  We have studied the effect of the misfit on the equilibrium shape of
three-dimensional pyramidal islands grown on a foreign substrate in the case of
incomplete wetting (Volmer-Weber mode of growth). We have found that tensile
islands have smaller aspect ratios compared with compressed islands owing to
its better adhesion to the substrate. The average strains of consecutive layers
decrease faster with thickness in compressed than in tensile islands. The
strains decrease rapidly with thickness, with the consequence that above a
certain height, the upper layers of the pyramid become practically unstrained
and does not contribute to a further reduction in the upper base. As a result,
the truncated pyramids are not expected to transform into full pyramids. Our
results are in good agreement with experimental observations in different
systems.
