Light intensity field enhancement (LIFE) induced localized edge abrasion of silica-coated silver nanoprisms

Abstract

Silver nanoprisms (AgNPrs) exhibit localized surface plasmon resonance (LSPR) in the near infrared (NIR) region of the electromagnetic spectrum. LSPR-driven electric field enhancement around AgNPr edges has been investigated in various studies. A coating of dielectric materials such as silica on the surface of the AgNPrs is employed to extend the application of these nanoparticles under biocompatible conditions and to increase the thermal stability. Upon interactions with optical excitation (pulsed laser excitation), the AgNPrs undergo light intensity field enhancement (LIFE) at the corners. In the cases of hybrid hetero-structures of AgNPrs with silica coatings (AgNPr@SiO₂), LIFE leads to nano-structural deformations. In this study, we demonstrate that, depending on the intensity of the light excitation, the medium properties and the geometrical sharpness of the corners of the prisms, LIFE could induce localized damage or abrasion at the edges of the immediate dielectric contact, which in this case was the silica coating. A theoretical study was conducted to establish the influence of the finite radius of curvature (ROC) of the corners on the plasmonic interactions to generate LIFE during optical excitation. Experiments were performed on AgNPr@SiO₂ using nanosecond pulsed laser excitation at 900 nm and electron microscopic analysis of the nanostructures revealed the localized edge abrasion of the silica at the prism corners. To further study the effect of the direct plasmonic excitation during LIFE, pulsed laser excitation on ultra-thin graphene oxide (GO) wrapped AgNPr@SiO₂ (GO-AgNPr@SiO₂) was conducted. Due to the GO wrapping and subsequent changes in light absorption, the extent of the LIFE at the corners diminishes, which leads to structural stability and preservation of the hetero-structure morphology.