| In the first part of the dissertation, changes in the electrical properties of a chemical sensor constructed from mats of GaN nanowires decorated with gold nanoparticles as a function of exposure to Ar, N2 and methane are investigated. The Au nanoparticle-decorated nanowires were found to exhibit chemically selective electrical responses. Compared to vacuum, the sensor exhibited a nominal response to Ar and slightly greater response to N2. Upon exposure to methane the conductivity was suppressed by 50% relative to vacuum. The effect was fully reversible and was independent of exposure history. A model to explain both qualitatively and quantitatively the mechanisms at work within the nanowires that make them sensitive to their environment is developed. It was concluded that using mats of nanowires could be a new and easy method by which to fabricate chemical sensors where the sensor's sensitivity can be determined by either controlling the average size of the nanowires within the mat or the average carrier density.; In the second part of this dissertation, the use of carbon nanotubes (CNTs) is explored. The first consists of a model for using CNTs as selective ionic sensors is introduced and calculations of how the current-voltage characteristics change as a function of ion adsorption is presented. It was found that it is possible to predict how changes in the band structure of the CNTs manifest themselves in measurable external electrical parameters, such as conductivity, at room temperature. The mechanism by which the electronic properties are modified is by radial distortion of the nanotube caused by the mutual repulsion of the ions that have been absorbed onto a thin insulating layer of polymer. Depending on the chirality of the nanotube, the radial distortion is found to cause very different types of changes to the current-voltage behavior. For the case of zigzag nanotubes, at fixed bias, the current is found to be strongly modulated as a function of amount of absorbed charge.; The second application of CNTs is as directional magnetometers. A model consisting of a complete description of the electronic current in metallic single-walled carbon nanotubes within axially oriented magnetic fields at nonzero temperatures is presented. The goal was to construct a model that used experimentally measurable parameters to predict the actual electrical response of the CNTs. It was found that the current in a zigzag carbon nanotube that is metallic at zero magnetic field is strongly modulated as a function of the magnitude of an axially oriented magnetic field. This property was used as the basis to propose a design of a carbon nanotube based directional magnetometer that could be designed to sense magnetic fields from 1 T to 8 T and at temperatures from 0 K up to 100 K. (Abstract shortened by UMI.)... |
