Electron Diffraction

Abstract

This chapter describes the elastic Coulomb interaction of an incident electron wave with a crystalline specimen. We start with the scattering of the electron wave function of the incident electrons by a single atom. The integral form of the Schrödinger equation results in a recursive description of the scattered electron wave function Ψ _S as a Born series. The scattered electron wave is calculated in the first Born approximation, and we find that the atomic scattering amplitude for electrons quickly decreases with increasing scattering angle. The periodic arrangement of atoms in the crystalline specimen together with electron scattering leads to electron diffraction. The structure amplitude of the crystal unit cell is used to describe the diffraction of electrons by a thin-foil specimen. This kinematical approximation reveals the origin of the chemically sensitive beams that constitute the basis of composition evaluation by the CELFA method. Dynamical effects of electron diffraction are taken into account using the Bloch wave formalism. With respect to the CELFA technique, we discuss the dependence of the beams on the specimen thickness and show how this dependence can be influenced by varying the excitation condition. Finally, we set out the basis of strain state analysis by discussing the correlation between the atomic positions and the positions of maximum image intensity that appear in the amplitude “image” of the wave function at the exit surface of the object in the framework of channeling theory. Further information about the topics discussed in this chapter may be found in [1, 2, 3].