Optical phonon studies of FeF2 epitaxial thin films

Abstract We have measured the IR active optical phonons of 0.25–2.0 μm FeF 2 thin films, grown epitaxially on ZnF 2 by FTIR reflectance. At T −1 , which we attribute to the E u 1 (TO), E u 3 (TO) and E u 2 (TO) modes of the FeF 2 thin film, respectively. The change in the line shape of the E u 1 (TO)-related absorption was studied as a function of decreasing film thickness. These changes are accurately fit by a simple oscillator model where the film thickness is varied in accordance with its nominal value. An absorption at 115 cm −1 , not attributable to any bulk phonon, may be a surface mode.