Transformation of Sn nanowires to oxide nanotubes by a localized corrosion process

Amorphous SnO nanotubes were synthesized from Sn nanowires (NWs) electrodeposited into anodic aluminum oxide templates by a localized corrosion process in an aqueous solution composed of chromic, phosphoric, and hydrochloric acids. Initially, phosphoric acid dissolves the template, while chromic acid generates a SnO passivation layer on the NW surface. As a volume expansion occurs during the surface oxidation, some cracks occur at the top surface of the passivation layer. In addition, Cl ions from the hydrochloric acid assist the cracking. Subsequently, Sn atoms in the core of the NW dissolve into the acidic solution while the oxide layer at the shell remains to form nanotubes. Finally, Sn NWs with a length of 10 μm and diameter of 30 nm are completely transformed to amorphous SnO nanotubes with a wall thickness of 10 nm. After heat-treatment, the amorphous nanotubes were crystallized into polycrystalline SnO phase with a rough surface morphology.

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► Localized-corrosion of Sn nanowires.
► Transformation of Sn nanowires to amorphous SnO nanotubes.
► Vertically-aligned SnO nanotubes on substrates.