Study On The Properties Of Thin Films Of Doped Nano-TiO₂ And Nano-ZnO

In order to better study the effects of thin films of doped nano-TiO₂, the phase transformation of undoped TiO₂ thin films was first studied. Thin films of TiO₂ were prepared on a quartz plate by sol-gel/spin-coating. The samples were annealed at 800 to 1100oC and their Raman, transmission and fluorescence spectra were obtained. As the annealing temperature increased, the Raman spectra showed that the anatase form of the samples transformed into a rutile phase with a mixed anatase/rutile phase as an intermediate. The transmission spectra showed that the absorption edge of the samples red shifted during the phase conversion. Overall, the sample refractive index n increased during the phase conversion but its thickness d and band gap Eg decreased during the phase conversion. The fluorescence spectra contained two spectral bands around 557 to 570nm and around 794 to 812nm. During the phase transformations, the spectral intensity of the bands around 557 to 570nm changed from strong to zero and the spectral intensity of the bands around 794 to 812nm changed from weak to strong.TiO₂ thin films doped with rare-earth yttrium, lanthanum and samarium were prepared on quartz plate by sol-gel/spin-coating technique. The samples were annealed at 700 to 1100 oC and the Raman spectra of the samples were obtained. Analyses of Raman spectra show that as increasing annealing temperature, the anatase form of undoped TiO₂ thin films transforms eventually into the rutile phase with mixed anatase/rutil phase as an intermediate. Yttrium doping, lanthanum doping and samarium doping of TiO₂ thin films can inhibit the phase transformation, and the latter effect is stronger. Rare-earth doping can refine grain size of TiO₂ thin films and can increase in the internal stress, thereby preventing lattice vibration. The effect of La doping and Sm doping are stronger than yttrium doping. The samples shows significant the phonon confinement effect. That is to say characteristic Raman peaks blue shift and full width at half height increase and the peak shapeasymmetric stretch with decrease in grain size.Transparent and conductive c-axis oriented aluminum-doped zinc oxide (AZO) films have been prepared on glass substrate by DC magnetron sputtering process. For this purpose, a sintered ceramic disc of ZnO mixed with 2wt% Al2O3 was used as the target. The microstructure of AZO ceramic target was characterized by micro-Raman spectroscopy. The structural, optical and electrical properties of the films were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), UV-Visible spectrophotometer and four-probe tester respectively. As the substrate temperature increased, the results showed that grain size of the AZO films gradually increased, the films had a strong c-axis oriented and the crystallization of films became better. The absorption edge has a blue shift with increasing deposition temperature. The refractive index of the films decreased but films thickness and optical band gap increased with increasing deposition temperature. Resistivity of AZO films decreases with increasing deposition temperature but resistivity remained stable after substrate temperature reaches 350oC.Transparent and conductive c-axis oriented aluminum-doped zinc oxide (AZO) films have been prepared on glass substrate by dc reactive magnetron sputtering process. The structural, optical and electrical properties of the films were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), UV-Visible spectrophotometer and Hall effect measurement system. As the substrate temperature increased, the results showed that grain size of the AZO films gradually increased, the films had a strong c-axis oriented and the crystallization of films became better. The absorption edge first shows a red shift, and then switches to the blue shift with increasing substrate temperature. Optical band gap of AZO films first decreases and then increases with increasing substrate temperature. Resistivity of AZO films decreases with increasing substrate temperature but the rate of decline of resistivity becomes slow after substrate temperature reaches 250oC. The carriers concentration of AZO films increases with substrate temperature increase.