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Title: Chameleon metals : investigating the response to light of sub-wavelength metallic meshes
Author: Coyle, Steven
ISNI:       0000 0001 3394 2035
Awarding Body: University of Southampton
Current Institution: University of Southampton
Date of Award: 2004
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Films made from gold and platinum have been shown to have interesting optical responses, most notably dramatic colour changes with variation in thickness. The description of such behaviour is complicated by the strongly diffractive nature of the original template and the contribution of localised features of self-assembled colloidal arrangements. Further intricacy is provided by the morphology of the pore mouth of individual cavities within the mesh as the film is grown above one radius thickness of the colloids. Currently, no model satisfactorily describes the reflectivity of these films. Instead, five different approaches are investigated; interference based on reflections off the flat top surface and from within the voids themselves, a confined plasmon model based on studies of metallic voids, diffraction off a two dimensional grating, a surface plasmon model based on a two dimensional plasmonic band gap materials and finally, a finite element analysis of the voids. The results generated with these models are compared against systematic white light experiments of the reflectivity of gold and platinum films deposited through well-ordered templates composed of a monolayer of spheres of diameter 700nm, graded in thickness from 0nm-700nm. Normal incidence reflectivity show several noticeable features; thin films below one quarter sphere height exhibit behaviour consistent with reflections off a grating; thicker films show several reflectivity minima which move towards longer wavelength with increasing film thickness. Reflectivity studies of the polarisation response show a distinct difference between gold and platinum films; gold shows reflectivity minima consistent with scattering of surface plasmons off the voids. Platinum, which is incapable of supporting surface plasmon modes, has a response almost identical to that of normally incident unpolarised light.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available