The direct observation of the structure of real crystals by lattice imaging

Abstract

The electron-microscope technique of lattice imaging can in favourable circumstances be used to observe the structure of materials directly. The technique is described, and examples of cases in which a direct correlation between image contrast and structural features has been established are given. Procedures for computing contrast in n-beam lattice images are outlined, and the important experimental parameters, thickness and orientation of the specimen, and spherical aberration and defocusing of the microscope objective, are discussed in some detail.

Use of lattice imaging in the electron microscope in the structure determination of the 126Rpolytype of SiC

“…2) essentially represent the lattice resolution of c planes of the 126R polytype. The lattice image contrast may bear a close correlation with the crystal structure provided that (Allpress & Sanders, 1973;McConneil, Hutchison & Anderson, 1974) (1)it is possible to select an objective aperture which excludes those beams which are severely affected by spherical aberration and still include many reflections to contribute to the image, lattice planes to be resolved are exactly oriented parallel to the beam and (3) the crystal foils are thin enough to approximate to phase gratings. The first two conditions are exactly satisfied in obtaining the lattice image shown in Fig.…”

Minimum detectable solute concentration in atomic-resolution transmission electron microscopy

“…Some of the more important parameters are the objective aperture size (Reimer, 1984;Bursill, Shen, Smith & Blanchin, 1984;Rose & Gronsky, 1986) and position (Cowley, 1973), microscope accelerating voltage (Spence, 1981;Reimer, 1984), objective-lens defocus (Allpress & Sanders, 1973;O'Keefe, 1973;Cowley, 1975;Reimer, 1984;Ourmazd, Rentschler & Taylor, 1986) and crystal and beam alignment (Smith, Saxton, O'Keefe, Wood & Stobbs, 1983). While consideration of all these parameters is beyond the scope of this article, it is worth discussing the effects of several of these, in order to evaluate the possibility of using (2) with ]Za--ZMI=2ZM for estimating Cmi n under slightly different microscope conditions and thereby extending the usefulness of the results.…”

n-Beam lattice images. VI. Degradation of image resolution by a combination of incident-beam divergence and spherical aberration

“…The aperture size is usually carefully selected to match the value of the spherical aberration coefficient (Cs) of the objective lens (Scherzer, 1949). The effects of spherical aberration and of the introduction of an objective aperture introduce complications into the interpretation of the lattice image, and these have been discussed in general in part I,* in Allpress & Sanders (1973) and in detail in part IV. * It was shown in part IV that for a thin-enough crystal, the image could be simply approximated by * Previous papers in this series are: Part I -Allpress, Hewat, Moodie & Sanders (1972).…”