Al–Cu core-shell nanoparticles as an alternative to noble metal plasmonics: A computational study

Abstract

While aluminum has been considered as an alternative to gold and silver as a plasmonic material, its utility has been restricted by spontaneous surface oxidation. One of the ways to bypass this problem is to coat Al with another metal: however, this has been extremely challenging until recently. New reports on the stabilization of Al(0) in water by coating it with a thin Cu shell have opened up a fresh avenue to explore corrosion resistant aluminum plasmonics. However, the effect of a Cu shell on the plasmonic properties of Al is hitherto unknown and needs to be understood. Moreover, almost no studies have been carried out on the optical properties of Al-core metallic-shell nanoparticles. Hence, for the first time, we report here a study on the absorption and scattering cross-sections of Al–Cu core shell nanoparticles (spheres, cubes and cuboids with a characteristic dimension between 50 and 100 nm) under an illumination of 300–900 nm. Notably, the addition of a 10 nm Cu shell shifts the scattering peak of a 100 nm Al nanosphere from 390 nm to 590 nm. The peak absorption and scattering wavelengths of core-shell nanocubes increase almost linearly with shell thickness. The effect of oxidation of the Cu shell is shown to be negligible for small oxide thicknesses (~1 nm). Thus, a Cu shell seems to improve the plasmonic performance of Al. We hope that these results spur further investigations into the size-controlled synthesis of Al–Cu core-shell nanoparticles for low-cost plasmonic applications.