| Description |
TiO2 is an extensively studied material due to its nontoxic, environmental friendly, corrosion-resistant nature and wide band gap (~3 eV). TiO2 nanotubes (T-NTs) synthesized via electrochemical anodization have been studied extensively, with particular focus on their electrical and optical properties. The advantage of T-NT is the large surface area to volume ratio. T-NT has been used to demonstrate many applications such as sensors and energy harvesting. These applications have traditionally been demonstrated via T-NT synthesized on Ti foil. However, there is currently no commercially available T-NT- based device, which may be due to a lack of fabrication techniques, to make such devices on a large scale. One of the requirements for fabricating compact T-NT- based devices is the need for a stable and planar substrate. The titanium foils commonly used for T-NT synthesis are mechanically flexible, making them more prone to bending, limiting the integration of T-NT with microfabrication techniques. Here, we present the synthesis of T-NT on Si wafer at room temperature from direct current (D.C.) sputtered as well as e-beam evaporated thin Ti film. Hundred nm SiO2 was used to electrically isolate the T-NT from the substrate. We demonstrate integration of the synthesis of T-NT with photolithography, which is one of the most important requirements for scaling up a T-NT-based device. The T-NT was stable up to 500oC, which is required for improved charge transport. The T-NT was 1.4 times longer than the thickness of the Ti film, showing selective electric field-assisted etching of Ti by the electrolyte. We also report site-specific and patterned growth of the T-NT. The effect of properties of thin films such as grain size, residual stress and density on the morphology of T-NT was studied to improve the stability and quality of the T-NT. We demonstrate the synthesis of TiO2-WO3 composite nanotubes for photoelectrochemical cells with up to a 40% increase in photocurrent in comparison to plain T-NT. The T-NT was extensively studied and characterized using SEM, AFM, UV-Vis spectroscopy, XRD, and XPS. |
