Nanostructure Fabrication Using Inorganic Sols and Electron Beam LithographyPublic Deposited
Dimensionally constrained material systems are at the forefront of current materials research because of their novel and often enhanced physical, chemical and biological properties. The dimensionality effects are pervasive through different classes of materials including ceramics, metals and polymers. Often times dimensionality effects are manifested as internal structure variations in polycrystalline materials. This is evident from some recent reports indicating that "internal" microstructural inhomogenities such as grain boundaries and porosity even in dimensionally constrained systems can further enhance their performance metrics such as gas sensitivity, for example. These results, coupled with the maxim that "microstructure is a material's DNA" underscore the need for novel approaches to enable tailoring of the "internal" microstructure of constrained nanopatterned systems and their characterization. This dissertation reports one such approach. We have developed an enabling nanopatterning technique termed as soft-electron beam lithography (soft-eBL) which utilizes liquid precursors (e.g., sol) as the material source for patterning variety of materials and composites with dimensional control down to 30 nm. Among several advantages, soft-eBL is capable of patterning structures on almost any substrate - single crystals, fragile ultra-thin membranes and insulators. We have exploited these unique attributes of soft-eBL to fabricate nanopatterns of simple and complex functional oxides with defined sizes and shapes. For example, we showed that by controlling the width of ZnO nanopatterned lines on an amorphous substrate, it is possible to define the number of grains per unit line length, such as a beaded (or a bamboo) structure where a single grain spans the entire line width. Using Soft-eBL we were able to demonstrate the effect of dimension, line-width to be specific, on the reduced crystallization rate in ceramic oxide nanostructures. The average grain size in lines was found to be smaller than in thin films prepared in identical conditions. The dissertation further reports an experimental protocol to fabricate miniaturized gas sensing devices using soft-eBL nanostructures of ceramic oxides. As a part of this work, we have built a set-up in-house to measure the gas sensing properties of active nanostructures at different temperatures. The hydrogen sensing properties of tin oxide lines showed that decreasing line width improves the gas sensing performance. The gas sensing properties of these structures were benchmarked against commercial hydrogen sensor which was also tested under identical conditions. The soft-eBL 1D nanostructures showed better sensitivity and stability compared to commercial hydrogen sensor.