Surface-Enhanced Raman Scattering Spectroscopy Reveals the Phonon Softening of Yttrium-Doped Barium Zirconate Thin Films

Stress-induced changes in the lattice dynamics strongly affect the proton transport in perovskites. Phonon softening as a result of tensile stress is expected to enhance the proton conductivity in yttrium-doped barium zirconate (BZY) thin films. Vibrational properties of materials are extensively studied by Raman spectroscopy. However, the sensitivity of Raman scattering in BZY films is low. Surface-enhanced Raman spectroscopy can characterize the vibrational motions of nanomaterials through the amplification of electromagnetic fields generated by the excitation of localized surface plasmons. In this work, we use commercial Ag nanowires to enhance the Raman signal and successfully measure the Raman spectra of BZY thin films. Qualitative analysis to the spectra from films with three different thicknesses allows us to resolve the difference between phonon frequencies of highly textured film and less textured polycrystalline films. We found that a highly textured film with preferred (100) orientation under tensile stress exhibits phonon softening with lower Zr–O stretching vibration energy. This work enables future investigation on the stress-induced phonon-assisted proton transport in thin films.