Nanoplasmonic Sensing for Monitoring the Initial Stages of Atmospheric Corrosion of Cu Nanodisks and Thin Films

Nanoplasmonic sensing as a powerful experimental technique for corrosion kinetics monitoring is demonstrated. Its versatility is illustrated by studies of initial corrosion carried out on model systems consisting of copper nanodisks and extended copper films in both dry (<0.5% relative humidity, RH) and humid (65 ± 5% RH) air. Samples with and without a protective self-assembled monolayer of octadecanethiol (ODT) were studied. Thus, we studied four different corrosion situations. Two versions of the technique were employed, direct and indirect nanoplasmonic sensing (INPS). The former used disk-shaped nanoparticles as both sample structures and sensing particles, the latter used extended films as the sample, with the nanoplasmonic sensing particles embedded under the sample. Corrosion kinetics were recorded with high sensitivity and high temporal resolution (submonolayer detection limit; temporal resolution 1-2 seconds). In dry air, six times lower oxidation rates were observed for ODT-covered Cu compared to bare Cu, demonstrating the protection efficiency of the ODT as a corrosion inhibitor. In humid air, a higher oxidation rate was measured for both bare (2.4 times higher) and ODT-covered (1.7 times higher) samples, compared to the same samples exposed to the dry air environment. Oxidation occurred first after a short induction period during which water was adsorbed. For the Cu nanodisks (direct sensing) and Cu films (indirect sensing) studied here, very similar oxidation kinetics were observed.