COMPLEX IMAGE-RECONSTRUCTION OF WEAK SPECIMENS FROM A 3-SECTOR DETECTOR IN THE STEM

A criterion is presented for evaluating the suitability of different d etector geometries in the scanning transmission electron microscope (S TEM) for the-imaging of weak specimens at double the conventional brig ht-field resolution. This criterion is then used to demonstrate that a detector disc divided into three sectors (rather than four, as usuall y employed) is the simplest configuration that allows for the subseque nt reconstruction of the complex specimen function. A robust method is described by which the complex specimen function can be reconstructed from the images obtained by such a detector configuration. Computer s imulations are presented, and methods are suggested by which the detec tor and objective aperture alignment, and the objective focusing and s tigmation, can be straightforwardly optimised using the recorded image s.