RESEARCH ACTIVITIES   Raman Scattering from Acoustic Phonons Confined in Nanocrystals 43. Hervé Portales, L. Saviot, Eugene Duval, Minoru Fujii, Shinji Hayashi, N. Del Fatti, and F. Vallée, "Resonant Raman Scattering by Breathing Modes of Metal Nanoparticles,” Journal of Chemical Physics, Vol. 115, No. 8, pp. 3444-3447, August (2001). Low-frequency Raman scattering experiments have been performed on metal nanoparticles embedded in two different thermally treated matrices. In addition to the well-known Raman scattering by the nanoparticle quadrupolar vibrational mode, the spectra measured in the 3–40 cm−1 frequency range exhibit several new bands. They are ascribed to resonant scattering by the nanoparticle breathing mode and its harmonics, in very good agreement with time-resolved measurements. 40. Hervé Portales, Eugene Duval, L.Saviot, Minoru Fujii, Kenji Sumitomo, and Shinji Hayashi, "Raman Scattering by Electron-hole Excitaions in Silver Nanocrystals,” Physical Review B, Vol. 63, 233402, pp. 1-4, May (2001). Raman scattering experiments from silver nanocrystals embedded in films of amorphous silica are reported. In addition to the low-frequency peak due to vibrational quadrupolar modes, a broadband is observed in the high-frequency range, with a maximum at about 1000 cm-1. The linear dependence of the position of this maximum on the inverse cluster radius is in agreement with Raman scattering by single or collective electron-hole excitations. 39. Eugene Duval, Hervé Portales, L. Saviot, Minoru Fujii, Kenji Sumitomo, and Shinji Hayashi "Spatial Coherence Effect on the Low-frequency Raman Scattering from Metallic Nanoclusters,” Physical Review B, Vol. 63, 075405, pp. 1 - 6, February (2000). The low-frequency plasmon-resonant Raman scattering by the vibrational modes of silver nanoclusters embedded in amorphous SiO2 films is studied experimentally and theoretically. By electron microscopy it is observed that the concentration of defects in nanocrystals decreases and the intensity of Raman scattering increases by thermal annealing. It is shown that the degree of spatial coherence inside clusters has a strong effect on the Raman intensity and on its frequency dependence. 10. Minoru Fujii, Yoshihiko Kanzawa, Shinji Hayashi and Keiichi Yamamoto, "Raman Scattering from Acoustic Phonons Confined in Si Nanocrystals,” Physical Review B, Vol. 54, No. 12, pp. R8373-R8376, September (1996).  We have observed Raman scattering from acoustic phonons confined in Si nanocrystals. It was found that the Raman spectra depend strongly on the size of the nanocrystals and the peaks shift to higher frequencies as the size decreases. We also found that the depolarized Raman spectra appear at much lower frequencies than the polarized ones. 7. Minoru Fujii, Takeshi Nagareda, Shinji Hayashi and Keiichi Yamamoto, "Raman Scattering from Acoustic Phonons Confined in Microcrystals: Small Gold and Silver Particles Embedded in SiO2 Thin Films,” Journal of Physical Society Japan, Vol. 61, No. 2, pp. 754-755, February (1992). 6. Minoru Fujii, Takeshi Nagareda, Shinji Hayashi and Keiichi Yamamoto,　 "Low-Frequency Raman Scattering from Small Silver Particles Embedded in SiO2 Thin Films,” Physical Review B, Vol. 44, No. 12, pp. 6243-6248, September (1991). [Erratum] Intense, low-frequency Raman scattering from localized acoustic vibrations of small, spherical Ag particles embedded in SiO2 thin films has been observed. It was found that the Raman peak shifts to higher frequencies as the particle size decreases. For Ag particles smaller than 4 nm, the size dependence of the peak frequency can be well explained by Lamb’s theory, which gives vibrational frequencies of a homogeneous elastic body with a spherical form. The Raman scattering observed is relatively strong and believed to be enhanced by the excitation of the surface plasmons localized in the Ag particles; the enhancement mechanism is analogous to the case of surface-enhanced Raman scattering from molecules adsorbed on rough metal surfaces.