Mechanical and dielectric properties of self-assembled, periodic nanoporous silica and organosilica materials

In recent years self-assembled, organic supramolecular or colloidal arrays have been used as templates for the design of a wide range of novel nanostructured porous materials, using sol-gel chemistry. Herein, mesoporous silica and organosilica films, and colloidal crystal (opal) films, have been synthesized, and various mechanical and dielectric properties investigated.; A series of spin-coated mesoporous silica films were synthesized using a surfactant template, using evaporation-induced self-assembly (EISA). The porosity was controlled by the surfactant/silica molar ratio, thermally-induced collapse at 300--900°C, and deposition within the channels. The Young's modulus (E) and hardness (H) were measured using nanoindentation, and the results have been compared with conventional models for porous materials. A series of molecular mechanics atomic models of mesoporous silica were used to simulate the elastic and plastic deformation as a function of pore diameter.; Highly-ordered, periodic mesoporous organosilica (PMO) thin films were synthesized from bridged silsesquioxane precursors of the type (EtO) 3SiRSi(OEt)3 (where R is an organic group), and a novel three-ring [(EtO)2Si( CH2)]3 precursor. Detailed structural characterization has been performed using PXRD, SAXS, SEM, and TEM. PMO films may have important applications as low dielectric constant (k) materials in microelectronics. Capacitance measurements showed that k decreased with organic content to ∼1.8. A novel 'self-hydrophobization' behaviour has been demonstrated, using a bridge-terminal transformation of the organic groups at 400--550°C, to lower k and make the films highly resistant to moisture adsorption. A series of novel dendrimer and 'semi-dendrimer' PMO thin films have been synthesized using cationic and block copolymer templates, to further increase the organic content. As a result, the number of organic bridges attached to each Si is increased as a series, from 0 to 4.; Finally, chemical vapour deposition (CVD) was used to sinter silica opal films to systematically control the optical Bragg diffraction and the structural connectivity. SiCl4 and Si(OMe)4 vapour were used to deposit silica layers to grow necks between silica spheres. Nanoindentation was used to measure E and H as a function of the silica deposition.