Effect of Sputtering Parameters on the Morphology of TiO2 Nanotubes Synthesized From Thin Ti Film on Si Substrate

In this paper, we present the analysis of the properties of direct current (dc) magnetron sputtered Ti thin film that affect the morphology of TiO₂ nanotubes synthesized by electrochemical anodization. Si wafer with thermally grown silicon dioxide was used as the substrate for deposition of Ti films. By varying the properties of the sputtered film, morphology of the anodized film can be varied from tubular to nanoporous TiO₂. Three sputtering parameters that affect the properties of the film were studied, which include sputtering power, process gas (argon) pressure, and substrate temperature. Anodization of these films was carried out at 30 V (dc) using an ethylene glycol-based electrolyte. We show that the properties of thin film such as grain size and residual stress (bi-axial) do not affect the morphology of the anodized film and density alone influences the morphology of the anodized film. Most of the applications demonstrated by TiO₂ nanotubes require annealing at high temperatures (350-800 °C) for calcination. Low residual stress in the thin film is required to prevent delaminating of the nanotubes from the substrate when exposed to high temperatures. We demonstrate that by varying the sputtering parameters, Ti films with low stress can be deposited which is required to have stable TiO₂ nanotubes or nanoporous structure, based on the requirement of the application.