Influence of oxygen plasma treatment on structural and spectral changes in silica-coated gold nanorods studied using total internal reflection microscopy and spectroscopy

Abstract

This paper shows how oxygen plasma treatment affects the structural, localized surface plasmon resonance (LSPR) spectral, and spatial orientation changes in single gold nanorods coated with a mesoporous silica shell (AuNRs@SiO₂) in comparison with bare AuNRs with the same aspect ratio (AR). Single AuNRs@SiO₂ subjected to different plasma treatment times were characterized using scanning electron microscopy and total internal reflection scattering (TIRS) microscopy and spectroscopy. The AR of the single AuNRs without a silica shell was decreased by structural deformation, while their LSPR linewidth was increased with increasing plasma treatment time. In contrast, single AuNRs@SiO₂ showed much higher structural and spectral stability due to the silica shell under the energetic plasma treatment. Furthermore, there was no noticeable variation in the three-dimensional (3D) orientations of single AuNR cores in the silica shell before and after the plasma treatment. The results support that no significant structural and spectral changes occur in single AuNRs@SiO₂ and that the silica coating enhances the stability of AuNR cores against oxygen plasma treatment. Therefore, fundamental information on the relationship among plasma treatment time, structural change, LSPR damping, and defocused orientation patterns is provided at the single-particle level.