Nanopolar reorientation in ferroelectric thin films

The influence of varying oxygen pressure P(O-2) during the growth of Ba0.4S r0.6TiO3 thin films is investigated using dielectric and local optical prob es. A transition from in-plane to out-of-plane ferroelectricity is observed with increasing P(O-2). Signatures of in-plane and out-of-plane ferroelect ricity are identified using dielectric response and time-resolved confocal scanning optical microscopy (TRCSOM). At the crossover pressure between in- plane and out-of-plane polarization (P-c=85 mTorr), TRCSOM measurements rev eal a soft, highly dispersive out-of-plane polarization that reorients in p lane under modest applied electric fields. At higher deposition pressures, the out-of-plane polarization is hardened and is less dispersive at microwa ve frequencies, and the dielectric tuning is suppressed. Nanopolar reorient ation is believed to be responsible for the marked increase in dielectric t uning at P(O-2)=P-c. (C) 2001 American Institute of Physics.