J. Phys. IV France
Volume 129, October 2005
Page(s) 51 - 54

J. Phys. IV France 129 (2005) 51-54

DOI: 10.1051/jp4:2005129011

Confined acoustic modes in nanoparticles

Y. Li, H.S. Lim, Z.K. Wang, S.C. Ng and M.H. Kuok

Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117542

Brillouin scattering from aggregates of monodisperse polystyrene spheres has been measured as a function of their diameters (20 - 990 nm). In this range of sphere sizes studied, confined acoustic modes and two types of bulk longitudinal acoustic modes are observed. One type exists within larger spheres (diameter > 700 nm), while the other propagates in aggregates of smaller spheres (diameter $\le$ 80 nm) which are considered as polystyrene-air composites. The frequencies of the confined acoustic modes are found to be proportional to inverse sphere diameter, in accordance with Lamb's theory.

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