Phase Contrast in Electron Microscopy

Abstract

Phase shifting of scattered or non-scattered waves into antiphase with respect to each other has provided the most advantageous optical contrasting technique for light microscopy. Analogously, attempts have been made in electron microscopy to achieve phase contrast, both in-focus and out-of-focus. Results have been complicated by lens aberrations, power supply instabilities, interpretation of defocused images and, in the case of lattice images, by the question of the actual imaging mode.Defocus contrast has been further complicated by lateral displacement of dark field images from the corresponding bright field image as commonly observed with inorganic crystals (e.g. MgO). By means of image plane detectors (Fig. 1) the defocus contrast variation of polystyrene latex spheres (P.S.L.) (Fig. 2) has been related to the lateral shift of dark field images arising from carbon-carbon nearest neighbor scattering. Lateral displacement arises from defocusing and from spherical aberration at focus (resulting in the variation of in-focus contrast for different microscopes used without an objective aperture).