Magnesium nanoplasmonics: synthesis, characterisation, and applications

Abstract

At the nanoscale, light-matter interactions differ markedly from bulk behavior. In metal nanoparticles, resonant oscillations of conduction-band electrons driven by light lead to localised surface plasmon resonances (LSPRs). Au and Ag are widely studied metals capable of sustaining LSPRs, but there is growing interest in earth-abundant alternatives that offer potentially different properties at a much lower cost. This thesis focuses on establishing metallic Mg as a viable plasmonic material. First, synthetic routes for Mg nanoparticles are explored. Seed-mediated colloidal methods are investigated, leading to the production of monodisperse and isotropic metallic Mg nanoparticles. Top-down lithographic approaches are then developed to fabricate Mg nanoarrays sustaining LSPRs. Next, Mg’s hexagonal close packed crystal structure, unique among plasmonic metals, leads to various Mg crystal shapes, including twinned structures, cubes, and spheroids, which are probed for their near-field optical properties both experimentally and numerically. Using similar techniques, the effects of size and composition on the plasmonic properties of Cu and Cu–CuPd nanorods are investigated. Finally, Mg nanoparticles are evaluated for surface-enhanced Raman spectroscopy (SERS) applications, harnessing the concentrated electric field generated by LSPRs. The enhancement factors are experimentally and numerically quantified. SERS on Mg nanoparticles is then used to monitor plasmon-driven chemical reactions at the nanoparticle surface for both Mg and Mg–Pd structures. This thesis advances synthetic strategies, deepens our understanding of Mg’s plasmonic properties, and expands its range of applications, thereby solidifying its role as an earth-abundant alternative to noble metal plasmonics.