Author:
Leslie C. E.,Fryer J. R.,Gilmore C. J.,Nicolson W.
Abstract
Imaging of organic crystals in the electron microscope is limited by their sensitivity to the electron beam, with even the most stable molecules only giving a resolution of ~3Å. By contrast, electron diffraction requires a lower beam intensity, and so can give much better resolution, down to ~lÅ under favourable conditions. Intensities may be measured directly from the diffraction pattern, and the phase determination problem can be surmounted by applying the maximum entropy method, which chooses phases by likelihood estimation.It was decided to apply this method to the organic molecule anthanthrene, C22H12 (fig. 1), since x-ray studies found that the crystals were monoclinic with a = 12.10Å, b = 10.34Å, c = 10.74Å, β = 92.2°, space group P21/a and Z = 4, but no details of the atomic co-ordinates were given in the literature. A previous study of the molecule, using KC1 as the substrate, produced epitaxial layers showing the acprojection being most common at room temperature.
Publisher
Cambridge University Press (CUP)