Electron Microscope Out-of-focus Image of the Edge of a Crystal Lattice

Abstract

IN 1957, Cowley and Moodie¹ pointed out, theoretically and by optical analogue experiments, that so-called Fourier images can be observed in out-of-focus images of a periodic object. According to them, Fourier images are interference fringe systems arising from the transmitted primary and several diffracted waves, and are a series of images in particular planes both in front of and behind the object and having the same geometrical form as the periodic object. In electron microscope images, passing through the focus, of copper-phthalocyanine, Komoda² observed that the periodic structure in the image appeared again after it had become diffuse. He concluded that the periodic structures appearing at a different focus are the Fourier images of the crystal lattice predicted by Cowley and Moodie. In the out-of-focus image of copper-phthalocyanine crystal taken by Komoda, we have detected a few extra lines outside an edge of the crystal (see Fig. 1). Such lines are not explicable by the theory of Cowley and Moodie. By using a light optical analogue, it has been shown that these lines are due to effects arising from the termination effect of the Fourier images and Fresnel diffraction of electron waves at the edge of the crystal.