Template-based fabrication of SrTiO3 and BaTiO3 nanotubes.

In response to the growing need for metal oxide nanotubes and nanowires for nanoelectronic applications, polycrystalline titanate nanotubes are synthesized in this work at near-ambient conditions without the application of an external electric field or pre-existing solids. Nanotubes of complicated metal oxides including strontium titanate and barium titanate are fabricated inside anodic aluminum oxide (AAO) templates from aqueous solutions using a simple, inexpensive, reproducible, and environmentally friendly procedure. The deposition solution is prepared by dissolving ammonium hexafluorotitanate and strontium nitrate in a boric acid solution at a pH of 2.5. The typical lengths of SrTiO(3) nanotubes are 5-30 microm, with an average diameter of approximately 250 nm, which is defined by the pore diameter of the AAO template. After annealing at 800 degrees C in air, the resulting nanotubes are polycrystalline cubic SrTiO(3). The Sr:Ti ratio in the nanotube is controlled by the hydrolysis of TiF(6)(2-) ions, and the concentration of Sr(2+) and stoichiometric SrTiO(3) nanotubes can be obtained. As an additional controlling factor, the surface properties of the AAO can be modified by (octadecyl)trichlorosilane. Barium titanate is also prepared in a similar manner with barium nitrate and ammonium hexafluorotitanate as precursors. The polycrystalline cubic BaTiO(3) nanotubes are 12-30 microm long and approximately 250 nm in diameter.