The generation of planar defects in silicon nanowires (SiNWs) synthesized by means of a vapor-liquid-solid (VLS) procedure using Au as a catalyst in an ultra-high vacuum chemical vapor deposition (UHV-CVD) system was investigated. Faceting, the formation of planar defects and the diffusion of Au in SiNWs occurred simultaneously, proportional to the growth temperature and the ratio of the H-2 precursor gas. The planes located on the sidewalls of the wire after Au diffusion were faceted (1 1 1) and (1 00) surfaces, which represent equilibrium configurations of Si due to surface energy minimization during rapid wire growth under unstable conditions. Moreover, {1 1 1} twin defects were formed on the sidewalls of the faceted boundaries where the Au clusters were mainly located, due to the surface tension of the Au atoms, resulting in clusters at the liquid/solid interfaces in SiNWs with a < 1 1 1 > growth direction. (C) 2012 Elsevier Ltd. All rights reserved.