The extension of scanning transmission electron microscopy by use of diffraction information

The information contained in the intensity distribution of the convergent beam electron diffraction pattern, produced in the detector plane for each incident beam position in a scanning transmission electron microscope, may be used to enhance the resolution of the microscope or else to decrease the electron irradiation of the specimen involved in deducing information at any particular level of resolution. The structural information concerning the specimen may be obtained, for example by interpretation of the Patterson function using image-seeking methods. The statistical error involved due to the finite number of electrons available may be derived by considering the efficiency of use of the information contained in Patterson function peaks. The most efficient means for using the available information appears to be that based on information theory concepts, which employ the integral over the product of the observed diffraction pattern intensity and the intensity calculated for known or postulated groupings of atoms. The reduction in radiation damage possible by use of this method, relative to that involved in the separate imaging of individual atoms, may be by a factor of approximately n, where n is the number of atoms in the known or postulated group being sought.