Controlled lateral growth of silica nanowires and coaxial nanowire heterostructures

Silica nanowires, grown on gold-coated silicon substrates by the active oxidation of silicon, are shown to undergo an initial stage of rapid longitudinal growth, followed by a stage of sustained lateral growth. During lateral growth, the average nanowire diameter increases linearly with annealing time and proceeds uniformly along the nanowire length at a rate of order 2 nm/min, thereby providing a simple and effective means of control. These observations are discussed with regard to predictions of a simple growth model based on the kinetic theory of ideal gases and are shown to provide a useful process for fabricating more complex silica-based coaxial core-shell heterostructures.