Active-oxidation of Si as the source of vapor-phase reactants in the growth of SiO_x nanowires on Si

Gold-coated silicon wafers were annealed at temperatures in the range from 800-1100 °C in a N₂ ambient containing a low (3-10 ppm) residual O₂ concentration. A dense network of amorphous silica nanowires was only observed on samples annealed at temperatures above 1000 °C and was correlated with the development of faceted etch-pits in the Si surface. Comparison with known thermodynamic data for the oxidation of Si and vapor-pressures of reactants shows that nanowire growth is mediated by a vapor-liquid-solid mechanism in which the dominant vapor-phase source of reactants is SiO produced by the active oxidation of Si.