Preparation And Photoelectric Properties Of Defective TiO₂ Nanomaterials

TiO₂ is an importamt broad band semiconductor which is widely used and the nano-TiO₂ materials which has large specific surface area,stable physical and chemical properties as well as high electron injection rate and conductivity has become a promising candidate for enhancing the photoelectric properties of functional nano-devices.With the development of nano-fabrication technology,it has made obvious improvements in the preparation and application of TiO₂ nanomaterials.As a flexible and low low-cost synthetic method for TiO₂ nanotubes,anodization has many advantages in preparation morphology-controllable TiO₂ nanotubes.By adjusting the experiment parameters,highly ordered one-dimensional TiO₂ nanotube arrays can be acquired,and the crystallization behavior can be controlled by annealing process.All these facts lay the foundation for the application of TiO₂-based photodetectors.In this essay,TiO₂ nanotube arrays were fabricated by anodization and the effect of electrolyte component,anodization voltage and time on anodic TiO₂ was studied and the results showed that,the anodization voltage mainly determined the size and morphology of the TiO₂ nanotubes,and the electrolyte concentration and oxidation time affected the length of the TiO₂ nanotubes.By controlling these parameters,length-controllable TiO2 nanotubes can be acquired.Besides,by recording and analyzing the current-time curve during anodization,the mechanism of anodization reaction was explored.Annealing treatment was employed to study the phase transition regulation of TiO₂and XRD,SEM and TEM technics were employed to analyze the phase transition process.The results showed that the crystal structure of TiO₂ is determined by annealing temperature and when it increases,the TiO₂ nanotubes changes from amorphous to crystalline with its crystal structure transits from anatase to rutile.Besides,the XRD result was consistent with the HRTEM test.ESR test was used to characterize the oxygen vacancies within the TiO₂ and the result confirmed the existence of oxygen vacancies?V₀?in as-prepared anodic TiO2 and by annealing treatments,the concentration of V₀ could be controlled.The concentration of V₀ gradually decreased with the increasing of annealing temperature.Besides annealing,the two-step anodization method could also provide a higher V₀ contained TiO₂ material with the structure of nanotube and nano-rings.TiO₂ nanotube showed significant improvement in light absorption compared with commercial P25.In the ultraviolet region,TiO₂ annealed at 450?showed the highest light absorption with a pure anatase phase,which indicates that the uv-light absorption was determined by the crystal phase of TiO₂.In the visible light region,light absorption decreases with the increasing of annealing temperature and this was caused by the decreasing of oxygen vacancy concentration.Photodetector was fabricated on the basis of the prepared nano-TiO₂ with Ag nanowire employed as the transparent conductive electrode.The tests showed that Ag nanowire strongly enhanced the conductivity of TiO₂ arrays and thus made it possible to fabricate photodetector with lager active area.Under ultraviolet illumination of 365nm wavelength,the ratio of photocurrent to dark current was more than 4 magnitudes.Under 1V bias,the photo responsivity of the detector reached 3.54A/W and the rise time and fall time of the detector were 0.5s and 0.8s respectively.Besides,the device had excellent ultraviolet selectivity and linearity properties.