Collective dynamics in nanostructured polycrystalline ferroelectric thin films using local time-resolved measurements and switching spectroscopy Samantha Wicks a , Katyayani Seal b , Stephen Jesse b , Varatharajan Anbusathaiah a , Sarah Leach c , R. Edwin Garcia c , Sergei V. Kalinin b , Valanoor Nagarajan a, * a School of Materials Science and Engineering, University of New South Wales, Sydney, NSW 2052, Australia b The Centre for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN 37922, USA c School of Materials Engineering, Purdue University, West Lafayette, IN 47907, USA Received 6 March 2009; received in revised form 17 July 2009; accepted 26 August 2009 Available online 24 September 2009 Abstract Grain-to-grain long-range interactions and the ensuing collective dynamics in the domain behavior of nanostructured polycrystalline Pb(Zr,Ti)O 3 ferroelectric thin films have been investigated. To identify the key factors and interactions controlling local polarization dynamics we utilize a synergistic approach based on focused ion beam (FIB) milled damage-free nanostructures to isolate single grains and grain clusters, time-resolved piezoresponse force microscopy and switching spectroscopy PFM (SSPFM) (PFM) to address polar- ization dynamics within individual grains, and finite-element simulations to quantify the local ferroelectric interactions and hence assess the weight of several possible switching mechanisms. The experiments find that of the three possible switching mechanisms, namely direct electromechanical coupling, local built-in electric field and strain, and grain boundary electrostatic charges, the last one is the dominant mechanism. Although finite-element simulations find that direct electromechanical coupling and local built-in field-induced switching are possible, calculations confirm that for the utilized material properties, the aforementioned mechanisms are energetically unfavored. Ó 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Keywords: Ferroelectricity; Nanostructure; Piezoelectricity 1. Introduction Nanostructured polycrystalline ferroelectric thin films have found a broad range of applications in high-density memory, micro electromechanical systems, sensors and actuators [1]. Ferroelectric polarization switching under- pins fundamental device functionality, motivating an extensive experimental effort to understand nanoscale domain morphology and domain behavior [2–10,11]. While most of the studies to date have focused predominantly on single-crystal or epitaxial films, scalability and cost consid- erations dictate that ferroelectric devices are fabricated from polycrystalline (albeit textured) films. In polycrystal- line materials, microstructural features such as grain boundaries are inevitable, and crystallographic orienta- tional disorder provides nucleation centers for polarization reversal and pinning [12]. Spatial coupling between electri- cal and mechanical fields at interfaces such as grain bound- aries lead to highly intricate nanoscale domain switching behaviors [13–15] that are associated with long-range elas- tic and piezoelectric interactions that result in complex col- lective grain dynamics. Recently, it was demonstrated that the local switching of individual grains in polycrystalline films resulted in unex- pected domain reorientation [16]. The results were explained on the basis of the presence of collective interac- tions within the polycrystalline material. However, details 1359-6454/$36.00 Ó 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.actamat.2009.08.057 * Corresponding author. E-mail address: nagarajan@unsw.edu.au (V. Nagarajan). www.elsevier.com/locate/actamat Available online at www.sciencedirect.com Acta Materialia 58 (2010) 67–75