Electrochemical investigation on the inhibitive nature of barrier layer on the growth rate of TiO<inf>2</inf> nanotube arrays

Electrochemical anodization is a cost effective and easy to scale-up method for the fabrication of TiO2 nanotube arrays. In this article we have elucidated the role of barrier layer on nanotube growth by analyzing nanotube arrays fabricated at different anodization times (1 minute - 24 hours). During the growth process, at the initial stage, a very fast growth (∼1.5 μmmin-1) is observed, which slows down as time progresses. The growth efficiency has been calculated by using the charge consumed for each specimen anodized for different time duration. The impact of barrier layer on the growth of the nanotube arrays has been studied using Electrochemical Impedance Spectroscopy (EIS) and Mott-Schottky (M-S) analysis. The thickness of the barrier layers was calculated from the barrier layer capacitance values. The minimum barrier layer resistance of 375 Ω paves the way for the very high growth rate obtained. The decrease in the carrier densities or defects (from 42 × 1019 to 1.86 × 1019 cm-3) with increase in the anodization duration limits the ion transfer rate. Thinner barrier layers (∼30 nm) with higher carrier density and lower resistance ensures rapid growth rate of nanotube arrays during anodization.