Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session A30: Ferroelectric HeterostructuresFocus
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Sponsoring Units: DMP DCMP Chair: Marty Gregg Room: 329 |
Monday, March 14, 2016 8:00AM - 8:36AM |
A30.00001: Observation of Polar Vortices in Oxide Superlattices Invited Speaker: R Ramesh The complex interplay of spin, charge, orbital, and lattice degrees of freedom has provided for a plethora of exotic phase and physical phenomena. Among these, in recent years, topological states of matter and spin textures have emerged as fascinating consequences of the electronic band structure and the interplay between spin and spin-orbit coupling in materials. In this work, we leverage the competition between charge, orbital, and lattice degrees of freedom in superlattices of PbTiO$_{\mathrm{3}}$/SrTiO$_{\mathrm{3\thinspace }}$to produce complex, vortex-antivortex pairs (that exhibit smoothly varying ferroelectric polarization with a 10 nm periodicity)$_{\mathrm{\thinspace }}$that are reminiscent of topological features such as skyrmions and merons. Using a combination of advanced layer-by-layer growth techniques, atomic-resolution mapping of structure and local polar distortions using scanning-transmission electron microscopy, and phase-field modeling approaches we present a comprehensive picture of the nature of the varying polarization profile in such vortex states. The continuous rotation of the polar state into the vortex structures is thought to occur from an interplay of polar discontinuities at the PbTiO$_{\mathrm{3}}$/SrTiO$_{\mathrm{3}}$ interface (where ), the phase transformation strain and gradient energy in the PbTiO$_{\mathrm{3}}$ layer, and the strain imposed by the substrate. Finally, the implications of these observations are discussed as they pertain to producing new states of matter and phenomena in ferroic materials. [Preview Abstract] |
Monday, March 14, 2016 8:36AM - 8:48AM |
A30.00002: The ultrafast response of polar vortices under optical excitation Vladimir Stoica, Yakun Yuan, Zijian Hong, Ajay Yadav, Anoop Damodaran, Yi Zhu, Hua Zhou, Donald Walko, John Freeland, Xiaoyi Zhang, Haidan Wen, Long-Qing Chen, Ramamoorthy Ramesh, Venkatraman Gopalan Polar vortices were recently discovered in PbTiO$_{\mathrm{3}}$-SrTiO$_{\mathrm{3}}$ superlattices [1], stabilized at the nanoscale in the presence of depolarizing fields and mechanical stresses. We have found that these exotic structures, non-existent in the bulk ferroelectrics, possess rich ultrafast responses to fs laser excitation, which is attractive for high-density information storage and nanoscale actuation. Using optical pulse excitation above the bandgap of PbTiO$_{\mathrm{3}}$ layers and structural and second harmonic generation probes of ferroelectric order dynamics, a series of reversible and irreversible nano-ordering transitions were observed. X-ray diffraction and diffuse scattering on nanodomains aided the phase identification during time-resolved measurements. In this talk, we will discuss the dynamic interplay between collinear and toroidal ferroelectric domains aided by understanding from phase field modelling. [1] A.K. Yadav, R. Ramesh et el., "Observation of Polar Vortices in Oxide Superlattices", accepted, Nature (2015). [Preview Abstract] |
Monday, March 14, 2016 8:48AM - 9:00AM |
A30.00003: Ultra-thin single crystal perovskite ferroelectric on Silicon. Saidur Bakaul, Claudy Serrao, Ramesh Ramamoorthy, Sayeef Salahuddin Single crystalline ultra-thin films (sub-10 nm) of ferroelectric complex oxides are important for tunnelling memory [1] devices. Commercially viable realization of such devices requires their integration with the peripheral Si-based input-output electronics. Integration of single crystalline films of such oxides using direct synthesis remains challenging due to the fundamental crystal chemistry and mechanical incompatibility of dissimilar interfaces. In this work we report epitaxial transfer of ultra-thin single crystalline, oxide films (down to 1 unit cell) onto Si substrates, at room temperature. The thickness of the transferred films has been confirmed by atomic force microscopy. Piezoelectric force microscopy shows ferroelectric property is retained in the transferred film. Electrical transport studies on these transferred ultra-thin films are ongoing. [1] Z. Wen, C. Li, D. Wu, A. Li and N. Ming, Ferroelectric-field-effect-enhanced electroresistance in metal/ferroelectric/semiconductor tunnel junctions. Nat. Mater. 12, 617 (2013) [Preview Abstract] |
Monday, March 14, 2016 9:00AM - 9:12AM |
A30.00004: First-principles simulation of negative capacitance in a polydomain ferroelectric-paraelectric bilayer capacitor under bias Shusuke Kasamatsu, Satoshi Watanabe, Cheol Seong Hwang, Seungwu Han The use of negative capacitance materials is gaining attention in recent years as a path to achieving further scaling of nanoelectronic devices [1]. For example, it has been reported that the ferroelectric thin film in a ferroelectric (FE)-paraelectric (PE) bilayer capacitor exhibits negative capacitance, i.e., the bilayer capacitor has a higher capacitance than the capacitor with a single PE layer [2]. However, the mechanism for this effect, especially with regard to the dynamics of polarization domains under bias voltage, is poorly understood. To tackle this issue, we performed first-principles simulation of a metal/FE/PE/metal capacitor with 180$^\circ$ stripe domains under bias using our recently developed orbital-separation approach [3]. We find an antiferroelectric-like behavior with a polydomain-monodomain transition under 0.3 V. Capacitance boost (i.e., negative capacitance) is observed within the monodomain regime, and the transition itself is also found to be a source of capacitance enhancement. [1] G. Catalan et al., Nature Mater. 14, 137 (2015). [2] D. Appleby et al., Nano Lett. 14, 3864, (2014); A. I. Khan et al., Appl. Phys. Lett. 99, 113501 (2011). [3] S. Kasamatsu et al., Phys. Rev. B 84, 085120 (2011); Phys. Rev. B 92, 115124 (2015). [Preview Abstract] |
Monday, March 14, 2016 9:12AM - 9:24AM |
A30.00005: Negative Capacitance in a Ferroelectric Capacitor Asif Khan, Korok Chatterjee, Brian Wang, Steven Drapcho, Long You, Claudy Serrao, Saidur Bakaul, Ramamoorthy Ramesh, Sayeef Salahuddin The Boltzmann distribution of electrons poses a fundamental barrier to lowering energy dissipation in conventional electronics, often termed as Boltzmann Tyranny$^{\mathrm{1}}$. Negative capacitance in ferroelectric materials, which stems from the stored energy of phase transition, could provide a solution, but a direct measurement of negative capacitance has so far been elusive. Here we demonstrate the negative differential capacitance in an epitaxial ferroelectric film, by constructing a simple R-C network and monitoring the voltage dynamics across the ferroelectric capacitor$^{\mathrm{2}}$. When a voltage pulse is applied, the voltage across the ferroelectric capacitor is found to be decreasing with time--in exactly the opposite direction to which voltage for a regular capacitor should change. The results are analyzed on the basis of the Landau-Khalatnikov equation, which shows that as the ferroelectric polarization switches its direction, it passes through the unstable negative capacitance region. Analysis of this behavior from a capacitor presents an unprecedented insight into the intrinsic energy profile of the ferroelectric material. \newline 1. Salahuddin et al. Nano Lett.~8, 405 (2008). 2. Khan et al. Nature Mater. 14, 182 (2015). [Preview Abstract] |
Monday, March 14, 2016 9:24AM - 9:36AM |
A30.00006: The interface between ferroelectric and 2D material for a Ferroelectric Field-Effect Transistor Nahee Park, Haeyong Kang, Sang-Goo Lee, Young Hee Lee, Dongseok Suh We have studied electrical property of ferroelectric field-effect transistor which consists of graphene on hexagonal Boron-Nitride (h-BN) gated by a ferroelectric, PMN-PT (i.e. (1-x)Pb(Mg$_{\mathrm{1/3}}$Nb$_{\mathrm{2/3}})$O$_{\mathrm{3}}$-xPbTiO$_{\mathrm{3}})$ single-crystal substrate. The PMN-PT was expected to have an effect on polarization field into the graphene channel and to induce a giant amount of surface charge. The hexagonal Boron-Nitride (h-BN) flake was directly exfoliated on the PMN-PT substrate for preventing graphene from directly contacting on the PMN-PT substrate. It can make us to observe the effect of the interface between ferroelectric and 2D material on the device operation. Monolayer graphene as 2D channel material, which was confirmed by Raman spectroscopy, was transferred on top of the hexagonal Boron-Nitride (h-BN) by using the conventional dry-transfer method. Here, we can demonstrate that the structure of graphene/hexagonal-BN/ferroelectric field-effect transistor makes us to clearly understand the device operation as well as the interface between ferroelectric and 2D materials by inserting h-BN between them. The phenomena such as anti-hysteresis, current saturation behavior, and hump-like increase of channel current, will be discussed by in terms of ferroelectric switching, polarization-assisted charge trapping. [Preview Abstract] |
Monday, March 14, 2016 9:36AM - 9:48AM |
A30.00007: Symmetry, strain, defects, and the nonlinear optical response of crystalline BaTiO$_{\mathrm{3}}$/silicon. Kristy Kormondy, Stefan Abel, Youri Popoff, Marilyne Sousa, Daniele Caimi, Heinz Siegwart, Chiara Marchiori, Marta Rossell, Alex Demkov, Jean Fompeyrine Recent progress has been made towards exploiting the linear electro-optic or Pockels effect in ferroelectric BaTiO$_{\mathrm{3}}$ (BTO) for novel integrated silicon photonics devices. In such structures, the crystalline symmetry and domain structure of BTO determine which electro-optic tensor elements are accessible under application of an external electric field. For epitaxial thin films of BTO on Si (001), the role of defects in strain relaxation can lead to very different crystalline symmetry even for films of identical thickness. Indeed, through geometric phase analysis of high-resolution scanning transmission electron microscopy images, we map changes of the in-plane and out-of-plane lattice parameters across two 80-nm-thick BTO films. A corresponding 20{\%} difference in the effective electro-optic response was measured by analyzing induced rotation of the polarization of a laser beam ($\lambda \quad =$ 1550 nm) transmitted through lithographically defined electrodes. Understanding, controlling, and modelling the role of BTO symmetry in nonlinear optics is of fundamental importance for the development of a hybrid BTO/Si photonics platform.. [Preview Abstract] |
Monday, March 14, 2016 9:48AM - 10:00AM |
A30.00008: \textbf{Memristive behavior in BaTiO}$_{\mathrm{\mathbf{3}}}$\textbf{ thin films integrated with semiconductors} SRINIVASA RAO SINGAMANENI, John Prater, Jay Narayan BaTiO$_{\mathrm{3}}$ has been studied for emerging non-volatile memory applications. However, most of the previous work has focused on this material when it was deposited on insulting oxide substrates such as SrTiO$_{\mathrm{3}}$. Unfortunately, this substrate is not suitable for CMOS-based microelectronics applications. This motivated us to carry out the present work. We have studied the resistive switching behavior in BaTiO$_{\mathrm{3}}$/La$_{\mathrm{0.7}}$Sr$_{\mathrm{0.3}}$MnO$_{\mathrm{3}}$ (BTO/LSMO) heterostructures integrated with Si (100) using pulsed laser deposition$^{\mathrm{1,2}}$. I-V measurements were conducted on BTO (500nm)/LSMO (25nm) devices at 200K, with the compliance current of 10mA. Here, Pt was used as a top electrode and LSMO served as bottom electrode. A few important observations are noted: (a) broad hysteresis in forward and reverse voltage sweeps --ideal for memory applications, (b) the ratio of high resistance to low resistance state is \textasciitilde 600 --important for switching devices, (c) the device is stable at least up to 50 cycles. However, we found that hysteretic behavior was collapsed after 36 cycles upon oxygen annealing of the device at 1 atmospheric pressure, 200$^{\mathrm{o}}$ C for 1 hour, inferring the important role of oxygen vacancies in the resistive switching behavior of BTO/LSMO device. The comprehensive experimental data will be presented and discussed.$^{\mathrm{1,2}}$\underline {S.R.S}, \textit{et al.,} J. Appl. Phys., \textbf{116}, 094103 (2014); J. Appl. Phys., \textbf{116}, 224104 (2014). [Preview Abstract] |
Monday, March 14, 2016 10:00AM - 10:12AM |
A30.00009: Non-local domain switching in ferroelectric nanostructures Seuri Jeong, Kwang-Eun Kim, Chan-Ho Yang Nanoscale ferroic materials have attracted considerable interest due to their novel properties including electronic, electromachanical and magnetoelectric properties. Until now, exotic ferroelectric structures have been described theoretically such as flux-closure domains, but experimental studies for ferroelectric multi-domains in nanostructures have been a lack of research due to their large domain wall energy. In this study, we realized the radial-quadrant domain structures using strain relaxation known as flexoelectricity. Moreover, we observed that local electric polarization switching can affect distant domain regions to minimize free energy. Our findings provide basic concepts to demonstrate and understand ferroelectric nano-scale multi-domain structures. [Preview Abstract] |
Monday, March 14, 2016 10:12AM - 10:24AM |
A30.00010: Removing pinhole shorts during large scale ferroelectric switching through ionic liquid interfaces Anthony Wong, Andreas Herklotz, Nina Wisinger, Philip Rack, Thomas Ward Ferroelectrics are a classification of materials that spontaneously polarize, accumulating charge at interfaces, and have non-linear hysteretic polarization curves. Switching fields required for ferroelectric materials are often very high, requiring thin insulating layers and high applied voltages. This commonly leads to electric pinholes and limits the areal sizes that can be polarized at a time. Ionic liquids have recently received heavy interest for the formation of electronic double layers which lead to huge electric fields at interfacial regions with low applied biases, and without the thickness constraint associated with conventional capacitors. We will show recent results which demonstrate that ionic liquid gating may offer the ideal solution to switch large regions of a ferroelectric film without limitations associated with pinhole defects. This has great importance to practical applications and fundamental interface studies that require large sample regions to be uniformly polarized. [Preview Abstract] |
Monday, March 14, 2016 10:24AM - 10:36AM |
A30.00011: ABSTRACT WITHDRAWN |
Monday, March 14, 2016 10:36AM - 10:48AM |
A30.00012: Investigation of properties of lithium niobate crystals in confined geometries Keith Veenhuizen, Greg Stone, Bastian Knabe, Sean McAnany, Karsten Buse, Himanshu Jain, Volkmar Dierolf The properties of ferroelectric materials in confined geometries, specifically lithium niobate nanocrystals and crystal lines in glass, were studied. Batches of LiNbO$_3$ nanocrystals have been synthesized from various initial ratios of lithium to niobium using the sol-gel method. The batches were analyzed via Raman spectroscopy and SEM imaging to gain information about their size, morphology, stoichiometry, and defect content. The nanocrystals are very sensitive to the initial stoichiometric ratio in the synthesis step. Raman spectra reveal the resultant nanocrystal stoichiometry depends on the initial stoichiometry of the batch, the spectra also reveal an extra phase is present besides LiNbO$_3$ in some batches, and high quality spherical nanocrystals can be synthesized at certain initial stoichiometric ratios. In addition, lines of LiNbO$_3$ were crystallized in lithium-niobo-silica glass systems with varying amounts of silica to understand and control the nucleation and crystallization of the crystals in glass. [Preview Abstract] |
Monday, March 14, 2016 10:48AM - 11:00AM |
A30.00013: Direct writing of functional ferroelectric waveguides in glass Carl Liebig, Jonathan Goldstein, Gary Cook Femtosecond lasers modify the refractive index of many transparent materials for writing high quality waveguides due to their ability to confine the optical damage to an intended region [1]. They also can precipitate microcrystalline structures in glass and have demonstrated the production of ferroelectric crystals that can be used for optical waveguiding [2,3]. Ferroelectric crystals such as lithium niobate are some of the most widely used optical materials due to their strong electro-optic, piezoelectric, and photorefractive properties. The structure and alignment of the precipitated ferroelectric crystals can be controlled through the incident beam profile, writing speed and the starting material composition[2]. In this study crystalline waveguide structures were be written in 33LiO$_{\mathrm{2}}$-33Nb2O$_{\mathrm{5}}$-34SiO$_{\mathrm{2}}$ (mol{\%}) glass, characterized, the structural orientation determined, and their waveguiding performance tested. This procedure was then modified to functionalize the precipitated waveguides for photonic and holographic applications. [1] C. Mauclair et al., Opt. Exp. 16, (2008). [2] A. Stone et al., Sci. Reports \textbf{5}, 10391 (2015). [3] T. Komatsu et al., J. Sol. State Chem. 184, 411 (2011). [Preview Abstract] |
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