Fabrication of Titania Nanotubes on Glass and Transparent Conducting Oxide Substrates by Anodization of Titanium Films. ANDREW LEENHEER (Colorado School of Mines Golden, CO 80401) DAVID GINLEY (National Renewable Energy Laboratory, Golden, CO, 89401)

Arrays of titania (TiO₂) nanotubes could potentially provide a good electron-conducting contact for organic thin-film solar cells. In this work, we fabricated titania nanotubes by anodizing thin films of titanium on both glass and transparent conducting oxide (TCO) substrates. Titanium thin films (500-700 nm) were deposited by radio-frequency (RF) sputtering. Films were anodized in acidic electrolytes containing small amounts of hydrofluoric acid at constant voltage ranging from 7 to 15 volts. After anodization, scanning-electron microscope (SEM) analysis revealed a nanotube structure. Titania nanotube structures were successfully grown on glass in an electrolyte containing sulfuric acid, trisodium citrate, and potassium fluoride, with nanotube diameters around 50 nm. By monitoring the anodization current over time, the stages of nanotube formation were elucidated. Additionally, nanotubes were formed on a TCO substrate by anodizing in an electrolyte containing acetic acid and hydrofluoric acid. The dimensions and shape of the nanotubes appear to be controlled by the voltage, electrolyte pH, and anodization time. While not completely transparent, the arrays fabricated are promising for use in organic solar cells.