Synthesis and characterisation of sodium tungsten bronze nanoparticles for applications in plasmonics

Plasmon resonances in metal nanostructures have the potential to revolutionise many important technologies. However, the standard materials used in plasmonics, gold and silver, have high damping losses and low chemical stability, respectively. These limitations have has hindered the integration of plasmon resonances into practical applications and devices. Although several alternative materials have been proposed, few have optical properties superior to gold, and fewer still also offer high chemical stability and low production costs. This thesis describes an investigation into the sodium tungsten bronzes and their prospects as alternative plasmonic materials. A furnace-assisted nanoparticle synthesis technique was developed and characterised using ex- and in-situ X-ray and neutron powder diffraction. Highly-pure nanoparticle samples were prepared at the gram-scale, with low material costs and very short synthesis times. Scanning and transmission electron microscopy were used to characterise the size, morphology, composition and crystallinity of the nanoparticles. Optical and electron spectroscopy experiments, supported by density functional theory and boundary-element method calculations, showed that the sodium tungsten bronzes support high-quality bulk and nanoparticle plasmon resonances at visible and near-infrared wavelengths, with the resonance quality and frequency increasing with the sodium content. The properties of the as-prepared nanoparticles make them ideal for applications such as plasmonics-enhanced photocatalysis and photovoltaics, and performance improvements have been demonstrated experimentally. Overall, the sodium tungsten bronzes are promising materials for plasmonics, and with further study and optimisation, they could become an important part of the plasmonics-enhanced technologies of the future.