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Title: Fabrication and characterisation of nanowire arrays : magnetic and plasmonic interactions at the nanoscale
Author: Toal, Brian
ISNI:       0000 0004 5373 0306
Awarding Body: Queen's University Belfast
Current Institution: Queen's University Belfast
Date of Award: 2015
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In this thesis the fabrication and characterisation of nanostructured arrays are discussed. Nanowires, nanotubes and core-shell nanostructures are produced through electrodeposition into the pores of anodised aluminium oxide templates. The electrochemical process is optimised for all materials used. Using nickel, it is demonstrated that the dimensions of the nanowires within the template alter the wavelength position of a reflectivity minima associated with a sub-wavelength optical resonance, corresponding to enhancement of Kerr rotation. The magnetic properties are largely dictated by magnetostatic interactions resulting in an easy axis of magnetisation perpendicular to the nanowire long axis Cobalt nanowires produce a larger Kerr rotation than analogous nickel samples. The magnetic properties are altered by the uniaxial magnetocrystalline anisotropy, confirmed by x-ray diffraction to lie along the long axis of the nanowires. It is therefore possible to rotate the easy axis of magnetisation from the plane of the substrate to the nanowire long axis by increasing the aspect ratio and inter-wire separation. Cobalt nanotubes create a highly complex magneto-optical response with multiple resonances. Nickel-iron alloy nanowires were also made, and the results are compared for changing geometry as well as varying concentration levels. It is revealed through transmission electron microscopy that the grain structure is richly textured with nanocrystalline grains and high volume fraction of grain boundaries. The magnetoplasmonic properties of gold-core cobalt-shell nanowire arrays conclude the thesis. It is found that a nanometric cobalt layer is sufficient to demonstrate magnetic control over optical properties. The optical properties of the array are characteristic of the plasmonic resonances associated with the gold nanowires and the magnetic properties are similar to those of cobalt nanotubes. Combined, however, the wavelength and magnitude of the relative phase shift between P and S polarised components of incident light can be altered with the application of a magnetic field.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available