The Si c(4 x 4) structure formed on Si(0 0 1)-(2 x 1) surface using monomethylsilane (MMS) and dimethylsilane (DMS) was studied by reflection high-energy electron diffraction (RHEED), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). From the XPS measurement, it was found that Si-C bonds existed in the Si c(4 x 4) surface layer. The crystal structure of surface layer, however, was not the one of cubic SiC (3C-SiC) crystal, because 3C-SiC spots were not observed on RHEED pattern. Therefore, Si1-xCx alloy layer would have been formed on the surface. From the angle-resolved XPS (AR-XPS) measurement, the thickness of the alloy layer was estimated to be 0.3 nm. From the AFM images of the Si surface after SiC nucleation, the Si c(4 x 4) layer is considered to play a role as buffer layer relaxing the lattice mismatch between Si and SiC. (C) 2003 Elsevier Science B.V. All rights reserved.