Damped and overdamped acoustic phonons in tin nanoparticles detected by low frequency Raman scattering

Confined acoustic phonons were measured in tin nanoparticles of different s izes, embedded in a SiOx thin film, using surface light scattering measured by a Sandercock interferometer. This kind of scattering is usually called low-frequency Raman. Confinement effects were also detected by the broadeni ng of Raman optical modes of tin in the smallest particles, The eigenfreque ncies of the acoustic modes scale as the inverse of the particle size and a re in agreement with theoretical calculations of vibrations in a sphere. Th e vibrational modes of the smallest size particles turned out to be overdam ped. This is in agreement with femtosecond pump-and-probe spectroscopy meas urements, where oscillations were detected for the big particles (but not f or the smallest particles) at frequencies comparable to those observed in o ur measurements. By increasing temperature, melting of nanoparticles was al so observed. (C) 2001 Elsevier Science B.V. All rights reserved.