Manipulating morphology, pore geometry and ordering degree of TiO2 nanotube arrays by anodic oxidation

In this paper, the effect of controlling parameters of the anodic oxidation process including surface preparation, anodizing temperature and repeating of anodization on the surface morphology and nanotube geometry, i.e. pore wall thickness, pore diameter and tube length of titanium oxide was investigated. Following previous studies which reported the 'electropolishing process and two-step anodic oxidation for fabrication of highly ordered TiO2 nanotube arrays', we here demonstrate the critical effect of first step anodizing time on the pore/tube ordering defined. A linear growth rate of the ordered pores called domain is observed. Anodizing temperature also plays an extremely important role in the tube geometry as a lower temperature gives rise to smaller pore diameters with blocked pore openings. The mechanism of formation of an irregular porous layer that blocks the pore openings at low temperatures is understood by a limited ionic mass transport assumption. This report brings to attention the desirable properties of the structurally oriented TiO2 for dye-sensitized solar cell applications.