Preventing Aluminum Photocorrosion for Ultraviolet Plasmonics.

Aluminum can sustain plasmonic resonances down into the ultraviolet (UV) range to promote surface-enhanced spectroscopy and catalysis. Despite its natural alumina passivating layer, we find here that under 266 nm pulsed UV illumination, aluminum can undergo a dramatic photocorrosion in water within a few tens of seconds and even at low average UV powers. This aluminum instability in water environments is a critical limitation. We show that the aluminum photocorrosion is related to the nonlinear absorption by water in the UV range leading to the production of hydroxyl radicals. Different corrosion protection approaches are tested using scavengers for reactive oxygen species and polymer layers deposited on top of the aluminum structures. Using optimized protection, we achieve a 10-fold increase in the available UV power range leading to no visible photocorrosion effects. This technique is crucial to achieve stable use of aluminum nanostructures enabling UV plasmonics in aqueous solutions.