Infrared characterization of SrTiO/sub 3/ thin films using attenuated total reflectance

Attenuated Total Reflectance was used to measure the phonon vibration frequencies over the range 425-800 cm/sup -1/ of SrTiO/sub 3/ thin films deposited either directly on LaAlO/sub 3/, or on YBCO-coated LaAlO/sub 3/ single crystal substrates. In the s-polarized spectra, the transverse optic Ti-O stretching vibration shifted to lower frequencies as the film thickness increased, which was attributed to damping caused by the generation of lower frequency phonon modes. The transverse Ti-O stretching vibration was also observed in the p-polarized spectra, but was more heavily damped, which indicates the damping is more pronounced when the electric field has a component perpendicular to the film surface. Damping of the transverse modes was attributed to coupling of these modes to other phonon modes, and may be a source of the high losses at microwave frequencies.