Local structure determination of amorphous materials through parallel nano beam electron diffraction

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Progress was made in treatment of 2D class-average diffraction patterns in order to remove diffuse ring signals caused by non-aligned signals. This allows for isolation of structural features from structural motifs for further processing into 3D. Diffraction patterns were simulated from amorphous structures produced by molecular dynamics and from isolated atomic clusters to compare with the experimental patterns. In both cases there are differences with experimental patterns and class-averages arising from the simulations limited volume size and tiling artifacts. Tests were made with various phase retrieval algorithms for their ability to recover phases from diffraction patterns with limited signal and noise. The Oversampling smoothness algorithm was the best performing algorithm among the tested for realistic data. To better match the experimental data, the finite convergence of the probe beam should also be taken into account and has yet to be implemented. Clustering algorithms such as SLICEM were tested for separating out class-averaged diffraction patterns into those originating from different structures. While clusters could be achieved for the experimental data, when tested with simulated data, the clustering accuracy was found to be very low. Different clustering algorithms developed for non-periodic diffraction data will be required. The ability to orient 2D patterns into a 3D diffraction pattern was tested and found to be possible on the experimental data although methods to fill in the gaps between 2D planes will be required.