Diffraction Contrast in TEM Images
This chapter explains diffraction contrast in bright- and dark-field conventional transmission electron microscopy, workhorse techniques in materials research. Materials parameters that affect diffraction intensity in kinematical theory are presented, and compared to parameters in dynamical theory. The phase-amplitude diagram is developed for kinematical diffraction theory, and is first used for problems that can be solved analytically, such as intensity fringes in bend and thickness contours. Including the effects of strain fields in phase-amplitude diagrams is shown to be a powerful method for determining qualitatively the diffraction contrast effects from the crystal containing a dislocation. The weak-beam dark-field method for a calculating dislocation strain contrast is described, and the quality of its images is discussed with examples. Phase shifts at interfaces are included in the phase amplitude diagram method. Intensity fringes in the diffraction contrast from moiré effects, stacking faults, and domain boundaries are explained. Some results from dynamical theory are cited without proof, and used to describe diffraction contrast effects from crystals of modest thickness.