Automated electron diffraction tomography - a new tool for nano crystal structure analysis

Automated electron Diffraction Tomography (ADT) comprises an upcoming method for ab intio structure analysis of nano crystals. ADT allows fine sampling of the reciprocal space by sequential collection of electron diffraction patterns while tilting a nano crystal in fixed tilt steps around an arbitrary axis. Electron diffraction is collected in nano diffraction mode (NED) with a semi-parallel beam with a diameter down to 50 nm. For crystal tracking micro-probe STEM imaging is used. Full automation of the acquisition procedure allowed optimisation of the electron dose distribution and therefore analysis of highly beam sensitive samples. Cell parameters, space group and reflection intensities can be determined directly within a reconstructed 3d diffraction volume using a dedicated software package (ADT3D). Intensity data sets extracted from such a volume usually show a high coverage and significantly reduced dynamical effects due to off-zone acquisition. The use of this data for ab initio structure solution by direct methods implemented in standard programs for X-ray crystallography is demonstrated. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim