Progressive Lattice Distortion in Stressed Crystal Lamellae

F. W. Cuckow
1959 Proceedings of the Royal Society A  
Plat© 12 J The literature contains many references to the appearance of fringe patterns on crystals, under examination in the electron microscope, which are attributed to bending of the crystal. An unusually detailed and extensive but still incomplete pattern is presented in an electron micrograph of a sodium chloride crystal sheet. The corresponding electron diffraction pattern was of the 'two-dimensional' type. Diffraction and fringe patterns were present throughout extensive rotation of the
more » ... ve rotation of the specimen. The fringe pattern is repetitive and cannot be explained by reasonable degrees of bending of the sheet. It is shown to be consistent with the loss of electrons by Bragg reflexion from a lamellar single crystal in a special state of shear strain. Ideally, the strain progresses uniformly in all radial directions but is considered to have been induced experimentally by the contraction of a membrane attached to one side acting in opposition to the natural rigidity of the crystal. For the ideal state of strain it is shown that the fringe pattern is an enlargement by a two-dimensional vernier coincidence process of the intersections of origin reflecting planes with the basal plane, the magnification being simply related to the shear strain. The pattern is identical geometrically with Neumann's linear crystallographic projection. I n t r o d u c t io n t Postal address: 114,
doi:10.1098/rspa.1959.0074 fatcat:x6vemszx7jcwtl4ugsnqgzceae