Stress-Induced Shape Transition ofCoSi2Clusters on Si(100)

${\mathrm{CoSi}}_2$ clusters on a Si(100) surface grow in a square shape at first, but at a critical size a shape transition to clusters with large aspect ratios occurs. Each cluster is connected to an implanted layer of cobalt by a thermally induced defect that serves as a diffusion channel. In this novel growth mode the existing clusters can grow with a continuous supply of cobalt while cluster-cluster interaction is prevented from becoming a dominant factor to the cluster shape as a result of the large distance between defects. Our data are in good agreement with calculations on the balance between surface and interfacial energies on the one hand and stress relaxation due to an elastic distortion of the substrate on the other.