We analyze the structural, vibrational, and elastic properties of epitaxial novel FeSi films on Si(111) in the CsCl structure by Rutherford-backscattering spectrometry, x-ray-diffraction, infrared transmittance/ reflectance, and Brillouin-light-scattering measurements. By comparing our results for different film thicknesses and by interpreting them on the basis of semiempirical total-energy calculations, we are able to relate the changes in vibrational properties with the progressive strain relaxation as a function of sample thickness. For the thickest film (890) we obtain indications that a structural transition to the (bulk) ε phase is about to take place. © 1994 The American Physical Society.