Size of small Si and Ge clusters on Si(1 1 1) and Ge(1 1 1) surfaces

We determined the average size of small Si and Ge clusters confined to one half of a (7 × 7) or (5 × 5) unit cell of a Si or Ge(1 1 1) surface. The growth conditions were chosen in order to produce clusters with the size close to their maximal size. The size of Si and Ge clusters confined to a Si(1 1 1)-(7 × 7) half unit cell was determined to be 8.3 ± 1 atoms and 7.5 ± 1 atoms, respectively for a growth temperature of 400 K. This is the same value within the error and shows that the material of the clusters is less important for the cluster size. On the Ge surface it was found that the reconstruction unit cell is important for the cluster size. On the (5 × 5) reconstructed Ge(1 1 1) surface the Si clusters have a smaller size of 4.7 ± 1 atoms compared to 8.2 ± 1 atoms on the Ge(1 1 1)-(7 × 7) surface.