Convergent beam electron diffraction — A novel technique for materials characterisation at sub-microscopic levels

Abstract

This paper presents a review of the developments in Convergent Beam Electron Diffraction (CBED), a technique widely used for determination of structure, symmetry details and atom positions in a crystal as small as 20A in size. The understanding of this technique is related to the rapid advancements in the field of transmission electron microscopy with respect to development of coherent, finer probes and electron optics for higher spatial resolution. Energy filtering devices enable imaging of several finer features in the CBED pattern from which useful information about a crystal can be obtained. These include (i) three-dimensional information about the reciprocal lattice, (ii) point and space group symmetry details, (iii) lattice parameter from regions as fine as 2 nm, (iv) atom positions within a unit cell and (v) defects in crystals and (vi) thickness. Due to abundant data obtained from microscopic regions, this technique is unique and finds wide application in materials characterization. It has been used for studying problems like identification of the presence of lattice strain, identification of point defects etc. in a material used often in the nuclear industry, namely 9Cr-1Mo steel. The present paper provides the current status of CBED starting from its historical development, the information that can be obtained and its use in a variety of applications.