Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session D17: Focus Session: Phase Transitions and Domains in Ferroelectric Nanostructures II |
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Sponsoring Units: FIAP Chair: Alex Demkov, The University of Texas Room: Baltimore Convention Center 313 |
Monday, March 13, 2006 2:30PM - 2:42PM |
D17.00001: High Spatial and Temporal Resolution Optical Probes of Ferroelectric Thin Films Hongzhou Ma, Jeremy Levy, Mike D. Biegalski, Darrell G. Schlom, Susan Trolier-Mckinstry, Won-Jeong Kim, James S. Horwitz Optical probes can provide unique insight into the local ferroelectric properties of thin films. We will describe two techniques that provide sensitive measures of domain structure and dynamics with high spatial and/or temporal resolution: (1) confocal scanning optical microscopy (CSOM), which measures in-plane domain structure of ferroelectric films, and (2) GHz apertureless near-field scanning optical microscopy (GHz-ANSOM) which probes ferroelectric domain dynamics with high spatial resolution ($<$50~nm) and temporal resolution ($\sim $ps). The electro-optic effect, measured using CSOM on strained SrTiO$_{3}$ films, shows clear hysteresis at room temperature, indicating the existence of ferroelectric domains below the diffraction limit. The microwave dynamics of such nanoscale domains can be revealed using GHz-ANSOM. [Preview Abstract] |
Monday, March 13, 2006 2:42PM - 2:54PM |
D17.00002: Domains and Hysteresis Loops in Ferroelectric Thin Films with Metallic and Semiconductor Electrodes A.M. Bratkovsky, A.P. Levanyuk Detailed thermodynamic description of the ferroelectric (FE) thin films with metallic and semiconductor electrodes is presented. We show that imperfect screening by the electrodes results in uncompensated depolarizing field and leads to a tilt of the hysteresis loops, as observed experimentally. We solve for the domain instability analytically and find a simple criterion for stability of homogeneously polarized state in thin films with realistic metallic electrodes. In most cases the film breaks into domains, and they can exist in near cubic (perovskite) ferroelectrics down to ``atomic'' thicknesses (one unit cell thick). Domain structures under bias voltage are investigated. In the case of semiconductor electrodes the screening is poor at small values of polarization $P$ and highly nonlinear at larger $P$ close to a spontaneous polarization in the bulk. This formally allows for the ``Batra-like'' jumpwise transition at lowering temperature, which is not observed since it is preempted by domain instability. Additional boundary conditions [1] modify the above behavior, but mainly for a homogeneous state. The unusual phase behavior in cases of symmetric and asymmetric boundary conditions is discussed together with available experimental data.\newline $[1]$~A. M. Bratkovsky and A. P. Levanyuk, Phys. Rev. Lett. {\bf 94}, 107601 (2005) and to be published. [Preview Abstract] |
Monday, March 13, 2006 2:54PM - 3:30PM |
D17.00003: Domain Structures in Nano-Toroids and Ultra-Thin Single Crystals Invited Speaker: Rationalisation of the formation of domain structures, in ferroics of limited dimensions, has been a topic of interest since the 1940's [1], with early work, specifically in ferroelectrics, in the 1950's [2]. Experimental studies at that time primarily involved domain investigations using optical microscopy, on samples down to the order of hundreds of microns. More modern studies, extending domain research into the thin and ultrathin film regime [3], suggest that our understanding of certain aspects of domain behaviour remain relatively unchanged, despite the intervening decades. This might imply that reduction of scales into the nanometre range will not reveal anything new or interesting in ferroelectric domain research. In this talk, we hope to illustrate that this is not the case. We describe results from two recent research programmes on the characterisation of ferroelectric domain structures in single crystal BaTiO$_{3}$ (BTO) using Scanning Transmission Electron Microscopy. In both studies sample preparation was performed using a Focused Ion Beam Microscope (FIB). In the first study, the domain periodicity has been measured as a function of thickness of parallel-walled BTO slabs from several hundred nanometres down to $\sim $50nm. Early work [2] suggested that the domain width should vary as the square root of slab thickness, and this is consistent with our data. However, we find, in plotting data from several works on different ferroelectric materials, with differing surface boundary conditions, across six decades in thickness, that all data lie on the \textit {same} parent function, with the \textit{same} constants of proportionality. This is totally unexpected, as the proportionality constants should be material and surface boundary state dependent. We suspect that this reveals fundamental aspects in the physics of ferroelectric domain formation that will be discussed. The second study was motivated by modelling done in 1994 by Gorbatsevich and Kopaev [4] and more recently by Fu and Bellaiche [5] and Naumov, Bellaiche and Fu [6]. Here, the influence of depolarization fields at ferroelectric surfaces were found to create polarization vortex structures when the ferroelectrics were sufficiently small. In toroidal shapes, Gorbatsevich and Kopaev even envisioned ordering of the vortices to produce nanoscale ferroelectric `solenoids'. We have used the FIB to make toroidal structures and have characterized their domain morphologies. At the time of writing, only conventional domain behaviour has been observed down to scales of the order of $\sim $100nm. However, results on smaller scales to be performed over the next few months will be described, as well as the novel imaging techniques we intend to use to probe for the ferroelectric vortices. [1] C. Kittel, Physical Review, \textbf{70}, 965 (1946) [2] T. Mitsui and J. Furuichi, Physical Review, \textbf{90}, 193 (1953) [3] S. K. Streiffer \textit{et al.} Phys. Rev Lett. \textbf {89}, 067601 (2002) [4] A. A. Gorbatsevich {\&} Yu V. Kopaev, Ferroelectrics \textbf {161}, 321 (1994) [5] I. Naumov \textit{et al.} Nature \textbf{432}, 737 (2004) [6] H. Fu and L. Bellaiche, Physical Review Letters, \textbf {91}, 257601 (2003) [Preview Abstract] |
Monday, March 13, 2006 3:30PM - 3:42PM |
D17.00004: Three perimeter effects in ferroelectric nanostructures Andreas Ruediger, Frank Peter, Rainer Waser As the lateral size of ferroelectric nanoislands is now well below 50 nm, the question of size effects becomes increasingly relevant. Three independent techniques provided data of pronounced ferroelectric features along the perimeter: impedance spectroscopy [1], piezoelectric force microscopy [2] and pyroelectric current sensing [3]. However, as we can show, all three observations are related to the measurement technique that interferes with the lateral confinement and still there is no direct evidence of a lateral size effect in ferroelectric nanostructures. We discuss some scenarios of further downscaling and possible consequences. [1]M.Dawber, D.J. Jung, J.F. Scott, “Perimeter effect in very small ferroelectrics“,Appl. Phys. Lett. 82, 436 (2003) [2 ]F. Peter, A. Ruediger, R. Dittmann, R. Waser, K. Szot, B. Reichenberg, K. Prume, “Analysis of shape effects on the piezoresponse in ferroelectric nanograins with and without adsorbates”, Applied Physics Letters, 87, 082901 (2005) [3] B.W. Peterson, S. Ducharme, V.M. Fridkin, “Mapping surface Polarization in thin films of the ferroelectric polymer P(VDF-TrFE)”,Ferroelectrics, 304, 51 (2004) [Preview Abstract] |
Monday, March 13, 2006 3:42PM - 3:54PM |
D17.00005: Static Field Anisotropies in Composition-Graded Ferroics J.V. Mantese, A.L. Micheli, N.W. Schubring, R.W. Hayes, G. Srinivasan, S.P. Alpay Compositionally graded ferroelectrics and ferrites are formed as the dielectric and inductive analogues of semiconductor junction devices. The internal, or ``built-in,'' ferroic fields are intrinsic to the structures and are determined from ferroelectric hysteresis and ferromagnetic resonance microscopy. The dynamic response of the ferroelectric and magnetic analysis graded ferroic devices (GFD's) is determined from quasi-static analysis in terms of the spatially dependent order parameters, the polarization and magnetization, respectively; yielding values for the internal ferroic fields consistent with experimental observations. Our results are extended to the general class of ferroic and other ``smart'' materials via a spatially dependent free energy potential. [Preview Abstract] |
Monday, March 13, 2006 3:54PM - 4:06PM |
D17.00006: Geometry Conditions Affecting Piezoresponse Force Microscopy Frank Peter, Bernd Reichenberg, Andreas R\"{u}diger, Krzysztof Szot, Rainer Waser Piezoresponse force microscopy provides valuable insight into the inverse lateral and vertical piezoelectric effect on the nanoscale. When examining ferroelectric grains as opposed to continuous thin films, the measured response is substantially influenced by the topography. Furthermore, a lateral piezoresponse exists in axially symmetric samples. An analysis of the piezoelectric tensor of the material and the radially symmetric electric field applied by the cantilever shows that the lateral as well as the vertical piezoresponse depends on more than one piezoelectric coefficient. This results in an increase of the unexpected lateral response near the perimeter of a grain. Due to the geometry of the cantilever this enhancement is only visible on certain sides of a grain. As a result of a mechanical crosstalk, a part of the lateral signal at the cantilever can be observed in the vertical response. [Preview Abstract] |
Monday, March 13, 2006 4:06PM - 4:18PM |
D17.00007: Calculations of anomalies in properties of relaxor ferroelectric films Maya Glinchuk, Evgeniy Eliseev For the first time, we have calculated the properties of thin relaxor ferroelectric films in a framework of random field theory allowing for a misfit strain between the film and a substrate via surface piezoelectric effect, that causes a built-in electric field in the strained films. We demonstrate that this misfit-induced electric field, as well as the random electric fields created by randomly distributed electric dipoles and charged defects, lead to a smearing of ferroelectric phase transition, namely, they wash out a dielectric susceptibility maximum and a spontaneous polarization temperature dependence. As an example, a dependence of an order parameter and the dielectric susceptibility on the film thickness, temperature, and random fields distribution function was obtained. For the first time, we have shown that a frequency dispersion of susceptibility temperature maximum in relaxor thin films obeys modified Vogel-Fulcher law. In the proposed modified Vogel-Fulcher law the freezing temperature and activation energy depend on the film thickness, namely, freezing temperature decreases and activation energy increases with film thickness decrease. The obtained results quantitatively agree with the available experimental data for PbMg$_{1/3}$Nb$_{2/3}$O$_{3}$ relaxor thin films. [Preview Abstract] |
Monday, March 13, 2006 4:18PM - 4:30PM |
D17.00008: Charge pumping and ferroelectricity in the disordered one-dimensional system Chyh-Hong Chern, Shigeki Onoda, Shuichi Murakami, Naoto Nagaosa We consider the adiabatic charge pumping in the isolated disorder system in one dimension. Different from the Thouless charge pumping, the system has no gap even though all the states are localized, i.e., Anderson Localization. The charge pumping can be done by making a loop adiabatically in the 2- dimensional parameter space $\vec{Q}=(Q_1,Q_2)$ of the Hamiltonian. It is because there are many $\delta$-function- like fluxes distributing over the parameter space with random strength, in sharp contrast to the single $\delta$-function in the pure case. This provides a new and more efficient way of charge pumping. On the other hand, we also consider the situation when system is connected with leads, in which the weakly disordered ferroelectrics will be formulated in the Landauer-Buttiker formalism. In this case, the ``vortex'' structure emerges in the parameter space, which is the origin of the charge transfer for one lead to the other. The vortex core corresponds to the perfect transmittance which can be explained as a resonance tunneling. The time required for the adiabatic charge transfer is also estimated. [Preview Abstract] |
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