Stabilization of Ferroelectric Polarization of Ultrathin Films by Surface Modification with Ion Beams

Abstract

The stabilization of spontaneous polarization in ultrathin ferroelectric films was studied. For this purpose, surface modification by implantation of metal ions with energies of 10²–10³ eV was proposed. Based on Lindhard–Scharff–Schiøtt (LSS) theory, this approach made it possible to consider the electronic energy-loss mechanism during interaction and excitation of the electronic subsystems of the interacting ions. The Thomas–Fermi screening length λ_F–D and Debye screening length λ_D were calculated to determine the conditions for screening the electric charge of free electrons. The importance of accounting for the temperature dependence of the dielectric permittivity ε(T) of the ferroelectric target when selecting the temperature conditions for surface modification by ion beams was demonstrated. This dependence is associated with activation processes of the ferroelectric phase transition having different activation energies, including activation and interaction of the defect, domain, and electronic structures of the ferroelectric. To select the metal ion for implantation, the interaction potential U between the implanted metal ions and the ions of the cubic perovskite crystal structure was calculated using the Thomas–Fermi model with an exponential function describing electron screening of the nuclei. SrTiO₃, BaTiO₃, PbTiO₃, and the Pb(Zr,Ti)O₃ solid solution were used as model samples.