INVESTIGATION OF THE STRUCTURE OF BARIUM-TITANATE THIN-FILMS BY RAMAN-SPECTROSCOPY

Raman spectroscopy was used to examine the structure of barium titaniu m oxide thin films grown by metal-organic chemical vapor deposition (M OCVD) and laser-assisted deposition: The spectra were compared with th e spectra of a ceramic specimen and a single crystal. Raman peaks spec ific to the tetragonal ferroelectric phase of BaTiO3 were seen in the spectra of several films. Other Raman peaks were ascribed to impurity (non-BaTiO3) phases in the films or to the substrates (fused quartz, M gO). Some of the Raman peaks showed a strong polarization dependence. The MOCVD films were also characterized by x-ray diffraction, energy-d ispersive x-ray spectroscopy, and transmission electron microscopy. Th e film-to-film variation of the strength of BaTiO3 features in the Ram an spectrum, relative to impurity-phase features, was qualitatively co nsistent with the x-ray diffraction and electron microscopy results. S patially resolved Raman measurements showed that the structure of the laser-deposited film varies significantly over the deposited area. The temperature dependencies of the Raman spectra of two MOCVD films were examined in the 25-175 degrees C range. Raman peaks due to the tetrag onal phase of BaTiO3 were observed at temperatures well above the Curi e temperature of bulk single-crystal BaTiO3 (132 degrees C). This obse rvation suggests that the tetragonal ferroelectric phase is stabilized by an anisotropic film-substrate interaction that gives rise to a two -dimensional stress in the plane of the film. (C) 1994 American Instit ute of Physics.