High-temperature stability of silver nanoparticles geometrically confined in the nanoscale pore channels of anodized aluminum oxide for SERS in harsh environments

Abstract

We report the ability of nanoscale pore channels of anodized aluminum oxide (AAO) to endow entrapped silver nanoparticles (Ag NPs) within with structural and oxidation stability for potential surface-enhanced Raman scattering (SERS) at elevated temperatures. AAO was prepared via two-step anodization of high purity aluminum foil in phosphoric acid. Ag NPs of controlled size and coverage were obtained via in situ seeded growth from aqueous AgNO₃ solution inside the AAO pore channels. The structural and chemical characteristics and the SERS activity of the Ag NPs before and after environmental exposure in air at up to 600 °C for as long as 5 days were evaluated using scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. We show that the Ag NPs entrapped in the AAO pore channels exhibit enhanced structural and oxidation stability and thus retain significant SERS activity upon high-temperature treatment, indicating the intricate role of geometric confinement in retarding Ostwald ripening, evaporation loss, as well as oxidation of Ag NPs.