Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session B10: Focus Session: Ferroelectrics II |
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Sponsoring Units: DMP Chair: Javier Junquera, Universidad de Cantabria Room: 304 |
Monday, March 16, 2009 11:15AM - 11:51AM |
B10.00001: Switching behavior and scaling effects in ferroelectric capacitors Invited Speaker: In this presentation, we discuss the results of direct time-space resolved studies of domain switching behavior in micrometer capacitors by means of piezoresponse force microscopy (PFM). The PFM approach allows an insight in the mechanism of polarization reversal and its change as a function of the capacitor size and microstructure. Simultaneous visualization of the instantaneous domain configurations arising during polarization reversal and sub-ms transient current measurements allow us to establish direct relationship between the electrically measured polarization reversal signal and domain switching kinetics and determine the relative contribution of nucleation and wall motion mechanisms into polarization reversal as a function of capacitor size. Effect of microstructure on domain switching kinetics has been studied by comparing the switching behavior of polycrystalline and epitaxial capacitors. It is shown that in epitaxial capacitors the domain kinetics can be described by the classic nucleation model. In the polycrystalline capacitors, interaction of moving domain walls with microstructural defects gives rise to a completely different time dependence of polarization due to a wide distribution of local switching times. In this case the domain kinetics can be fitted by nucleation-limited switching model. [Preview Abstract] |
Monday, March 16, 2009 11:51AM - 12:03PM |
B10.00002: Resolving Deterministic Mesoscopic Mechanisms of Local Bias-Induced Phase Transitions in Ferroelectric Materials S.V. Kalinin, S. Jesse, M.P. Nikiforov, P. Maksymovych, N. Balke, A. Baddorf, H.J. Chang, A.Y. Borisevich, S.J. Pannycook, S. Choudhury, Y. Li, L.-Q. Chen Polarization switching in ferroelectric and multiferroic materials is invariably controlled by defects that act as nucleation and pinning site. Using the synergy of high-resolution spectroscopic Piezoresponse Force Microscopy, materials systems with atomically engineered defects, and phase field modeling, we demonstrate that deterministic mesoscopic mechanisms of polarization switching can be determined. In particular, the artificial bicrystal grain boundary in (100) BiFeO$_{3}$ is found to impede ferroelectric switching, but facilitate ferroelastic switching for one of the constituent crystals. The coupling between ferroelastic domain walls and ferroelectric polarization switching is demonstrated and attributed to the kinetic effects. These studies open the pathway for probing kinetics and thermodynamics of local bias-induced phase transitions and dissipation on a single-defect level using field confinement by an SPM tip. The future potential for atomistic studies is discussed. [Preview Abstract] |
Monday, March 16, 2009 12:03PM - 12:15PM |
B10.00003: Nanometer/Nanosecond Resolved Domain Dynamics Allowing Mapping of Distinct Nucleation and Growth Activation Energies Bryan Huey, Nicholas Polomoff, Vincent Palumbo, James Bosse A high speed variation of AFM is employed to uniquely monitor ferroelectric domain dynamics. Through pump/probe schemes, 20 nanometer resolution and 10 nanosecond temporal resolution is maintained. Consecutive images during switching therefore provide maps of nucleation times, while domain wall growth velocities as high as 25 m/s are observed. By imaging a specific region repeatedly with several pulse amplitudes, activation energies can also be extracted as a function of position, revealing completely independent energies for nucleation and growth that are sample dependent. [Preview Abstract] |
Monday, March 16, 2009 12:15PM - 12:27PM |
B10.00004: Optical cystallography and ferroelectric domain imaging of BaTiO$_3$ nanocrystals with tip-enhanced phonon Raman spectroscopy Samuel Berweger, Catalin C. Neacsu, Yuanbing Mao, Hongjun Zhou, Stanislaus S. Wong, Markus B. Raschke The capability of probing phase transitions, stress, electron-phonon coupling, or doping via their effect on the vibrational structure of crystals has positioned phonon Raman spectroscopy as a powerful tool for the study of semiconductors and dielectrics. In extending the technique to the near-field, the symmetry selectivity of the phonon Raman response allows for optical crystallography on the nanoscale in tip-enhanced Raman spectroscopy taking advantage of the local field enhancement provided by the nanometer size apex of a plasmonic scanning probe tip. The general selection rules that provide the necessary degrees of freedom are derived as a superposition of the crystal Raman tensor, momentum conservation for phonon and light emission, and the symmetry of the near-field tip scattering geometry. The capabilities are demonstrated for the spectrally and spatially resolved identification of intrinsic ferroelectric domains of individual BaTiO$_3$ nanocrystals by probing the A$_1$ TO and E TO phonon modes with nanometer spatial resolution. [Preview Abstract] |
Monday, March 16, 2009 12:27PM - 12:39PM |
B10.00005: Effects of Surface Modification on Photo-Induced Ferroelectric Nanolithography Yang Sun, Chi Xu, Chiyu Zhu, Robert Nemanich This study focuses on the photo-induced deposition of silver on polarity patterned ferroelectric surfaces. The results establish that ferroelectric nanolithography is dependent on the excitation wavelength and that surface modification can affect the process. Depending on the nature of the surface screening, the deposition occurs predominantly on positive domains (internal screening) or at domain boundaries (external screening). In this experimental study periodically poled lithium niobate (PPLN) is used as a template for ``nanolithography'' of metallic nanoparticles and nanowires through a photochemical process. It is shown that the location and rate of Ag nanostructure deposition is dependent on the UV excitation wavelength. Selective deposition is explained by considerations of band-bending, the mechanism of polarization surface charge screening, and the absorption depth of the UV light. In exploring the effects of surface modification, a nm-thick titanium oxide layer is grown on the PPLN surface by molecular beam deposition and the photo-induced Ag deposition process is repeated. It is found that Ag reduction is more selective to the domain boundaries and the positive domains. The results are analyzed in terms of our understanding of the photo-induced process. [Preview Abstract] |
Monday, March 16, 2009 12:39PM - 1:15PM |
B10.00006: Time-Resolved Studies of Polarization Switching in Pb(Zr,Ti)O$_{3}$ Capacitors Invited Speaker: The space and time scales of polarization switching in ferroelectric oxides are fundamentally coupled by the speed of elastic deformations that is approximately the speed of sound. Studying this fast polarization dynamics is essential for understanding the relationships between structure and properties of ferroelectric and multiferroic materials. In last several years, new opportunities have been created for synthesizing ultrathin ferroelectric films and for probing fast structural dynamics in these materials at the nanometer scale. Polarization switching dynamics of Pb(Zr,Ti)O$_{3}$ ferroelectric thin films, which have a large magnitude of switchable polarization and relatively large piezoelectric coefficients, have been comprehensively investigated at millisecond and microsecond time scales. In this talk, I will discuss new regimes of polarization dynamics and piezoelectric strain that can be probed at the nanosecond time scale in Pb(Zr,Ti)O$_{3}$ thin film capacitors using time-resolved x-ray microdiffraction. Using this approach, we have visualized the motion of domain walls during polarization switching, tested piezoelectric strain predictions at strains up to nearly 3{\%}, and found an unusual stability of unswitched polarization in ultrathin films at the nanosecond time scale. [Preview Abstract] |
Monday, March 16, 2009 1:15PM - 1:27PM |
B10.00007: Phase diagram in strained epitaxial BaTiO$_3$/SrTiO$_3$ superlattices studied by ultraviolet Raman spectroscopy Dmitri Tenne, J.D. Schmidt, P. Turner, A. Soukiassian, D.G. Schlom, S. Nakhmanson, X.X. Xi, Y.L. Li, L.Q. Chen, M. Bernhagen, P. Reiche, R. Uecker, R. Katiyar Strain effect on phase transitions in nanoscale BaTiO$_3$/SrTiO$_3$ ferroelectric superlattices (SLs) has been studied by ultraviolet (UV) Raman scattering. A series of coherently strained (BaTiO$_3$)$_8$/(SrTiO$_3$)$_4$ SLs have been grown by molecular beam epitaxiy on rare earth scandate (GdScO$_3$, DyScO$_3$, SmScO$_3$, NdScO$_3$) and SrTiO$_3$ substrates. This allowed a systematic strain variation in the SLs. UV Raman data allowed the determination of the ferroelectric phase transition temperature ($T_c$) and indicated the presence of different ferroelectric phases with out-of-plane and in-plane components of polarization in SLs, depending on strain and temperature. Experimental Raman results are supported by first-principles calculations of structural instabilities in BaTiO$_3$/SrTiO$_3$ SLs and thermodynamic phase-field modeling of phase diagrams and ferroelectric polarization as a function of temperature and strain. [Preview Abstract] |
Monday, March 16, 2009 1:27PM - 1:39PM |
B10.00008: Polarization rotation in epitaxially strained perovskite-oxide superlattices Serge Nakhmanson Utilizing first-principles computational techniques, we have mapped out $\Gamma$-point structural instabilities in (BaTiO$_{3}$)$_{8}$/(SrTiO$_{3}$)$_{4}$ superlattices held at varying degrees of epitaxial strain and constrained to P4mm symmetry with fully developed polarization in the out-of-plane direction. We find that at compressive strains larger than -0.5\% (with respect to a fully relaxed P4mm structure) the superlattices exhibit no structural instabilities. However, at a smaller compressive strain, an in-plane ferroelectric instability emerges in the SrTiO$_{3}$ layers. This instability is then complemented by a similar instability in the BaTiO$_{3}$ layers that develops at tensile strain of more than 0.2\%, suggesting nonzero polarization components for both in- and out-of-plane directions throughout the whole superlattice. [Preview Abstract] |
Monday, March 16, 2009 1:39PM - 1:51PM |
B10.00009: Local polarization discontinuities in perovskite superlattices via compensating heterointerfaces Eamonn Murray, David Vanderbilt Using first-principles methods, we investigate an approach to the production of multicomponent perovskite superlattices with discontinuities in the layer polarizations. The recent paper of Wu and Vanderbilt\footnote{X. Wu and D. Vanderbilt, Phys. Rev. B. {\bf 73}, 020103(R) (2006).} demonstrated how 180$^\circ$ domain walls could be formed in a perovskite superlattice through chemical substitution of atoms in the layer at the domain boundary. We examine an alternative approach in which large discontinuities in the local polarization are induced by constructing superlattices out of II-IV and I-V perovskite constituents. The ``polar discontinuities'' at the heterointerfaces provide compositional charges that approximately cancel the polarization bound charges, thereby allowing stable polarized regions to form. We illustrate the concept via first-principles calculations on KNbO$_3$/SrTiO$_3$ superlattices. We also show how the Wannier-based definition of layer polarization described by Wu {\it et al.}\footnote{X. Wu {\it et al.}, Phys. Rev. Lett. {\bf 97}, 107602 (2006).} may appropriately be applied to a system containing non-neutral layers, and use this to quantitatively examine the local variations in polarization in the KNbO$_3$/SrTiO$_3$ system. [Preview Abstract] |
Monday, March 16, 2009 1:51PM - 2:03PM |
B10.00010: Enhanced piezoelectricity in PbTiO$_{3}$/BaTiO$_{3}$ superlattices Valentino R. Cooper, Karin M. Rabe Short period ferroelectric/ferroelectric PbTiO$_{\rm 3}$ (PTO)/BaTiO$_{\rm 3}$ (BTO) superlattices are studied using density functional theory. Contrary to the trends in paraelectric/ferroelectric superlattices the polarization remains nearly constant for PTO concentrations below 50\%. In addition, a significant decrease in the $c/a$ ratio below the PTO values is observed. We predict an enhancement in the $d_ {33}$ piezoelectric coefficient peaking at $\sim$75\% PTO concentration due to the different polarization-strain coupling in PTO and BTO layers. Further analysis with a superlattice effective Hamiltonian reveals that these trends are bulk properties which are a consequence of the reduced $P$ brought about by the polarization saturation in the BTO layers. [Preview Abstract] |
Monday, March 16, 2009 2:03PM - 2:15PM |
B10.00011: ABSTRACT WITHDRAWN |
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