Electron dynamics in metallic nanoparticles

We studied the dynamics of electrons in copper and silver nanoparticles emb edded in a transparent matrix, using the technique of pump-probe femtosecon d spectroscopy. Comparative measurements are made in thin films of the same metals. Tn the case of the nanoparticles, the electron dynamics is strongl y influenced by the surface at the boundary of the metal and the surroundin g dielectric matrix. A detailed study of the pump-probe signals near the pl asmon resonance of the nanoparticles reveals the importance of electron-ele ctron scattering during several hundreds of femtoseconds. The influence of these scattering processes on the real and imaginary parts of the metal die lectric function is compared in the nanoparticles and thin films. In additi on, the non-thermal component of the electrons and the heat transfer to the surrounding dielectric are measured. The results are analyzed with a model of effective medium, where the metal dielectric function is described in t he random phase approximation, including the surface effects in a phenomeno logical way. (C) 2000 Elsevier Science B.V. All rights reserved.