Tunable growth of TiO(2) nanostructures on Ti substrates.

A simple and facile method is described to directly synthesize TiO(2) nanostructures on titanium substrates by oxidizing Ti foil using small organic molecules as the oxygen source. The effect of reaction temperature and oxygen source on the formation of the TiO(2) nanostructures has been studied using scanning electron microscopy, x-ray diffraction, transmission electron microscopy, Raman spectroscopy and water contact angle measurement. Polycrystalline grains are formed when pure oxygen and formic acid are used as the oxygen source; elongated micro-crystals are produced when water vapour is used as the oxygen source; oriented and aligned TiO(2) nanorod arrays are synthesized when ethanol, acetaldehyde or acetone are used as the oxygen source. The growth mechanism of the TiO(2) nanostructures is discussed. The diffusion of Ti atoms to the oxide/gas interface via the network of the grain boundaries of the thin oxide layer is the determining factor for the formation of well-aligned TiO(2) nanorod arrays. The wetting properties of the TiO(2) nanostructured surfaces formed are dictated by their structure, varying from a hydrophilic surface to a strongly hydrophobic surface as the surface structure changes from polycrystalline grains to well-aligned nanorod arrays. This tunable growth of TiO(2) nanostructures is desirable for promising applications of TiO(2) nanostructures in the development of optical devices, sensors, photo-catalysts and self-cleaning coatings.