Strategies in electron diffraction data collection

his chapter describes the strategies in electron diffraction (ED) data collection. X-ray diffraction (XRD) is the most powerful technique for structure resolution, and it is the standard technique to which every structural resolution method must be compared. The X-ray scattering can be considered kinematically, and consequently the diffracted intensities are simply proportional to the square modulus of the Fourier transform of the electronic density. In the study of unknown structures, the ability to grow single crystals of suitable dimensions for a conventional X-ray diffractometer is the key factor for success: the problem of structure solution becomes very simple in most cases because it is provided almost automatically by advanced computer software programs. In multiphase samples, ED exhibits major advantages: when a transmission electron microscope (TEM) is used, each grain can be identified by means of energy-dispersive microanalysis or just from its diffraction pattern, which reveals symmetry and cell parameters. The chapter also discusses two steps of structure resolution: (1) extraction of reliable ED intensities and (2) reduction of the unavoidable dynamic effects by means of a particular acquisition technique.