Low Temperature Fabrication of One-Dimensional Nanostructures and Their Potential Application in Gas Sensors and Biosensors
Nanomaterials are the heart of nanoscience and nanotechnology. Research into nanostructures has been vastly expanding worldwide and their application spreading into numerous branches of science and technology. The incorporation of these materials in commercial products is revolutionising the current technological market. Nanomaterials have gained such enormous universal attention due to their unusual properties, arising from their size in comparison to their bulk counterparts. These nanosized structures have found applications in major devices currently under development including fuel cells, computer chips, memory devices, solar cells and sensors. Due to their aforementioned importance nanostructures of various materials and structures are being actively produced and investigated by numerous research groups around the world. In order to meet the market needs the commercialisation of nanomaterials requires nanomaterial fabrication mechanisms that will employ cheap, easy and low temperature fabrication methods combined with environmentally friendly technologies. This thesis investigates low temperature growth of various one-dimensional nanostructures for their potential application in chemical sensors. It proposes and demonstrates novel materials that can be applied as catalysts for nanomaterial growth. In the present work, zinc oxide (ZnO) and silicon (Si) based nanostructures have been fabricated using low temperature growth methods including hydrothermal growth for ZnO nanowires and plasma-enhanced chemical vapour deposition (PECVD) technique for Si nanostructures. The structural, optical and electrical properties of these materials have been investigated using various characterisation techniques. After optimising the growth of these nanostructures, gas and biosensors have been fabricated based on Si and ZnO nanostructures respectively in order to demonstrate their potential in chemical sensors. For the first time, in this thesis, a new group of materials have been investigated for the catalytic growth of Si nanostructures. Interesting growth observations have been made and theory of the growth mechanism proposed. The lowest growth temperature in the published literature is also demonstrated for the fabrication of Si nanowires via the PECVD technique. Systematic studies were carried out in order to optimise the growth conditions of ZnO and Si nanostructures for the production of uniformly shaped nanostructures with consistent distribution across the substrate. v The surface structure and distribution of the variously shaped nanostructures has been analysed via scanning electron microscopy. In addition, the crystallinity of these materials has been investigating using Raman and X-ray diffraction spectroscopies and transmission electron microscopy. In addition to the fabrication of these one-dimensional nanomaterials, their potential application in the chemical sensors has been tested via production of a glucose biosensor and an isopropyl alcohol vapour gas sensor based on ZnO and Si nanostructures respectively. The operation of the devices as sensors has been demonstrated and the mechanisms explored.
- PhD