We analyze the structural, vibrational, and elastic properties of epit
axial 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 comparin
g our results for different film thicknesses and by interpreting them
on the basis of semiempirical total-energy calculations, we are able t
o relate the changes in vibrational properties with the progressive st
rain relaxation as a function of sample thickness. For the thickest fi
lm (890 angstrom) we obtain indications that a structural transition t
o the (bulk) epsilon phase is about to take place.