Hybrid structures for molecular level sensing
With substantial molecular mobility and segment dynamics relative to metals and ceramics, all polymeric materials, to some extent, are stimuli-responsive by exhibiting pronounced chemical and physical changes in the backbone, side chains, segments, or end groups induced by changes in the local environment. Thus, the push to incorporate polymeric materials as sensing/responsive nanoscale layers into next-generation miniaturized sensor applications is a natural progression. The significance and impact of this research is wide-ranging because it offers design considerations and presents results in perhaps two of the most critical broad areas of nanotechnology: ultrathin multifunctional polymer coatings and miniaturized sensors. In this work, direct evidence is given showing that polymer coatings comprised of deliberately selected molecular segments with very different chemistry can have switchable properties, and that the surface composition can be precisely controlled, and thus properties can be tuned: all in films on the order of 20 nm and less. Furthermore, active sensing layers in the form of plasma-polymerized polymers are successfully incorporated into actual silicon based microsensors resulting in a novel hybrid organic/inorganic materials platform for microfabricated MEMS sensors with record performance far beyond contemporary sensors in terms of detection sensitivity to various environments. The results produced in this research show thermal sensors with more than two orders of magnitude better sensitivity than what is attainable currently. In addition, a humidity response on the order of parts per trillion, which is four orders of magnitude more sensitive than current designs is achieved. Molecular interactions and forces for organic molecules are characterized at the picoscale to optimize polymeric nanoscale layer design that in turn optimize and lead to microscale hybrid sensors with unprecedented sensitivities.