The influence of hydroxide on the initial stages of anodic growth of TiO₂nanotubular arrays

Abstract

Understanding the mechanism for growing TiO(2) nanotubes is important for controlling the nanostructures. The hydroxide nano-islands on the Ti surface play a significant role at the initial stage of anodization by forming the very first nano-pores at the interface between hydroxide islands and substrate and eliminating the H(2)O electrolysis. A quantitative time dependent SEM study has revealed a nanotube growth process with an initial linear increase of pore diameter, film thickness and number of pores. During the anodization of titanium, different current transient curves are observed for Ti samples with or without hydroxide on the surface. The transient current profile has been quantitatively analyzed by fitting several distinctive stages based on a growth mechanism supported by SEM observations. It is found that a saturated cubic dependent equation is appropriate to fit a short current upturn due to the increase of the surface area.

Anodic formation of nanoporous and nanotubular metal oxides

“…Hydroxide has also been confirmed to coexist with oxide by XPS measurements in the outer part of the compact layer formed at the early stage anodization of Ti just before the subsequent pore initiation process for the anodization of Ti without acid pre-treatment. 39 From the SEM images, the compact oxide film has a rather rough surface with nano-islands similar to the hydroxide nano-islands created by acid pre-treatment as reported by Al-Abdullah et al 38 Therefore it is probable that the hydroxide also has an inhomogeneous distribution across the compact oxide surface.…”

“…In experiment, the inhomogeneous distribution of hydroxide in ATO at the early stage anodization of Ti has already been reported previously. A recent work by Al-Abdullah et al 38 on the influence of hydroxide on the initial stages of anodic TiO 2 nanotube growth showed, based on X-ray photoelectron spectroscopy (XPS) and SEM results, that hydroxide nano-islands could form on the Ti surface by dipping the polished Ti plate in an acidic solution prior to anodization. Etching pits were then found to form at the vicinity of the preformed hydroxide nanoislands during the subsequent anodization, suggesting that hydroxide particles can enhance the formation of pits to initiate the pore formation.…”

Non-chapped, vertically well aligned titanium dioxide nanotubes fabricated by electrochemical etching

“…The presence of fluorides in the electrolyte causes the chemical dissolution of the titanium oxide to form the water-soluble [TiF 6 ] −2 complex. On the other hand, the complex also occurs with the Ti 4+ ions that are ejected at the interface of oxide-electrolyte by the following overall reactions [20][21][22][23][24][25][26].…”

Formation, morphology control and applications of anodic TiO2 nanotube arrays

“…2B). In a very recent work by Chen and co-workers, 70 it was proposed that some hydroxide nano-islands on the Ti surface could play an important role at the initial stage of anodization by forming the very first nano-pores at the interface between hydroxide islands and the substrate. In general, any defects in the oxide layer or at the oxide/Ti interface would initiate the pore formation.…”