Computer-aided determination of crystal-lattice orientation from electron channeling patterns in the SEM

The paper presents the major steps of a mathematical procedure that permits the simulation of Electron Channeling Pattern @CP) maps of any mineral species for which unit-cell constants, the atomic species and their equivalent positions are known. The basis of calculation is the Bragg equation, the structure factor d and the atomic scattering factors of the atomic species. Simulated spherical ECP maps for chromite and quartz are presented and compared to traditional ECP maps, which were constructed from ECP photomicrographs, good results. The fraction of the ECP sphere that covers all possible orientations of a crystal is discussed for all 32 point groups. It is shown that Lauegroup symmetry is the determining factor, which results in a loss of "resolution" in certain point groups. The ECP simulation leads to the creation of a software package CHANNEL, which permits rapid ECP-pattern recognition and lattice-orientation determination, in principle without the need for previous construction of an ECP map.

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