Plasmonics under Attack: Protecting Copper Nanostructures from Harsh Environments

The functionality of well-tailored nanomaterials can only be retained if they are robust to the environmental factors in which they operate. The inability of Cu to withstand such factors is largely responsible for its current status as a second-tier plasmonic nanomaterial. Herein, it is demonstrated that atomic layer deposition can be used as a pliable technique for the application of oxide coatings to substrate-based Cu nanostructures where suitably protected structures become robust to oxidation, high temperatures, and aqueous, acidic, and alkaline solutions without unduly influencing important plasmonic properties. Moreover, strategies are presented for maximizing plasmonic near-fields and allowing for the transport of hot electrons while maintaining coating integrity. The findings demonstrate that there does not exist a one-solution-fits-all approach but that coating design must follow an application-specific methodology. Within the scope of the investigation, alumina, hafnia, titania, and combinations thereof were all shown to be effective under certain conditions, but where hafnia shows the greatest durability in extreme pH environments and alumina-hafnia multilayers provide Cu with protection from oxidation to temperatures as high as 600 degrees C. The work advances the use of Cu nanostructures as durable plasmonic materials and provides broad-based strategies for protecting other vulnerable nanomaterials from harsh environments.