Study On The Optical And Dielectric Properties Of Ordered Porous TiO₂-AAO Films

As an environmentally-friendly material,TiO₂ is an odorless,non-toxic,stable material and which can be obtained easily.The excellent optical and electrical properties of which make it widely used in medicine and chemical industry,environmental governance and optoelectronics device manufacturing and other fields.However,with the continuous research on TiO₂,some disadvantageous physical properties,such as high intrinsic resistivity,low mobility,and wide band gap,have limited its further development in the above fields.Based on the literature surveying,this thesis takes a different approach,for example,we had synthesized the ordered porous composite films,and followed by high temperature treatment or plasma treatment.It proved that these methods can specifically regulate the photoelectric properties of TiO₂,improve the performance of TiO₂,and break the current application of TiO₂ bottleneck.Based on the above discussion,we have carried out the following works.Firstly,ordered porous alumina?AAO?thin film was prepared by the secondary oxidation method and used as the base material.Then,TiO₂ was sputter-deposited on the AAO template by DC reactive magnetron sputtering technology and ordered porous TiO₂-AAO composite film was successfully prepared.Next,scanning probe microscope?SPM?,S-4800 cold-field emission scanning electron microscope?SEM?,X-ray diffractometer?XRD?,energy spectrometer?EDS?,ultraviolet spectrophotometer?UV-vis?,photoluminescence spectrometer?PL?,semiconductor characteristic analysis system?4200-SCS?,etc.were used to characterize the structure,phase,optical and electrical of the samples.The specific work is as follows:?1?Ordered porous AAO templates with different pore diameters were prepared by the secondary oxidation method in a low-temperature environment at 6 ? and 0.3mol/L oxalic acid electrolyte by adjusting the oxidation voltage.Then,TiO₂ films of different thicknesses were successfully sputtered on the AAO template by using DC magnetron sputtering method.In the process,appropriate sputtering power and controlling the sputtering time were selected.And following,the TiO₂-AAO composite films were respectively subjected to high temperature treatment or plasma treatment under different atmospheres.?2?The sample morphology,crystal structure,and elemental composition were studied by scanning probe microscope?SPM?,S-4800 cold-field emission scanning electron microscope?SEM?,X-ray diffractometer?XRD?,and energy spectrometer?EDS?.From the results of SPM and SEM,we can find that the sample has obvious ordered porous structure.XRD test can be found that,under different preparation conditions,amorphous and anatase polycrystalline TiO₂ samples can be obtained.?3?The optical characteristics of the samples were characterized by using ultraviolet spectrophotometer?UV-vis?and photoluminescence spectrometer?PL?.The results showed that the optical properties of the TiO₂-AAO composite film are not only related to the pore diameter of the sample,but also significantly affected by the plasma treatment in a nitrogen atmosphere.However,we found that the film thickness is not significantly affected to them.The results show that the nitrogen plasma treatment can effectively reduce the optical band gap of the material.And we believe that nitrogen plasma treatment can generate many new oxygen vacancies in the above thin film materials;at the same time,nitrogen may also form new energy levels near the minimum value of the conduction band.The new band gap state may lead to red shift of the absorption band edge and quenching of intrinsic photoluminescence.?4?Au/TiO₂/Al₂O₃/ Al capacitors were prepared by using the polycrystalline TiO₂ samples.The semiconductor performance was used to perform I-V tests on the samples.The ferroelectric voltage analyzer?TF Analyzer 2000E?was used to test the hysteresis loops.The dielectric properties of the sample were analyzed by precision impedance analyzer?Agilent 4294A?.The results show that TiO₂-AAO composite films have higher resistivity,higher energy storage density,and lower dielectric loss.