Controlling properties of metamaterials with chiral fields using light and chiral molecules

Kelly, Christopher (2021) Controlling properties of metamaterials with chiral fields using light and chiral molecules. PhD thesis, University of Glasgow.

Abstract

Metamaterials have unique and tuneable properties not found in nature, and the ability to control their properties is crucial to their applications. The desired properties can be attained through specific design of their physical structure, but often lack the ability to be dynamically control after being constructed. In this thesis it has been demonstrated that the properties of inorganic metafilms and chiral metamaterials can be manipulated post-fabrication by reversible perturbations from chiral electromagnetic fields and molecules. Such perturbations have been applied to chiral gold metamaterials that exhibit the plasmonic analogue of electromagnetically induced transparency. Circularly polarised light (that is chiral) and chiral molecules have been demonstrated to asymmetrically modify the coupling between electromagnetic modes in these metamaterials by their interactions with chiral nearfields. This experimental observation has then been validated by numerical electromagnetic simulations that replicate the effect, and confirm that asymmetries in the coupling are a result of differing optical chirality densities in the fields depending on the relative handedness of light, chiral nanostructure and chiral molecule. It has then also been shown that simulations can replicate asymmetries resulting from anisotropic chiral biomolecule (protein) layers on the metamaterial surface, by use of an anisotropic chiral response tensor. Luminescence spectroscopy has been used as a probe of changes in chemical symmetries of inorganic metafilms and metamaterials. Europium (III) oxide, Eu2O3, has been used owing to its strong luminescence and the sensitivity of those emissions to the europium symmetry environment. A luminescence microscope has been custom built and tested to optimise luminescence signal and stability. Chiral light interacting with unstructured films chiral nanostructures in the films have been shown to change the relative luminescence intensity of the hypersensitive transition in Eu2O3. A model describing the mechanism of these changes has been proposed involving the exchange of optical chirality between light and the films. From the continuity equation for the conservation of optical chirality density, it has been found that optical chirality from incident fields can be exchanged between materials at their interfaces. This exchange results in a bulk chiral polarisation of ions in the film that changes the electronic symmetry around the Eu3+ ion and its emission intensities. Electromagnetic simulations have validated this hypothesis by demonstrating an exchange of chirality into the film in a three-layer system (air, Eu2O3, polycarbonate).

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Subjects: Q Science > QD Chemistry
• Colleges/Schools: College of Science and Engineering > School of Chemistry
• Supervisor's Name: Kadodwala, Professor Malcolm and Lapthorn, Dr. Adrian
• Date of Award: 2021
• Depositing User: Theses Team
• Unique ID: glathesis:2021-82325
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 20 Jul 2021 13:57
• Last Modified: 20 Jul 2021 13:57
• Thesis DOI: 10.5525/gla.thesis.82325
• URI: https://theses.gla.ac.uk/id/eprint/82325