Free-Standing Arrays of Isolated TiO2 Nanotubes through Supercritical Fluid Drying

A common complication in fabricating arrays of TiO2 nanotubes is that they agglomerate into tightly packed bundles during the inevitable solvent evaporation step. This problem is particularly acute for template-fabricated TiO2 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 (CO2) to prepare arrays of template-fabricated TiO2 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.