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Title: Super-resolution imaging of plasmonic hotspots
Author: Mack, David
ISNI:       0000 0004 6059 2933
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2017
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As the need to control and manipulate light on the nanoscale increases, intense expectations are being placed on the field of plasmonics to provide novel and consistent ways of controlling light, to achieve the desired optical properties and performance on these scales for both scientific and industrial applications. These properties include, high electromagnetic near-field enhancements, designer optical surfaces with control over scattering and absorption properties and nanoscale light waveguiding. One of the promising properties of plasmonics is their ability to generate electromagnetic (EM) hotspots. These are near-field structures, small in volume, but with extremely high field intensities. To better understand and apply these phenomena, techniques to characterize and image the spatial structure of these fields will become important. This is, in part, due to the extreme sensitivity of these fields to small structural and environmental changes to the plasmonic antenna. Here we present work on a single molecule fluorescence localization based super-resolution technique for the study and imaging of electromagnetic near-field structures generated around plasmonic antennas, with a special interest in the study of EM hotspots. The experimental work encompasses developing a suitable optical setup for fluorescent molecule detection, sample design and fabrication using electron beam lithography, as well as finite difference time domain simulations of plasmonic antenna properties. The technique has been used to probe the near-fields around a variety of plasmonic antennas. Analysis of the results demonstrated that the localization process can be complicated by the coupling of the fluorescence emission with the plasmonic system. When emission-coupled events occur, the results generally do not report the real position of the molecules, nor the EM enhancement distribution at the illuminating wavelength. To circumvent this issue, fluorescent molecules with a large Stokes shift have been used in order to spectrally decouple the emission process of the dye from the plasmonic system, leaving only the absorption strongly in resonance with the enhanced EM field in the antenna's vicinity. The real position of the emitters in this complex but interesting scenario are then found directly. The technique is demonstrated to provide an effective way of exploring either the EM field or the LDOS with nanometre spatial resolution.
Supervisor: Maier, Stefan ; Torok, Peter Sponsor: Leverhulme Trust
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral