3D electron crystallography
All structures are 3-dimensional, but each EM image is just a 2D projection of the 3D structure. Until recently, almost all work in the EM field has been 2D. 3D electron crystallography can be made by combining several HRTEM images and/or ED patterns taken from different orientations (zone axes). A crystal with all unit-cell dimensions over 5 Å will never give rise to projections that can be interpreted in terms of atomic coordinates. A 3D structure is needed. The procedure from image collection and interpretation, in terms of zone axis and projected symmetry, to combination of data into a 3D map, is demonstrated. All the steps are followed in great detail, using a very complex intermetallic structure as an example. HRTEM images (before and after image processing) and ED patterns from several zone axes are show together with a table of amplitudes and phases extracted from the HRTEM images and ED patterns. The remarkably clear 3D potential map is interpreted in terms of atomic structure.
Keywords: 3D electron crystallography, 3D reconstruction, high-resolution electron microscopy, electron diffraction, combining 2D projections, zone axes, merging projections, intermetallic compounds, 3D potential map, 3D atomic coordinates, contrast transfer function, symmetry, origin determination
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