Electro-assisted Self-assembly And Properties Of Silica Films

In recent years, the self-assembly technology of films has attracted much attention. In this thesis, by electro-assisted self-assembly technique, mesoporous silica films were preformed by using cationic surfactant cetyltrimethyl ammonium bromide (CTAB) as template, tetraethyl orthosilicate (TEOS) with sodium nitrate as precursor, fluorine doped tin oxide films coated glass (FTO glass) or highly oriented pyrolytic graphite (HOPG) as substrates. The silica films were respectively characterized by cyclic voltammograms (CV), DTA-TG, infrared spectrometer, scanning electron microscopy (SEM), transmission electron microscopy (HRTEM), electron diffraction patterns, UV-visible spectrophotometer and fluorescence spectroscopy. The effects of voltages, solution composition, induced times and TEOS/CTAB ratio on the assembly process, morphology and optical properties of silica films were investigated. The preparation of the Co doped silica films was attempt. And the growth mechanism of the silica films and the action mechanisms of the surfactant and hydrochloric acid were explained reasonably.Results showed that the silica thin films could be prepared with cationic surfactant (CTAB) as template at -3.5 V. A variety of morphologies of silica thin films could be obtained in acidic condition. With the increasing of the potential and induced time, the intensity of silica film's absorbance increased, and the transmittance of silica film decreased in the visible light region. Mesoporous silica films could be formed only if the concentration of CTAB solution was equal to or greater than its critical micelle concentration (CMC) or the concentration of TEOS reached a definite extent. After calcination at 500℃, the mesoporous silica films had MCM-41 structures, because of the addition of surfactant CTAB. Besides, after calcination, due to non-bridged oxygen holes centers (NBOHC) exist, which led to the emission of 2.5 eV light under the excitation of 3.5 eV incident light. With the increasing of Co doping, the absorption of Co/silica film gradually increased, and the transmittance decreased. In the process of electro-assisted self-assembly, the SiO₂ pre-polymers were formed of surfactant CTAB and silicate ions of TEOS by electrostatic interactions. When the pH value decreased, SiO₂-hybrid surfactant micelles aggregates were synthesized. Under the moving charges induced, mesoporous silica thin films were formed of self-assembly of the hybrid micelles aggregates in the conductive substrate.