UC San Diego

Plasmonic nanostructures are known to degrade easily through chemical, thermal, and oxidative mechanisms. Atomic layer deposition (ALD) of uniform, conformal, and ultrathin layers of alumina is a versatile method for fabricating protective coatings against degradation and aging of metal nanostructures. We demonstrate that a ~1 nm coating completely protects against aggressive peroxide etching and thiophenol contamination. A ~3 nm coating is shown to completely protect against photo-oxidation effects. To fabricate our protective alumina coatings, we used Ag nanocubes (AgNCs) as the core nanostructure. These AgNCs are molecularly passivated with (3-mercaptopropyl)trimethoxysilane to uniformly control the surface chemistry and establish binding sites for alumina deposition. The alumina is then deposited via ALD on the angstrom scale to precisely control the oxide coating thickness. This inorganic coating scheme can be advantageously used to protectively coat any plasmonic metal nanostructure for any size and shape.