Nanostructured L3-templated silica thin films for enhancing the sensitivity of resonators

Nanostructured materials have become prevalent in a large number of applications, such as molecular sieves, high surface area catalysts and nano-composites. The nanostructure of a material used needs to be well characterized to facilitate its use in these applications. In this thesis we describe the synthesis and characterization of thin films of one such nanostructured material: L3-templated silica for its use in improving the sensitivity of gravimetric piezoelectric resonators (e.g. quartz crystals).;We detail the characterization of L3-templated silica films, beginning with a study of the structure of the dry surfactant (CpCl) and ending with a description of the nanostructured silica thin films synthesized from the surfactant. Grazing incidence small angle x-ray scattering (GISAXS) and water vapor accumulation isotherms are used to characterize the film structure. Water vapor accumulation allowed us to quantify the structural features of the material such as specific surface area and the channel opening. By varying the conditions under which thin films of the material are synthesized we are able to tune the nanostructure within the films to have structural properties desirable for sensing applications.;Following the characterization of the L3-templated silica films, we used quartz crystals as the resonators and coated them with three different thin films (< 1 mum thick) of porous silica: silica xerogel, silica templated by an ordered hexagonal phase of surfactant micelles, and silica templated by an isotropic L3 phase surfactant micellar system. We compared the sensitivity of coated resonators to the presence of water vapor. The crystals coated with hexagonal phase-templated silica displayed a sensitivity enhancement up to 100-fold compared to an uncoated quartz crystal in the low pressure regime. L3 phase-templated silica displayed the highest sensitivity (>1000 fold) in the high partial pressure regimes, which is attributed to an optimal combination of high surface area, channel size uniformity and channel accessibility. This approach to increasing resonator sensitivity is not limited to the detection of water vapor; it should be directly applicable to the sensing of other gasses. Some of the ideas presented can also be extended to improve the performance of sensors used in liquid environments.