Structural dynamics of PZT thin films at the nanoscale
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0902-T06-09.1
Structural dynamics of PZT thin films at the nanoscale Alexei Grigoriev1, Dal-Hyun Do1, Dong Min Kim1, Chang-Beom Eom1, Bernhard Adams2, Eric M. Dufresne2, and Paul G. Evans1 1 Department of Materials Science and Engineering, University of Wisconsin Madison, Madison, Wisconsin 53705, USA 2 Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, USA ABSTRACT When an electric field is applied to a ferroelectric the crystal lattice spacing changes as a result of the converse piezoelectric effect. Although the piezoelectric effect and polarization switching have been investigated for decades there has been no direct nanosecond-scale visualization of these phenomena in solid crystalline ferroelectrics. Synchrotron x-rays allow the polarization switching and the crystal lattice distortion to be visualized in space and time on scales of hundreds of nanometers and hundreds of picoseconds using ultrafast x-ray microdiffraction. Here we report the polarization switching visualization and polarization domain wall velocities for Pb(Zr0.45Ti0.55)O3 thin film ferroelectric capacitors studied by timeresolved x-ray microdiffraction. INTRODUCTION An important problem in physics is the study of structural phase transitions in solid state systems. A displacive phase transition in ferroelectrics results in the reversal of the remnant polarization direction in response to a briefly applied electric field. This polarization switching in solid ferroelectrics, such as the perovskites BaTiO3 or Pb(Zr,Ti)O3 (PZT), is a complex process involving nucleation and growth of polarization domains. There are constraints on the transition speed, which is ultimately limited by the speed of sound to several km/s [1]. To resolve structural details of the polarization domain evolution it is essential to combine submicrometer spatial resolution and sub-nanosecond time resolution in one experiment. The spatial resolution of traditional microscopies, scanning and transmission electron microscopies and scanning tunneling microscopy is sufficient in many cases to observe individual atoms. The time resolution of these methods is, however, fundamentally limited by probe-sample interactions and the response time of the probes that makes their application to structural dynamics problems seldom [2]. X-rays are better suited for studying dynamics. At present, the best time-resolution demonstrated in x-ray pump-probe experiment is less than 1 ps [3]. X-ray diffraction is not only sensitive to subtle changes of a lattice spacing of a crystalline solid but it is also able to distinguish between structurally similar polarization states using anomalous x-ray scattering [4]. The contrast between opposite polarizations is a result of the noncentrosymmetric unit cell of ferroelectrics. The (002) and (00-2) Bragg reflections of the tetragonal phase of PZT correspond to opposite polarization states and can differ in intensity by 30% or more [4]. The development of x-ray microscopy is closely coupled to advances in x-ray radiation sources
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