ITERATIVE STRUCTURE RETRIEVAL TECHNIQUES IN HREM - A COMPARATIVE-STUDY AND A MODULAR PROGRAM PACKAGE

A retrieval technique for crystal structures using high-resolution ele ctron microscopy is presented. The inversion of the complex structure- to-image relation is performed by numerical optimization of the config uration space of object models. Unlike structure refinement in X-ray c rystallography, the method operates on unknown defect structures on a nanometre scale. The diversity of crystal defects examined and the dif ferences in microscope types and alignment conditions makes it necessa ry to adapt the basic algorithm to a broad variety of needs resulting in a modular program package for general use. New developments, such a s a real space slice function calculation. problem adapted optimizatio n strategies, and finally an examination of iterative matching of imag e series and exit wavefunctions are presented.