Direct synthesis of amorphous silicon dioxide nanowires and helical self-assembled nanostructures derived therefrom

Bulk quantities of amorphous silica nanowires and novel braided helical silica nanostructures have been synthesized by a simple and cheap route. Actually, direct thermal treatment of a commercial silicon powder in the presence of graphite yields pure amorphous silica nanowires with lengths up to 500 mum for diameters in the range 10-300 nm. Electron Energy-Loss Spectroscopy (EELS) analysis indicates that the nanowires consist of Si and O elements in atomic ratio 1 : 2, corresponding to SiO2. The formation of silicon dioxide nanowires can be related to the in-situ formation and subsequent decomposition of silicon oxide SiO (g). The nanowires are gathered to form bundles and braid-like nanostructures have been observed in some cases. The formation of these helical nanoobjects results from the self-assemblage of silica nanowires, may be due to the gas flowing during the process.