Electron holography, as originally described by Gabor (1949), is based on the formation of an interference pattern or “hologram” in the transmission electron microscope (TEM). In contrast to most conventional TEM techniques, which only record spatial distributions of image intensity, electron holography allows the phase shift of the high-energy electron wave that has passed through the specimen to be measured directly. The phase shift can then be used to provide information about local variations in magnetic induction and electrostatic potential. This chapter provides an overview of the technique of electron holography. It begins with an outline of the experimental procedures and theoretical background that are needed to obtain phase information from electron holograms. Medium-resolution applications of electron holography to the characterization of magnetic domain structures and electrostatic fields are then described, followed by a description of high-resolution electron holography and alternative modes of electron holography. The majority of the experimental results described below are obtained using the off-axis, or “sideband,” TEM mode, which is the most widely used mode of electron holography at present. For further details about electron holography, the interested reader is referred to several recent books (e.g., Tonomura et al., 1995; Tonomura, 1998; Völkl et al., 1998) and review papers (e.g., Tonomura, 1992; Midgley, 2001; Lichte, 2002; Matteucci et al., 2002).
KeywordsSpecimen Thickness Reference Wave Magnetic Contribution Micromagnetic Simulation Electron Holography
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