Irradiation-induced brightening of tarnished Ag nanoparticles

We demonstrated that the plasmonic properties of corroded Ag nanoparticles (NPs) were recovered upon low-energy Ar+ irradiation. An intense surface-plasmon resonance (SPR) band, corresponding to extinction of ∼0.18, appears in the UV-Vis extinction spectrum of Ag NPs deposited on SiO2 substrates. The SPR band intensity gradually increases up to 0.22 within two days after preparation of the Ag NPs, and then decreases and eventually disappears, when the Ag NPs are stored in normal laboratory air for 1-2 months. The decrease in SPR intensity over time indicates tarnishing of the Ag NPs. X-ray photoelectron spectroscopy reveals the buildup of adsorbed impurities, containing carbon, nitrogen, and sulfur on the Ag NPs. The SPR band intensity recovers to half of the initial value (0.22) by irradiation with Ar+ ions at an energy of 0.4 keV to a fluence of 6.8 × 1014 ions cm−2. Irradiation decreases the atomic ratios of C/Ag, N/Ag and S/Ag. The C/Ag ratio decreases from 1.7 to 0.54, N/Ag decreases from 0.38 to 0.18 and S/Ag decreases from 0.12 to 0.06. The irradiated Ag NPs are found to exhibit the surface-enhanced Raman scattering, indicating restoration of their plasmon resonance upon removal of the adsorbed species.