Free-standing arrays of isolated TiO2 nanotubes through supercritical fluid drying.

A common complication in fabricating arrays of TiO(2) nanotubes is that they agglomerate into tightly packed bundles during the inevitable solvent evaporation step. This problem is particularly acute for template-fabricated TiO(2) nanotubes, as the geometric tunability of this technique enables relatively large inter-pore spacings or, from another perspective, more space for lateral displacement. Our work showed that agglomeration results from the surface tension forces that are present as the ambient solvent is evaporated from the nanotube film. Herein, we report a processing and fabrication approach that utilizes supercritical fluid drying (CO(2)) to prepare arrays of template-fabricated TiO(2) nanotubes that are free-standing and spatially isolated. This approach could be beneficial to many emerging technologies, such as solid-state dye-sensitized solar cells and vertically-oriented carbon nanotube electrodes.

Fabrication of highly-ordered TiO(2) nanotube arrays and their use in dye-sensitized solar cells.

Highly ordered TiO(2) nanotubes were successfully fabricated using a nanoporous alumina templating method. A modified sol-gel route was used to infiltrate the alumina pores with Ti(OC(3)H(7))(4) which was subsequently converted into TiO(2) nanotubes. The average external diameter, tube lengths, and wall thickness achieved were 295 nm, 6-15 microm, and 21-42 nm, respectively. Diffraction data reveals that the nanotubes consist solely of the anatase phase. Dye-sensitized solar cells using TiO(2) nanotube arrays as the working electrode yielded power conversion efficiencies as high as 3.5% with a maximum incident photon-to-current conversion efficiency of 20% at 520 nm.