Transition from 2D to 3D growth during Ag/Si(1 1 1)-(7×7) heteroepitaxy

The Stranski–Krastanov growth of Ag on Si(1 1 1)-(7×7) surface at coverages from 0.5 to 2.5 ML, different temperatures (<500 K) and deposition rates has been investigated by STM. A 2D wetting layer with complex structure has been observed. Deposition beyond critical thickness leads to the formation of 3D islands with a very low height-to-size ratio. The critical thickness increases with temperature. At the onset of 3D growth almost all islands have a uniform height of 2 ML of Ag(1 1 1). During further deposition, 3D islands higher than 2 ML appear. The top layers of the islands are always fully completed. 3D island densities, size and height distributions are discussed. A qualitative change in the morphology of the wetting layer and the temperature dependence of 3D island density at elevated temperatures have been observed.