PHONON-MODE HARDENING IN EPITAXIAL PBTIO3 FERROELECTRIC THIN-FILMS

Using (110) NdGaO3 wafers as the lattice matched substrates, PbTiO3 th in films have been epitaxially grown by metal-organic chemical vapor d eposition under reduced pressure. Highly resolved Raman spectra of the thin films have been recorded by a grazing-angle scattering technique . The E(1TO) mode of the epitaxial film has been observed to have a 7- cm(-1) upward shift compared to the bulk PbTiO3 single crystal, which is different from the soft-mode behavior observed in PbTiO3 ultrafine powder and polycrystalline thin films. This transverse optical mode up shift phenomenon is attributable to the residual in-plane compressive stress in the epitaxial thin film caused by the film-substrate interac tion. This phonon-mode-shift phenomenon provides a method to estimate the residual stresses existing in a ferroelectric thin film.