Previously, we have developed the electrochemical step edge decoration (ESED) method for preparing metal nanowires based on the idea of step-edge selective electrodeposition of metal. This strategy, while quite versatile, can not be used to prepare nanowires that are composed of insulators, like silica (SiO₂). But the strategy outlined in the figure below, based on chemical vapor deposition or CVD, can be used to prepare insulators:

In this paper, we show that the deposition by chemical vapor deposition (CVD) of silica nanowires can be carried out by exposing a graphite surface first to humid air, and then to a silica precursor, SiCl₄, that can be hydrolyzed to SiO₂. Exposure to humid air (> 30% relative humidity, (RH)) at room temperature caused water to condense selectively at hydrophilic step edges on an otherwise hydrophobic graphite surface. Upon exposure of this surface to SiCl₄ vapor, a reaction with condensed water at step edges caused the formation of SiO₂ according to the reaction: SiCl₄ + 2H₂O -> SiO₂ + 4HCl. The shape and size of the SiO₂ nanostructures varied with the RH: Below 20% RH, nanoparticles of SiO₂, aligned at step edges, were observed. For RH of 35-50%, continuous nano- and microribbons of SiO₂ were obtained. For higher RH, micron-scale silca particles and ribbons were both observed. At a RH of 35%, silica ribbons as small as 80 nm (width) x 20-40 nm (height) up to 500 µm in length could be prepared, as shown in the Figure below.