We report detailed structural analysis of < 111 > oriented silicon nanowires (NWs) grown by UHV-CVD using the VLS process with a gold catalyst. STEM-HAADF observations have revealed an unexpected inhomogeneous distribution of gold nanoclusters on the NW surface. Gold is mainly distributed on three sides among the six {112}-sidewalls and is anchored on upward {111} facets. This original observation brought us a new comprehension of the faceting mechanisms. The stability of the < 111 > growth direction needs the formation of facets on {112}-sidewalls with energetically favorable planes. We demonstrate that the initial formation of covered facets with a three-fold symmetry is driven by the formation of {111} Au/Si interfaces between the nucleated Si NW and the Au droplet.