Scanning Microscopy


The high spatial and temporal coherence of a field emission gun (FEG) increases the information limit of high-resolution transmission electron microscopes (HRTEM), but has also its implications on the localisation of the high resolution information in the image. In this paper, we present the results of a combined theoretical and experimental study of delocalisation in HRTEM. First, we derive a spatial frequency analysis of the delocalisation for crystal defects. Next, the delocalisation is studied from a real-space point of view, in terms of the impulse-response function, for which an instructive asymptotic mathematical analysis has been set up. Finally, we present experimental HRTEM images of crystal defects and of an amorphous Ge film, which are recorded with a Philips CM20 FEG electron microscope, and which illustrate the delocalisation phenomena.

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