A scanning tunneling microscopy (STM) investigation into the surface morphology of Si and Si0.8Ge0.2 films grown at 500 degreesC on Si (100) with and without 0.8 monolayers (ML) of an Sb surfactant is presented. The presence of Sb induces the formation of large three-dimensional islands in Si and Si0.8Ge0.2 leading to a rougher surface morphology than films grown without Sb. The roughness of the Sb/SiGe surface is greater than Sb/Si surface, which we propose is due to more favorable exchange energetics between Sb and Ge than between Sb and Si. Encapsulation of the SiGe surface by an Si top layer results in the burial of the SiGe islands leading to compositional abrupt but physically rough interfaces. (C) 2004 Elsevier B.V. All rights reserved.