Ferroelectricity and local currents in epitaxial 5- and 9-nm-thick Pb(Zr,Ti)O3 ultrathin films by scanning probe microscopy

Ferroelectricity and local currents in 5- and 9-nm-thick Pb(Zr,Ti)O3 ultrathin films epitaxially grown on SrRuO3∕SrTiO3(100) are investigated by current-sensitive atomic force microscopy (CS-AFM) and contact-resonance piezoresponse force microscopy (CR-PFM). CS-AFM observations reveal that large local currents flowed at the step edge of SrRuO3 bottom electrodes. Using CR-PFM, clear contrasts were observed for antiparallel domains, which were not observable by conventional PFM. The observed difference in the deflection signals of flexural vibrations of the cantilever between antiparallel domains is qualitatively explained by coupled contributions from piezoelectric vibrations of the PZT and electrostatic interaction between the cantilever and bottom electrodes. Based on this interpretation, both the 5- and 9-nm-ultrathin PZT films are concluded to exhibit a stable ferroelectric state.