The Si capping of small Ge dots nucleated on a C-precovered Si(001) surface has been investigated by means of reflection high-energy electron diffraction and atomic force microscopy. The growth at 500 °C of three Ge monolayers on the C-induced c(4×4) reconstruction leads to the nucleation of isolated dots, without any wetting layer. Up to a nominal thickness of 5 nm, the surface evolution during the Si cap layer deposition reveals island preservation. A mean size enhancement is even observed for these covered islands. Contrary to the Si capping situation of Ge islands on bare Si surfaces (without C seeding), where a surface smoothing is observed after few monolayers, the modified C-induced surface strain promotes a final Si adatom adsorption on the top of the Ge islands. A rough morphology is therefore maintained during the cap layer growth by this selective Si coverage. The general surface smoothing and the in-plane lattice parameter recovery toward Si bulk values are also strongly delayed. © 2004 American Institute of Physics.