Developing of morphology and ordering of TiO2 nanotube arrays by two-step anodic oxidation in organic electrolyte

Highly ordered anodic TiO2 nanotube arrays have attracted great attention due to fast electron transport and high surface - to - volume ratio. In this work, firstly, the effect of different surface characteristics on the structure, tube morphology and ordering of titanium oxide nanoporous films were investigated and then highly ordered anodic TiO2 nanotube arrays were produced by two-step anodic oxidation. Current transients were recorded during the potentiostatic anodization. Morphology of the TiO2 nanotube arrays were studied using field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM). We found that anodic oxidation of titanium after electropolishing produces the most homogeneous TiO2 nanotubes with a high ordering degree across the surface. FESEM images show that TiO2 nanotube formed on electropolishing surfaces exhibits a smooth surface at the top of the grown film. By contrast, TiO2 nanotube formed on mechanical polishing surfaces exhibits a rough top surface and different tube sizes. As a results, The requisites for the fabrication of extremely regular arrays of valve metal oxide nanotubes are the electropolishing of the valve metal and a two-step anodization process.