TiO₂ Deposit Mechanisms Using SILAR Technique And Sythesis/Structural Characterization Of High-Surface-area Films

In this paper, using the Successive-Ionic-Layer-Adsorption-and-Reaction (SILAR) deposited technique, ultrathin TiO₂ films were deposited on glass and Kapton substrate and the corresponding initial deposition mechanism was investigated. Afterwards, high-surface area TiO₂ thin films have been synthesized by two kinds of different methods: (1) SILAR depositing on a roughened Kapton substrate by atomic oxygen etching process; (2) using a cationic surfactant template to deposit high surface area TiO₂ thin films on smoothing substrate. The structures and the growth processes were investigated using complementary techniques such as X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR), Fourier transform infrared spectroscopy (FTIR), atomic force microscope (AFM), scanning electron microscopy (SEM), Raman spectroscopy (Raman).The results indicate that the thickness of the SILAR TiO₂ films increases linearly with the depositing cycles. The TiO₂ film nucleates in an island mode, but grows in a layer-by-layer 2-dimentional mode after the films is covered the substrate. It is also found that coverage on the substrate and the deposition efficiency of depositing films will increase, as extending the deposition adsorption and reaction time. Through the measurements of water contact angle, the work of adhesion continues increase with creasing the deposited cycles, namely high reaction activation could be maintained on the surface in whole deposited process. In as-deposited films, highly active oxygen-vacancy defects were observed, which may be the reason of keeping the Gibbs surface-free-energy of films reducing.SEM and AFM observations show that high-surface-area TiO₂ function films were obtained by depositing on etched Kapton substrate. The surface roughness greatly increased, in a measured scale of 5μm×5μm, the surface roughness changes from 1.60μm of the pristine Kapton substrate to 24.39μm of the deposited one. On the other hand, a more significantly rough TiO₂ films were deposited by adding a cationic amine surfactant template during SILAR deposition. It is interested to note that , as-deposited TiO₂ films on glass substrate is amorphous, the surface roughness changes from 1.13μm of the glass substrate to 26.57μm in scale of 20μm×20μm. After 773K heat treatment, the amorphous film was transformed to be an anatase structure, its surface roughness increases to 47.61μm. However, using the same cationic template technique, an ordered-like surface morphology of the TiO₂ films was deposited on Kapton substrate. Using Raman spectroscopy analysis, the as-deposited film shows an anatase structure without heat treatment. The surface roughness can reach 51.65μm, in a measured scale of 20μm×20μm. From the abovementioned results, it should be also noted that the substrate structure shows significant influence on the deposited TiO₂ film structure.