The influence of mechanical strain on the optical properties of spherical gold nanoparticles

We utilize classical Mie scattering theory to investigate the effects of tensile and compressive mechanical strain on both the far field (absorption, scattering and extinction efficiencies) and near field (surface enhanced Raman scattering) optical properties of spherical gold nanoparticles with diameters ranging from 10 to 100 nm. By accounting for the strain effects on both the ionic core (bound) and conduction (free) electrons through appropriate modifications of the bulk dielectric functions, we find that gold nanoparticles are relatively sensitive to the effects of mechanical strain due to the fact that the plasmon resonance wavelength for spherical gold particles, which occurs around lambda = 520 nm, is nearly coincident with the interband transitions of the core electrons. Specifically, we find that tensile strain leads to significant enhancements ranging from 60% to 120% in the far field optical efficiencies, while compressive strain leads to similar decreases, and that the plasmon resonance wavelength can be red or blueshifted up to 100 nm due to the applied strain. Finally, we find that tensile strain also strongly enhances the local electric (E)-field at the surface of the nanoparticles, which is of considerable interest for surface-enhanced Raman scattering applications; 5% tensile strain is found to enhance the vertical bar E vertical bar(4) intensity by 63%. The present results demonstrate the potential of mechanical strain, and specifically that of tensile mechanical strain in enhancing and tailoring the optical properties of gold nanoparticles. (C) 2009 Elsevier Ltd All rights reserved.