Experimental identification of the optical phonon of CoSi2 in the infrared

A weak but clear optical structure was detected at 329 cm−1 by both reflectance and transmittance measurements in the far infrared on a 430 Å film of CoSi2 grown on Si(100). This is the first observation of the IR vibrational mode of the cubic structure of CoSi2 and the result is in very good agreement with theoretical calculations. In order to characterize the sample, the reflectance was extended up to 5.2 × 104 cm−1 and the refractive index was also directly obtained in a more limited spectral range by spectroscopic ellipsometry. The IR structure was then quantitatively analyzed by means of a fit procedure, obtaining the values of ω0 = 327 cm−1 for the phonon energy, of γ = 10.5 cm−1 for the damping parameter and of ∼ 0.006 electronic charges for the screened effective ionic charge.