Metal oxide nanowire growth via intermediate hydroxide formation: A thermochemical assessment

In this study we apply reaction thermodynamics to show that a significant volatile hydroxide vapor partial pressure forms at a metal-oxide interface and is a likely precursor source for nanowire growth. The growth of WO₃ and CuO nanowires are used as examples for reactions dependent on only H ₂O and O₂+H₂O, respectively. Optimal temperatures, H₂O (and O₂) partial pressures for volatile hydroxide formation are calculated and experimentally investigated. We conclude that metal oxide nanowires can be readily grown at relatively low temperatures (close to or less than 500°C) over short anneal times (tens of minutes). The growth of these metal oxide nanowires, with many oxidation states, by this simple thermal technique is readily suited for a range of emergent large surface area nanostructured optical and electrical applications, including sensing, photocatalysis and ultracapacitors.