Blueshift of the surface plasmon resonance in silver nanoparticles studied with EELS

TL;DR

This study investigates the size-dependent blueshift of surface plasmon resonance in silver nanoparticles using electron energy-loss spectroscopy, comparing experimental results with three theoretical models to understand the underlying physics.

Contribution

It provides a detailed experimental measurement of plasmon blueshift in silver nanoparticles and compares it with advanced semiclassical models to explain the phenomenon.

Findings

Measured a 0.5 eV blueshift from 26 nm to 3.5 nm particles

Semiclassical models qualitatively explain the blueshift but underestimate its magnitude

Quantum confinement and nonlocal effects are important for accurate modeling

Abstract

We study the surface plasmon (SP) resonance energy of isolated spherical Ag nanoparticles dispersed on a silicon nitride substrate in the diameter range 3.5-26 nm with monochromated electron energy-loss spectroscopy. A significant blueshift of the SP resonance energy of 0.5 eV is measured when the particle size decreases from 26 down to 3.5 nm. We interpret the observed blueshift using three models for a metallic sphere embedded in homogeneous background material: a classical Drude model with a homogeneous electron density profile in the metal, a semiclassical model corrected for an inhomogeneous electron density associated with quantum confinement, and a semiclassical nonlocal hydrodynamic description of the electron density. We find that the latter two models provide a qualitative explanation for the observed blueshift, but the theoretical predictions show smaller blueshifts than observed experimentally.in a homogeneous medium.