Investigation of confined acoustic phonons of tin nanoparticles during melting

Both confined acoustic and optic phonons were detected in tin nanoparticles embedded in a SiO(x) thin film, using inelastic light scattering, for different values of the particle size. The eigenfrequencies of the acoustic modes are in agreement with theoretical calculations for the free vibrations of an elastic sphere. By increasing the temperature, clear effects of particle melting on the optical and acoustic modes were observed, together with the detection of a coupling with a strong central peak. The observation of melting, and surface melting, through direct investigation of the nanoparticle acoustic vibrational eigenmodes represents a novel and relevant feature of this work.