Abstract
In the present work we report on the formation of bundles of high aspect ratio TiO
2 nanotubes and WO
3 nanopores structures with very thin tube or pore walls using anodization under “high voltage” conditions in perchlorate or chloride containing electrolytes. The bundles of TiO
2 nanotubes consist of separated tubes with diameters in the range of approximately 20–40
nm and the WO
3 nanopores consist of pores with diameters in the range of 30–50
nm. Growth occurs locally at specific surface locations. Both the TiO
2 and the WO
3 structures can be grown up to several dozens of micrometers in length within few minutes. We suggest that the growth of these high aspect structures is initiated by localized anodic breakdown event, triggered by a sufficiently high applied anodic field.