Preparation And Properties Of TiO₂/ITO Compound Material By Chemical Vapor Deposition

As a member of the TiO₂ semiconductor composite system, TiO₂/ITO possesses excellent chemical stability, photosensitization, non-toxic and pollution free like nano TiO₂, meanwhile, it has many physical properties of ITO glass, such as high conductivity and infrared light reflectivity. At present, it has been widely used in photosensitive solar energy fuel cell. Different methods are employed by researchers to prepare compound materials and investigate the performance of them, aiming at optimizing the property and expanding the applied range.In the study, APCVD was used to investigate the preparation and property of the TiO₂/ITO composite material. The growth mechanism was discussed, and the influence of deposition temperature, deposition time, Si/Ti molar ratio and O₂ flux on its nucleation growth and photoelectric property was investigated. Furthermore, the performance advantages of the composite material were explored by comparing with TiO₂ nano materials prepared on common glass substrates. It showed that:?1? High-density rutile TiO₂ nanowires were successfully induced by deposited TiSi2 thin film on ITO conductive glass. The nanowires were tightly attached on the ITO thin film, forming the TiO₂/ITO composite materials. The large number of nanowires growed along [001] with the diameter of 10-50 nm and the length of 1-2?m, and the draw ratio was beyond 25. The nanowires growed with high density and balanced distribution, exhibiting as a sea urchin. The kind of morphology showed larger specific surface area than single nanowire.?2? As we all know, it was crucial to the growth of nanowires that appropriate deposition temperature, deposition time, Si/Ti molar ratio and O₂ flux were chosen in the study. Obviously, the rise of the deposition temperature was benefit for the maturation of nanowires. And increasing number of nanowires, which were with diameter of 30 nm and length of 1.5?m, growed from the TiSi2 particles at 780 oC, arranging to be clusters and showing as sea urchin. The nanowires showed the best growing situation at the moment, reaching the best combination compactness, while higher temperature like 800 oC would be bad for the further growth of the nanowires, under the situation, the nucleation rate and phase content of TiO₂ reduced and the nanowires became thin and curl, then nanowire clusters were sparse; As the deposition time increased, the growth efficiency of TiO₂ crystalline phase rised and reached best performance when deposited for 240 min. However, insufficient raw material would be against for TiO₂ nucleation and composite molding with longer deposition time; As Si/Ti molar ratio increased from 1 to 5, the main composition of inducing layer on ITO became TiSi2 from Ti5Si3. And TiSi2 showed stronger inducing capacity than Ti5Si3, it was shown in study that best structure and morphology of TiO₂ nanowires were reached when the molar ratio was controlled at 4; With the O₂ flux increasing, more and more O₂ in the system was helpful for the accumulation and molding of TiO₂ nanowires. But 14 sccm was the best flow for growth, exorbitant flux will break the containing impact among each growth direction of TiO₂ nanowires, deviating the best crystal morphology. The nanowires grown at this moment became tubby and curve, scattering sporadically and arranging disorderly on the surface of sample. At the same time, the combination between nanowires and ITO was affected, which had disadvantage to the composition.?3? Under ultraviolet radiation, the photocatalytic performance of TiO₂/ITO for methylene blue degradation was investigated. In order to show the best photocatalytic performance, it was essential to have the factors such as large phase content of TiO₂ phase, high crystalline, lush growth condition, tight arrangement of nanowires cluster as sea urchin and tight combination between nanowires and ITO. In our study, the best degradation by TiO₂/ITO reached 65% under ultraviolet radiation; On the other hand, the optics contact angle of water drop was employed as measurement to judge the hydrophilic performance of composite. The prepared samples, which had outstanding phase growth, good linetype growth and high flatness of composite film, exhibited the best hydrophilia. After ultraviolet radiation, the water drop almost layed on the surface of the sample, and the contact angle was near 0o; the square resistance was employed as measure to judge the electrical properties of the composite. The square resistance value was closely related to the combination tightness, the phase content, the crystalline and the surface topography. It was shown in our study that the square resistance of TiO₂/ITO was generally small, presenting good conductivity. The local minimum resistance value was low to 5.32×10-3?/sq.?4? Compared with single TiO₂ nanowires prepared with same experiment condition, TiO₂/ITO showed material advantage obviously. Due to the recovery of ITO to the flaw of nano TiO₂, the nanowires grown in the composite material showed higher crystalline, larger density, bigger specific surface area; When the methylene blue solution was degraded by TiO₂/ITO, the instant degradation rate and degradation degree was greater than that was degraded by single TiO₂ nanowires, owing to the limit of ITO for the recombination of photo-induced carrier. Meanwhile, the excellent crystal growth and surface performance did combined action with recovery of ITO, resulting in ductility enlargement of water drop on the surface of material and showing greater hydrophilia; Moreover, there was no doubt that the join of ITO enhanced the conductivity of the composite. The square resistance value of composite material was smaller about three orders of magnitudes than that of single TiO₂ nanowires, the advantages on electrical performance presented explicitly.