250 μm long anodic TiO2 nanotubes with hexagonal self-ordering

In this work we show that the growth of more than 250 mu m thick self-organized TiO2 nanotube layers is possible, using an electrochemical approach in organic electrolytes. The tubes can grow as a hexagonal close packed pore array. Crucial parameters that decide on the dimensions are the fluoride ion concentration, the voltage and the anodization time. Self-organized tube formation is restricted to a critical parameter range. Highest aspect ratio tubes can be achieved under a set of very optimized conditions.