. Electron microscopy; proceedings of the Stockholm Conference, September, 1956. Electron microscopy. The Resolution of Crystal Lattices 91. Fig. 9. Sodium faujasite crystal showing (111) planes. lattice rows in the direction of the beam is highly relaxed. With a 50 /< objective aperture, the spectra contributing to the image from the phthalocyanine crystals are the (20T), (402), 201) and (402). These spectra are assumed to recombine with the zero order beam in the image plane and form an image of the crystal grating in accordance with the simple Abbe theory of image formation by a lens. Th
. Electron microscopy; proceedings of the Stockholm Conference, September, 1956. Electron microscopy. The Resolution of Crystal Lattices 91. Fig. 9. Sodium faujasite crystal showing (111) planes. lattice rows in the direction of the beam is highly relaxed. With a 50 /< objective aperture, the spectra contributing to the image from the phthalocyanine crystals are the (20T), (402), 201) and (402). These spectra are assumed to recombine with the zero order beam in the image plane and form an image of the crystal grating in accordance with the simple Abbe theory of image formation by a lens. This has been confirmed by excluding all spectra except the zero order from the image by using a 10 // objective aperture when it is found that the image of the planes disappears. Further confirmation of this mechanism is obtained from the fact that an array of parallel lines rather than a cross grating of dots is seen in the image. The projection of the lattice in the direction of observation should show a series of planes (010) perpendicular to the (20T) planes. The spacing of ^^^l^r- iHM m these planes however is A and the first permis- sible spectrum from them, (020), corresponds to a Bragg spacing of A. This is excluded from the image by a 50 // aperture so that the image of these planes is not seen. It is doubtful on other grounds whether such a small spacing could be resolved. Firstly, the permis- sible misorientation of the crystal with respect to the electron beam, arising from the relaxation of the third Laue condition becomes smaller as the spacing to be resolved is reduced. Secondly the effect of spherical aberration in distorting the wavefront of a beam diffracted at a wide angle through the lens becomes so severe as to cause the diffracted beam to be no longer able to interfere coherently vsith the zero order beam and form the image. The effect of spherical aberration may already be severe even. Please note that these images are extracted from scanned pag
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