Ferroelectric PbTiO3/BaTiO3 superlattices: Growth anomalies and confined modes

We have used laser ablation to grow series of PbTiO3/BaTiO3 (PTO/BTO) multilayers with a modulation wavelength Lambda that varies between 50 Angstrom < Lambda < 360 Angstrom. Modeling the x-ray-diffraction patterns of the multilayers indicates that the PTO layers are a-axis oriented. The Raman measurements reinforce this interpretation. The soft-mode Raman line shifts abruptly in frequency above Lambda = 240 Angstrom due to possible strain relaxation of the multilayer, and the Lambda dependent position of an asymmetric line in the vicinity of 200 cm(-1) is modeled as a confined mode, a signature of a modulated structure.