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Title: Laser fabricated plasmonic nanoparticle templates for sensor applications
Author: Spear, Jacob Leonard
ISNI:       0000 0004 7965 9106
Awarding Body: Nottingham Trent University
Current Institution: Nottingham Trent University
Date of Award: 2019
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Traditionally, localised surface plasmon resonance, LSPR, spectroscopy sensing surfaces are produced with a highly specific functionalised layer atop a plasmonic nanostructure. Here we present that by removing this functionalisation, not only is the diffculty of the fabrication procedure reduced, but the 'naked' plasmonic nanoparticle template is still able to act as a high quality optical sensing surface for detecting the surface abundance of a lead salt, showing a clear and measurable shift to the optical response of the template from as little as 0:0001at% or 100ppm. The increased desire for exible devises is driving a need to be able to fabricate a high quality micro- and nano- structures on flexible substrates. This research describes a methodology for the laser fabrication of a plasmonic nanoparticle template on a polymer substrate by modifying the polymer surface to increase the surface roughness of the polymer substrate and the inclusion of a silicon dioxide interlayer between the polymer and the metallic thin film. By combining these two processes, laser annealing can be transplanted onto a substrate as thermally sensitive as PET and still allow for the fabrication of a plasmonic nanoparticle template, with the highest quality template being produced with a PET=SiO2(100nm)=Ag(10nm) structure. Through the a simultaneous experimental and computational investigation of the effect an interlayer has on the laser annealing process, caused by multiple reflections within a silica interlayer. Demonstrating a direct correlation between the experimentally seen variance of the processing window - increased threshold energy and a reduction to the ablation limit with the calculated minimum and maximum absorption of the laser line in the silver thin film. Allowing this understanding to provide an additional control on the laser annealing process. Further to this, a novel optical characterisation technique to assess the angle and polarisation dependent reflectance, at both specular and diffuse angels. Due to the lack of a commercially available system to measure this effect, a custom designed and built goniometric system to accurately and reliably quantify this effect was produced. The analysis of the angle and polarisation dependent reflectance of the nanoparticle templates revealed that the S-polarisation reflectance showed minimal (up to a maximum of 5 nm) variation at any angle of incidence, while the P-polarisation reflectance showed a dramatic blue shift to the LSPR peak of the nanoparticle templates at steep angles (above 50°). This colour changing phenomenon can be attributed to a combination of thin film interference, and the differing planes being probed by the two separate polarisations.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available