Nano beam diffraction and precession in an energy filtered CS corrected transmission electron microscope

Abstract

AbstractNano beam diffraction is a prerequisite to collecting structural information from particles as small as 1 nm in diameter. We describe here a novel ray path, where the limiting illumination aperture is arranged higher up in the illumination system of a transmission electron microscope (TEM) so that it can be demagnified further. This results in a high flexibility concerning the illuminating field and electron beam convergence angle without any need for readjustments of pivot points and refocusing of the diffraction lens. We show that artifact‐free diffraction patterns can be obtained with diffraction fields down to 20 nm in diameter under genuine parallel illumination conditions. The limitations of the nano beam diffraction mode by physical diffraction effects are discussed. Either the illumination field or the diffraction spots or both may show diffraction fringes as a result of these effects. Zero energy loss filtering of (precession) electron diffraction spot patterns increases their contrast and makes weak diffraction spots visible. A method to acquire (energy filtered precession) electron diffraction spot pattern in a spherical aberration (CS) corrected TEM has been developed and first results are presented. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)