Infrared Spectroscopic, X-ray and Nanoscale Characterization of Strontium Titanate Thin Films

Attenuated total reflectance (ATR) measurements were performed using Fourier transform infrared (FTIR) spectroscopy in the ATR mode with a thallium iodobromide (KRS-5) crystal to measure the frequencies of the v3 and v4 phonon absorption bands in thin strontium titanate films deposited on single-crystal yttrium-barium copper oxide (YBCO), lanthanum aluminate, magnesium oxide, and strontium titanate substrates. The KRS-5 crystal enabled FTIR-ATR measurements to be made at frequencies above 400 cm^-1. Atomic force microscopy (AFM) and X-ray diffraction (XRD) measurements were also made to further characterize the films. The measurements were repeated on single-crystal specimens of strontium titanate and the substrates for comparison. Softening in the frequency of the v4 transverse optical phonon in the lattice-mismatched films below the established value of 544 cm^-1 is indicative of the highly textured, polycrystalline ceramic nature of the films and is consistent with the XRD and AFM results.