Spectral Properties and Relaxation Dynamics of Surface Plasmon Electronic Oscillations in Gold and Silver Nanodots and Nanorods

TLDR

Nanoparticle research has attracted attention because size confinement yields new electronic and optical properties, and noble metal colloids exhibit strong color from surface plasmon absorption. This study investigates the surface plasmon absorption characteristics of gold and silver nanoparticles ranging from 10 to 100 nm. The authors examined how size, shape, and composition affect the plasmon absorption peak and bandwidth, and used femtosecond laser excitation to monitor electron–electron and electron–phonon scattering dynamics. They found that electron–phonon relaxation is size- and shape-independent for particles smaller than the electron mean free path, while intense laser heating induces shape changes—photoisomerization of rods into spheres or fragmentation—dependent on pulse energy and width.

Abstract

The field of nanoparticle research has drawn much attention in the past decade as a result of the search for new materials. Size confinement results in new electronic and optical properties, possibly suitable for many electronic and optoelectronic applications. A characteristic feature of noble metal nanoparticles is the strong color of their colloidal solutions, which is caused by the surface plasmon absorption. This article describes our studies of the properties of the surface plasmon absorption in metal nanoparticles that range in size between 10 and 100 nm. The effects of size, shape, and composition on the plasmon absorption maximum and its bandwidth are discussed. Furthermore, the optical response of the surface plasmon absorption due to excitation with femtosecond laser pulses allowed us to follow the electron dynamics (electron−electron and electron−phonon scattering) in these metal nanoparticles. It is found that the electron−phonon relaxation processes in nanoparticles, which are smaller than the electron mean free path, are independent of their size or shape. Intense laser heating of the electrons in these particles is also found to cause a shape transformation (photoisomerization of the rods into spheres or fragmentation), which depends on the laser pulse energy and pulse width.