ERROR ANALYSIS OF CRYSTALLINE PTYCHOGRAPHY IN THE STEM MODE

We analyse errors associated with ptychographical phase determination of coherent convergent beam electron diffraction (CBED) patterns. The basis of this method is to observe the CBED patterns, as the probe is scanned across the specimen, in the regions where diffracted orders overlap, and measure the phases of the resulting sinusoidal intensity variations in such regions. The method is shown to be insensitive to the objective lens transfer function (i.e. to defocus, astigmatism and alignment), the degree of spatial coherence, specimen drift, and errors in probe scan rate. The robustness of this technique is confirmed by presenting results of its application to data recorded from an optical analogue of a scanning transmission electron microscope.