Lithography-free synthesis of freestanding gold nanoparticle arrays encapsulated within dielectric nanowires

A lithography-free method for producing freestanding one-dimensional gold nanoparticle arrays encapsulated within silicon dioxide nanowires is reported. Silicon nanowires grown by the vapor-liquid-solid technique with diameters ranging from 20 nm to 50 nm were used as the synthesis template. The gold nanoparticle arrays were obtained by coating the surface of the silicon nanowires with a 10 nm gold film, followed by thermal oxidation in an oxygen ambient. It was found that the thermal oxidation rate of the silicon nanowires was significantly enhanced by the presence of the gold thin film, which fully converted the silicon into silicon dioxide. The gold-enhanced oxidation process forced the gold into the core of the wire, forming a solid gold nanowire core surrounded by a silicon dioxide shell. Subsequent thermal treatment resulted in the fragmentation of the gold nanowire into a uniformly spaced array of gold nanoparticles encapsulated by a silicon dioxide shell, which was observed by in situ annealing in transmission electron microscopy. Analysis of many different silicon nanowire diameters shows that the diameter and spacing of the gold nanopaticles follows the Rayleigh instability, which confirms this is the mechanism responsible for formation of the nanoparticle array.