Acoustic vibrations of a silica-embedded gold nanoparticle: elastic anisotropy

TL;DR

This study investigates the elastic anisotropy of silica-embedded gold nanoparticles by analyzing their acoustic vibrations, confirming the production of well-controlled, spherical nanocrystals via ion implantation and modeling their vibrational modes.

Contribution

It introduces a novel molecular dynamics method to calculate acoustic phonon frequencies considering gold's elastic anisotropy in embedded nanoparticles.

Findings

Gold nanocrystals are successfully produced with controlled size and shape.

The vibrational modes are accurately modeled considering elastic anisotropy.

Ion implantation is effective for synthesizing spherical gold nanocrystals in silica.

Abstract

Spherical gold nanoclusters are grown by 1.8 MeV Au++ ion implantation into an amorphous silica matrix and subsequent air annealing at 873 K. Ultraviolet and visible light absorption confirms the presence of a dipolar surface plasmon peak at the expected location for a gold sphere in silica. Grazing incidence X-ray diffraction shows peaks corresponding to fcc gold with lattice spacing close to that of bulk gold, as well as allowing estimation of cluster size using Scherrer's formula. Low frequency Raman scattering reveals a relatively narrow peak, suggesting a narrow distribution of nanocrystal diameters. Acoustic phonon frequencies corresponding to the spheroidal quadrupolar vibrations of a continuum sphere with the anisotropic elasticity of gold are calculated using a novel method of molecular dynamics and extrapolation to the continuum limit using relatively small numbers of point masses. The study confirms high energy ion implantation as a method capable of producing gold nanocrystals with spherical shape and well controlled size.