Magnetic field-assisted electroless anodization: TiO2 nanotube growth on discontinuous, patterned Ti films

Abstract

We present a magnetic field-assisted oxidation and etching process that transforms Ti thin films on arbitrary substrates into self-organized TiO₂ nanotube arrays without the direct application of an anodization voltage between the cathode and the Ti film/substrate. In effect, the Ti film/substrate electrode is at a floating potential determined by the ionic Hall voltage. The development of such a magnetic field-assisted electroless anodization process, frees the anodization technique of forming nanostructured semiconductors and metal oxides from the constraints of substrate conductivity and film continuity imposed by the traditional anodization process, and allows the creation of uniform anodic nanostructures on pre-existing high-aspect ratio patterns as well as on substrates containing both conductive and non-conductive areas. Using magnetic field assisted electroless anodization, we demonstrate the formation of microscale patterns of high quality TiO₂ nanotubes from discontinuous Ti films deposited on thermal oxide-coated Si substrates and patterned by a lift-off process.