Dynamics of photo-induced charge carriers in anodized titania nanotube array

Abstract

Theoretical development of anodized TiO2 nanotube array was made by using high field conduction theory. The theory reveals that the high electric field (>106 V cm−1) due to low resistance offered by titanium electrode in the beginning of anodization results the rapid formation of compact TiO2 layer defined by pilling-bedworth ratio (PBR). The increasing thickness in the oxidized layer proportionally develops the stress in the oxide layer which results micro-cracks in the TiO2 layer to minimize the energy strain by increasing the surface area. These cracks steer the formation of TiO2 nanotube array throughout the anodization process. The presence of fluoride ions in the as prepared electrolyte etches at these preferred sites (micro-cracks) and leads the formation of bowl like ordered foot prints. The etching in the oxide layer undergoes continuously until an equilibrium is reached between electrochemically assisted oxidation and chemically assisted dissolution process. Furthermore, on account of frequent use of TiO2 nanotube array in light harnessing applications, the theoretical dynamics of photo-induced charge carriers were also studied using carrier continuity equation under quasi state condition.