Maximizing nanoparticle light absorption: Size, geometry, and a prospect for metal alloys

In this work, we show how to maximize absorption of plasmonic nanoparticles in terms of size, geometry, and material. We determined that the main effect dictating the optimal amount of optical losses is radiation damping, and how it depends on nanoparticle size and geometry. Based on this, we find that for many combinations of sizes and geometries, losses in pure metals are far from optimal. To overcome the aforementioned issue, alloying is presented as a straightforward and flexible way of modulating the optical losses. Furthermore, strategies for tuning the optical losses to values above, between, and even below those in pure plasmonic metals are developed in terms of selecting the right alloy composition. In some cases, alloys showed a multifold increase in absorption when compared to pure plasmonic metals. The physical reasons governing such changes are elucidated based on the electronic structure changes during alloying of different metals, which enables generalization of the results to other systems. In addition to increasing absorption, electronic structure changes can also be utilized for channeling the absorbed energy to suit different purposes, such as hot carrier generation for photocatalysis or solar energy harvesting. Overall, these results establish alloying as a powerful tool for designing nanostructures for applications that utilize light absorption.