Raman and x-ray photoelectron spectroscopy study of ferroelectric switching in Pb(Nb,Zr,Ti)O3 thin films

Abstract

The ferroelectric switching process in Pb(Nb,Zr,Ti)O3 thin films was studied by performing Ramanspectroscopy and x-ray photoelectron spectroscopy (XPS). Switching was achieved using a macroscopic polarization experiment above and below the Curie temperature. Two samples in opposite switching states were obtained and characterized in order to correlate both vibrational-bands distortions of the bulk and changes in the elemental states of the surface. We have assigned the symmetrical A1(2TO) (332 cm−1) and A1(3TO) (603 cm−1) vibrational modes to the ferroelectric phase. Their corresponding peaks-area showed symmetrical behavior when the sample was polarized in opposite directions, while the quantity of phonons associated to the ferroelectric phase was conserved. We found that binding energies in the XPS signals of the Ti 2p, Nb 3d, Zr 3d, and Pb 4f levels increased when comparing to the values found in a non-polarized sample. Moreover, a high population of oxygen vacancies diffused to the surface of the ferroelectric capacitor under the application of external electric fields. Our novel results show the correlation between vibrational and ferroelectric behaviors and highlight the possibility to perform in situ treatments to decrease thedegradation of current technological capacitors.