Self-organized Anodic TiO2 Nanotube Layers: Influence of the Ti substrate on Nanotube Growth and Dimensions

In this contribution, various Ti thin substrates were explored and compared for the anodic growth of self-organized TiO2 nanotube layers for the first time. In order to evaluate differences in the electrochemical anodization characteristics and the tube dimensions, five different Ti substrates from four established suppliers were anodized in the widely used ethylene glycol electrolytes containing 88 mM NH4F and 1,5 vol.% water. Two anodizations were carried out to elucidate an influence of the pre-anodized substrates used for the second anodization. By thorough evaluation of the nanotube dimensions, large variations between the dimensions of the nanotubes were found for the different substrates, ranging from ∼32 μm to ∼50 μm for the nanotube length and from ∼109 nm to ∼127 nm for the nanotube diameter after the second anodization. Upon AFM measurements, Goodfellow Ti substrates (99.99% purity), yielded the smoothest surface and the highest degree of ordering from all substrates. Moreover, considerably different consumption of Ti substrates via anodization was revealed by profilometric measurements between the original non-anodized part of the Ti substrates, and the anodized part after the removal of the nanotube layer. Orientation imaging microscopy revealed considerable differences in the size and orientation of the substrate grains.