The Microstructure And Properties Of CeO₂/TiO₂ Films Prepared By Magnetron Sputtering Technique

TiO₂ nano-sized powders with the purity of 99.9% and CeO₂ powders with the purity of 99.99% are adopted as raw materials. The CeO₂/TiO₂ and TiO₂ sputtering target is successfully prepared. The CeO₂/TiO₂ film is successfully deposited on hard substrate (ordinary glass) and flexible substrate (polyethylene terephthalate, PET; polyimide, PI) by radio frequency magnetron sputtering (RF-MS). With the help of modem analyzers, for examples, XRD, EDS, SEM and AFM, the chemical composition, phase constitution and morphology of TiO₂ and CeO₂/TiO₂ films are analyzed. UV-VIS transmittion of the films were investigated with UV-VIS spectral photometer. The transmission mechanisms of films are also discussed.The experiment results show that the thicknesses of CeO₂/TiO₂ films are uniform. The thickness increases with prolonging sputtering time and adding sputtering power. However, the enhancement of sputtering pressure reduces the thickness of films, With the increase of the target-substrate distance, the thickness firstly adds and then decrease.XRD analysis show that as-deposited films on glasses are crystal, and as-deposited films deposited on PET and PI are all amorphous, and after annealing under 150℃×12h, the films become crystal. Meantime, there is only the anatase diffractive crest in the XRD figure and have no other diffractive crestes. The anatase diffractive crest is the preferential orientation of (101).The results of SEM and AFM reveal that thin films are tightness, regular and no crack. The sputtering process parameter have great effect on the morphology of films. There are not crystal grains in the SEM figure of as-deposited films, but a good many grains arises in the AFM morphology of CeO₂/TiO₂ films, the quantity of grains on the surface of the films appear after annealing under 150℃for a long time. The shape of grains is sphere. When the annealing time is 12h, the sizes of grains are almostuniform and about 120nm.The results of interface bonding strength tested by scarification method show that CeO₂/TiO₂ films sputtered on glass substrate and PET substrate both have good adhesion properties. Furthermore, there are no formation of cracking and pull-out phenomenon appeared after folding the films deposited on PET substrate for several times. Transparent mucilage glue stick time after time, and the films still intact. Meantime, the attaching force increase with the enhancing of sputtering power. The bonding strength is (61.95±1.23)N at 100W.TiO₂ absorbs ultraviolet light strongly(absorption edge is at 380nm)but visible light weakly. TiO)2 must be excited by high-energy ultraviolet. Transfering the absorbing edge from ultraviolet light to visible light has actual significance for the use on photo-electronic transformation, solar energy using and photocatalytic, and so on. In this paper, the transmittion spectrums show that the transmittion rate of CeO₂/TiO₂ films lowers that of TiO₂. Because Ce-O in CeO₂/TiO₂ films is favor of absorbing energy. The absorbing edge and cut off edge of composite films are more than those of TiO₂ films. Moreover, they both add with the increase of CeO₂ content. Thickness and roughness have effect on transmittion rate.CeO₂/TiO₂ complex films belong to the indirect optical gaps. calculating and analysising for the indirect optical gaps indicate Eg(CeO2/TiO₂)2). Under the optimal sputtering processing parameters, the bandgap of CeO₂/TiO₂ films is about 2.62±0.02eV and absorption edges wavelengths and cutoff wavelengths of CeO₂/TiO₂ complex films are red shift, if compared with pure TiO₂.