Plasma-induced recovery of plasmonic sensitivity of aged silver nanoparticles to ethanol vapor and plasma exposure-time dependence

摘要

Plasma-induced recovery of the plasmonic properties of tarnished silver nanoparticle (Ag NP) aggregates has been examined from the viewpoints of morphological and compositional changes. Atomic force microscopy and transmission electron microscopy reveal that worm-like Ag NP aggregates form on a SiO2 substrate by aging for 28 days in ambient air. The aged Ag NP aggregates lose their plasmonic sensitivity to ethanol vapors because of sulfide scale formation and/or impurity adsorption. The lost plasmonic sensitivity is drastically recovered along with the reduction of silver sulfide and the removal of surface contaminants by Ar plasma exposure for 5-10 s. The recovery upon such a short duration of plasma exposure is not accompanied by a significant change in the morphology of the Ag NP aggregates. A plasma exposure for 10(3) s results in morphological changes, e.g., isolation of Ag NPs. Prolonged plasma exposure gives rise to a very sharp resonant peak in the optical extinction spectrum but lowers the plasmonic sensitivity. Thus, a brief plasma exposure has been found to be suitable for the recovery of the plasmonic sensitivity of tarnished Ag NPs to ethanol vapors.