The question was addressed of whether the core structure of screw dislocations in Mo, in the bulk, could be obtained from high-resolution electron microscopy images of such dislocations when viewed end-on in a thin foil. Atomistic simulations of the core structure of screw dislocations in elastically anisotropic Mo were carried out using bond order potentials. These simulations automatically took account of the effects of the surface relaxation displacements (anisotropic Eshelby twist). They showed that the differential displacements of the atoms at the surface were different with components perpendicular to the Burgers vector about five times larger than those in the middle of the foil, the latter being characteristic of the bulk. Nye tensor plots showed that the surface relaxation stresses strongly affect the incompatible distortions. High-resolution electron microscopy simulations of the computed structure reflect the displacements at the exit surface, modified by interband scattering and the microscope transfer function. Nye tensor plots obtained from the high-resolution electron microscopic images showed that interband scattering also affects the incompatible distortions. It was concluded that it would be very difficult to obtain information on the core structure of screw dislocations in the bulk Mo from high-resolution electron microscopic images, even under ideal experimental conditions, and that quantitative comparisons between experimental and simulated images from assumed model structures would be essential.

Effect of Eshelby Twist on Core Structure of Screw Dislocations in Molybdenum: Atomic Structure and Electron Microscope Image Simulations. R.Gröger, K.J.Dudeck, P.D.Nellist, V.Vitek, P.B.Hirsch, D.J.H.Cockayne: Philosophical Magazine, 2011, 91[18], 2364-81