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 SiO2, Al2O3, and TiO2 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.