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 Å 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 $\sim 0.6$ to $\sim 1.6\mathrm{ps}$ 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.