Study on Phonon Brillouin Spectrum of Crystal Films

On the basis of the theory of phonon Green's function,the phonon stru cture of simple cubic crystal film is studied,the lineshape formula of phonon Brillouin spectrum is deduced, and the numerical results are reported. It is fou nd that short-wavelength phonons participate in Brillouin scattering as well as long-wavelength phonons so that the phonon Brillouin spectrum splits. The split is inversely proportional to the thickness of crystal film.