Ultrafast electron relaxation via breathing vibration of gold nanocrystals embedded in a dielectric medium

Relaxation dynamics of electrons in gold nanocrystals with diameters of 3.0–17.5 nm embedded in ${\mathrm{SiO}}_2,$ ${\mathrm{Al}}_2{\mathrm{O}}_3,$ and ${\mathrm{TiO}}_2$ matrices have been investigated by means of femtosecond pump and probe spectroscopy. The experiments show that the energy relaxation rates depend on both the nanocrystal size and the matrix material. A model taking account of electron-breathing mode interaction, electron-bulk phonon interaction, and thermal diffusion through the interface can explain well the observed results. The breathing mode damping in the medium on a time scale of a few picoseconds plays an important role in the electron-energy dissipation process of the nanoscale composite system.