Abstract
Molecularly templated mesoporous materials have played a prominent role in material chemistry since their discovery in the early nineties. Due to their ordered structure, uniform pore diameter in the nanometer range and variety of morphologies, these materials are expected to have potential in the development of nanotechnology. Two complementary topics on the applications of mesoporous materials are targeted. One is to modify the surface properties of mesoporous materials to have the desired functionality; the other is to make uniform and orderly arranged nanomaterials inside mesoporous materials. This thesis is intended to demonstrate our studies on both of the fields, corresponding to the functionalization and inclusion chemistry of mesoporous silica. At the beginning of this thesis, an introduction of general backgrounds of mesoporous materials, their related chemistry and characterization techniques is given. In Chapter 2, iron oxide nanoparticles in MCM-41 have been prepared by decomposition and oxidation of hydrophobic iron precursor, ferrocene, incorporated in the templating surfactant micelles. The method was found to be effective to produce confined iron oxide nanoparticles almost exclusively inside the host MCM-41. The incorporation of ferrocene affects both the morphology and mesoscopic structure of MCM-41. The iron in the as-synthesized sample was found to be oxidized and decomposed in nitrogen at 300℃, then transformed into discrete tetrahedral Fe(III) center grafting on the pore wall after calcination at 600℃ in oxygen. Further heating at 800℃ in vacuum results in octahedral-coordinated, highly dispersed and uniform iron oxide nanoparticles inside the channels of MCM-41. Chapter 3 describes a method of templating synthesis of metal nanostructures in functionalized mesoporous silicas. Strong electrostatic interaction between ionic metal precursors and charged functional groups on the pore surface enhances the incorporation amount of ionic metal precursors in the mesopores of the host silica. Besides, the distribution of metal ions in the functionalized host silica is very uniform. After reduction, various monometallic and bimetallic nanostructures including nanoparticles, nanowire bundles and nanowire networks can be templated synthesized. The morphology of metal nanostructure depends on the architecture of the host mesoporous silicas, the loading of ionic metal precursor and the intrinsic properties of the metal. In addition to their preparation, the formation mechanism of platinum nanowires in MCM-41 has also been studied. HREM studies show that the nanowires grow preferentially along <110> axes with preferred Pt(111) stacking on the pore walls of hexagonal-shaped channels of MCM-41. In Chapter 4, mesoporous silica has been fabricated into film morphology by spin coating a mixture of triblock copolymer and silica sol solution on silicon wafer. A method of in-situ derivatization of silica sol solution is applied to modify the sol to become hydrophobic. The resulting hydrophobic mesoporous silica film has smooth surface and controllable thickness. The film exhibits low dielectric constant in the range of 1.42 to 2.50, which is applicable as interconnect insulator in semiconductor industry for current and future technology nodes. It also meets practical IC process requirements including low process temperature, high thermal and dielectric stability and reliable mechanical properties. Post synthetic processes, including vapor phase reactions and plasma treatments, have also been studied, which are found to stabilize the dielectric properties of the silica films.