Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session J39: Phase Transitions in Surfaces and Films: Ferroelectrics and Multiferroics |
Hide Abstracts |
Sponsoring Units: DCMP Chair: T. Kimura, Los Alamos National Lab Room: Conference Center 514 |
Tuesday, March 22, 2005 11:15AM - 11:27AM |
J39.00001: Thickness dependent ferroelectric properties of BaTiO3 ultra-thin films J. Y. Jo, Y. S. Kim, D. J. Kim, T. W. Noh, T. K. Song, J.-G Yoon For decades, ferroelectricity in ultra-thin ferroelectric films has attracted much attention because of high-density nonvolatile memory application. Recently, first-principle calculation on the thickness limit of ferroelectricity in BaTiO$_{3}$(BTO) thin films was reported [1]. Experimental evidence of thickness limit and macroscopic polarization behaviors in the ultra-thin ferroelectric films were rarely studied. In this work, we investigated thickness dependence of polarization retention properties and coercive field in BTO films. SrRuO$_{3}$/BTO/SrRuO$_{3}$ capacitors were prepared with BTO layer thickness from 30 nm to 5 nm. From the electrical measurements, we observed that the upper limit of the critical thickness should be less than 5 nm. All the capacitors showed rapid relaxation of polarization in 1 s, and coercive field is independent of thickness. We would discuss these thickness-dependent polarization relaxation and coercive field in connection with depolarization field, which plays an important role in ultra-thin ferroelectric capacitor [2]. [1] J. Junquera and P. Ghosez, Nature (London) \textbf{422}, 506 (2003). [2] A. M. Bratkovsky and A. P. Levanyuk, Phys. Rev. Lett. \textbf{84}, 3177 (2000). [Preview Abstract] |
Tuesday, March 22, 2005 11:27AM - 11:39AM |
J39.00002: Effective Hamiltonian modeling of ferroelectric ultra-thin films Inna Ponomareva, Ivan Naumov, Igor Kornev, Huaxiang Fu, Laurent Bellaiche We have further extended first principles Hamiltonian approaches [1,2] that are applicable to the bulk systems (i.e., 3D systems periodically repeated in all three Cartesian directions) to study ferroelectric properties of ultra-thin films. The main feature of our new approach is that we treat the dipole-dipole interactions for the systems with 2D periodicity {\it exactly}, based on the symmetrized Green's function $\mathcal{G}(\mathbf{r'},\mathbf{r})$ of the Laplace equation. Although essentially microscopic, our model nevertheless accurately reproduces macroscopic characteristics such as depolarization and Lorentz fields in the limit of thick films. Within this approach, the finite-temperature behavior of different ferroelectric ultra-thin films have been simulated under different boundary conditions. Our results (1) are compared with those obtained in the framework of a 3D-like approach [3] that uses thick vacuum gaps between the periodic replicas of the films within an atomistic Hamiltonian, (2) provide a deep microscopic understanding of ferroelectric thin films. This work is supported by NSF grants DMR-0404335 and DMR-9983678 and by ONR grants N 00014-01-1-0365, N 00014-04-1-0413 and N 00014-01-1-0600. [1] Zhong {\it et al}, Phys. Rev. Lett. {\bf 73}, 1861 (1994); Phys. Rev. B {\bf 52}, 6301 (1995). [2] L. Bellaiche {\it et al}, Phys. Rev. Lett. {\bf 84}, 5427 (2000). [3] I. Kornev {\it et al}, Phys. Rev. Lett. {\bf 93}, 196104 (2004). [Preview Abstract] |
Tuesday, March 22, 2005 11:39AM - 11:51AM |
J39.00003: Ferroelectricity in Ultrathin Perovskite Films in Metal-Ferroelectric-Metal Junctions C. Duan, R. Sabirianov, W.-N. Mei, S.S. Jaswal, E. Tsymbal We present first-principles studies of electronic and ferroelectric properties of Metal/Ferroelectric/Metal junctions. We consider KNbO$_{3}$ as the ferroelectric, while strontium ruthenite, SrRuO$_{3}$, and platinum, Pt, as metals. These materials have a match in the lattice constants, which eliminates the appearance of stresses and misfit dislocations. We utilize the projector augmented plane wave method to perform the first principles calculations. The fully relaxed geometry of the structure is obtained assuming that the substrates have bulk lattice parameters away from the interface. We use the Berry phase formalism to obtain the polarization of the ferroelectric layer. The calculation of the electric polarization requires a proper subtraction of the Berry phase for the reference paraelectric structure from that for a distorted structure. We show the existence of ferroelectricity in these heterostructures at ferroelectric thickness of 0.22nm. We find that for the case of asymmetric leads, i.e. for the SrRuO$_{3}$/KNbO$_{3}$/Pt junction, the electrostatic potential profile across the ferroelectric layer is asymmetric with respect to the direction of the electric polarization suggesting a change in transport properties with switching the electric polarization. This work is supported by Nebraska Research Initiative and National Science Foundation. [Preview Abstract] |
Tuesday, March 22, 2005 11:51AM - 12:03PM |
J39.00004: UV Raman study of ferroelectric BaTiO3/SrTiO3 superlattices D.A. Tenne , X.X. Xi, A. Soukiassian, J.H. Haeni, W. Tian, D.G. Schlom, Y.L. Li, L.Q. Chen, K.M. Rabe, X.Q. Pan, R.S. Katiyar The results of the first experimental study of ferroelectric short-period superlattices (SLs) by ultraviolet (UV) Raman spectroscopy will be presented. The high quality (BaTiO$_{3})_{m}$/(SrTiO$_{3})_{n}$ SLs (m, n are between 4 and 10 unit cells) with atomically smooth interfaces were grown by molecular beam epitaxy on SrTiO$_{3}$ substrates. Raman spectroscopy with UV excitation (351.1 nm) made possible the observation of superlattice phonons without overwhelming substrate signal in the spectra. Raman data on the BaTiO$_{3}$ phonons show that BaTiO$_{3}$ layers in SLs remain in the tetragonal phase in the entire temperature range studied (80-400K), and the low-temperature phases characteristic for bulk BaTiO$_{3}$, are suppressed. Biaxial compression of BaTiO$_{3}$ layers in SLs is likely cause for such a behavior, according to the calculated phase diagram for BaTiO$_{3}$ as a function of temperature and strain. Features attributed to the first-order Raman scattering in SrTiO$_{3}$ layers indicate that the inversion symmetry is broken, and the SrTiO$_{3}$ layers in the SLs are polar. Supported in part by DOE (Grant {\#} DE-FG02-01ER45907). [Preview Abstract] |
Tuesday, March 22, 2005 12:03PM - 12:15PM |
J39.00005: Domain Size Dependence of Piezoelectric Properties of Ferroelectrics Avadh Saxena, Rajeev Ahluwalia, Turab Lookman, Wenwu Cao The domain size dependence of piezoelectric properties of ferroelectrics is investigated using a continuum Ginzburg-Landau model that incorporates the long-range elastic and electrostatic interactions. Microstructures with desired domain sizes are created by quenching from the paraelectric phase by biasing the initial conditions. Three different two-dimensional microstructures with different sizes of the $90^{o}$ domains are simulated. An electric field is applied along the polar as well as non-polar directions and the piezoelectric response is simulated as a function of domain size for both cases. The simulations show that the piezoelectric coefficients are enhanced by reducing the domain size, consistent with recent experimental results of Wada and Tsurumi (Brit. Ceram. Trans. {\bf 103}, 93, 2004) on domain engineered $BaTiO_{3}$ single crystals. [Preview Abstract] |
Tuesday, March 22, 2005 12:15PM - 12:27PM |
J39.00006: Atomistic View of Manganite Thin Films by Scanning Tunneling Microscopy Jianxing Ma, Ward PLummer, Jian Shen Perovskite manganites Ln1-xMxMnO3(Ln=La, Pr, Nd, M=Ca, Sr, Ba, Pb) have been extensively studied due to the famous CMR effect. However, the underlying mechanism is not yet well understood. It is generally accepted that polaron plays a very important role. Scanning tunneling microscopy and spectroscopy (STM/S) capable of obtaining atomic structure and electronic information near the Fermi level at atomic resolution has been extremely successful in studying layered transition metal oxide superconductors. To study the manganites with STM/S, we have developed an in-situ Laser MBE system. Atomic resolution has been successfully achieved in manganite thin films. Results pertaining to phase separation and polaron effects will be discussed in this talk. Research sponsored by the U. S. Department of Energy under contract DE-AC05-00OR22725 with the Oak Ridge National Laboratory, managed by UT-Battelle, LLC [Preview Abstract] |
Tuesday, March 22, 2005 12:27PM - 12:39PM |
J39.00007: Control of La$_{0.5}$Ca$_{0.5}$MnO$_3$ superstructure through epitaxial strain release S. Cox, E.J. Rosten, J.C. Loudon, J.C. Chapman, D.-J. Kang, M.J. Calderon, P.B. Littlewood, P.A. Midgley, N.D. Mathur Intergranular variations of superlattice periodicity in polycrystalline La$_{1-x}$Ca$_{x}$MnO$_3$ have been attributed to variations in strain. Here we control the superlattice periodicity within a continuous crystal. A focussed ion beam microscope (FIB) was used to pattern an electron transparent window in an untwinned coherently strained epitaxial thin film of La$_{0.5}$Ca$_{0.5}$MnO$_3$ grown on NdGaO$_3$ by pulsed laser deposition. It was found that the wavenumber could be reduced by 3\% in regions isolated by cuts from the rest of the window. We attribute this variation to the release of epitaxial strain beyond the resolution of the electron microscope. [Preview Abstract] |
Tuesday, March 22, 2005 12:39PM - 12:51PM |
J39.00008: Intrinsic Character of the 3x3 to R3xR3 Phase Transition in Pb/Si(111): True variable Temperature STM Experiments Ivan Brihuega, Oscar Custance, Ruben Perez, Jose Maria Gomez-Rodriguez We have studied the (3x3) to (root 3 x root 3) reversible phase transition in Pb/Si(111) by means of variable temperature scanning tunneling microscopy and density functional first-principles calculations. This phase transition consists on a lowering of the symmetry of the system produced by a change of the surface periodicity that evolves from a (root 3 x root 3) at room temperature to a (3x3) at low temperature. We have been able to prepare extremely large domains completely free of defects. These large free of defects regions, together with our ability to track the same area with atomic resolution in a temperature range between 40 K and 200 K have allowed us to detect the intrinsic character of the phase transition at temperatures around 86 K. This intrinsic character is in full agreement with our first-principles calculations. Moreover, our results show that the hypothesis that point defects play a fundamental role as the driving force, reported for similar systems, can be discarded for Pb/Si(111). [Preview Abstract] |
Tuesday, March 22, 2005 12:51PM - 1:03PM |
J39.00009: Observing a Wetting Transition for Water Shinya Segawa, Robert Weiler, Rafael Garcia A liquid is said to wet a solid surface if it spontaneously spreads out uniformly over the surface. It is said to not wet the surface, if it remains a droplet on the surface, exhibiting a finite contact angle. A wetting transition is defined as an abrupt change from non-wetting to wetting or vice-versa. Water does not wet most semiconductor and metal surfaces near room temperature. However, recent state-of-the-art theoretical calculations [1] predict that water should exhibit a wetting transition on these surfaces, completely wetting them at high temperatures. The search for this wetting transition is difficult because at high temperatures, water can be quite oxidizing and has a very high vapor pressure. An experimental cell has been constructed suitable for careful thermodynamic optical studies of liquid water droplets on solid surfaces. Preliminary experimental results will be presented. [1] M. Gatica, X. Zhao, J. K. Johnson and M. W. Cole, J. Phys. Chem. B 108, 11704 (2004). [Preview Abstract] |
Tuesday, March 22, 2005 1:03PM - 1:15PM |
J39.00010: Surface and Interface studies of Au overlayers on 4H-SiC(000-1) Chariya Virojanadara, Leif Johansson The effects of Au overlayers prepared on the SiC(000-1) surface have been investigated. A 2x2 reconstructed surface was prepared by Si deposition at substrate a temperature of 800$^{o}$C. A 3x3 reconstructed surface was prepared by in situ heating to ca 1050$^{ o}$C. By utilizing high resolution photoemission and synchrotron radiation together with low energy electron diffraction, the formation of ordered overlayer structures was identified and features developing in the Si 2p, C 1s and Au 4f core level spectra were investigated in detail. After Au deposition on the 2x2 reconstructed surface and annealing a new stable $\surd $7x$\surd $7 R 19$^{o}$ surface reconstruction was identified by LEED and surface related components were observed in Si 2p and Au 4f core levels. After Au deposition on the 3x3 reconstructed surface and annealing no new stable reconstruction was observed to form. In the C 1s core level no significant changes were possible to detect after Au deposition and annealing. These findings will be presented and discussed. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700