Aspects of Bloch-Wave Channeling in High-Voltage Electron Microscopy

Abstract

It is shown that the crystal orientation which maximizes the electron transmission for high‐energy electrons incident upon medium and heavy atomic‐weight materials is the symmetry position. This is contrary to the generally held view that the symmetry position is an orientation of particularly poor penetration. A simple explanation of the effect in terms of Bloch‐wave channeling is given. (The term Bloch‐wave channeling denotes the wave model analog of particle channeling as it refers to the enhanced transmission of Bloch waves, or of particles in a particle representation, due to their channeling between the atomic planes, thus minimizing inelastic scattering.) It is shown that considerably thicker specimens of heavy materials in particular may be studied in a 1‐MV microscope by using the symmetry position rather than the Bragg position.