Structure in the Brillouin Spectra of Thin Films

Abstract

Unsupported films with thicknesses of the order of the wavelength of light are shown to have Brillouin peaks with triplet or quadruplet structure, reflecting the discrete values of the phonon wave vector perpendicular to the surface of the film. The observation of this structure in the spectra of a polymer and a crystal film is reported here. The feasibility of making a high-frequency phonon spectrometer using thin films is discussed.