Investigation of AgCo Nanoparticles As a Useful Plasmonic Material

Developing Localized Surface Plasmon Resonance (LSPR) sensors that are cost-effective, sensitive, and long lasting has been an important goal for those in the field of plasmonics. The starting point in creating improved sensors is finding the right materials that will overcome these major challenges. Presently Au and Ag are the most important LSPR metals because of their excellent plasmonic properties. However Au is expensive and has weaker plasmons than Ag, which suffers from environmental degradation. This thesis describes the investigations of a promising new plasmonic material, bimetallic AgCo, that can be used to solve some outstanding problems in LSPR sensing. The localized surface plasmon resonance (LSPR) characteristics of arrays of near hemispherical shaped AgCo nanoparticles (NPs) were investigated using broadband optical spectroscopy measurements. Arrays with varying NP size and composition were made by our collaborators using pulsed laser dewetting self-organization. The LSPR wavelength was significantly red-shifted from the value of pure Ag, consistent with predictions of effective medium models. The normalized bandwidth of the Ag-Co plasmons for compositions between 20 to 30% Co was comparable to that of pure Ag indicating the high quality of LSPR in this material. The sensitivity to detecting refractive index change was measured by immersion in liquids of various refractive index. The Ag-Co system showed comparable or better sensitivity than pure Ag NPs and was in the range of 50-100 nm/Refractive Index Units (RIU) for the range of size and composition studied. Another key result was the significantly improved stability of the LSPR wavelength and sensitivity values of the AgCo system as compared to Ag following storage of the samples for long times under ambient conditions or following annealing in air for 100 minutes at various temperatures. While pure Ag nanoparticles degraded substantially, the AgCo wavelength and sensitivity remained virtually unchanged. In total, these results showed that the AgCo system is substantially superior to pure Ag in many respects and could potentially replace Au and Ag as the materials of choice in future plasmonic applications.

This if the final draft. I have changed a few things since last time. Please let me know if this is still fine to submit.