| Summary: | 碩士 === 國立清華大學 === 化學系 === 92 === Formation of nanowires and nanoparticles inside the channels of periodic mesoporous silica materials has been an active area of research in recent years. Porous silica materials have tunable pore diameters (2 to >10 nm), and long-range ordered structures. These features make mesoporous silica materials useful template materials for the formation of size-confined nanoparticles and nanowires within the pores. The nanowires and nanoparticles may exhibit quantum confinement effects and/or may not be easily prepared using other methods.
Various metal and semiconductor materials are incorporated into the channels of mesoporous silica powders, but only one nitride material (i.e. GaN) synthesized inside mesoporous MCM-41 material was reported. TiN has many useful properties including high hardness, good electrical conductivity and chemical inertness. Therefore the synthesis of TiN nanowires and nanoparticles within the mesoporous silica may have some interesting applications. Through the reaction of ammonolysis of TiN precursor, Ti(NMe2)4, at 700-750 °C for 1-6 hours, we synthesized the TiN nanowires and nanoparticles inside the mesoporous channels of SBA-15, a mesoporous silica with a pore size of about 5-6 nm. The length of TiN nanowires can be as long as several hundred nanometers. The functionalization of pore surfaces with methyl groups generate hydrophobic surfaces that facilitate the impregnation of Ti(NMe2)4 and minimize reactions between the TiN precursor and the hydroxyl groups on the surface of SBA-15. The final products have been characterized by XRD to confirm the formation of TiN and the retention of a hexagonally ordered structure. TEM and EELS images show that the TiN nanoparticles and nanowires are in the channels of mesostructures. The decreases in both the surface area and the total pore volume of mesoporous silica after TiN nanowires formation, as measured by nitrogen adsorption-desorption isotherms provide further evidence for the formation of the TiN nanowires inside the mesopores.
Since 1999, researchers have used silsesquioxane precursor combining with structure directing molecules to obtain various periodic mesoporous organosilica (PMOs), but most of these PMO materials is in the powder form. In order to apply these materials for electronic and optical applications (e.g. in low-k dielectric materials), PMO materials in the thin film morphology should be adopted. Towards this end, we have developed a very good recipe for the preparation of periodic mesoporous organosilica thin films using 1,4-bis(triethoxysilyl)benzene as the silica precursor and CTAB as the structure directing agent.
To prepare the thin films with a highly ordered structure, we have varied several parameters, such as the pH value, surfactant concentration, and the pulling speed, to watch the changes in the structures of the PMO films. XRD patterns and fluorescence spectra are used to characterize the as-prepared samples and the films after the removal of the surfactant. According to the results of XRD patterns, a hexagonal phase structure was obtained with 5.0 wt % CTAB and 0.5 ml of HCl. With surfactant concentration increasing from 5.0 wt % to 10.0 wt %, the mesostructures of the PMO films changed from a hexagonal to a lamellar phase structure. It was found that when a very low concentration of HCl was used as the catalyst, three sharp peaks at 2θ= 8.81, 17.63, and 26.69° (d = 10.03, 5.03, and 3.34 Å )appear in the XRD pattern. These peaks may indicate the presence of crystalline arylsilica ordering in the silica framework. A higher pulling speed (10 cm/min) was also found to produce films with better mesostructure.
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