Selected-Zone Dark-Field Electron Microscopy

Abstract

Selection of image-forming electrons that have passed through a small annular zone of the objective lens drastically reduces the resolution-limiting influence of chromatic aberration. Special objective-lens aperture diaphragms are needed for this new method of obtaining high-quality images. The manufacture of the diaphragms is described. High-resolution and high-contrast images of crystallographic specimens in the light of selected Bragg-diffracted beams without preference to azimuthal orientations were obtained. In particular, {111}-lattice planes of gold were observed as well as interference fringes (``pseudo'' lattice images) between two nonsymmetrical Au {111} diffracted beams, displaying spacings and azimuthal directions characteristic of regular {200}- and {220}-lattice fringes, although the {200} and {220} diffracted beams were omitted by the specific annular aperture used. Such ``pseudo'' lattice images allow deposit orientation determinations in the same way as ``ordinary'' lattice images.