Condensed-Matter Physics & Materials Science Seminar
"How you can use your TEM as powerful electron diffraction tool : Precession Electron Diffraction combined with 3D diffraction tomography for ab-initio structure determination and TEM based nanoscale orientation imaging"
Presented by Stavros Nicolopoulos, NanoMEGAS, Belgium
Wednesday, May 1, 2013, 10:30 am
Bldg. 735, Conf. B
Hosted by: Lijun Wu
Precession electron diffraction (PED) in a TEM is a new emerging promissing 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 intensitities .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. PED tomography can be the ideal tool to solve crystal structures even in cases where X-Ray synchtrotron data may fail to solve the structure. Another new precession diffraction based application has been recemtly 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 m2), 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.Resulting high quality nanoscale (1-2 nm) orientation / phase maps obtained with TEM-FEG/LaB6 are much superior to equivalent EBSD-SEM orientation maps.Such orientation/ phase maps may be produced very fast , making the technique highly attractive for high throughput TEM based orientation imaging analysis.