Abstract
Specific misfit dislocation configurations are observed by two-beam dark-field transmission electron microscopy in a system formed by a Ge
0.4
Si
0.6
ultrathin film grown on a (0 0 1)Si surface tilted 6° around a
axis. An unusual interfacial feature is the presence of triple dislocation nodes linked to 'Y-centres' formed by the meeting of two near-60° dislocations and a slightly inclined edge misfit dislocation. It is shown, from the comparison of experimental and computer-aided images, requiring three-dimensional elastic fields of angular dislocations, that some Lomer misfit dislocation terminations are not simply the emerging points of a single dislocation, but very probably linked to two short dislocation legs of threading dislocations in the film.