In-situ scrutiny of the transition melting of pristine (Au) and metal oxide (Au-gallia)-supported plasmonic nanostructures

Morphological and compositional stabilities of pristine and metal-oxide-supported gold/gold-gallia nanostructures were determined at elevated temperatures (800 degrees C) for the first time. Emphasis was on the size and shape dependence of the transitional melting temperatures, from which conclusions were drawn predominantly from monitoring in-situ changes to plasmonic properties of the nanostructures. The morphological, crystalline, optical and elemental analyses supported and revealed new insights into temperature-driven morphological transformations. The experimentally-derived melting temperature of pristine nanostructures was corroborated using theoretical melting models, with the best results for the liquid skin melting model. The shape deformations and thermal expansion of pristine nanostructures were precluded by reinforcement of the plasmonic Au nanostructures with a matrix material of gallium oxide, which gave markedly different results in terms of enhancing thermal stability at temperatures where the pristine nanostructures were completely vaporized. The interfacial energies were likely the reason for the enhanced stability against shape transitions and/or melting, wherein it was found that the formative steps of gallia were insufficient to achieve these effects and that complete phase formation was necessary for stabilization. The insights concerning the reasons for the enhancements, the supportive role of the metal oxide matrix, the plasmonic stabilities of the Au nanoparticles, the shape dependence of the melting transitions and the crystalline stabilities of the composites in this report will help in predictive composite design for high-temperature applications such as sensing, catalysis, energy storage and design of compatible optical communication devices.