ON CONTRAST PATTERNS PRODUCED BY SELF-INTERSTITIAL ATOMS IN FIELD ION MICROSCOPE IMAGES OF A BCC METAL

摘要

A general method was presented for calculating the contrast pattern to be expected from a single self-interstitial atom (S1A) in a field ion microscope (FIM) image. It was assumed that the SIA was embedded inside a FIM specimen well below the surface. The SIA was uncovered and eventually removed by the field evaporation of successive atomic planes. Atoms on the surface were displaced outwards from the surface as a result of the dilatational field of the SIA. This outward displacement of atoms resulted in 3 possible contrast effects. These 3 contrast effects were:(a) a bright spot;(b) an extra bright spot;and (c) a vacant lattice site. A single SIA atom can produce all these contrast effects, and the totality of these effects was termed a contrast pattern. The atom displacements were obtained from the a-iron interatomic potential of R. A. Johnson, without allowing for surface relaxation effects. De tailed atomic displacement maps were presented for the {111} planes with a <110> split and a <111> split crowdion SIA configurations located many inter planar spacings underneath these surfaces. It was shown that the resulting atomic displacement maps contained sufficient information to allow the configuration of the SIA to be determined.