  Strain relief in lattice mismatched heteroepitaxy is mediated by formation
and/or propagation of dislocations. Due to their technological significance,
the process of strain relief in materials with face-centred cubic (fcc)
lattices has been analyzed by several researchers1,2 following the work by
Matthews and co-workers in the late 1960s to early 1970s3-6. In the Matthews
model, it is assumed that the strain relieved by any misfit dislocation is
equal to the edge component of the dislocation burgers vector in the interface
plane. This assumption has been used in all subsequent analyses of strain
relief in lattice mismatched heteroepitaxy [1,2]. Based upon the known
three-dimensional atomic structure of the dislocations in fcc lattices, we show
that the assumption is not valid for the 60 degree dislocations that
form/expand via the conservative glide process. For compressively (tensilely)
strained films the assumption is valid only for the 90 degree dislocations that
form/expand via aggregation of vacancies (interstitials).
