds and important application examples will be presented.
Another new precession diffraction based application has been recently developed for a TEM based phase and orientation maps for nanocrystal (EBSD-SEM like). A TEM precession interface may perform a scanning through a sample area (typical area 5x5 μm2), collecting a large number of PED patterns which are compared one by one by cross-correlation techniques with a series of generated diffraction patterns (templates) of all possible orientations of known phases existing on the sample scanned area. .Such orientation/ phase maps may be produced very fast , making the technique highly attractive for high throughput TEM based orientation imaging analysis. Several application examples will be presented ranging from metals, thin films, semicinductors, nanoparticles , even organic crystals.
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