Characterising the interactions of low-dimensional carbon nanostructures with molecules and nanowires.

Since their discovery and isolation graphene and carbon nanotubes have fascinated both the scientific and industrial communities due to their unique physical properties. Many of the properties and potential applications are influenced by the interactions between the graphitic nanostructures and other materials. Some of the important interactions include gas-on-solid adsorption using the carbon nanostructures as hydrogen storage media or gas sensors. In addition filling nanotubes with various materials allows the fundamental study of encapsulated 1D nanowires and their influence on the electronic properties of the nanotubes. Density functional theory has been used to examine the ionization energy, polarizability and quadrupole moments of diatomic molecules, graphene sheets and single wall carbon nanotubes. The theoretical work continues using density functional theory to investigate hydrogen and oxygen physisorption to a graphene plate and segments of the (10, 0) and (9, 0) carbon nanotubes. A range of adsorption sites, both external and internal to the nanotubes, have been studied with the molecular axis oriented parallel or perpendicular to the nanotube wall. It is found that both hydrogen and oxygen bind weakly to the graphitic nanostructures in all adsorption sites studied. The adsorption energies of oxygen to the carbon nanostructures are found to be stronger than hydrogen adsorption energies. In addition binding energies are a factor of two larger for diatomic molecules bound inside the carbon nanotubes than for adsorption outside the nanotubes or on the graphene plate. Hydrogen interaction energies are shown to be enhanced by the addition of a second (10, 0) nanotube segment. Differences in binding energy characteristics are attributed to the curvature of the nanostructure and the interactions between electrons of the nanotube and the adsorbed molecule. The graphitisation and purity of several nanotube powders was examined using the analytical techniques of thermogravimetric analysis, transmission electron microscopy and x- ray photoelectron spectroscopy. A high-quality nanotube sample was successfully filled with a mercury tellurium compound via the molten media method. Preliminary results of the characterisation of the encapsulated nanowires, using scanning tunnelling microscopy, are inconclusive. However dry-deposition techniques were successful in isolating carbon nanotubes from the nanotube ropes of the filled sample