Contrast from dislocations in field-ion images (the origin of the ‘cross-over’ effect)

Abstract

The contrast from dislocated crystals in the field-ion microscope is well understood in terms of the geometrical interaction between the dislocation and the surface. This paper considers the modification of the evaporated end form of the specimen close to the dislocation and assumes a constant width of the imaging pole rings. The type of contrast to be expected from single dislocations, dipoles and loops is considered and compared with real examples. In particular it is shown that the ‘cross-over’ effect arises from dipoles or loops.