Abstract
Implementation of a computer program package for automated collection and processing of rotation electron diffraction (RED) data is described. The software package contains two computer programs: RED data collection and RED data processing. The RED data collection program controls the transmission electron microscope and the camera. Electron beam tilts at a fine step (0.05-0.20°) are combined with goniometer tilts at a coarse step (2.0-3.0°) around a common tilt axis, which allows a fine relative tilt to be achieved between the electron beam and the crystal in a large tilt range. An electron diffraction (ED) frame is collected at each combination of beam tilt and goniometer tilt. The RED data processing program processes three-dimensional ED data generated by the RED data collection program or by other approaches. It includes shift correction of the ED frames, peak hunting for diffraction spots in individual ED frames and identification of these diffraction spots as reflections in three dimensions. Unit-cell parameters are determined from the positions of reflections in three-dimensional reciprocal space. All reflections are indexed, and finally a list with hkl indices and intensities is output. The data processing program also includes a visualizer to view and analyse three-dimensional reciprocal lattices reconstructed from the ED frames. Details of the implementation are described. Data collection and data processing with the software RED are demonstrated using a calcined zeolite sample, silicalite-1. The structure of the calcined silicalite-1, with 72 unique atoms, could be solved from the RED data by routine direct methods.
Highlights
Single-crystal diffraction can be achieved using X-rays, neutrons or electrons
We have previously reported the rotation electron diffraction (RED) method for data collection (Zhang et al, 2010), where the transmission electron microscope, crystal tilt and CCD camera were controlled by scripts written in Gatan’s DigitalMicrograph
We present the RED data collection program, which controls the transmission electron microscope and the camera for automated three-dimensional electron diffraction data collection
Summary
Single-crystal diffraction can be achieved using X-rays, neutrons or electrons. While the first two have always been both quantitative and three dimensional, electron diffraction (ED) was until very recently mainly done in two dimensions. For three-dimensional structure determination, it was necessary to collect a small number of electron diffraction patterns manually (often on photographic film), each one very accurately aligned along a zone axis ([100], [110], [111], [120] etc.). Very complicated structures could be determined in this way, such as -AlFeCr (Zou et al, 2003) with 129 unique atoms, it took months if not years to collect, process and analyse such data This made the technique inferior to X-ray and neutron diffraction, which for decades have been done automatically in hours or days. One important advantage of the RED method is that data collection can be controlled entirely by software and performed on a conventional transmission electron microscope without any additional hardware. We have previously reported the RED method for data collection (Zhang et al, 2010), where the transmission electron microscope, crystal tilt and CCD camera were controlled by scripts written in Gatan’s DigitalMicrograph A previous implementation was made using Gatan DigitalMicrograph scripting, and the technical details and procedures
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