Vertical arrays of SiO₂ micro/nanotubes templated from si pillars by chemical oxidation for high loading capacity buoyant aquatic devices

A simple and facile method to fabricate SiO₂ micro- or nanotubes has been demonstrated based on room temperature wet chemical oxidation of a porous layer of Si pillar templates that have been prepared by metal-assisted chemical etching (MaCE). Under typical conditions, Si pillars produced by the MaCE have been found to be covered with a thin nanoporous Si layer. The porous Si skin layer has been chemically oxidized by simple dipping in AgNO₃ solution at room temperature, which has led to seamless SiO₂ shell layer thanks to the accompanying volume expansion during the wet oxidation. Following wet removal of core Si by KOH yields the SiO₂ micro- or nanotubes, either in test tube shape or in open shape at both ends, depending on processing method. The vertical arrays of the SiO₂ tube on the Si substrate, after hydrophobic siloxane oligomer printing, has been found to have very large loading capacity on water, due to extremely high porosity (>90%) and good enough mechanical stability. The novel method to fabricate SiO ₂ tubes can shed new light in design of novel aquatic devices, other than simple mimicking the leg of a water strider. Also, the method may be very helpful in various applications of SiO₂ nanotubes.