Environment-controlled agglomeration in nanoporous Ag films with ultrathin silicon oxide

Abstract

Silver (Ag) nanostructures have been employed extensively in various applications, including plasmonic devices, metamaterials, and optical devices. This is attributed to their low cost, high catalytic activity, low loss in the visible and near-infrared regions. However, the thin films and nanoparticles of Ag are susceptible to agglomeration and recrystallization, which reduces surface energy and internal stress. This study examines the phenomenon of agglomeration in nanoporous Ag films under a range of atmospheric conditions over an extended period. The Ag films were prepared by gas flow sputtering (GFS) and subsequently subjected to aging under different environments and humidity levels, including air, vacuum, dry air, and nitrogen (N₂). To suppress Ag agglomeration and analyze the samples under each aging condition, a 2 nm-thick silicon oxide capping layer was applied. The surface morphology, particle area, crystallite size, and chemical bonding states were analyzed. The findings indicated that humidity facilitated the agglomeration of Ag particles, whereas silicon oxide effectively impeded the growth of Ag particles by hindering surface diffusion. Furthermore, surface-enhanced Raman scattering (SERS) analysis indicated that the application of a silicon oxide coating effectively controls the aggregation of the nanoparticle size and enhances the stability of Ag-based SERS substrates.