Acoustic mode quantization in nanostructures

Abstract

Brillouin light scattering has been employed to investigate the confined acoustic modes of three different nanostructures, viz. silica and polystyrene nanospheres, hollow carbon microspheres, and GeO2 nanocubes. The confined acoustic modes observed show significantly different features from those of the corresponding bulk. Based on elasticity theory, the eigenfrequencies of these modes have been calculated and they agree well with the experimental data. Furthermore, by fitting the calculated mode frequencies to the experimental ones, the elastic properties of these nanostructures have been determined. In addition, the controversy surrounding selection rules for Raman and Brillouin light scattering from eigenvibrations of nanospheres has been discussed. The Brillouin selection rules for a sphere with a diameter of the order of the excitation light wavelength have been derived by group theory.