Electron dynamics in metallic nanoparticles

We studied the dynamics of electrons in copper and silver nanoparticles embedded in a transparent matrix, using the technique of pump-probe femtosecond spectroscopy. Comparative measurements are made in thin films of the same metals. Tn the case of the nanoparticles, the electron dynamics is strongly influenced by the surface at the boundary of the metal and the surrounding dielectric matrix. A detailed study of the pump-probe signals near the plasmon resonance of the nanoparticles reveals the importance of electron-electron scattering during several hundreds of femtoseconds. The influence of these scattering processes on the real and imaginary parts of the metal dielectric function is compared in the nanoparticles and thin films. In addition, 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 the random phase approximation, including the surface effects in a phenomenological way. (C) 2000 Elsevier Science B.V. All rights reserved.