Residual stress estimation in ferroelectric PbTiO3 thin films by Raman spectroscopy

A comparative analysis of Raman spectra from polydomain PbTiO3 thin films with both polydomain and single-domain PbTiO3 crystals is presented. The Raman signature of ferroelectric thin films is complex when used for stress analysis. Raman spectroscopy of a stress-free polydomain PbTiO3 single crystal reveals that the profile of phonon modes can be significantly modified by the existence of quasimodes. The different potential origins of quasimodes are discussed, and it is emphasized that quasimodes should be taken into account for an accurate estimation of residual stress values in ferroelectric films via Raman scattering. We finally propose and illustrate that the E(3TO) hard mode is more reliable for the estimation of biaxial residual stress in PbTiO3 than the commonly used E(1TO) soft mode.