RESUMO
When strained Stranski-Krastanow islands are used as "self-assembled quantum dots," a key goal is to control the island position. Here we show that nanoscale grooves can control the nucleation of epitaxial Ge islands on Si(001), and can drive lateral motion of existing islands onto the grooves, even when the grooves are very narrow and shallow compared to the islands. A position centered on the groove minimizes energy. We use as prototype grooves the trenches which form naturally around islands. During coarsening, the shrinking islands move laterally to sit directly astride that trench. In subsequent growth, we demonstrate that islands nucleate on the "empty trenches" which remain on the surface after complete dissolution of the original islands.
RESUMO
Self-assembled SiGe islands grown on Si(001) leave behind characteristic "footprints" that reveal that small islands shrink, losing material to nearby larger islands. The critical size, dividing shrinking from growing islands, corresponds to the pyramid-to-dome shape transition, consistent with "anomalous coarsening" While shrinking, {105}-faceted pyramids transform into truncated pyramids and ultimately into unfaceted mounds. The similarity to behavior during island growth indicates that island shape and facet formation are thermodynamically determined.
RESUMO
We grow single and twofold stacked island layers on patterned substrates and investigate the material distribution in and around the patterned area. For both layers a pronounced material depletion region occurs outside the pattern. The material gradients across the planar-patterned interface are symmetric in the first, but highly asymmetric in the second layer. We can describe these phenomena by simulations that take into account the surface curvature for the first and a strain-field modulated surface for the second layer.
