Optical response of plasmonic silver nanoparticles after treatment by a warm microwave plasma jet

This work investigates the effect of plasma treatment on the morphology and composition of 15 x 15 mm(2) silver nanoparticle (70-80 nm) thin films. The silver nanoparticles are deposited onto thermal silica (SiO2/Si) substrates by spin-coating, then they are treated by an open-to-air microwave argon plasma jet characterized by a neutral gas temperature of 2200 & PLUSMN; 200 K. Scanning electron microscopy analysis reveals that the number of isolated nanoparticles in the film sample decreases after exposure to multiple jet passes, and that polygonal structures with sharp corners and edges are produced. Similar structures with much rounder edges are obtained after conventional thermal annealing at temperatures up to 1300 K. Based on localized surface plasmon resonance analysis in the range of 350-800 nm, the main extinction band of silver nanoparticles experiences a redshift after treatment with the plasma jet or with thermal annealing. Moreover, both treatments induce surface oxidation of the nanoparticles, as evidenced by x-ray photoelectron spectroscopy. However, only the plasma-exposed samples exhibit a significant rise in the surface-enhanced Raman scattering (SERS) signal of oxidized silver at 960 cm(-1). 29 x mu m(2) mappings of hyperspectral Raman IMAging (RIMA) and multivariate curve resolution analysis by log-likelihood maximization demonstrate that the SERS signal is controlled by large-scale micrometer domains that exhibit sharp corners and edges.

Automated summary

This study investigates the effect of plasma treatment and thermal annealing on the morphology and composition of silver nanoparticle thin films. The results show that both treatments result in a decrease in isolated nanoparticles and the formation of polygonal structures with sharp corners and edges. The main absorption band of the silver nanoparticles experiences a redshift after treatment, and surface oxidation occurs. Only the plasma-exposed samples exhibit a significant increase in the surface-enhanced Raman scattering signal. Large-scale micrometer domains with sharp corners and edges control the surface-enhanced Raman scattering signal.