Characterising Plasmonic Nanostructures with Interferometric Cross Polarised Microscopy

Abstract

Plasmonic nanostructures such as gold nanoparticles and nanorods have been the target of many optical studies. Their enhanced optical properties as a result of their plasmonic nature has made them a popular candidate as an alternative to fluorescent markers. Within this thesis interferometric cross polarised microscopy (ICPM), an all optical, confocal like imaging technique is investigated as a means to characterise individual nanostructures. ICPM is first applied to the study of markers used in correlative light electron microscopy. A method that images a fluorescent molecule in light microscopy, and an electron dense gold nanoparticle in electron microscopy, where the two are bound together. Using ICPM it was determined that due to the proximity of the two parts of the probe the fluorescent signal would be significantly quenched, preventing any correlation between the images. Imaging gold nanoparticles with ICPM has often resulted in deviations in the detected scattering signature. It was found that even small variations in a nanoparticles shape is enough to induce extra field components, as a result of their asymmetry. These extra components significantly change the spatial distribution of the detected scattering signature. Through analysis of large arrays of asymmetric nanoparticles, a theoretical model was produced with good agreement with the experimentally collected data. This model is shown to enable a means of detecting the orientation of an individual nanorod in 3D. The same theory was then applied to closely spaced scattering nanostructures, showing that gap sizes as small as 20 nm could be identified. Finally, a chlorine plasma etch method for anisotropic etching of crystalline gold is explored as a method of manufacturing ultra smooth structures, for low loss plasmonic devices, and single photon quantum applications.

Date of Award	23 Jan 2020
Original language	English
Awarding Institution	University of Bristol
Supervisor	Henkjan Gersen (Supervisor)