Intrinsic properties of high-aspect ratio single- and double-wall anodic TiO2 nanotube layers annealed at different temperatures

Abstract

In this work, we present the influence of thermal annealing on morphological, structural, electrical, optical, and photoelectrochemical properties of double- (DW) and single-wall (SW) TiO2 nanotube (TNT) layers. High-aspect ratio TNT layers with a thickness of ~5 µm and ~20 µm with an average inner diameter of ~250 nm and ~130 nm, respectively, were prepared via electrochemical anodization of Ti foil in two different fluoride containing ethylene glycol-based electrolytes. The inner wall of the native DW TNT layers was quantitatively removed via a mild pre-annealing followed by a selective etching treatment in piranha solution, yielding SW TNT layers. The obtained SW TNT layers annealed at 300 – 500 °C possess enhanced conductivity by 1 – 2 orders compared to their DW counterparts. The photoelectrochemical properties of SW TNT layers are enhanced compared to their DW counterparts in the annealing temperature range 300 – 800 °C. In principle, the SW TNT layers could be potentially favored to the DW TNT layers in electrical and photoelectrochemical applications due to their more superior intrinsic properties.