Low frequency Raman scattering from confined acoustic phonons in freestanding silver nanoparticles

We report here the observation of the low frequency Raman scattering (LFRS) from acoustic phonons in freestanding silver. Silver nanoparticles (size around 3–4 nm) of spherical shape have been synthesized using a solid-state route. A blue shift along with broadening of the band is observed with a decrease in particle size. Size dependence of acoustic phonon in silver nanoparticles is explained using Lamb's theory. Our results show that the observed LFRS originates from different spheroidal modes due to the confinement of acoustic vibrations in Ag nanoparticles. Size distribution is obtained from LFRS and compared with TEM.