Computer simulation of field ion emission patterns of solid solution alloys

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Abstract
A plot of the positions of atoms which lie in an outer shell of given thickness on a spherical crystal gives a pattern very similar to a field ion image. Such a plot can also be made of binary solid solutions by assuming that the two species have different evaporative properties, but that they behave similarly in producing the field ion image. This is equivalent to assuming that the shells corresponding to the two species have different outer diameters but similar inner diameters. Patterns have been computed for 25, 50 and 75 at. % solid solutions and for the ratios of the shell thickness for species A to that for species B zero, 0·25, 0·5 and 0·75. The set of computed patterns can be used to deduce from given experimental images which species has been preferentially evaporated from the surface layers. An attempt is made to explain the irregularities in experimental field ion images of solid solutions in terms of static atomic displacements and it is shown that such an explanation is not possible.