Ultrafast electronic dynamics in solid and liquid gallium nanoparticles

The electron thermalization process both in solid and liquid metallic gallium nanoparticles with radii in the range 50-90 Angstrom is investigated by femtosecond pump-probe measurements. The results show that the temporal behavior of the electron energy relaxation is similar in both phases, with a time constant varying from similar to 0.6 to similar to 1.6 ps by increasing the nanoparticle size. We interpret the experimental data in terms of a size-dependent electron-surface interaction model and show the importance of the energy exchange with surface phonons in the electronic thermalization.