C2H4 mediations were used to modify the Stranski-Krastanow growth mode of Ge dots on Si(0 0 1) at 550 degrees C by ultra-high vacuum chemical vapor deposition. With appropriate C2H4-mediation to modify the Si surface, the elongated Ge hut clusters can be transformed to highly uniform Ge domes with a high Ge composition at the core. These C2H4-mediated Ge dots, almost bounded by {1 1 3} facets, have an average diameter and height of 55 and 9 nm, respectively. We propose two major mechanisms to depict the formation of these C2H4-mediated Ge dots: (i) an almost hydrogen-passivated Si surface to limit the nucleation sites for dot formation, and (ii) the incorporation of Ge atoms, repelled by the C-rich areas, into the existing Ge dots. This work provides a useful scheme to tune the topography of Ge dots in an UHV/CVD condition for possible optoelectronic applications. (C) 2008 Elsevier B. V. All rights reserved.