Room Temperature Growth of Silica Nanowires on Top of Ultrathin Si Nanowires Synthesized with Sn-Cu Bimetallic Seeds

Si nanowires (NWs) are grown by the vapor–liquid–solid method using Cu–Sn bimetallic catalysts in a plasma-enhanced chemical vapor deposition (PECVD) reactor. The microstructure of the NWs is analyzed by transmission electron microscopy and energy-dispersive X-ray spectroscopy. An amorphous SiO₂ region, much larger than the native oxide, is present on top of each crystalline SiNW: in SiNWs with diameter below 10 nm, it takes the form of a silica NW of up to 50 nm in length. The new NW separates the initial catalyst particle into one that stays in contact with the SiNW and one or more that lies at the top of the new NW. The former is made of Cu and Cu₃Si and contains no Sn, whereas the latter keeps amounts of both elements. The observed microstructure appears to be the result of a mechanism of Si oxidation catalyzed by Cu₃Si. The deposit after SiNW growth, in the PECVD reactor, of a protecting 2 nm thick layer of hydrogenated amorphous Si, completely suppresses this mechanism. Reference for future applications based on Cu–Sn-catalyzed quantum-sized SiNWs is provided.