Local surface plasmon contrast between liquid and solid Ga nanostructure：strong shape dependence and small size effect

Gallium (Ga) is highly valuable as an "active" plasmon in nanooptics due to its low melting point. We numerically investigate the surface plasmon difference between liquid and solid states for spherical and cylindrical Ga nanostructures. In the deep UV-visible region, it is found that the liquid Ga nanostructures can exhibit more pronounced plasmon than the solid, and very high liquid-solid optical contrast is achieved in cylindrical Ga nanostructures. However, for spherical Ga particles in vacuum, the liquid-solid optical contrast is very low, and only extremely small Ga spheres have high liquid-solid optical contrast. In order to achieve high liquid-solid optical contrast, an appropriately large aspect ratio or small size of Ga nanostructures is required.The research will promote the fundamental understanding of the surface plasmon of liquid and solid Ga, and be important for optical sensing, phase-change optical storage and high-contrast optical switches.