Absorption suppression of silver nanoparticles in the presence of an AFM tip: A harmonic oscillator model

Abstract

We numerically calculated the optical absorption of silver nanoparticles (AgNP) in the presence of metallic and dielectric AFM probes, illuminated by transverse magnetic (TM) polarized, total internal reflected waves. Nanoscale probes localize and enhance the field between the apex of the tip and the particle. However, such probes can actually suppress the optical absorption of the AgNP. To better understand this phenomenon, we fitted the numerical absorption data with the equation of a driven damped harmonic oscillator (HO), and we found that the AFM tip modifies both the driving force and increases the overall damping of the oscillator by introducing an additional radiative decay path. For a 50 nm diameter AgNP the introduction of either a metallic or dielectric AFM probe suppresses absorption.