Influence of crystalline defects on 2-beam crystal lattice images-Experimental

Abstract

Of particular interest in the study of crystal lattice imperfections are the magnitude and extent of their influence on atornic structure. In the present work two-beam crystal lattice images have been used to examine directly the perturbing influence of Guinier-Preston zones in Al-4% Cu, damaged regions in neutron irradiated Ge and dislocations in deformed and partially crystallized Ge. The 2–02 Å; spacing of (200) planes was resolved in Al-4% Cu while the 3–26 Å spacing of (111) planes was resolved in the Ge specimens. The crystal lattice images were obtained using a high vacuum, short focal length (2.1 mm) Siemen's Elmiskop 1 operated at 100 kv with pointed filaments and thin film objective apertures. The experimental observations reveal: (1) that the G.P. [1] zones are coherent with the matrix (200) planes and produce an observable tensile distortion out to ∼ 20 Å on either side of its centre; (2) that when a damaged region in Ge has a size equal to the foil thickness, then the lattice image disappears over the small region occupied by the damaged region; (3) that a 60° edge dislocation in Ge produces an apparent asymmetry in the displacement of (111) planes; and (4) that the resolved (111) planes in Ge have a pronounced s-shape as they cross an inclined screw dislocation.