Preparation And Impedance Analysis Of The Titanium-Dioxide-Nanotube Arrays

TiO₂(Titanium Dioxide) is an important inorganic functional material,which has already attracted extensive interest in many fields.Among its various microscopic forms as nano crystals,eg.nano-particles,nanotubes and continuous thin films,The TiO₂ nanotubes are especially interesting due to the larger specific surface area compared to the others,which leads to the high adsorbing capability and may potentially enhance their performances as sensors,catalyst carriers or solar cells etc. Even more exciting is the possibility of synthesizing novel nano-compounds by filling the TiO₂ nanotubes with inorganic,organic,metallic or magnetic nano particles, which may dramatically improve the performance of these materials.This thesis focuses on the fabrication,the humidity-sensitive characteristicand equivalent-circuit study of the TiO₂ nanotube arrays.In this work an anodic-oxidafion method was adopted and pure Titanium foils were used as raw materials.By varying the parameters of anodic oxidation in the HF-based electrolyte and studying the obtained nanotubes,it's revealed that the oxidation voltage is the main factor that affects the formation of TiO₂ nanotubes, while with increasing oxidation time the morphology of TiO₂ nanotubes undergoes a transition from the disordered continuum to the ordered arrays of separated nanotubes. The electrolyte concentration can be used to control the thickness of the tube walls. The optimal conditions thus found are:30 minutes of oxidation using a voltage of 20 volts in 0.5wt%aqueous solution of HF.The nanotubes obtained are well ordered and have apertures of about 50-100 nms in diameter,and the tube-wall thickness is around 20-30 nms. TiOzApart from the anodization of Titanium foils,also studied in this work was the growth of titanium thin films using Magnetron Sputtering equipment.The obtained Ti thin films were then oxidized using the aforementioned technique to form the TiO₂ nanotubes.Various growth parameters,including the sputtering power,the Argon pressure,the substrate temperature and the deposition time were studied to investigate their influences on the quality of the Titanium films.Among these,the sputtering power was identified as the most important parameter for growing continuous and compact Titanium layer of enough thickness.The Argon pressure during the sputtering process affects the deposition rate,while the substrate temperature can be used to control the layer quality.The layer thickness is essentially proportional to the sputtering time.With a Set of optimal paremeters used in the experiments,ie.the sputtering power as 200W,the sputtering pressure as 0.SPa,and the substrate temperature as 250℃,2 hours of sputtering yield a Titanium film with the thickness of approximately 1.2μm.Successful anodic oxidation was carried out on these samples to fabricate the TiO₂ nanotubes.Finally,the electronic property and the humidity sensing characteristics of the TiO₂ nanotubes was studied using the Complex Impedance Spectroscopy(CIS) measurements under different humidity conditions.The results revealed an equivalent circuit of two RC circuits in series.The physical meaning of the EC components was discussed in this thesis.The thin film has the good sensitivity to the humidity.