Fourier transform “darkfield” techniques

Abstract

The standard approach to localizing single crystal regions in a transmission electron microscope (TEM) is to form tilted-illumination darkfield images with a diffracted beam down the microscope axis, and other electrons cut off by a centered objective aperture.This capability for localizing periodicities is powerful and shared by few other diffraction techniques.High resolution TEM’s with point resolution and information limit below the spacing between atoms (e.g. 0.2 nm) are capable of putting information on all of the large crystal periodicities directly into phase contrast images.The refinement of techniques for finding and characterizing the crystals associated with spots, corresponding to the diffracted beams, in power spectra from such images has thus become a regular subject in the microscopy literature [e.g. 1-3]. Here, we illustrate that such techniques are useful for more than localizing crystallite boundaries.We also suggest one strategy for improving on the useful, but ad hoc, strategies now in hand.