Facetine has been observed in some Si nanocrystals (Si nc) embedded in SiO2 using high-resolution transmission electron microscopy (HRTEM). Statistical analyses of the interface-energy (Si nc/SiO2) ratios for different facets of the single-crystalline Si nc have been carried out. For these single-crystalline Si nc, the interfacial energy ratios of {100} and {113} relative to f {111} facets, are 1.1 and 0.89, respectively. The influences of planar defects such as twins and stacking faults on the faceting and interfacial energy of Si nc/SiO2 are discussed in terms of their possible contribution to the interfacial energy. (c) 2005 Elsevier B.V. All rights reserved.