Unusual catalyst-free epitaxial growth of silicon nanowires by thermal evaporation

We report a catalyst-free epitaxial growth of silicon nanowires on polyhedral facets of mother Si nanoparticles by thermal evaporation process. Single silicon nanowires and octopuslike silicon nanowires (OSNWs) were synthesized under different temperatures. The OSNWs have several directions including ⟨112⟩, ⟨110⟩, and the unusual directions of ⟨100⟩ and ⟨111⟩. A catalyst-free temperature-dependent epitaxial growth model was suggested. Using the Wulff theory and first principle calculations, these growth directions can be explained by the preferential selection of temperature-dependent surface energies. It thus revealed an important but simple growth model in which the growth directions could be delicately controlled through only determining temperature and substrate orientation.