Fabrication of Vertically Oriented TiO₂ Nanotube Arrays Using Dimethyl Sulfoxide Electrolytes

We detail anodic oxidation variables affecting the fabrication of vertically oriented TiO 2 nanotube arrays using an electrolyte of dimethyl sulfoxide (DMSO) containing either hydrofluoric acid (HF), potassium fluoride (KF), or ammonium fluoride (NH 4 F). Various anodization variables including F - ion concentration, voltage, anodization time, water content, and previous use of the electrolyte can be combined to achieve nanotube arrays with length and morphology relevant to required applications. Using an anodization potential of 60 V with an electrolyte of 2% HF in DMSO, 70 h duration, nanotubes are achieved having a length of 101 μm, inner diameter 150 nm, and wall thickness 15 nm for a calculated geometric area of 3475. The weak adhesion of the DMSO fabricated nanotubes to the underlying oxide barrier layer and low tube-to-tube adhesion facilitates their separation for applications where dispersed nanotubes are desired. We examine the photoelectrochemical properties of 45 μm long nanotube arrays, crystallized by annealing at 580 °C for 6 h in oxygen gas, tested under UV (320−400 nm) and solar simulated light (AM 1.5) illumination.