Symposium Organizers
James F. Scott University of Cambridge
Venkatraman Gopalan The Pennsylvania State University
Masanori Okuyama Osaka University
Manuel Bibes Universite Paris-Sud
K1: Multiferroics I
Session Chairs
Gustau Catalan
Ram S. Katiyar
Monday PM, November 26, 2007
Grand Ballroom (Sheraton)
9:00 AM - K1.1
The β Phase of Multiferroic Bismuth Ferrite and Itsγ-β Metal-Insulator Transition.
Ratnakar Palai 1 , Ram Katiyar 1 , James Scott 2
1 Department of Physics, University of Puerto Rico, San Juan, Puerto Rico, United States, 2 Department of Earth Science, University of Cambridge, Cambridge, England, United Kingdom
Show AbstractWe have carried out extensive experimental studies, including differential thermal analysis, polarized and high-temperature Raman spectroscopy,high-temperature X-ray diffraction, optical absorption and domain imaging, and show that epitaxial (001) thin films of multiferroic bismuth ferrite (BiFeO3) are monoclinic at room temperature insteadof tetragonal or rhombohedral like bulk as reported earlier. We report a ferroelastic and orthorhombic order-disorder β-phase between 820 and 950 oC contrary to the earlier report before the transition towrad a high-temperature cubic phase. The transition sequence rhombohedral-orthorhombic in bulk (monoclinic-orthorhombic in (001)BFO thin film) resembles that of BaTiO3 or PbSc1/2Ta1/2O3. The transition to the high-temperature cubic γ-phase causes an abrupt collapse of the bandgap toward zero (insulator-metal transition) at the orthorhombic-cubic β-γ transition around 950\dc. Our band structure models confirm this metal-insulator transition, which is similar to the metal-insulator transition inBa0.6K0.4BiO3 and perovskitr rare-earth nickaltes (RENiO3 (RE= La, Pr, Nd, Sm).
9:15 AM - K1.2
Bismuth Ferrite Nanostructures.
Tae-Jin Park 1 , Georgia Papaefthymiou 3 , Arthur Viescas 3 , Arnold Moodenbaugh 2 , Yuanbing Mao 1 , Stanislaus Wong 1 2
1 , SUNY Stony Brook, Stony Brook, New York, United States, 3 , Villanova University, Villanova, Pennsylvania, United States, 2 , Brookhaven National Laboratory, Upton, New York, United States
Show AbstractBismuth ferrite has been a focal point of research because in bulk form, it is an antiferromagnetic, ferroelectric, and ferroelastic multiferroic material with electrical, magnetic, and structural ordering temperatures well above room temperature. The combined action of exchange and spin-orbit interactions produces spin canting away from perfect antiferromagnetic ordering. The direction of the resulting small moment, however, rotates, superimposing a spiral spin arrangement with a wavelength of 62 nm, thereby producing a helimagnetic order and a vanishing magnetization in the bulk. Thus far, incorporation of bismuth ferrite into practical devices has been hindered by leakage problems that lead to low resistivity, presumably due to defect and non-stoichiometry related issues. Hence, there has been a pressing need to generate high-quality samples. Our group has recently prepared single-crystalline bismuth ferrite nanoparticles which show strong size-dependent magnetic properties that correlate with: (a) increased suppression of the known spiral spin structure (period length of ~62 nm) with decreasing nanoparticle size and (b) uncompensated spins and strain anisotropies at the surface. Zero-field-cooled and field-cooled magnetization curves exhibit spin-glass freezing behavior due to a complex interplay between finite size effects, interparticle interactions, and a random distribution of anisotropy axes in our nanoparticle assemblies.In addition, we have generated bismuth ferrite nanotubes from alumina membranes with relatively large pore sizes, which mainly consist of straight and smooth structures with relatively few extraneous particulate debris. These tubes possess outer diameters in the range of 240 to 300 nm (wall thicknesses of approximately 10 nm), with lengths ranging from several microns to as much as 50 microns, corresponding to the entire length of the template membranes used. In the case of bismuth ferrite nanotubes prepared from smaller-diameter pores, the lengths of the nanotubes are not only understandably shorter but also more irregular and polydisperse. Their lengths attained several microns at best with diameters in the range of 140 to 180 nm. Finally, we have successfully prepared single-crystalline, submicron-sized bismuth ferrite cubes of reproducible shape using a facile, large-scale solid-state reaction employing a molten salt technique in the presence of a nonionic surfactant. The role of surfactant as well as alterations in the molar ratio of Bi to Fe precursors have been examined under otherwise identical reaction conditions and correlated with the predictive formation of different shapes of bismuth ferrite products.
9:30 AM - **K1.3
Spintronics with Multiferroics.
Agnes Barthelemy 1 , Helene Bea 1 , Martin Gajek 1 , Manuel Bibes 2 , Stephane Fusil 1 , Karim Bouzehouane 1 , Benedicte Warot Fonrose 4 , Richard Mattana 1 , Eric Jacquet 1 , Cyrille Deranlot 1 , Josep Fontcuberta 3 , Albert Fert 1
1 , Unité Mixte de Physique CNRS/Thales, Palaiseau France, 2 , Université Paris Sud, Orsay France, 4 , CEMES, Toulouse France, 3 , ICMAB, Barcelona Spain
Show AbstractMonday, November 26New Presenter - *K1.3Spintronics with Multiferroics. Helene Bea
10:00 AM - K1.4
Magnetic Properties of Orthorhombic TbMnO3 and YbMnO3 Thin Films Grown by Pulsed Laser Deposition.
Diego Rubi 1 , Christophe Daumont 1 , Gustau Catalan 2 , Beatriz Noheda 1
1 Zernike Institute for Advanced Materials, University of Groningen, Groningen Netherlands, 2 Earth Sciences Department, Cambridge University, Cambridge United Kingdom
Show Abstract10:15 AM - K1.5
Ferroelectric ad Magnetic Properties of Bi-Layer-Structured Multiferroic Bi5Ti3FeO15 Thin Films Prepared by Pulsed Laser Deposition.
Seiji Nakashima 1 , Yoshitaka Nakamura 1 , Masanori Okuyama 1
1 Graduate school of engineering science, Osaka University, Toyonaka, Osaka, Japan
Show Abstract Natural superlattice using Bi-Layer-Structured maltiferroics is considered to be useful for ordering magnetic transition metal ions. Bi5Ti3FeO15 (BTFO15) (m=4) is one of the leading candidate for material of multiferroic natural superlattice due to simultaneous existence of ferroelectricity, weak ferromagnetism and ME effect. However, these materials in thin film form have not been well investigated. Zhang et al. have reported that BTFO15 thin film prepared by pulsed laser deposition (PLD) shows remanent polarization (Pr) of 6.4 μC/cm2 1). But, magnetic properties of BTFO15 thin films have not been investigated yet. In this study, we have investigated not only electric properties but also magnetic properties of BTFO15 thin films prepared by PLD.The 350-nm-thick BTFO15 thin films were deposited on Pt(200nm)/TiO2(50nm)/SiO2(600nm)/Si(625μm) substrate by PLD with an ArF excimer laser (λ = 193 nm). For BTFO15 thin film deposition, the oxygen pressure was varied from 0.01 to 0.12 Torr and the deposition temperature was varied from 400 to 520 oC. Circular Pt electrodes were formed on the surface of the thin films by sputtering through a shadow mask with a diameter of 220 μm. The X-ray diffraction patterns indicate that the films of layered perovskite phase of BTFO15 (m=4) was successfully obtained, but these films have mixed phases of Bi4Ti3FeO15 and pyrochlore. The BTFO15 thin film prepared at the temperature of 520oC and the oxygen pressure of 0.12 Torr shows good ferroelectric hysteresis loop, and large twice remanent polarization (2Pr) of 32 μC/cm2 was obtained at a maximum applied electric field of 1120 kV/cm (40 V) in spite of coexistence of Bi4Ti3FeO15 and pyrochlore phases. In addition, magnetic M-H hysteresis loop measurement was also performed with applying magnetic field perpendicularly to the film plane. The BTFO15 thin film prepared at the temperature of 520 oC and the oxygen pressure of 0.12 Torr shows a well-saturated weak ferromagnetic hysteresis loop at R.T., with twice the remanent magnetization (2Mr) value of 0.6 emu/cm3 for a maximum magnetic field of 10 kOe.Reference1) S. T. Zhang, Y. F. Chen, Z. G. Liu, N. B. Ming, J. Wang and G. X. Cheng: J. Appl. Phys. 97 (2005) 104106.
10:30 AM - K1:Multif1
break
10:45 AM - K1.6
Coupling Between Ferroelectric Polarisation and Magnetic Structure in BiFeO3 Single Crystals.
D. Lebeugle 1 , A. Forget 1 , A. Colson 1 , Michel Viret 1 , A. Goukassov 2
1 DSM/DRECAM/SPEC, CEA Saclay, Gif sur Yvette France, 2 LLB, CEA Saclay, Gif sur Yvette France
Show AbstractFerroelectric and magnetic properties of BiFeO3 single crystals have been studied as well as the coupling between the two orders. It is found that the compounds are antiferromagnetic and ferroelectric with a large polarisation at room temperature. The single crystals were synthesized by a flux growth method below their ordering temperature which leads to high quality crystals in a single polarisation domain state. A large spontaneous polarization of 100 μΩ cm-2 is inferred from the first polarization loop, a value never reported in the bulk. On the magnetic front, squid and neutron diffractionmeasurements show that the crystals are antiferromagnetic with a cycloidal sur-structure. The cycloid is found to be affected when changing the polarisation by an applied electric field. The neutron diffraction data coupled to observations with polarised light show unambiguously that the direction of the cycloid is linked to the direction of the polarisation vector. Its evolution with the changingdomain structure will be discussed in detail in the frame of the expected coupling between ferroelectricity and magnetism in this compound.
11:00 AM - **K1.7
Multiferroics: Different Ways To Combine Magnetism AndFerroelectricity.
Daniel Khomskii 1
1 II Physikalisches Insitut, University of Koeln, Koeln Germany
Show Abstract11:30 AM - K1.8
Magnetic Symmetry and Phase Transitions in Low-Dimensional Magnetoelectrics.
Avadh Saxena 1 , Turab Lookman 1
1 , Los Alamos National Lab, Los Alamos, New Mexico, United States
Show AbstractMultiferroic materials such as hexagonal rare earth manganites exhibit triangularantiferromagnetic ordering in the basal plane which can be characterized bytwo-dimensional (2D) magnetic symmetry. Reduced dimensionality is also desirablefor achieving large (usually nonlinear) magnetoelectric coupling at highertemperatures. As an example, the magnetization in BaMnF4 orders two dimensionallybelow the transition temperature with a change in the b-axis dielectric constant.Moreover, there can be phase transitions between different 2D magnetic phases.We can also envision effectively one-dimensional (1D) magnetoelectrics. Fromthis perspective we study one- and two-dimensional magnetic (or color) symmetry,enumerate 1D and 2D magnetic point groups and illustrate their role in possiblemultiferroic phase transitions. Since strain couples to both polarization andmagnetization, we also enumerate different ferroelastic species for the 2Dmagnetic groups. Finally, we suggest possible composition of magnetoelectricchains and planar multiferroics.
11:45 AM - K1.9
Novel Ferromagnetic Phase with Aanisotropy and Spin-glass Transition in BiFeO 3 Thin Films.
Ratnakar Palai 1 , H. Huhtinen 2 , R. Martinez 1 , R. Katiyar 1
1 Department of Physics, University of Puerto Rico, San Juan, Puerto Rico, United States, 2 Department of Physics, University of Turku, Turku, Turku, Finland
Show Abstract12:00 PM - **K1.10
New Functionalities with Multiferroics: Electrical Control of Magnetism.
Lane Martin 1
1 Materials Science and Engineering, University of California, Berkeley, Berkeley, California, United States
Show AbstractMagnetoelectric multiferroics, or materials that simultaneously show magnetic and ferroelectric order, have piqued the interest of researchers worldwide with the promise of coupling between magnetic and electric order parameters. Over the last few years, much has been learned about the underlying interactions in these materials and how the properties of these materials can be controlled. An excellent example of this is BiFeO3 (BFO), a material system in which recent evidence points to direct and controllable coupling between antiferromangetism and ferroelectricity. Armed with materials like BFO, researchers can begin to create new types of functionality that stand to revolutionize the next generation of devices by taking advantage of different types of coupling in materials. For instance, by using the coupling between ferroelectricity and antiferromagnetism (i.e., that found in magnetoelectrics like BFO) and the coupling between antiferromagnetic and ferromagnetic materials (exchange coupling) we stand poised to gain control of ferromagnetism with an applied electric field at room temperature. Although exchange coupling, especially exchange bias (EB), has been used in a wide variety of applications including permanent magnets, recording media, and domain stabilizers in recording heads based on anisotropic magnetoresistance over the years, to this point no one has yet demonstrated an EB system that has electrically tunable properties. To address these issues, I will discuss the growth and study of model ferromagnetic/magnetoelectric-multiferroic thin film heterostructures. We will explore the motivation for this work, the structure and chemistry of the systems involved, and delve into the properties of these systems. From understanding the nature of coupling between ferroelectricity and antiferromagnetism in magnetoelectric-multiferroics to investigating the mechanism for exchange interaction between a ferromagnet and an antiferromagnet, we will build a picture of the science underlying this new functionality. We will discuss the possibility of simple device structures based on these interactions and how one might ultimately control magnetism with an applied electric field, thus enabling a new generation and a new direction in data storage, logic, and spintronic applications. This work was done with help from Y.-H. Chu, M.B. Holcomb, J. Seidel, Q. He, Q. Zhan, K. Lee, and the entire CONCEPT group under the direction of Professor R. Ramesh. This work was supported by the Department of Energy.
12:30 PM - K1.11
Non Linear Optical Probing of Multiferroicity and Phase Transitions in BiFeO3.
Amit Kumar 1 , Sava Denev 1 , Eftihia Vlahos 1 , Mahesh Krishnamurti 1 , Lane Martin 2 , Ying-Hao Chu 2 , Matt Langner 3 , Joe Orenstein 3 , Ramamoorthy Ramesh 2 , Venkatraman Gopalan 1
1 Materials science and Engg., Pennsylvania State University, University Park, Pennsylvania, United States, 2 Materials Science and Engg., University of California Berkeley, Berkeley, California, United States, 3 Materials Science Divison, Lawrence Berkeley National Lab, Berkeley, California, United States
Show AbstractBismuth Iron Oxide BiFeO3 is being studied extensively by researchers to utilize its multiferroic properties for designing multi-state memory devices. In this work, we present the first results of the non linear optical probing of this material to study the simultaneous ferroelectric and antiferromagnetic ordering below the Neel temperature. Optical second harmonic generation (SHG) has been employed to determine the crystallographic and magnetic symmetries of thin BiFeO3 films grown in different orientations at temperatures ranging from room temperatures to above the Neel Temperature. SHG spectra combined with optical spectroscopy from the BiFeO3 films suggest the role of magnons in the decay of aniferromagnetic order parameter above the Neel temperature.
12:45 PM - K1.12
Fabrication of Hexagonal RMnO3 (R = Er, Ho, Dy, Tb, and Gd) Epitaxial Thin Films and Their Physical Properties.
S. Jang 1 , J. Lee 1 , D. Lee 1 , P. Murugavel 1 , H. Ryu 1 , J. Kim 2 , H. Kim 2 , K. Kim 2 , Y. Jo 3 , M. Jung 3 , J. Yoon 4 , J. Chung 5 , T. Noh 1
1 ReCOE & FPRD, Department of physics and astronomy, Seoul National University, Seoul Korea (the Republic of), 2 CSCMR, Department of physics and astronomy, Seoul National University, Seoul Korea (the Republic of), 3 Quantum material research team, Korea basic science research team, Daejon Korea (the Republic of), 4 Department of physics, University of Suwon, Suwon Korea (the Republic of), 5 Department of physics and CAMDRC, Soongsil University, Seoul Korea (the Republic of)
Show AbstractRecently, multiferroic rare-earth manganites RMnO3 (R = Gd, Tb, and Dy) have attracted a lot of attention because of their strong coupling between magnetization and electric polarization. In order to use such exciting materials in real applications, we need them in thin film forms with high ferroelectric and magnetic ordering temperatures. The bulk RMnO3 compounds with large R ionic size (i.e. R = Gd – Dy) have an orthorhombic structure. Although their electro-magnetic couplings are very strong, their ferroelectric and magnetic ordering temperatures are too low, typically much lower than the liquid nitrogen temperature, for device applications. On the other hand, the bulk RMnO3 compounds with smaller R ionic size (i.e R = Ho – Lu) have a hexagnoal structure. Their ferroelectric transition temperatures are larger than room temperature and magnetic ordering temperatures are near the liquid nitrogen temperture. Therefore, it would be highly desirable to fabricate these hexagnoal RMnO3 compounds in thin film forms. In addition, if we could stablize RMnO3 (R = Gd, Tb, and Dy) into hexagonal phases, we might be able to invesigate the noble physical phenomena using the artificial materials. Very recently, we successfully fabricated the metastable hexagonal RMnO3 (R = Gd, Tb, and Dy) materials using the epitaxial stabilization technique.[1,2,3] From the P-E hysterisis loop, we found that artificial h-RMnO3 (R = Dy and Tb) shows enhanced ferroelectric properties. For example, h-TbMnO3 thin film has a maximum polarization of 1.6 μC/cm2, which is 20 times larger than that of the orthorhombic phase, and its Curie temperature is about 60 K. In addition, these h-RMnO3 (R = Dy and Tb) compounds show multiferroic behaviors with reasonable size of electro-magnetic couplings. However, we also found a phase transition from ferroelectric to antiferroelectric-like phase around 100 K, which is much lower than the predictions for other bulk hexagonal RMnO3 (R = Ho – Lu).To understand this unusual phenomon, we also fabricated hexagonal ErMnO3 and HoMnO3 thin films,[4] and investigated the systematic variations of magnetic ordering temperatures, ferroelectric-antiferroelectric transition temperatures, and electronic structures. We found that these physical properties strongly depend on the external pressure, which can be applied using the lattice mismatch between the substrate and the film, as well as the chemical pressure. All of these intriguing findings suggest the the uniqueness of h-RMnO3 compounds as multiferroic materials and their potential applications. [1] J.-H. Lee et al., Adv. Mater. 18, 3125 (2006).[2] J.-H. Lee et al., Appl. Phys. Lett. 90, 012903 (2007). [3] D. Lee et al., Appl. Phys. Lett. 90, 182504 (2007).[4] P. Murugavel et al., Appl. Phys. Lett. 90, 142902 (2007).
K2: Multiferroics II
Session Chairs
Agnes Barthelemy
Susan Trolier-McKinstry
Monday PM, November 26, 2007
Grand Ballroom (Sheraton)
2:30 PM - **K2.1
Giant Sharp and Persistent Converse Magnetoelectric Effectsin Multiferroic Epitaxial Heterostructures.
Wilma Eerenstein 1 , Matthias Wiora 1 , José Prieto 1 , James Scott 2 , Neil Mathur 1
1 Materials Science, University of Cambridge, Cambridge United Kingdom, 2 Deapartment of Earth Sciences, University of Cambridge, Cambridge United Kingdom
Show AbstractMagnetoelectric coupling between magnetic and electrical properties presents valuable degrees of freedom for applications. The two most promising scenarios are magnetic-field sensors that could replace low-temperature superconducting quantum interference devices, and electric-write magnetic-read memory devices that combine the best of ferroelectric and magnetic random-access memory. The former scenario requires magnetically induced continuous and reversible changes in electrical polarization. These are commonly observed, but the coupling constants thus obtained are invalid for data-storage applications, where the more difficult to achieve and rarely studied magnetic response to an electric field is required. Here, we demonstrate electrically induced giant, sharp and persistent magnetic changes (up to 2.3×10−7 sm−1) at a single epitaxial interface in ferromagnetic 40 nm La0.67Sr0.33MnO3 films on 0.5 mm ferroelectric BaTiO3 substrates. X-ray diffraction confirms strain coupling via ferroelastic non-180° BaTiO3 domains. Our findings are valid over a wide range of temperatures including room temperature, and should inspire further study with single epitaxial interfaces.
3:00 PM - K2.2
Exchange Bias with Multiferroic BiFeO3 Epitaxial Thin Films.
Helene Bea 1 , Bertrand Dupe 1 , Xiaohong Zhu 1 , Manuel Bibes 2 , Frederic Ott 3 , Sylvain Petit 3 , Alexandra Mougin 4 , Benedicte Warot-Fonrose 5 , Stephane Fusil 1 , Mario Basletic 1 , Gervasi Herranz 1 , Cyrile Deranlot 1 , Eric Jacquet 1 , Karim Bouzehouane 1 , Agnes Barthelemy 1
1 , Unité Mixte de Physique CNRS/Thales, Palaiseau France, 2 , Institut d'Electronique Fondamentale, Université Paris-Sud, Orsay France, 3 , Laboratoire Léon Brillouin CEA/CNRS, Gif-sur-Yvette France, 4 , Laboratoire de Physique des Solides, Orsay France, 5 , CEMES-CNRS, Toulouse France
Show AbstractMultiferroic materials displaying several ferroic orders among ferroelectricity, ferro (or antiferro-)magnetism and ferroelasticity are currently widely studied due to both their multifunctionality and the coupling between these orders. For instance the magnetoelectric could allows the change of the magnetic order by an electric field or the electric polarization by a magnetic field.One of the best candidates for room temperature applications is BiFeO3 (BFO) which shows ordered states at high temperatures (it is antiferromagnetic at T < TN = 647K and ferroelectric at T < TC = 1043K). Examples of spintronics devices using an antiferromagnetic multiferroic (AFM) material have been proposed by Binek and Doudin [1]. Two types of devices are proposed using an AFM layer either as a tunnel barrier in a magnetic tunnel junction or as a pinning layer below a spin valve structure. In both cases, an exchange coupling between the AFM film and the ferromagnetic electrode is used to tune the magnetic state (parallel or antiparallel configurations of the magnetizations of the ferromagnetic electrodes) of the device by an electric field. A prerequisite is then to obtain AFM thin films displaying an exchange coupling with a ferromagnetic electrode.We have used the G-type antiferromagnetic spin structure of a BFO film (as evidenced by neutron diffraction experiments [2]) to induce, at room temperature, a sizeable (~60 Oe) exchange bias on a high TC ferromagnetic film of CoFeB [3] and on a spin valve structure. We will present an extensive study of this exchange bias as a function of BFO thickness and crystalline orientation with Alternative Gradient Force Magnetometer, Kerr magnetometry and Polarized Neutron Reflectometry. The influence of an electric field on exchange bias will be discussed.[1] Ch. Binek and B. Doudin, J. Phys.: Condens. Matter 17, L39 (2005)[2] H. Béa et al.; Phil. Mag. Lett., 87, 165 (2007)[3] H. Béa et al. ; Appl. Phys. Lett., 89, 242114 (2006)
3:15 PM - K2.3
Search for the Electric-field Effect on Exchange Bias Between Ferromagnetic Layers and Various Multiferroic Layers.
Makoto Murakami 1 , Sung Hwan Lim 1 , S. Fujino 1 , J. Hattrick-Simpers 1 , S. Lofland 2 , Sang-Wook Cheong 3 , M. Wuttig 1 , I. Takeuchi 1 4
1 Material Science and Engineering, University of Maryland, College Park, Maryland, United States, 2 Physics and Astronomy, Rowan University, Glassboro, New Jersey, United States, 3 Physics and Astronomy, Rutgers University, Piscataway, New Jersey, United States, 4 Center for Superconductivity Research, University of Maryland, College Park, Maryland, United States
Show AbstractWe have been studying exchange bias between ferromagnetic metallic layers and various multiferroic materials including (Bi,RE)FeO3, LuMnO3, TbMnO3, and Cr2O3. In this study, we will discuss the effect of external electric field on exchange bias on the ferromagnetic/multiferroic interfaces. Co and [Co/Pt]3 layers are deposited on multiferroic thin films and single crystals in high vacuum chambers in order to study in-plane and out-of-plane exchange bias, respectively. For investigating the effect of electric field on exchange bias, patterned 50 x 50 (μm)2 devices are used to apply up to 500 kV/cm. The magneto-optical kerr effect is used to measure magnetic hysteresis curves in the temperature range of 30-350 K. Perpendicular exchange bias is clearly observed in Cr2O3 thin films with ZnO:Al bottom electrodes on c-sapphire when the sample is field cooled through the Neel temperature. When the cooling magnetic field is small (< 20 Oe), we find appearance of double hysterisis curves, whose detailed shapes are delicately controlled by the magnitude and the sign of the field. In the case of Bi1-xSmxFeO3, where we find enhanced ferroelectric properties at a morphotropic phase boundary, the entire composition range is studied together using composition spread samples. Exchange bias field and coercivity were found to change continuously as a function of the composition. We find that the largest exchange bias field is observed at around the composition where the structural transition takes place between rhombohedral to pseudo-orthorhombic structures. Maximum piezoelectric properties are observed at this composition. These results suggest that exchange bias has strong correlation with the structure of the multiferroic thin films. We will discuss the difference in the exchange bias behavior between different multiferroic materials and their possible electric field effect. This work is supported by NSF DMR 0094265 (CAREER), NSF DMR 0603644, MRSEC DMR-00-0520471, and by the W. M. Keck Foundation.
3:30 PM - K2.4
Ferroelectric-dielectric Oriented Nano-columnar Composite Films for Tunable Applications.
Tomoaki Yamada 1 , Vladimir Sherman 1 , Silviu Cosmin Sandu 1 , Andreas Noeth 1 , Paul Muralt 1 , Alexander Tagantsev 1 , Nava Setter 1
1 Ceramics Laboratory, Swiss Federal Institute of Technology, EPFL, Lausanne Switzerland
Show Abstract The oriented nano composite film consisting of ferroelectric and low-K dielectric compounds is proposed as a potential candidate for the practical applications in microwave tunable devices. We here show the self-assembly grown ferroelectric-dielectric nano-columnar composite films having significantly low permittivity with appreciable tunability; which results in a few tens times larger coefficient of dielectric nonlinearity than that for pure ferroelectrics. In this study, BaTiO3(BTO)-CeO2 composite films are grown on Pt electrodes by pulsed laser deposition using the mixed ceramics target. The deposited BTO-CeO2 composite films showed distinctly different microstructures, particularly, depending on the volume fractions of two components. It was found that when there is a large contrast in two volume fractions, the minor component precipitates in between the columnar grains of major component (either BTO or CeO2). This precipitation, in fact, realized the nano-columnar composite structure in our system. Therefore, in such systems, the orientation of composite structure can be determined by the growth direction of the columnar major component. On the other hand, when the both volume fractions are comparable, no clear composite orientation was found. As an example, the 15mol%BTO-85mol%CeO2 film on Pt(111) surface has 2-8nm wide, long, BTO crystals lying in between “obliquely-grown” CeO2 columns. The film showed the permittivity about 50, which was significantly reduced by the existence of CeO2, but still showed appreciable tunability around 1.2 at 1MV/cm; while the layered CeO2/BTO/CeO2 film having the same volume fractions of compounds did not show any tunability. It indicates that such a small amount of precipitated BTO crystals can efficiently work as an active tunable component in the film. The tunability of this inclined composite will be similarly understood by the parallel composite model, where the ferroelectric component can be efficiently tuned by the applied electric field. On the other hand, the measured dielectric loss below 1% at 10GHz implies the considerable impact of the inclination of the composite orientation on the reduction of the dielectric loss, since only small reduction in dielectric loss can be expected in the parallel composite model as compared to the pure tunable ferroelectric. The further experimental analysis and theoretical approach will be presented.
3:45 PM - K2.5
Field Effect in Ferroelectric/Ferromagnetic Heterostructures.
Zsolt Marton 1 2 3 , Ho Nyung Lee 1 , Matthew Chisholm 1 , David Singh 1 , Takeshi Egami 1 2
1 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee, United States, 3 Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania, United States
Show AbstractFerroelectric polarization is employed to control the physical properties, such as the metal-insulator transition (MIT) and conductivity, of doped-manganite thin films in ferromagnetic (FM)/ferroelectric (FE) heterostructures. For the ferroelectric field effect system, we have epitaxially synthesized La1-xSrxMnO3 (LSMO)/PbZr0.2Ti0.8O3 (PZT) heterostructures by pulsed laser deposition on SrRuO3-covered SrTiO3 substrates. To achieve that largest modifications of the LSMO’s properties, highly polar PZT epitaxial thin films with a remanent polarization over 80 μC/cm2 have been employed. With such functionally cross-coupled heterostructures, we examine the interplay between the ferroelectric polarization and magnetic response as well as screening. With the electrode near a MIT, we find that the conductivity and the MIT temperature in ferromagnetic layers can be dramatically tuned by the ferroelectric polarization. In this work, we will present the ferroelectric control of magnetic properties in FE/FM heterostructures. The result of carrier density (Hall) measurement and the effect of thickness, strain state, and composition of the LSMO films on the MIT will be also discussed. Research sponsored by the Laboratory Directed Research and Development Program of Oak Ridge National Laboratory (ORNL), managed by UT-Battelle, LLC for the U. S. Department of Energy under Contract No. DE-AC05-00OR22725.
4:30 PM - **K2.6
Multiferroic Behaviors of Hexagonal YMnO3 and YbMnO3 Epitaxial Films.
Norifumi Fujimura 1 , Kazuhiro Maeda 1 , Keisuke Fukae 1 , Takeshi Yoshimura 1
1 Graduate School of Engr., Osaka Prefecture University, Osaka Japan
Show AbstractWhen the ionic radius of R is small (R=Ho-Lu, Y, and Sc), RMnO3 (where R is rare earth) crystallizes in a hexagonal structure. In this hexagonal structure, each Mn3+ ion with S=2 is surrounded by three in-plane and two apical oxygen ions; it is therefore subject to a trigonal crystal field. These MnO5 blocks are mutually connected two-dimensionally on their corners; thereby, a triangular lattice of Mn3+ ions is formed. Based on such a triangular lattice, these compounds experience several characteristic distortions. One is a Mn ‘‘trimer’’ (i.e. √3 × √3 ordering), which is characterized by the shift of three Mn3+ ions surrounding one oxygen ion toward the oxygen. Another is the displacement of ions along the c axis (perpendicular to the triangular-lattice plane) causing a ferroelectric polarization. Because the FE transition temperature of these compounds is fairly high (>900 K), they can be applied, for example, in ferroelectric gate field effect transistors. We also reported controlled polarization type FET is an attractive candidate for ferroelectric FET.We have examined the coupling between magnetic and FE ordering, which might eventually be exploited in a device where the magnetic properties can be altered by application of an electric field. Although the great difference between the critical temperature of magnetic and electric orderings (TN=80 K and TC=900 K) might suggest that no coupling is present, some evidence of coupling has been observed in terms of anomalies in the εr and loss tangent at the Néel temperature. In addition, magnetic and electric field effects on the interaction between FE and AFM domain structure have been demonstrated using magneto-optical techniques. Theoretical works have also been reviewed.Here, we demonstrate the correlation between dynamic FE domain switching and AFM ordering of YMnO3 epitaxial films deposited by pulsed laser deposition (PLD) method. The control of FE domain switching by applying the external magnetic field is also presented. Furthermore, magnetic-field induced ferromagnetism (FM) is demonstrated in ferroelectric YbMnO3 epitaxial film. The magnetic frustration of the film is also described.
5:00 PM - K2.7
Magnons Scattering and Phase Transitions in Multiferroic BiFeO3.
Mariola Ramirez Herrero 1 , Mahesh Krishnamurthi 1 , Amit Kumar 1 , Sava Denev 1 , Venkatraman Gopalan 1 , R. Ramesh 2 , J. Seidel 2 , E. Chu 2 , J. Orestein 2
1 Materials Science and Engineering, Penn State University, State College, Pennsylvania, United States, 2 Physicis and Materials Science and Engineering, University of California, Berkeley, California, United States
Show AbstractBismuth ferrite is one of the most widely studied multiferroic material because of its potential application in spintronics, data storage, microelectronics etc. Recent works based on Raman spectroscopy have pointed out the existence of intermediate phases between 820-950 C as well as pronounced phonon anomalies around the magnetic Néel temperature TN [1,2]. In this work, we report for the first time the observation of two and three magnons Raman scattering in BiFeO3 single crystal. Temperature studies up to 550 C show that the two-magnons contribution to the total Raman spectrum gradually decreases with temperature remaining constant after TN (~ 375 C). Additionally, several singularities at around 100 C and 250 C were observed, suggesting possible spin-reorientation transitions. Phonon anomalies were also observed at these temperatures pointing out the magnetoelectric coupling of this material.References:[1] R. Haumont, J. Kreisel, P. Bouvier and F. Hippert Phys. Rev. B 73, 132101, (2006).[2] R. Palai, R.S Katiyar and J.F. Scott. Submitted to Nature Materials. May 20 (2007)
5:15 PM - K2.8
Interface Coupling in La0.7Sr0.3MnO3/BiFeO3 Heterostructures.
Ying-Hao Chu 1 2 , Lane Martin 2 , Mark Huijben 1 2 , Jon Ihlefeld 3 , Pu Yu 1 , Mikel Holcomb 1 , Chan-Ho Yang 1 2 , Darrell Schlom 3 , Ramamoorthy Ramesh 1 2
1 Department of Physcis, UC Berkeley, Berkeley, California, United States, 2 Department of Materials Science and Engineering, UC Berkeley, Berkeley, California, United States, 3 Department of Materials Science and Engineering, Penn State Uinversity, University Park, Pennsylvania, United States
Show AbstractThe development and understanding of correlated oxide materials, especially multiferroic materials such as BiFeO3 (BFO), have piqued the interest of researchers worldwide with the promise of coupling between order parameters such as ferroelectricity and antiferromagnetism. Recent research suggests that there is exchange coupling and anisotropy between the metallic ferromagnet Co0.9Fe¬0.1 (CoFe) and the multiferroic BFO, showing the possibility to create multifunctional systems with new possibilities for device design. How does an oxide ferromagnet, such as La0.7Sr0.3MnO3(LSMO) interact with a ferroelectric antiferromagnet at the interface ? We are exploring this interaction using epitaxially grown heterostructures as our model system. We have probed the strength of this coupling using a combination of careful laser MBE growth experiments and physical property measurements, including XMCD and magnetic studies. In order to understand the factors that influence the interaction at the interface, reference systems (antiferromagnetic LFO/LSMO and ferroelectric PZT/LSMO) have also been prepared. The coupling behavior is being characterized by magnetic measurements, which shows a strong enhancement in the coercivity of the LSMO layer, suppression of magnetization, and different M-T behavior, suggesting the existence of exchange bias coupling. This work is supported by the US Department of Energy
5:30 PM - K2.9
Out-of-plane Magnetization of La0.67Sr0.33MnO3 Ferromagnetic Thin Films on SrTiO3 Measured by Magnetic Force Microscopy.
Evert Houwman 1 , Gabriella de Luca 1 , Guus Rijnders 1 , Dave Blank 1 , Gabriela Maris 2 , Natascha Niermann 2 , Sylvia Speller 2
1 MESA+ Institute of Nanotechnology, University of Twente, Enschede Netherlands, 2 Institute for Molecules and Materials, Radboud University, Nijmegen Netherlands
Show Abstract5:45 PM - K2.10
BiFeO3/(La,Sr)MnO3 Heterostructures By Molecular-Beam Epitaxy.
Jon Ihlefeld 1 2 , Carolina Adamo 1 , Darrell Schlom 1 , Ying-Hao Chu 2 3 , Lane Martin 2 3 , Ramamoorthy Ramesh 2 3
1 Materials Science and Engineering, Pennsylvania State University, University Park, Pennsylvania, United States, 2 Materials Science and Engineering, University of California, Berkeley, California, United States, 3 Department of Physics, University of California, Berkeley, California, United States
Show AbstractInterfaces between highly correlated muliferroics (such as BiFeO3) and oxide ferromagnets (such as (La,Sr)MnO3) present an interesting opportunity to explore electric field control of magnetism. BiFeO3 and La0.7Sr0.3MnO3 epitaxial heterostructures have been deposited on vicinal (001) SrTiO3 cut at 4° along <110> by reactive molecular-beam epitaxy. High quality BiFeO3 growth is achieved by supplying a bismuth over-pressure and utilizing the differential vapor pressures between bismuth oxides and BiFeO3 to control stoichiometry and phase assemblage. By using a vicinal substrate, the possible ferroelectric domain orientations are limited to two variants thus simplifying the overall domain structure. Exchange bias coupling between the ferromagnetic manganite and antiferromagnetic BiFeO3 has been investigated over a range of La0.7Sr0.3MnO3 thicknesses from 2 to 30 nm, while holding the BiFeO3 thickness constant at 75 nm. The films grown by MBE possess film crystalline qualities that are substrate limited and thus minimize the extrinsic defect contributions to the measured properties.
K3: Poster Session: Multiferoics, Magnetoelectrics and Piezoelectrics
Session Chairs
Neil Mathur
Stanislaus Wong
Tuesday AM, November 27, 2007
Exhibition Hall D (Hynes)
9:00 PM - K3.10
PUND Measurements for BiFeO3 Films – Temperature Dependence of the Ferroelectricity.
Hiroshi Naganuma 1 , Yosuke Inoue 1 , Soichiro Okamura 1
1 , Tokyo University of Science, Tokyo Japan
Show Abstract9:00 PM - K3.11
Effect of 3d Transition Metals Addition on the Ferroelectric and Magnetic Properties in Bi Ferrite Thin Films.
Hiroshi Naganuma 1 , Jun Miura 1 , Tomosato Okubo 1 , Soichiro Okamura 1
1 , Tokyo University of Science, Tokyo Japan
Show AbstractBi ferrite (BiFeO3) has been attracting much interest for future novel memory applications because of the coexistent of the antiferromagnetism and the ferroelectricity. However, the ferroelectric properties are spoiled due to the high leakage current density at room temperature. Therefore, in order to suppress the leakage current, many additional atoms have been examined to the Bi ferrite. Actually, some of the atoms such as Cr, Mn and La have improved the ferroelectricity due to the reduction of the leakage current, though the degree of improvement is different in each report, which might be caused by the different way of the preparation processes. Our aim in present study is fabricating the Bi ferrite films adding Cr, Mn, Ni, Cu and Co of 5at.% and evaluated systematically the ferroelectric as well as magnetic properties. Film specimens were fabricated by a chemical solution deposition (CSD) method followed by annealing 773 K in air. Film structure was confirmed by a conventional x-ray diffraction (XRD) patterns and an atomic force microscopy (AFM). Ferroelectricity and leakage current were evaluated by a ferroelectric tester (FCE-1A type) and HP 4140B at room temperature, respectively. Magnetic properties were measured by a vibrating sample magnetometer at room temperature. XRD analysis indicated that only the diffraction peaks attributed to the BiFeO3 structure could be observed exclude the Ni and Cr addition. Not only the BiFeO3 phase but also the secondary phase of Bi7CrO12.5 was formed for Cr additive specimen. In Ni addition, the diffraction peaks due to the BiFeO3 structure was too weak and it seems an amorphous structure and/or low crystallinity. The leakage current measurements at room temperature indicated that each additive had a tendency to decrease the leakage current when comparing at around 800 kV/cm. According to the P-E loops at room temperature, the high squareness together with more than 50 μC/cm2 of remanent polarization was obtained by Mn and Cu addition, though the Co and Cr additives degraded the shape of the P-E hysteresis loops. In the case of the Cr addition, the degradation of the ferroelectricity can be attributed to the formation of the secondary phase of Bi7CrO12.5. Ferroelectricity could not be observed for the Ni added specimen due to the low crystallinity. In our present investigation of 3d transition metals addition, it revealed that Mn and Cu atoms had improved the ferroelectricity when using the CSD process followed by post-annealing at 773 K for 10 min in air. It should be noted that the effect of Cu additive on ferroelectricity has not been reported yet. We will discuss the Cu concentration effect on ferroelectricity. The change of the magnetic properties by adding these additives will also discussed in the presentation.
9:00 PM - K3.12
Ferroelectric Properties of BiFeO3 - Fe2O3 Multiphase Nanocomposite Thin Films.
Sung Hwan Lim 1 , Volkan Ortalan 2 , Hung-Chih Kan 1 , Dominic Britti 1 , Anbusathaiah Varatharajan 3 , Nagarajan Valanoor 3 , Makoto Murakami 1 , Ray Phaneuf 1 , Nigel Browning 2 , Ichiro Takeuchi 1 , Lourdes Salamanca-Riba 1
1 Materials Science and Engineering, University of Maryland, College Park, Maryland, United States, 2 Chemical Engineering and Materials Science, University of California, Davis, California, United States, 3 School of Materials Science and Engineering, University of New South Wales, Sydney, New South Wales, Australia
Show Abstract9:00 PM - K3.13
Structural, Magnetic and Electrical Properties of Solid State Synthesized BixSm1-xFeO3 Ceramics.
Ajay Yadav 1 , Kanwar Nalwa 1 , Ashish Garg 1
1 Materials and Metallurgical Engineering, Indian Institute of Technology, Kanpur , Kanpur, Uttar Pradesh, India
Show Abstract9:00 PM - K3.14
Effect of A-site and B-site Cation Substitution on the Microstructure and Multiferroic Properties of Single-phase BiFeO3-A(Fe0.5Nb0.5)O3-A'(Fe0.5Nd0.5)O3 Solid Solution Ceramics.
Hanjong Paik 1 , Hyungchul Kim 1 , Kwangsoo No 1
1 Materials Science and Engineering, Korea Advanced Institute of Science and Technology, Daejeon Korea (the Republic of)
Show Abstract9:00 PM - K3.15
Dielectric Properties of Self-assembled (BiFeO3)0.5:(Sm2O3)0.5 Nanocomposite Films.
Hao Yang 1 , M. Jain 1 , H. Wang 2 , J. Yoon 2 , P. Dowden 1 , J. MacManus-Driscoll 3 , Q. Jia 1
1 Superconductivity Technology Center, Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 2 Department of Electrical and Computer Engineering, Texas A&M University, College Station, Texas, United States, 3 Department of Materials Science and Metallurgy, University of Cambridge, Cambridge United Kingdom
Show Abstract9:00 PM - K3.16
Large Polarization and Weak Magnetization in Pb Doped BiFeO3 Ceramics Prepared by Rapid Liquid Phase Sintering Process.
Manoj Kumar 1 , Poonam Uniyal 1 , K. Yadav 1
1 Department of Physics, Indian Institute of Technology Roorkee, Roorkee, Uttarakhand, India
Show Abstract9:00 PM - K3.18
Effect of Zr Doping on Electrical Properties of Chemical Solution Deposited Multiferroic BiFeO3 Thin Films.
Deepam Maurya 1 , Salil Sharma 1 , Ashish Garg 1 , Dinesh Agarwal 2
1 Materials and Metallurgical Engineering Department, Indian Institute of Technology Kanpur, Kanpur, U.P., India, 2 Materials Science Programme, Indian Institute of Technology, Kanpur, U.P., India
Show Abstract9:00 PM - K3.19
Cr Doped Bismuth Ferrite Thin Film Fabricated via Chemical Solution Depositon(CSD).
Yuhua Zhang 1 , Shengwen Yu 1 , Jinrong Cheng 1
1 Electronic Information Material, Shanghai University, Shanghai China
Show Abstract9:00 PM - K3.2
Liquid-phase Epitaxial Growth of BiFeO3 Thick Films using an Infrared Irradiation.
Takeshi Kawae 1 , Mitsuhiro Shiomoto 1 , Hisashi Tsuda 1 , Satoru Yamada 2 , Masanori Nagao 3 , Akiharu Morimoto 1 , Minoru Kumeda 1
1 Graduate School of Natural Science & Technology, Kanazawa University, Kanazawa Japan, 2 , Ishikawa National College of Technology, Tsubata Japan, 3 , National Institute for Material Science, Tsukuba Japan
Show Abstract9:00 PM - K3.20
Growth and Characterization of BiFeO3 and Bi(Fe0.5M0.5)O3 Films (M=Mn, Ni or Co).
Lei Bi 1 , Alexander Taussig 1 , Hyun-Suk Kim 1 , Gerald Dionne 1 , D. Bono 1 , Caroline Ross 1
1 Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show Abstract9:00 PM - K3.21
Effect of Heat Treatment on the Structure and Properties of Chemical Solution Processed Multiferroic Bi2CrFeO6 Thin Films.
Vijay Singh 1 , Deepam Maurya 1 , Chetan Jain 1 , Ashish Garg 1 , Dinesh Agrawal 2
1 Materials and Metallurgical Engg, Indian Institute of Technology Kanpur, Kanpur, UP, India, 2 Materials Science Programme, Indian Institute of Technology Kanpur, Kanpur, UP, India
Show Abstract9:00 PM - K3.22
Leakage Mechanisms and Ferromagnetic Resonance Analyses in Thin-Film Multifunctional BiFeO3—NiFe2O4 Nanostructures.
Steven Crane 1 , J. Seidel 2 , C. Bihler 3 , P. Shafer 1 , Q. He 2 , J. Hemalatha 4 , S. Goennenwein 5 , M. Brandt 3 , R. Ramesh 1 2
1 Materials Science and Engineering, University of California, Berkeley, Berkeley, California, United States, 2 Physics, University of California, Berkeley, Berkeley, California, United States, 3 Walter Schottky Institut, Technische Universität München, Garching Germany, 4 Physics, National Institute of Technology, Tiruchirappalli, Tamilnadu, India, 5 Walther Meissner Institut, Bayerische Akademie der Wissenschaften, Garching Germany
Show AbstractMultifunctional thin film nanostructures that include ferroelectric and soft magnetic materials are interesting for their potential applications in microwave communications as electrically tunable signal filters, chokes, and resonators. Ferromagnetic resonance (FMR) response has shown to be very dependent on the conduction properties of the thin film material. Because these films are composed of ferrimagnetic NiFe2O4 nanopillars embedded in a ferroelectric BiFeO3 matrix, understanding of the source of leakage current in both phases is essential for improving the FMR line width response. By altering deposition parameters, the conduction has been varied in overall magnitude and pathways from those through the BiFeO3 matrix to those through the NiFe2O4 pillars. Possible leakage mechanisms are discussed, and the leakage currents are then correlated to resonant line widths found in FMR measurements.S.P. Crane was funded by the National Science Foundation through the graduate research fellowship program. J. Seidel acknowledges funding from the Alexander von Humboldt Foundation. This project is funded by an ONR MURI program.
9:00 PM - K3.24
A Study of the Optimal Conditions for Epitaxial Growth of PbFe0.5Nb0.5O3 Films by RF Sputtering Assisted by Optical Spectroscopy.
Oscar Raymond 1 , Reynaldo Font 2 , Roberto Machorro 1 , Eduardo Martinez 1 , Jesús Siqueiros 1
1 Propiedades Opticas, Centro de Ciencias de la Materia Condensada, Universidad Nacional Autónoma de México, Ensenada, Baja California, Mexico, 2 Facultad de Física , Universidad de la Habana, La Habana Cuba
Show AbstractMultiferroic materials such as the single phase PbFe0.5Nb0.5O3 (PFN) compound, where ferroelectric and magnetic order coexist, are multifunctional materials generating great interest from the academic and technological point of view in the development of novel devices and intelligent systems. Here, a report of the best conditions for the obtainment of epitaxial PFN thin films on Si (111) by RF sputtering in controlled argon/oxygen/lead atmospheres is presented. Two targets fabricated with powders of pure PFN plus a ten percent weight of PbO to compensate for lead oxide volatilization were employed. The crystalline evolution of the samples and the parameter optimization for the deposit processes have been evaluated by X-Ray Diffraction, Scanning Electron Microscopy and Energy Dispersive Spectroscopy. A new cubic pyrochlore second phase with stoichometric formula Pb2FeNbO6.5, associated to Pb deficiency in the growth process was identified during different deposition runs. To investigate in situ the occurrence of Pb loss and improve conditions for pyrochlore-free films, a Wide Field Spectroscopy technique was employed to monitor the plasma emission in the sputtering process. Using a metallic Pb evaporator, and strictly controlling the intensity ratio of two spectral lines IPb(405.78 nm)/IFe (404.59 nm), (110) epitaxial PFN films were repetitively growth.Acknowledgment: This work was partially supported by DGAPA-UNAM (Projects No. IN109305-3) and CONACYT (No. 47714-F). The authors thank E. Aparicio, I. Gradilla, P. Casillas, J. Camacho and J. Hernández for their technical assistance.
9:00 PM - K3.25
Multiferroic Properties of Bi0.9L0.1FeO3-Pb(Fe0.5Nb0.5)O3 Solid Solution Ceramics at Room Temperature.
Hyungchul Kim 1 , Hanjong Paik 1 , Kwangsoo No 1
1 material science engineering, Korea advanced institute of science and technology, Daejeon Korea (the Republic of)
Show Abstract9:00 PM - K3.26
Synthesis and Multiferroic Studies on (1-x) NBT-x BiFeO3 Solid Solutions.
Venkata Ramana 1 , Shambuni Suryanarayana 1 , Tanikella Bhima Sankaram 1
1 Department of Physics, Osmania University, Hyderabad, Andhra Pradesh, India
Show Abstract9:00 PM - K3.27
AFM-Based Evaluation of Magnetoelectric Coupling in a Multiferroic Nanocomposite.
Brian Piccione 1 , John Blendell 1 , Edwin Garcia 1
1 Materials Science and Engineering, Purdue University, West Lafayette, Indiana, United States
Show Abstract9:00 PM - K3.28
Interface interactions in Ferromagnetic-Antiferromagnetic Superlattices.
Mark Huijben 1 , Ying-Hao Chu 1 , Lane Martin 1 , Chan-Ho Yang 1 , Manuel Valvidares 2 , Jeff Kortright 2 , Ramamoorthy Ramesh 1
1 Physics Department, UC Berkeley, Berkeley, California, United States, 2 Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractSuperlattices based on perovskite transition-metal oxides have attracted much attention because of the possibility of tuning the magnetic and electronic properties of a thin film, in ways that would not be possible in single-phase bulk materials, through interface effects such as exchange interactions, charge transfer, and epitaxial strain. In this study we investigate the magnetic properties in Ferromagnetic-Antiferromagnetic multiferroic superlattices by using atomic scale controlled growth through laser-MBE in combination with real-time RHEED monitoring. We will show the controlled coupling at the interfaces in La0.7Sr0.3MnO3/BiFeO3 superlattices and SrRuO3/BiFeO3 superlattices. This coupling behavior is characterized by structural measurements and magnetic measurements, including resonant x-ray reflectivity and standing wave analysis to depth-resolve magnetism (circular dichroism), structural and electronic anisotropy (linear dichroism), and valence state to gain a deeper fundamental understanding of the interactions at these interfaces. This work is supported by the US Department of Energy.
9:00 PM - K3.29
Impact of Magnesium Oxide Interlayer on Heteroepitaxial Growth of Barium Ferrite on Wide Bandgap Semiconductor 6H-SiC.
Zhuhua Cai 1 , Trevor Goodrich 1 , Zhaohui Chen 2 , Vince Harris 2 , Katherine Ziemer 1
1 Chemical Engineering, Northeastern University, Boston, Massachusetts, United States, 2 Electrical and Computer Engineering, Northeastern University, Boston, Massachusetts, United States
Show AbstractIntegration of nonreciprocal ferrite microwave devices (e.g. circulators, isolators, phase shifters, etc.) with semiconductor platforms has been a longstanding goal of the microwave device community to meet the demands of increasing microwave power and reduced device volume. Barium hexaferrite (BaM, BaFe12O19) is ideal for microwave device applications because of its high resistivity and particularly large uniaxial magnetocrystalline anisotropy (17 kOe) with the easy direction along the c-axis. Previous BaM films deposited on bare 6H-SiC by pulsed laser deposition (PLD) showed high microwave losses as determined by ferromagnetic resonance (FMR) peak-to-peak derivative linewidths (ΔH), which were broader than 1000 Oe. The magnetic quality of the films could not be improved by use of a magnesium oxide (MgO) interlayer grown by PLD due to high porosity and less c-axis perpendicular crystal orientation in the BaM film. However, with the introduction of an interwoven layer of MgO and BaM, approximately 16 nm thick at the film-substrate interface, improved BaM films with saturation magnetization of 4.3 kG, coercivity of 389 Oe, and FMR linewidth of 500 Oe, have been achieved. X-ray photoelectron spectroscopy (XPS) showed that the interwoven layers effectively prevent the interdiffusion between the BaM film and the SiC substrate. Atomic force microscopy (AFM) suggested that the MgO/BaM interwoven layers promote two-dimensional growth and improve c-axis perpendicular orientation of the BaM films, with a root-mean-square (rms) roughness of 5.72 ± 0.30 nm, which is possibly due to reducing the 4.4 % tensile lattice mismatch between the BaM and the SiC. X-ray diffraction (XRD) show the existence of primarily (0, 0, 2n) diffraction peaks with slight evidence of the random (107) orientation.Although the MgO/BaM interwoven layers addressed the interface mixing and lattice mismatch quite well, the resulting BaM film does not meet the device requirement of a FMR linewidth narrower than 150 Oe. Through the use of molecular beam epitaxy (MBE), 10 nm of crystalline MgO(111) was deposited for use as a template layer for BaM on 6H-SiC(0001). The resulting BaM films were epitaxially deposited by PLD with a FMR linewidth at 56 GHz of 220 Oe for the as-deposited BaM, and 96 Oe for the BaM after annealing to 1050 oC for 4 minutes. This resulted in a post-annealed film that is of sufficient quality to pursue the microwave device applications. XRD measurements of the annealed BaM showed a strong (0, 0, 2n) crystallographic alignment without any existence of random orientation peaks. AFM revealed a smooth surface with a rms roughness of 1.31 ± 0.23 nm. XPS showed a stoichiometric Fe/Ba ratio of 12 in the bulk film without any Si diffusion. The combination of high quality, thin, MBE-grown MgO interlayer and subsequent thick PLD-grown BaM film has been established to be a simple and effective method to realize integration of BaM with SiC for microwave device applications.
9:00 PM - K3.3
Structure, Switching and Piezoelectricity of Individual Domains in BiFeO3 Thin Films.
Rebecca Sichel 1 , Alexei Grigoriev 1 , Dal-Hyun Do 1 , Rasmi Das 1 , Seung-Hyub Baek 1 , Dong-Min Kim 1 , Chang-Beom Eom 1 , Bernhard Adams 2 , Eric Dufresne 2 , Zhonghou Cai 2 , Paul Evans 1
1 Materials Science Program, University of Wisconsin, Madison, Madison, Wisconsin, United States, 2 , Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractTime-resolved x-ray microdiffraction was used to study the structure, switching and piezoelectricity of multiferroic BiFeO3 (001) films on SrTiO3 substrates. We found that the BiFeO3 forms regions of strained rhombohedral stripe domains which make up larger mosaic blocks, all of which are anisotropically relaxed parallel to the substrate’s miscut direction. Domain formation in rhombohedral thin films on cubic substrates leads to local properties which are significantly different than the average over large areas. The focused x-ray microbeam (~110 nm) probes only a few domains at a time, enabling us to distinguish between neighboring domains whose polarization directions are separated by 71° or 109°. The piezoelectricity of individual domains can be studied using the (002) and (103) Bragg reflections to find the lattice constants as a function of time under applied AC fields. This piezoelectricity is highly anisotropic and depends on domain orientation. At high fields, the ferroelectric polarization direction switches and causes a structural change that can be observed with x-ray diffraction. Changes in the antiferromagnetic domain structure and spin orientation within antiferromagnetic planes can be measured in a similar manner with time-resolved magnetic resonant scattering around the Fe K-edge.
9:00 PM - K3.30
Nano-belt Structures and Formation Mechanism of BaTiO3-CoFe2O4 Thin Films.
Li Yan 1 , Jiefang Li 1 , Dwight Viehland 1
1 Materials Department, Virginia Polytechnic Institute and State University, Blacksburg, Virginia, United States
Show AbstractNano-belt structures were observed in BaTiO3-CoFe2O4 composite epitaxial thin films deposited on SrTiO3 substrates by Pulsed Laser Deposition. TEM, SEM and AFM were utilized to study the structures and morphologies of the nano-belt in the multiferroic thin films. Magnetic and ferroelectric properties were measured by SQUID and PFM. The formation mechanism of the nano-belt stuctures in BaTiO3-CoFe2O4 composite thin films is discussed.
9:00 PM - K3.31
Strain-mediated Magnetoelectric Coupling in BaTiO3-Co Nanocomposite Thin Films.
Jung H. Park 1 , Chung W. Bark 1 , Sangwoo Ryu 1 , Young K. Jung 1 , Hyun M. Jang 1 2
1 Department of Materials Science and Engineering, POSTECH, Pohang Korea (the Republic of), 2 Department of Physics, POSTECH, Pohang Korea (the Republic of)
Show AbstractMultiferroic materials that exhibit simultaneous magnetic and ferroelectric ordering are being intensively investigated. However, single-phase materials that show multiferroism at ambient conditions remain elusive. In view of these, we adopt an alternative approach to accomplish enhanced magnetoelectric (ME) coupling at room temperature. BaTiO3-Co composite thin films prepared using co-sputtering and post-annealing showed that Co particles of around 80 nm were uniformly distributed throughout the film and exerted a strong tensile stress on the ferroelectric matrix, BaTiO3. The relative dielectric permittivity changes as large as 1.6 % at 298 K under a static magnetic field of 1 T. The dynamic ME coupling effects were also observed, and the ME output at a magnetic-field frequency of 50 kHz is as high as 170 mV/cm.Oe. In-situ synchrotron x-ray microdiffraction experiment under a dc electric field clearly indicated the existence of a strong strain-mediated ME coupling in the present nanocomposite film.
9:00 PM - K3.32
Improper Ferroelectric Behavior in Magnetoelectric Pb(Zr,Ti)O3 – CoFe2O4 Multilayer Thin Films.
Nora Ortega 1 , Ashok Kumar 1 , Ram Katiyar 1
1 Physics, University of PUerto Rico, San Juan, Puerto Rico, United States
Show AbstractMagnetoelectric (ME) multiferroics are a class of materials, in which magnetic and electric polarizations coexist. There are few such single-phase materials in nature, which exhibit this dual phenomenon. Recently, synthesis of ME materials has drawn attention towards the fabrication of composite thin films. The composite thin films heterostructures having ME properties are the potential candidate for microsensors, and high-density information storage applications. In the present work we fabricated composite thin films of ferroelectric Pb(Zr,Ti)O3 (PZT) and ferromagnetic CoFe2O4 (CFO) multilayers (ML) with 3,5, and 9 layers PZT/CFO by pulsed laser deposition on Pt/TiO2/SiO2/Si substrate. The Transmission electron microscope (TEM) data shows ML structure with little inter-diffusion near the interface of ML. We studied frequency and temperature dependence of real (ε’) and imaginary (ε”) dielectric permittivity of ML thin films in the range of 100 Hz to 1 MHz and 100 to 650 K respectively. The dielectric data indicated that PZT/CFO ML thin films are a new class of improper-ferroelectric materials. The frequency dependence of the ε’ showed dispersion in low frequency region with merger at high frequency in the low temperature (<300 K) regions, nearly constant dielectric ε’ value at low frequency to a small saturated value at high frequency regions in the mid temperature regions (<500 K) and nearly constant ε’ in the temperature range of 500 to 650 K. The dielectric relaxation peak from dielectric loss spectra indicates deviation from the ideal Debye type relaxation. The observed dielectric relaxation has been explained by Maxwell Wagner type contribution at the interface between PZT and CFO layers. The inverse of dielectric constant of ML thin films showed step like behavior, which clearly indicated its improper ferroelectric character. We observed proper ferroelectric hysteresis loop in mid temperature regions (~300-400 K). With a decrease in temperature from 300 to 100 K, the saturation polarization reduced to less than 1 μC/cm2 indicating pinning of defects in the dielectric domains or enhancement in magnetic domains which suppress the dielectric effect, above 400 K, where we observed the leaky ferroelectric loop. We recovered ferroelectric properties of the ML structure at room temperature, both during heating and cooling process, indicating the intrinsic property of the ML. The temperature variation of the Raman spectra revealed that there is no structural phase transition in the investigated temperature range.
9:00 PM - K3.33
A Modified Sol-gel Process for Multiferroic Nanocomposite Films.
Ming Liu 1 , Xin Li 1 , Jing Lou 1 , Shijian Zheng 2 , Kui Du 2 , Nian Sun 1
1 Electrical and Computer engineering, Northeastern University, Bosotn, Massachusetts, United States, 2 Shenyang National Laboratory for Materials Science, Institute of Metal Research, Shenyang, Liaoning, China
Show Abstract Multiferroic composite thin films have drawn great attention due to their potential applications. Many methods have been developed to synthesis multiferroic thin film, such as Pulsed Laser Deposition, physical vapor deposition and Sol-Gel process. In this work, Multiferroic CoFe2O4-Pb (Zr,Ti)O3 (CFO-PZT) composite thin films with nanoscale mixture of the two phases were prepared by a modified Sol-Gel process, in which a mixed precursor solution of both CFO and PZT was used. X-ray diffraction and transmission electron microscopy examinations revealed the coexistence of perovskite PZT and spinel CFO that were mixed in nanoscale with mean grain sizes of 5~10 nm. Magnetic properties of the CFO-PZT nanocomposite were examined, which were consistent with their microstructures. The magnetoelectric coupling between CFO and PZT was demonstrated by a perpendicular external magnetic field induced electric polarization change . The static perpendicular magnetoelectric susceptibility α=ΔP/ΔH can be estimated with 1.8×10-3μC/Oe cm2. This modified sol-gel processing provides an alternative for multiferroic composite films, which is simpler and easier to control compared to the conventional layer-layer sol-gel process for multiferroic composite films.
9:00 PM - K3.34
Synthesis of Ordered Arrays of Multiferroic NiFe2O4–Pb(Zr0.52Ti0.48)O3 Core-Shell Nanowires.
Ming Liu 1 , Xin Li 1 , Hassan Imrane 1 , Yajie Chen 1 , Trevor Goodrich 2 , Zhuhua Cai 2 , Katherine Ziemer 2 , Jian Huang 3 , Nian Sun 1
1 Electrical and Computer engineering, Northeastern University, Bosotn, Massachusetts, United States, 2 Chemical Engineering, Northeastern University, Boston, Massachusetts, United States, 3 Center for Integrated Nanotechnology, Sandia National Laboratories, Albuquerque, New Mexico, United States
Show Abstract Multiferroic composite materials have drawn a great amount of interest due to their capability of efficient energy transfer and their potential applications in many multifunctional devices. Several synthesis methods have been developed in the bulk (3-D) and film (2-D) multiferroic materials. However, the preparation of 1-D multiferroic nanowire remains an challenge. In this work a synthesis method was developed for producing core-shell nanowire arrays, which involved a combination of a modified sol-gel process, electrochemical deposition, and subsequent oxidization in anodized nanoporous alumina membranes. This method was applied to generate ordered arrays of one-dimensional multiferroic NiFe2O4 core and Pb(Zr0.52,Ti0.48)O3 (PZT) shell nanostructures. Extensive microstructural, magnetic and ferroelectric characterizations confirmed that the regular arrays of core-shell multiferroic nanostructures were composed of a spinel NiFe2O4 core and perovskite PZT shell. This synthesis method can be readily extended to prepare different core-shell nanowire arrays, and is expected to pave the way for one-dimensional core-shell nanowire arrays.
9:00 PM - K3.35
Epitaxial Growth and Electric Properties of perovskite HoMnO3 Thin Films.
Daisuke Kan 1 , Makoto Murakami 1 , Sang-Wook Cheong 2 , Manfred Wuttig 1 , Ichiro Takeuchi 1 3
1 Department of Materials Science and Engineering, University of Maryland, Collegepark, Maryland, United States, 2 Department of Physics and Astronomy, Rutgers University, Piscataway, New Jersey, United States, 3 Center for Superconductivity Research, University of Maryland, Collegepark, Maryland, United States
Show AbstractHoMnO3 is one of particularly promising multiferroic materials with strong coupling of magnetic and dielectric properties in the hexagonal phase. Recently it was predicted that orthorhombic HoMnO3 has orders of magnitude larger polarization due to the existence of ferroelectric order in the E-type magnetic structure [1]. We have fabricated perovskite HoMnO3 thin films on SrTiO3 (001) substrates by pulsed laser deposition. The deposition is performed at the substrate temperature ranging from 600 to 700 degrees and oxygen pressure of 0.3 Torr. The crystal structures of the films are investigated by a 4-circle x-ray diffractometer. 2θ-θ scan shows that there are only (00l) peaks from the films without any secondary phases. The reciprocal space mapping around the SrTiO3 (103) Bragg reflection and the φ scan of the HoMnO3 (103) peak reveals the tetragonal symmetry of the films and the epitaxial relationship [100]HoMnO3 // [100]SrTiO3 and [001]HoMnO3 // [001]SrTiO3, confirming that the film has the perovskite structure and not the hexagonal one. We will also present electrical properties including ferroelectric properties of the perovskite HoMnO3 thin films. This work is supported by NSF DMR 0094265 (CAREER), NSF DMR 0603644, MRSEC DMR-00-0520471, and by the W. M. Keck Foundation. One of the authors (D. K.) acknowledges support by Postdoctoral Fellowships for Research Abroad from Japan Society for the Promotion of Science (JSPS).[1] I. A. Sergienko, Cengiz Sen, and Elbio Dagotto Phys. Rev. Lett. 97, 227204 (2006).
9:00 PM - K3.36
Magnetic Properties of Intercalated Disulfides and Layered Manganites.
J. Rasch 1 2 , M. Boehm 1 , J. Schefer 2 , L. Keller 2 , G. Abramova 3 , N. Volkov 3 , D. Mazaudier 4 , V. Sokolov 5 , G. Petrakovskii 3
1 , Institut Laue-Langevin, 6 rue Jules Horowitz, BP 156, 38042 Grenoble, Cedex 9, France, 2 Laboratory for Neutron Scattering, ETH Zurich & Paul Scherrer Institut, CH-5232 Villigen PSI Switzerland, 3 , L.V. Kirensky Institute of Physics SB RAS, Krasnoyarsk 660036 Russian Federation, 4 , Ecole Nationale Superieure de Physique de Strasbourg, BP 10413, 67412 Illkirch Cedex France, 5 , Nikolaev Institute of Inorganic Chemistry SB RAS, Novosibirsk 630090 Russian Federation
Show AbstractDue to the features of their crystal structure, quasi two-dimensional layered substances can be of great interest for new multilayer thin-film structures. Intercalation and cation substitution allow the tuning of the electronic and magnetic properties such as the colossal magnetoresistance (CMR) effect. Layered transition metal dichalcogenides exhibit a three dimensional crystal structure with strong anisotropy of the chemical bonds in crystallographic c direction, perpendicular to the layers.Two different families of layered quasi 2D compounds have been chosen for investigation: Pb3Mn7O15 and CuCrS2.Manganites with perovskite structure and mixed valence state of the Mn ions have been the subject of intense research [1]. Their chemical flexibility leads to a very rich phase diagram involving various metallic, insulating and magnetic phases [2]. Up to date information on the structural, electronic and magnetic properties of the mixed-valence (Mn3+/Mn4+) compound PbO-MnO2-Mn2O3 is missing. Bulk measurements (magnetization, magnetic susceptibility and specific heat) give evidence of strong antiferromagnetic correlations with a large negative Curie-Weiss temperature of Θp = -520 K. Single crystal neutron diffraction at the Swiss Neutron Spallation Source SINQ (TriCS) reveals two distinct magnetic phases in Pb3Mn7O15 at low temperature.The intercalated CuCrS2 is based on the chromium disulfide CrS2 with space group R3m [3]. In contrast to related isostructural compounds NaCrSe2, AgCrSe2 and NaCrS2, which all have positive Curie-Weiss temperatures [4], CuCrS2 shows a large negative Curie-Weiss temperature of Θp = -148 K [5]. The magnetic structure of NaCrSe2 was found to be commensurate, while AgCrSe2 and NaCrS2 form helices with rotating moments in the basal plane. For the more complex system CuCrS2, earlier neutron diffraction experiments discovered also a helical magnetic propagation vector [6], which could be confirmed with our powder but not with single crystal measurements. Another related compound LaCrS3 features complex magnetic properties which are reminiscent of spin glass behavior [7]. The reason is a two-dimensional triangular distribution of Cr3+ ions in which antiferromagnetic coupling leads to topological frustration. The chromium framework is also a characteristic evident in our compound CuCrS2.First results on CuCrS2 obtained with neutron diffration experiments are presented.Whether the crystallographic two-dimensionality is interrelated with the magnetic properties of Pb3Mn7O15 and CuCrS2 is the subject of our present investigations.References[1] N. Volkov et al., Phys. Rev. B 73 104401 (2006)[2] A. Moreo et al., Science 283 2034 (1999)[3] J.A. Wilson, A.D. Yoffe, Adv. Phys. 18 193 (1969)[4] F.M.R. Engelsman et al., J. Solid State Chem. 6 574 (1973)[5] G.M. Abramova et al., Phys. Solid State 46 2225 (2004)[6] M. Winterberger, Y. Allain, Solid State Comm. 64 1343 (1987)[7] A. Lafond et al., Phys. Rev. B 52 1112 (1995)
9:00 PM - K3.37
Engineered Biferroic 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3/La0.6Sr0.4MnO3 Epitaxial Superlattices.
Ayan Roy Chaudhuri 1 , S. Krupanidhi 1
1 Materials Research Centre, Indian Institute of Science, Bangalore, Karnataka, India
Show AbstractCoexistence of ferromagnetism and ferroelectricity in a material, and the coupling between them have attracted renewed importance due to both fundamental and technological interest. Control of ferroelectric polarization by magnetic field and vice versa can effect in designing of novel devices with paramateric values and flexibity. But the scarcity of intrinsic multiferroic materials and very small magnetoelectric coupling observed in them limit their possibility to be useful in any device application. To address these issues and in search of alternative multiferroic materials there is an upsurge of interest to fabricate artificial heterostructures consisting alternative layers of different ferromagnetic and ferroelectric materials. In this work symmetric and asymmetric superlattices (SLs) of ferromagnetic La0.6Sr0.4MnO3 (LSMO) and ferroelectric 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3(PMN-PT) with different periodicities have been fabricated on LaNiO3 coated LaAlO3 (100)substrates, by pulsed laser deposition. Symmetric SLs were consisted of equal thickness of PMN-PT and LSMO, whereas asymmetric SLs were consisted of constant LSMO layer thickness in each period and increasing PMN-PT sublayer thickness with increasing periodicity. The higher order satellite peaks in the X Ray Diffraction pattern adjacent to the main peak of the averaged lattice indicated that the films were heterostructurally coherent with sharp interfaces. All the SLs exhibited ferromagnetic hysteresis behavior over a wide range of temperatures between 10K and 300K, whereas only the asymmetric SLs exhibited a reasonably good ferroelectric behavior. Frequency independent Polarization hysteresis (P-E) loops and the Capacitance Voltage loops confirmed their ferroelectric characteristics. Coexistence of ferroelectricity and ferromagnetism essentially proves biferroic nature of the asymmetric SLs. Studies were conducted towards understanding the influence of LSMO layers on the electrical responses of the heterostructures. Absence of ferroelectricity in the symmetric SL structures has been attributed to their high leakage characteristics. Strong influence of an applied magnetic field was observed on the ferroelectric properties of the asymmetric SLs. P-E hysteresis loops in these SL were asymmetrically shifted along the electric field axis. On application of a magnetic field of 1.2T at room temperature the loops showed reduced asymmetry with an increase in remnant polarization and coercive field. Similar changes in P-E loops were observed on poling the samples with a 500 kV/cm DC bias. These observations indicated the presence of depolarizing fields at the interfaces, which get compensated due to interfacial charge accumulation on applying a magnetic or a DC electric field. Maxwell Wagner type relaxation as evidenced from the dielectric studies over a wide range of temperature and frequency establishes the interface dominated electrical properties in these biferroic SLs.
9:00 PM - K3.38
Giant Magnetoelectric Effect Based on Metglas/PZT Fiber and Sensor Applications.
Junyi Zhai 1 , Shuxiang Dong 1 , Zengping Xing 1 , Jiefang Li 1 , Dwight Viehland 1
1 MSE, Virginia Tech, Blacksburg, Virginia, United States
Show AbstractGiant magnetoelectric(ME) effect has been shown in Metglas and PZT fiber laminates. Unlike most magnetostrictive material, Metglas has large permeability which enables laminates can achieve maximum ME voltage coefficient at a very small DC magnetic field. Furthermore the shape and the thickness of the Metglas has important effect on both ME voltage coefficient and required DC bias. Passive AC magnetic sensor based on ME laminates can achieve 1.2 pT sensitivity at Resonance frequency. Active DC magnetic sensor based on the ME laminates that are wrapped with a coil can sense less than 1 nT magnetic field with a 10mA AC current which can be used as a new type of geomagnetic field sensor and potentially offering opportunities for a small global positioning device.
9:00 PM - K3.39
Magnetoelectric Transformer : Tunable Feature Discovered.
Shuxiang Dong 1 , Junyi Zhai 1 , Jie-Fang Li 1 , Dwight Viehland 1
1 Materials Science & Engineering, Virginia Tech, Blacksburg, Virginia, United States
Show Abstract9:00 PM - K3.4
X-ray Diffraction Study on the Strained States of Multiferroic BiFeO3 Films and Related Superlattices.
Chan-Ho Yang 1 , Ying-Hao Chu 1 , Lane W. Martin 1 , Mark Huijben 1 , Kilho Lee 1 , Micky Barry 1 , Seung Yeul Yang 1 , Ramamoorthy Ramesh 1
1 Department of Materials Science and Engineering, and Department of Physics, University of California, Berkeley, Berkeley, California, United States
Show AbstractThin film BiFeO3 has high potential of device application relating to multiferroic properties. It is a model system to study inter-coupling between ferroelectricity and antiferromagnetism because two order parameters are large and well ordered at room temperature. Bulk BiFeO3 is known to have rhombohedral structure (Space group R3c) but if grown on cubic-based substrates monoclinic distortions are induced due to heterogeneity between film and substrates. By using different orientations, miscut angles, lattice parameters of substrates and different film thickness, various strain states and twin structures can be realized in BiFeO3 films. X-ray reciprocal space mapping was utilized to clarify strained states. From the {203} peak splitting of BiFeO3 film grown on (001) SrTiO3, we could get information about variant of polarization, which was consistent with piezoforce microscopy (PFM) results. Also, by using the same technique, we tried to investigate structural distortions at high temperature without any concern about leakage current. These structural distortions are related with ferroelectricity and also connected to magnetic state via spin-orbit interaction. We will discuss electric polarization, magnetic easy axis and their inter-coupling based on the detailed structural information. Finally we will mention the structural modification of BiFeO3/SrRuO3 superlattices and BiFeO3/La0.7Sr0.3MnO3 superlattices as the thickness of BiFeO3 is decreased.
9:00 PM - K3.40
ME Sensor Modeling and Optimization.
Zengping Xing 1 , Dwight Viehland 1 , Jiefang Li 1 , Shuxiang Dong 1 , Junyi Zhai 1
1 Materials Science and Engineering, Virginia Tech, Blacksburg, Virginia, United States
Show AbstractEquivalent ME lamiante model is set up. Basing on this model, ME array and scale effect is proposed. How the array and scale effect affect the sensitivity(SNR) was also discussed. Theory prediction gave how the array number and the scale volum affect the senstivity. Experiment result confirm this prediction. These research gave more profound idea into how to design high sensitive ME sensor. A low frequency nano-Tesla sensitivity ME sample with large volume is also costructed.
9:00 PM - K3.41
Epitaxial Growth of Spinel Ferrite Oxide (Al,Ru,Fe)3O4 on a GaAs(001) Substrate Using a MgO Buffer Layer.
Teruo Kanki 1 , Yasushi Hotta 1 , Naoki Asakawa 1 , Toshio Kawahara 1 , Yoshikazu Terai 2 , Yasufumi Fujiwara 2 , Hitoshi Tabata 3 , Tomoji Kawai 1
1 The Institute of Scientific and Industrial Reseach, Osaka University, Osaka Japan, 2 Graduate School of Engineering, Osaka University, Osaka Japan, 3 Graduate School of Engineering, The University of Tokyo, Tokyo Japan
Show AbstractSpinel ferrite oxide (Al,Ru,Fe)3O4 is a ferrimagnet and shows cluster-glass behavior with temperature hysteresis of magnetization between zero-field-cooling (ZFC) and field-cooling (FC) measurements. One of the important features of this material is that the spin-freezing temperature Tg is controllable in a wide range beyond room temperature by substitutional doping of non-magnetic ions. Another remarkable feature is to show photo-induced magnetization (PIM), namely, the magnetization is changeable by irradiating light. The other materials showing the PIM effect, for example, the diluted magnetic semiconductors or Prussian blue analogs were reported. Those operation temperatures, however, are low. In (Al,Ru,Fe)3O4 films, on the other hand, room temperature operation of the PIM effect was realized and the highest operation temperature basically depends on the Tg. This is a very interesting event in creating new magneto-optical devices. In this study, we tried to grow (Al,Ru,Fe)3O4 films on a GaAs(001) substrate for the purpose of practical use of the PIM effect, realizing more effective and controlled PIM by using light-emitting element substrates such as GaInP in the future. (Al,Ru,Fe)3O4 films was prepared by a pulsed-laser deposition (PLD) technique. Then a MgO buffer layer was employed because it was difficult to fabricate crystalline (Al,Ru,Fe)3O4 films directly on a GaAs(001) substrates. It was found that MgO buffer layer grew to [001] direction when substrate temperature and oxygen pressure were over 300 C and 10-4 Pa, fortunately including the fabrication-condition for (Al,Ru,Fe)3O4 films. Crystalline (Al,Ru,Fe)3O4 films were consequently obtained on a GaAs(001) substrate. We will report not only results in the systematic research for epitaxial growth condition but also magnetic properties in the films.
9:00 PM - K3.42
Temperature and dc Bias Dependence of Acoustic Resonances in Ba0.25Sr0.75TiO3 Thin Films.
John Berge 1 , Martin Norling 1 , Andrei Vorobiev 1 , Spartak Gevorgian 1 2
1 Department of Microtechnology and Nanoscience, Chalmers University of Technology, Göteborg Sweden, 2 Microwave and High Speed Electronics Research Center, Ericsson AB, Mölndal Sweden
Show AbstractThin film bulk acoustic resonators based on 350 nm thick Ba0.25Sr0.75TiO3 films deposited by laser ablation have been fabricated on Si substrates. The resonators are acoustically isolated from the substrate by a Bragg reflector stack and were designed for a resonance frequency of 5.25 GHz using simulations based on the 1D Mason model. This structure has been proposed to be used as a tunable/switchable small sized resonator in microwave devices [1]. Without dc bias the resonances excited in the Ba0.25Sr0.75TiO3 film are very weak at room temperature and above in agreement with the expected paraelectric, and thus non-piezoelectric, phase of the material at these temperatures. Applying dc bias however induces piezoelectric effect in the Ba0.25Sr0.75TiO3 film and distinct acoustic resonances are observed, with resonance frequencies and electromechanical coupling coefficient dependent on the applied dc voltage. Series and parallel resonance frequencies were measured using on-wafer one-port reflection measurements as a function of dc bias voltage up to 15 V and temperature in the range 40-520 K. For temperatures up to approximately 120 K the series and parallel resonance frequencies are relatively temperature independent. Between 120 K and 150 K there is however a sharp increase in the resonance frequencies, probably related to the ferroelectric to paraelectric phase transition which for the bulk material counterpart should occur at approximately 140 K. For higher temperatures the resonance frequencies slowly decrease with increasing temperature up to 520 K. The series resonance is tuned to lower frequencies with increasing dc bias voltage for all temperatures, with a tunability of 1-2% for 15 V dc bias. The parallel resonance however reveals different tuning characteristics at high and low temperatures. For high temperatures, above approximately 170-200 K, the parallel resonance is shifted to lower frequencies with increasing dc bias, while for lower temperatures it is on the contrary shifted to higher frequencies with increasing dc bias. The observed resonance behaviour of the Ba0.25Sr0.75TiO3 based resonators is analyzed using the electromechanical equations describing the ferroelectric film under dc and ac electric fields [2, 3]. The difference in tuning direction of the parallel resonance at high and low temperatures may be attributed to a change in the sign of the coefficient M related to electrostriction nonlinear with respect to mechanical deformation. [1] J. Berge et.al.: Tunable solidly mounted thin film bulk acoustic resonators based on BaxSr1-xTiO3 films. IEEE Microwave and wireless components letters, accepted.[2] I. Vendik et.al.: Modelling of Tuneable Acoustic Resonators based on BSTO Films with Induced Piezoelectric Effect. EuMC, Munich, Germany, 8-12 October, 2007, accepted.[3] A. K. Tagantsev et.al.: Membrane based tunable TFBARs. Theory and experiment. EuMC, Munich, Germany, 8-12 October, 2007, Workshop presentation.
9:00 PM - K3.43
Fabrication of Highly Efficient Energy Harvesting MEMS Devices by Pb(Zr,Ti)O3–based Cantilever Beams.
Jung-Hyun Park 1 , Dongna Shen 1 , Sang Yoon 1 , Song-Yul Choe 2 , Dong-Joo Kim 1
1 Material Engineering, Auburn Univerity, Auburn University, Alabama, United States, 2 Mechanical Engineering, Auburn University, Auburn University, Alabama, United States
Show AbstractPiezoelectric-based energy harvesting devices using ubiquitous vibration source were fabricated and developed by MEMS process. Pb(Zr,Ti)O3 (PZT) films were optimized on 4-inch silicon wafers by chemical solution deposition method. MEMS process was utilized to construct cantilever structure that is designed to have ~100 Hz of resonant frequency whose value is similar to common ambient vibration frequency. Silicon proof mass was defined at the end of tip of cantilever beam to enhance deflection corresponding to generated voltage. Optimized deep reactive ion etching enabled to fabricate robust PZT cantilevers with Si proof mass. The precise control of process parameters resulted in the formation of thin and uniform Si layer with average thickness of 25 μm without curling of cantilevers for high performance of device. Cantilever beam stack structures were also systematically studied to enhance adhesion for long term reliable operation. Types of adhesion layers such as Cr, Ti, Ta and other oxide layers, and heat treatment for the formation of PZT films were also investigated. The PZT cantilever beam whose length is about 1000 μm generates about micro watt with loading 10 kΩ at 1-g, which may be sufficient for micro wireless sensor applications.
9:00 PM - K3.44
Nanomechanical Properties of Pb(Zr0.52Ti0.48)O3 Films by Nanoindentation.
Dan Liu 1 , Sang H. Yoon 1 , Bo Zhou 1 , Barton C. Prorok 1 , Dong-Joo Kim 1
1 Materials Engineering, Auburn University, Auburn, Alabama, United States
Show AbstractDuring the past several decades, PZT films are extensively given attention for their potential as sensors and actuators in microelectromechanical systems (MEMS) due to their excellent piezoelectric properties. Since piezoelectric behavior of PZT-based MEMS devices may depend on the mechanical coefficients, the scaling effects of PZT films’ mechanical properties should be determined if they are to be optimized for use in MEMS devices. This paper conducted investigation into the effects of the crystalline orientations and substrates on the nanomechanical properties of PZT films. The crystalline orientations of PZT films deposited by sol-gel method on platinized silicon substrates were controlled by combined parameters of a chelating agent and pyrolysis temperature. Since MEMS structures utilize different types of layer materials such as silicon nitride, silicon oxide for mechanical elements, mechanical properties of PZT films grown on different substrates and adhesion layers were also examined. Young’s modulus and hardness of these PZT films were determined by nanoindentation measurement. The experimental results show that (100)-oriented films show higher values compared to (111)-oriented films indicating clear dependence of film orientation. The influence of substrates on the mechanical properties of PZT thin films was also characterized. A model employing nanomechanics approach that allows film orientation and substrate will be discussed.
9:00 PM - K3.45
Polarized Raman Study of 0.67 PbMg1/3Nb2/3O3-0.33 PbTiO3Single Crystals.
Juan Cheng 1 , Kenneth Siu 1
1 Physics and Material Science, City University of Hong Kong, Hong Kong China
Show Abstract9:00 PM - K3.46
PMN-PT Single Crystal Piezo-Electric Acoustic Sensor.
Sung Q Lee 1 , Hye Jin Kim 1 , Sang Kyun Lee 1 , Jae Woo Lee 1 , Kang-Ho Park 1
1 , ETRI, Daejon Korea (the Republic of)
Show AbstractMEMS(Micro-Electro-Mechanical System) acoustic sensors are widely investigated and promising in many areas. Recently several kinds of MEMS acoustic sensor technologies have been proposed, such as condenser [1], electret [2], piezoresistive [3], and ferroelectric types [4]. Ferroelectric thin film MEMS acoustic sensors, which are based on the piezoelectric effect of a ferroelectric thin film, have a simple and robust fabrication process. Furthermore, they do not need external bias for signal readout and have a wider dynamic range [5]. In this paper, we present a first trial of a PMN-PT single-crystal piezoelectric MEMS acoustic sensor. The PMN-PT based acoustic sensor can offer the ability to passively sense without the power requirements. Furthermore this material exhibits extraordinary piezoelectric properties. The material, the single-crystal solid-solutions (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-PT), has been shown to possess piezoelectric coefficients and electromechanical coupling responses significantly larger than conventional ceramics. A four times enhancement in piezoelectric coefficients and much higher efficiencies in electrical to mechanical energy conversions have been found. The proposed ferroelectric acoustic sensor has the circular IDE (Interdigitate Electrode) patterns. Circular electrode configuration consisting of metallic area distributed over the PMN-PT surface can lead to efficient acoustic sensing. In case of the interdigitated electrode design, an external stress applied to the diaphragm results in output charge or voltage by d33 mode. In d33 mode, the poling direction is coincident with strain direction. In many perovskite ferroelectric materials, the d33 coefficient is two or more times larger than d31, and therefore our interest is the d33 mode with interdigitated electrode pattern. The fabrication of PMN-PT single crystal acoustic sensors is as follow. We use <001>-oriented and poled 20um-thick PMN-PT single crystal glued on a Si substrate. The sample undergoes a mechanical polishing down to 20~30μm-thick film. Next, Inductively Coupled Plasma etching process is used to thin the film down to 5μm. For the upper electrode patterning, Au e-bema sputtering is used following the Photo Resistive coating for lift off process. Then, back side etching process with deep RIE etching is used for releasing the membrane. The characteristic of polarization is analyzed. After 30min at 45V poling condition, it shows the hysteresis properties of piezoelectric PMN-PT acoustic sensor. After connecting the wire, we measured the sensitivity of PMN-PT single crystal acoustic sensor. It shows the 20mV/Pa at 10kHz resonance. We conclude that we can manufacture high sensitivity acoustic sensor using ferroelectric material of PMN-PT single crystal. And, based on single crystal, it shows the better characteristics than conventional PZT type acoustic sensor.
9:00 PM - K3.47
Morphotropic Phase Boundary Shift in Epitaxial xPb(Mg1/3Nb2/3)O3–(1-x)PbTiO3 Thin Film with Different Strain States.
Seung Hyub Baek 1 , Chang-Beom Eom 1 , Venu Vaithyanathan 2 , Darrell Schlom 2
1 Materials Science and Engineering, UW-Madison, Madison, Wisconsin, United States, 2 Materials Science and Engineering, Pennsylvania State University, University Park, Pennsylvania, United States
Show AbstractThe relaxor ferroelectrics such as Pb(Mg1/3Nb2/3)O3–PbTiO3 (PMN-PT) are very attractive material for sensors and actuators due to their large piezoelectric responses. However, the piezoelectric coefficients of these materials are maximum near the Morphotropic phase boundary (MPB), which is a nearly vertical line separating tetragonal and rhombohedral phase in phase diagram. Even though the MPB composition of the bulk is already known, thin films may have different MPB composition due to its mechanical boundary conditions such as strain and clamping effect by substrates. Thus, the determination of the MPB composition in the thin film is very important in terms of maximizing the piezoelectric responses for device applications. In order to understand the MPB shift according to the strain states, we have grown epitaxial PMN-PT/SrRuO3 heterostructures with various compositions of PMN-PT near the bulk MPB region by using off-axis sputtering. We used two different substrates; (001) SrTiO3 for compressive strain and (001) Si with SrTiO3 template layer for tensile strain. We have determined the compositions, structures, three dimensional strain states and piezoelectric coefficients and dielectric constant of the PMN-PT thin films. We will discuss the the effect of mechanical boundary conditions on the MPB compostion and piezoelectric coefficients. We will also discuiss the strain dependent phase diagram of PMN-PT thin films, which will help to guide the optimum composition of PMN-PT at given strain states of electromechanical device.
9:00 PM - K3.5
Spin Lattice Coupling in Multiferroic BiFeO3 Epitaxial Films with Rhombohedral R3c Symmetry.
Manoj Singh 1 , Ram Katiyar 1
1 Physics, University of Puerto Rico, San Juan, Puerto Rico, San Juan, Puerto Rico, United States
Show AbstractHighly (111) oriented BiFeO3 (BFO) thin films were grown on (111) SrTiO3 substrates by pulsed laser deposition. Polarized Raman -scattering studies employing two distinct backscattering geometries of these films revealed that the films were epitaxial with rhombohedral R3c symmetry was. All of the observed Raman lines were assigned to A1 and E symmetry modes based on their polarization selection rule. A1(TO) modes at 84, 136, 172 and 434 cm-1 were isolated from E(TO) modes by using side view backscattering geometry. Temperature dependent Raman spectra of (111) oriented BFO thin films were recorded between 25 and 9000C by employing normal backscattering geometries. The observed Raman modes show anomalous frequency shifts between 250- 400 0C and the two comparatively sharp A1 modes at 136 and 172 cm-1 vanished around the magnetic phase transition TN (370 0C) which can be interpreted as an experimental evidence of perturbation of antiferromagnetic ordering coupled with octahedral tilting and it indicates spin-lattice coupling at antiferromagnetic to paramagnetic transition temperature (TN). Differential Thermal Analysis (DTA) measurementa and anomalous change in Raman spectrum at 600 0C revealed another possible structural phase transition. The spectra did not show any soft mode behavior at the ferroelectrics to paraelectric transition temperature ~ (820 0C) revealing that this transition is first order.
9:00 PM - K3.51
A Novel Combinatorial Approach Using a Modified Molecular Beam Epitaxy (MBE) Technique for Development of Pb-Free Piezoelectric Materials.
Piers Anderson 1 3 , Samuel Guerin 1 , Brian Hayden 2 1 , Ian Reaney 3
1 , Ilika Technologies Ltd, Southampton, Hampshire, United Kingdom, 3 Dept of Engineering Materials, University of Sheffield, Sheffield, Yorkshire, United Kingdom, 2 School of Chemistry, University of Southampton, Southampton, Hampshire, United Kingdom
Show AbstractA novel synthesis technique enabling the co-evaporation of elements in order to synthesize inorganic material libraries in conjunction with Piezoresponse Force Microscopy (PFM), is used to screen and rapidly test Pb-free piezoelectrics. Our approach involves depositing thin-films under an ultra-high vacuum (UHV) environment from a combination of electron beam and Knudsen cell sources. Up to six elements can be deposited simultaneously to produce combination at the atomic scale in films ranging from sub-nanometer to 1000 nm in thickness. Each source is controlled individually, and this enables deposition of a wedge, for each element, which is fully controllable from a uniform film to a full 0-100% wedge across an array [S. Guerin & B. E. Hayden, Journal of Combinatorial Chemistry, 8(1), (2006), 66-73]. Careful selection of the relevant parameters allows accurate control of the wedge growth, and when combined with the other sources, the elemental composition of each field within a library. A RF atom source is used to create atomic oxygen during the deposition, in order to produce thin-film ceramics.
9:00 PM - K3.52
Growth and Characterization of Highly Oriented Lead-free (K0.5 Na0.5)NbO3 Thin Films by Chemical Solution Deposition.
Chiwon Kang 1 , Sang H. Yoon 1 , Jung-Hyun Park 1 , Joo Won Lee 1 , Minseo Park 2 , Dong-Joo Kim 1
1 Materials Research and Education Center, Auburn University, Auburn, Alabama, United States, 2 Department of Physics, Auburn University, Auburn, Alabama, United States
Show Abstract(K0.5 Na0.5)NbO3 (KNN) perovskite materials have been developed as a potentially promising lead-free piezoelectric material for environmentally and biologically benign piezoelectric devices. To date, however, there are few reports on the growth of good KNN thin films by chemical solution deposition and their properties for the device application. Excellent crystallinity at low temperature with uniform and controllable microstructure is required for the improvement in electrical properties including piezoelectric properties. KNN thin films were fabricated on SiO2/Si and Pt/Ti/SiO2/Si substrates by chemical solution deposition. By applying different annealing conditions highly oriented KNN was attained from 550 °C. Weight loss and exothermic peaks were confirmed by thermogravimetry differential thermal analysis (TG-DTA). Structural characterization of KNN was performed by X-ray diffraction and Raman spectroscopy. The surface morphology and roughness were evaluated by AFM and SEM. XRD and Raman spectroscopy exhibited that KNN films showed better crystallinity on Pt/Ti/SiO2/Si substrate in comparison with on SiO2/Si substrate due to lower energy barrier for nucleation and growth. At optimized condition AFM and SEM revealed uniform and dense microstructures. Electrical properties of KNN such as piezoelectric constant, polarization-electric field (P-E) hysteresis loop and leakage current density will be discussed. To enhance piezoelectric properties including piezoelectric constant, the effect doping elements on KNN will also be discussed.
9:00 PM - K3.53
Sintering Behavior and Characterization of Donor Doped KxNa1-xNbyTa1-yO3 Ceramics.
Koichi Kikuta 1 , Yoshiki Watanabe 1 , Shin-ichi Hirano 1
1 , Nagoya University, Nagoya Japan
Show AbstractKxNa1-xNbyTa1-yO3 (KNNT) ceramics has been achieved much attention as one of the candidates for lead free piezoelectric. Some solid solution systems of KNN were also studied in many groups. We have been reported on the sintering and electric properties of KNNT system with a sintering aid of K4.1CuTa7.7O22.3 (KCT). In this study, improvement of piezoelectric properties of KNNT ceramics was investigated by doping of donor elements. It is confirmed that an addition of donor reduced the coercive field and slightly enhanced the piezoelectric properties such as d33. Thus the sample can be poled under an electric field of 2kV/mm. A dense KNNT ceramics prepared by this study shows the piezoelectric constant d33 >200 pC/N, kp>0.47, and Qm>400. The effect of this doping on the sintering behavior of KNNT ceramics will be discussed
9:00 PM - K3.54
Synthesis and Characterization of (Na0.5K0.5)xLi(1-x)NbyTa(1-y)O3 Piezoelectric Ceramic.
Aide Torres-Huerta 1 2 , Jose Gonzalez-Reyes 2 , Maria Villafuerte Castrejon 2
1 CICATA-Altamira, Instituto Politécnico Nacional, Altamira, Tamaulipas, Mexico, 2 Metálicos y Cerámicos, Universidad Nacional Autónoma de México, Instituto de Investigaciones en Materiales, México, Distrito Federal, Mexico
Show Abstract9:00 PM - K3.56
Piezoelectric Properties of Lead Free (Na,K)NbO3-(BaSr)TiO3 Ceramics.
Ji-Won Choi 1 , Mi-Ro Kim 1 2 , Hyun-Cheol Song 1 , Yong-Soo Cho 2 , Seok-Jin Yoon 1
1 Thin Film Materials Research Center, Korea Institute of Science and Technology, Seoul Korea (the Republic of), 2 Department of Ceramic Engineering, YonSei University, Seoul Korea (the Republic of)
Show AbstractPb(ZrTi)O3(PZT) ceramics have widely used for actuators and sensors due to their excellent piezoelectric properties such as high piezoelectric constant(d33), mechanical quality factor(Qm), electromechanical coupling coefficient(kp). However, the volatility and toxicity of lead/lead oxide limits their application for electronic devices. Therefore lead free piezoelectric materials having good piezoelectric properties are absolutely demanded.(Na, K)NbO3 is one of the promising candidate materials for lead-free piezoelectric ceramics due to their combination properties of ferroelectric KNbO3 and antiferroelectric NaNbO3 which form a morphotropic phase boundary (MPB) at 50:50 compositions. However, (Na, K)NbO3 ceramics sintered by ordinary sintering process, which doesn’t use hot pressing or double crucible sintering, show relatively low d33(∼80 pC/N). BaTiO3 is a ferroelectric material, which shows high dielectric and piezoelectric constant. SrTiO3 is a paraelectric material, which shows low dielectric loss. Therefore, solid solution of NKN with BST will enhance the piezoelectric constant without degradation of quality factor.In this study we synthesized high d33 (Na, K)NbO3 by controlling the particle size and solid solution with (BaSr)TiO3 system by using ordinary sintering process, and analyzed their correlation between compositional and piezoelectric properties.
9:00 PM - K3.58
New Route of Complex Oxide Phases Synthesis by Using Low Hydrated Hydroxides of Niobium and Tantalum.
Dmitri Drobot 1 , Elena Nikishina 1 , Elena Lebedeva 1 , Andrey Novoselov 2 1
1 , Lomonosov Moscow State Academy of Fine Chemical Technology, Moscow Russian Federation, 2 , Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai, Miyagi, Japan
Show Abstract9:00 PM - K3.59
La- and Ti- Co-modified BiFeO3-PbTiO3 Piezoelectric Ceramics for High Temperature Applications.
Yufa Qi 1 , Jianguo Chen 1 , Jinrong Cheng 1 , Shenwen Yu 1 , Zhongyan Meng 1
1 Department of Electronic Information Material, Shanghai University, Shanghai China
Show Abstract9:00 PM - K3.6
Strain Control of Domain-wall Stability in Epitaxial BiFeO3 (110) Films.
Ma. de la Paz Cruz Jauregui 1 2 , Ying Chu 2 , Jing Zhang 3 , Pei Yang 2 , Florin Zavaliche 2 , Q. He 3 , Padraic Shafer 2 , Long Chen 3 , Ramamoorthy Ramesh 2
1 , Centro de Ciencias de la Materia Condensada. Universidad Nacional Autónoma de México, Ensenada, B.C., Mexico, 2 Materials Science and Engineering, and Department of Physics, University of California, Berkeley, California, United States, 3 Materials Science and Engineering, Pennsylvania State University, Pennsylvania State University, Pennsylvania, United States
Show AbstractWe have studied the stability of domains and domain walls in multiferroic BiFeO3 thin films using a combination of piezoelectric force microscopy (PFM) and phase-field simulations. We discovered that a film/substrate misfit strain may result in drastically different thermodynamic stability of two parallel domain walls with the same orientation, which otherwise have the same domain wall energy. A fundamental understanding of the underlying physics, the stress distribution in a domain structure, leads to a novel approach to control the ferroelastic domain stability in the multiferroic BiFeO3 system. As an example, we demonstrate that the ferroelastic switching in epitaxial BiFeO3 films grown on SrRuO3/SrTiO3 (110) can be controllably reproduced and stabilized by judicial choice of domain configurations.This work has been supported in part by ONR, under a MURI program and by CoNaCyT Proj. 52563.
9:00 PM - K3.60
Synthesis of BiFeO3 Crystallites Using a Magnetic Field Assistant Hydrothermal Method.
Xiaolong Yan 1 , Jianguo Chen 1 , Dengren Jin 1 , Shengwen Yu 1 , Jinrong Cheng 1
1 Electronic Information Material, Shanghai University, Shanghai China
Show Abstract9:00 PM - K3.61
High-Resolution Synchrotron X-Ray Studies of Strained Ferroelectric and Multiferroic Thin Films.
Jeffrey Klug 1 2 , Orlando Auciello 2 3 , Michael Bedzyk 1 2 4 , Ying-Hao Chu 5 , Michael Biegalski 6 , Ramamoorthy Ramesh 5 , Susan Trolier-McKinstry 6 , Darrell Schlom 6
1 Physics and Astronomy, Northwestern University, Evanston, Illinois, United States, 2 Materials Science Division, Argonne National Laboratory, Argonne, Illinois, United States, 3 Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois, United States, 4 Materials Science and Engineering, Northwestern University, Evanston, Illinois, United States, 5 Physics and Materials Science and Engineering, University of California, Berkeley, Berkeley, California, United States, 6 Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania, United States
Show Abstract9:00 PM - K3.62
Determination of Possion's Ratios for Epitaxial Oxide Thin Films Using Piezoelectric Substrates.
Michael Biegalski 1 , Hans Christen 1 , Kathrin Doerr 2
1 Center for nanophase materials science, Oak Ridge National Lab, Oak Ridge, Tennessee, United States, 2 Institute for Metallic Materials , IFW Dreseden, Dresden Germany
Show AbstractEpitaxial oxide thin films frequently exhibit different properties than their bulk counterparts. Epitaxial strain plays a key role in these changes, but in order to understand and model the consequences of lattice mismatch and differences in thermal expansion between substrates and films, knowledge of the films’ elastic properties is required. Unfortunately, the available techniques to determine these quantities, relying on mechanical deformation of the sample or acoustical measurements, are difficult or impossible for thin-film samples. Therefore, bulk values of quantities such as the Poisson’s ratio are typically used without the possibility of experimental confirmation. To address this problem we introduce a novel and general approach to measure the Poisson’s ratio of oxide thin films using an piezoelectric substrate, PMN-PT (0.70Pb(Mg0.5,Nb0.5)O3-0.3PbTiO3). The substrate is strained through the application of an electric field across the crystal, perpendicular to the film surface. The strain induced in the substrate results in a two-dimensional compression of the film, which can be quantitatively analyzed using four-circle x-ray diffraction. SrTiO3, MgO, and rare earth scandate films were grown epitaxially on polished PMN-PT substrates by pulsed-laser deposition. All films were grown in 10 mTorr O2 at 690 °C and growths were monitored using in-situ reflection high energy electron diffraction. SrRuO3 electrodes were deposited on top of the films to act as electrodes, ensuring a uniform field across the sample with a voltage (0-500V) applied between this layer and a metallic counter-electrode. By determining the change in the in-plane and out of plane lattice parameters of the film, the Possion’s ratio can be determined directly and independently of the substrate’s properties. It was found that the Possion’s ratios for the films investigated here vary only slightly from bulk values. The details of these results and the ability of this technique to accurately determine Possion’s ratio of epitaxial thin films will be presented. Research supported by the Division of Scientific User Facilities, U.S. Department of Energy (MDB, HMC) and the Deutsche Forschungsgemeinschaft, FOR 520 (KD).
9:00 PM - K3.63
Octahedral Tilt Transitions in Perovskite Thin Films.
Susan Trolier-McKinstry 1 , Daniel Tinberg 1
1 Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania, United States
Show AbstractIt has been shown for bulk materials that the transition from an untilted perovskite to a tilted perovskite can yield a significant reduction in both permittivity as well as piezoelectric coefficients. The ferroelectric transitions within bulk materials have been shown to be a function of the stress state of the material. Recently in thin films, the biaxial strain within the epitaxial thin film growth was utilized to stabilize ferroelectric phases. During these studies, it was noticed that strain had an affected the ferroelastic transitions as well. The goal of this project is to determine the how the tilt transitions within thin films are coupled with strain so that we may stabilize certain phases with large piezoelectric properties. Work has begun on epitaxial PZT films on the rhombohedral side of the morphotropic phase boundary. The effect of tilt transitions on both the linear and nonlinear dielectric and piezoelectric responses will be described.
9:00 PM - K3.64
Modelling Piezocomposites with Varying Porosity and Interconnectivity.
Andrew Dent 1 , Rhodri Lewis 1 , Chris Bowen 1
1 Materials Research Centre, University of Bath, Bath United Kingdom
Show AbstractFor certain applications the use of high density piezoceramics may not be desirable, such as sensing low frequency hydrostatic waves for sonar. Research into this field has established that piezoelectric composites with a low-density and high porosity can provide improved hydrostatic properties and high figures of merit. Piezocomposites with interconnecting struts in three-dimensions (3-3 connectivity), are well suited to hydrostatic applications with simple manufacturing routes via foam replication or burning out sacrificial polymer spheres. However, producing such materials with extensive porosity can result in regions that are isolated mechanically and / or electrically, such that a range of connectivity patterns from 3-3 to 0-3 may occur locally. To determine how these complex microstructures may be optimized, it is necessary to develop micromechanical models that can represent the piezocomposite with varying degrees of porosity and interconnectivity.Micromechanical models for 3-3 piezocomposites have relied on an idealised unit cell containing a single pore. This oversimplification has contributed to the observed differences between experimental and model results. With increased computational power and efficient finite element modelling techniques, large models have been created with numerous randomly placed pores, filled with a passive secondary phase at a predefined volume fraction. The resulting geometry features a variety of pore types and distributions depending on the volume fraction of porosity, from isolated to fully interconnected pores. This modelling approach better represents porous microstructures and has provided numerical predictions in good agreement with experimental data. Through modelling large ensembles of stochastic microstructures, the variability in composite properties is also revealed, as is found in practise.The modelling approach developed was applied to investigate key parameters including pore distribution, aspect ratio and volume fraction. The predicted composite properties (d33, d31, ε33, dh and gh) were used to calculate relevant hydrostatic figures of merit. Based on the simulated microstructures and performance indices, processing and material properties were identified for improved hydrophone materials. Such models are valuable for guiding piezocomposite design, when selecting a compromise between maximising a particular figure of merit and minimising the potential variation of performance between samples and devices.
9:00 PM - K3.65
Synthesis and Characterization of Multiferroic Composites Based on Manganate Perovskite Ceramics.
Andrei Kholkin 1 , G. Song 1
1 Dept. of Ceramics and Glass Engineering and CICECO, University of Aveiro, Aveiro Portugal
Show AbstractMuliferroic composites consist of ferromagnetic (FM) or antiferromagnetic (AFM) components intimately mixed with a ferroelectric (FE) material. High magnetoelectric coupling can be achieved via, e. g., magnetostrictive strain that is expected to modulate the properties of a ferroelectric. The ability to provide this modulation may lead to a variety of future potential devices including magnetic-field-tunable microwave resonators or magnetically switchable ferroelectric memories [1]. The manganate-type perovskites compounds are long time known to crystallize in two structural phases: a cubic phase (or close to it) and a hexagonal phase. This gives a possibility of forming not only a solid solutions but immiscible phase-separated composites. While investigating the doping effect of small Lu ions to (La,Sr)MnO3, Park et al. [2] discovered that a chemical immiscibility exists between FM-metallic (La,Sr)MnO3 (LSMO) and FE LuMnO3 (LMO). In this work, we investigated the effect of immiscibility in solid solutions LSMO and LCMO with LMO. The influence of the processing conditions on grain growth and solid solubility were studied in detail. X-ray, SEM, AFM and MFM were used to characterize the crystal structure and microstructure of sintered samples. Selected compositions were tested in terms of their magnetization, dielectric constant and ferroelectric properties at low temperatures. G. B. S. is grateful to FCT (Portugal) for the financial support. The work was done within EC-funded STREP “Multiceral” (NMP3-CT-2006-032616).1. J. Wang, et al., Science 299, 1719 (2003).2. S. Park, et al, Phys. Rev. Lett. 92, 167206 (2004).
9:00 PM - K3.66
Effect of Diamagnetic A2+ Substitution on the Magnetic and Ferroelectric Properties of Bi1-xAxFeO3 Multiferroics.
V. Khomchenko 1 , D. Kiselev 1 , Y. Pogorelov 2 , J. Vieira 1 , Andrei Kholkin 1
1 Dept. of Ceramics and Glass Engineering & CICECO, University of Aveiro, Aveiro Portugal, 2 IFIMUP/Dept. of Physics, University of Porto, Porto Portugal
Show AbstractIn the past few years there has been a revival of interest in the study of multiferroics, which have great potential for creation of novel magnetoelectric and magneto-optical devices. However, known single-phase magnetic ferroelectrics usually have low magnetic ordering temperatures, constricting possibilities of their applications. From this point of view, the most interesting results might be obtained for the BiFeO3- based perovskite compounds. BiFeO3 possesses a magnetic ordering and a ferroelectric polarization at room temperature, the property which might have made it a promising material for practical applications, but it is an antiferromagnet with a spatially modulated spin structure, which doesn’t allow net magnetization and also inhibits observation of the linear magnetoelectric effect. This spin structure can be suppressed with an application of high magnetic field, an epitaxial constraint, or a doping. The highest values of the spontaneous magnetization have been observed for the rare-earth doped samples, in which strong contribution from uncompensated spin magnetic moments of the rare-earth ions to the net magnetization exists. In case of diamagnetic A-site doping, the only possible reason of the appearance of spontaneous magnetization is a weak ferromagnetism predicted by the symmetry of the crystal structure of BiFeO3 from the suppression of the spin cycloid [1]. In this work, we carried out complex investigation of crystal structure, magnetic and ferroelectric behavior of A= Ca, Sr, Ba and Pb- substituted multiferroic perovskites. The Bi1-xAxFeO3 (x≤0.3) solid solutions were prepared and characterized by XRD, magnetometry [2], Mössbauer spectroscopy and piezoresponse force microscopy (PFM) measurements. It is shown that the crystal structure of the compounds is described with the space group R3c, permitting the spontaneous polarization, whose existence is confirmed both by both PFM and ferroelectric measurements. Magnetic properties are found to be determined by the ionic radius value of the substituting element. Experimental results suggest that the A-site substitution with the biggest ionic radius ions effectively suppresses the spiral spin structure of BiFeO3 and results in the net magnetization appearance. V. A. K. is grateful to FCT (Portugal) for the financial support. The work is done within EC-funded STREP “Multiceral” (NMP3-CT-2006-032616).[1] C. Ederer and N. A. Spaldin, Phys. Rev. B 71, 060401(R) (2005).[2] V. A. Khomchenko et al., Appl. Phys. Lett. 90, 242901 (2007).
9:00 PM - K3.67
Simultaneous Ordering of Dipole and Spin at Room Temperature in Strained Garnet Ferrite R3Fe5O12 Thin Films - Possibility of Room Temperature Multiferroics- .
Hitoshi Tabata 1
1 School of Engineering, The University of Tokyo, Bunkyo-ku, Tokyo, Japan
Show Abstract9:00 PM - K3.68
An Approach to Achieving a Terahertz Negative Index or Refraction Using Coincident Intrinsic Resonances.
Steven Kirby 1 , R. van Dover 1
1 Material Science and Engineering, Cornell University, Ithaca, New York, United States
Show AbstractA novel method of achieving a negative index of refraction in the far-infrared region using intrinsic material properties is proposed. SrTiO3 has a dielectric resonance at ~100 cm-1 that can be lowered by lowering the temperature or with Ba doping. NiO has an antiferromagnetic resonance at ~35 cm-1 that can be raised with an applied magnetic field or with Fe or Co doping. We show that SrTiO3 and NiO are readily chemically compatible and non-reacting at temperatures up to 1550°C and can be formed into polycrystalline composite bodies. Epitaxially grown thin heterostructures of (SrTiO3/NiO)n/MgO with n = 1,2 have also been fabricated with very high crystal quality. We present basic theory that suggests that this composite material can be used to achieve a negative index of refraction in the range from 35 cm-1 to 100 cm-1.
9:00 PM - K3.69
The Real Structure of ``PbCrO3."
Miguel Alario-Franco 1 , Angel Arevalo 1
1 Laboratorio de Altas Presiones, Universidad Complutense, Madrid Spain
Show Abstract9:00 PM - K3.7
The Origin of Enhanced Magnetization in Epitaxially Constrained BiFeO3 Thin Films.
Sangwoo Ryu 1 , Min G. Kim 3 , Jung H. Park 1 , Hyun M. Jang 1 2
1 Department of Materials Science and Engineering, POSTECH, Pohang, Gyung-buk, Korea (the Republic of), 3 Pohang Accelerator Laboratory, POSTECH, Pohang, Gyung-buk, Korea (the Republic of), 2 Department of Physics, POSTECH, Pohang, Gyung-buk, Korea (the Republic of)
Show AbstractMultiferroics are an interesting group of materials that simultaneously show ferroelectricity and spin ordering in the same phase. The only reported perovskite that shows room-temperature multiferroism is rhombohedral BiFeO3 (BFO). However, there are some controversial arguments about the origin of the enhanced magnetization and polarization observed in epitaxially constrained BFO films. To clarify the origin of enhanced magnetization, we have intentionally fabricated principal [111]-axis-oriented rhombohedral BFO thin films having Fe ions exclusively in the trivalent state. The saturation magnetization (Ms) of these epitaxial films grown on SrTiO3 (111) increased substantially with decreasing film thickness and did correlate well with the estimated epitaxial strain. We will discuss the origin of this increase in Ms using the Landau-Ginzburg-Devonshire free energy function and in terms of the modulation of cycloidal spin structure caused by the epitaxial constraint.
9:00 PM - K3.8
Deposition and Characterization of Low-pressure Metal-organic Chemical Vapor Deposited Epitaxial Thin Films of Iron Oxide and Bismuth Ferrite.
Manish Singh 1 , Yi Yang 1 , Christos Takoudis 2
1 Department of Chemical Engineering, University of Illinois at Chicago, Chicago, Illinois, United States, 2 Departments of Chemical Engineering and Bioengineering, University of Illinois at Chicago, Chicago, Illinois, United States
Show AbstractMultiferroics have generated a lot of interest recently in the field of materials research and physics. These materials have more than one ferroelectric property in the same phase. Magnetoelectric multiferroics have ferroelectric and ferromagnetic domains in the same phase with a coupling between them. This coupling provides extra degree of freedom in design of devices and novel applications. Among the several known magnetoelectrics, BiFeO3 is known to be the only material that exhibits ferroelectromagnetism at room temperature. Compared to other deposition techniques like molecular beam epitaxy and pulsed laser deposition, there have been very few reports on the use of metal-organic chemical vapor deposition (MOCVD) of multiferroic films. The cyclopentadienyl (Cp) ligand is a monoanionic ligand with the formula C5H5. Iron precursors based on the Cp ligand show promise in their use in depositing iron oxide and multiferroic thin films. The two iron precursors used in this study: (i) ferrocene (Fe(C5H5)2) and (ii) n-butylferrocene ((C4H9C5H4)Fe(C5H5)) are air and moisture stable. They have sufficient vapor pressures to allow their use as precursors for metalorganic chemical vapor deposition. The alkyl-substituted ligands can alter the properties of the precursors thereby providing a way to tune their properties. So while ferrocene which has unsubstituted Cp ligands, is a solid, n-butylferrocene having a butyl-substituted Cp ligand, is a liquid at room temperature. Liquid and gaseous precursors are preferable for MOCVD because of the ease in their delivery to the reactor.In this study, thin iron oxide films are first deposited at low pressure on different substrates using Cp-based iron precursors using oxygen as the oxidizer. The use of n-butylferrocene as a precursor for such an application has not been reported till now. These iron precursors are then used with triphenyl bismuth and oxygen to deposit BiFeO3 films. The films are characterized for their quality and composition using Fourier-transform infrared spectroscopy and energy-dispersive x-ray spectroscopy. Film surface morphology is evaluated using scanning electron microscopy. X-ray diffraction is used to identify the phases present in the film.
9:00 PM - K3.9
Stress Dependence of Structural and Ferroelectric Properties of Polycrystalline BiFeO3 Thin Films on Diaphragm Structure.
Seiji Nakashima 1 , Dan Ricinschi 1 , Yoshitaka Nakamura 1 , Masanori Okuyama 1 , Hironori Fujisawa 2 , Masaru Shimizu 2
1 Graduate school of engineering science, Osaka University, Toyonaka, Osaka, Japan, 2 Graduate school of engineering, University of Hyogo, Himeji, Hyogo, Japan
Show Abstract Multiferroics have attracted much attention from viewpoint of application such as memory, sensors, actuators, and so on. Among multiferroic substances, perovskite BiFeO3 (BFO) is a leading candidate, which shows giant ferroelectric polarization (Pr ~ 152μC/cm2) in thin film form. Properties of the BFO thin film is strongly affected by lattice parameter change induced by the stress, but the mechanism has not been clarified completely yet. When the influence of stress in thin film is investigated, changing substrate material is generally tried by many workers. However, especially in polycrystalline thin film, it is difficult to investigate the influence of stress only, because the crystallinity, orientation, garain size, growth mode of the thin film etc. also change. Therefore, we have proposed to use membrane or diaphragm structure substrate for changing continuously stress in the films. We have already reported that ferroelectric and multiferroic properties of BFO thin film on Pt(200nm)/TiO2(20nm)/SiO2(600nm)/Si(15μm) diaphragm structure was enhanced by induced stress1). However, change of detailed crystal structure by reducing Si thickness has not been clarified. In this study, we have investigated the detailed crystal structural change using reciprocal space mapping, and have tried to clarify the relationship between ferroelectric properties and crystal structure of the polycrystalline BFO thin films. The diaphragm structure of 7mm x 7mm area and 15μm thickness was fabricated by etching Si of Pt(200nm)/TiO2(20nm)/SiO2(600nm)/Si(625μm) substrate. 350-nm-thick BFO thin films on the diaphragm structures and Pt/TiO2/SiO2/Si(625μm) substrate were deposited by pulsed laser deposition (PLD). Substrate temperature and oxygen pressure were 500oC and 0.12Torr, respectively. Results of reciprocal space mapping measurements indicate that obtained BFO thin films have distorted rhombohedral structure. The lattice parameters of (110) oriented grains of BFO thin film on Pt/TiO2/SiO2/Si(625μm) plate substrate were a=b=0.395 nm, c=0.399nm, α=β=89.37o and γ=89.13o, respectively. On the other hand, those on Pt/TiO2/SiO2/Si(15μm) diaphragm structure were a=b=0.394 nm, c=0.396nm, α=β=89.75o and γ=89.00o, respectively. These results indicate that crystal lattice angles change mainly due to stress change of BFO thin film by reducing Si thickness. In addition, BFO thin film on the diaphragm structure was compressed about 0.69% in parallel to film plane, and was expanded about 0.15% perpendicularly to the film plane. It is considered that these crystal structural changes induced the enhancement of ferroelectric and magnetoelectric properties which have been already reported1). Reference1) S. Nakashima, K.Y.Yun, Y. Nakamura and M. Okuyama, Mat. Res. Soc. Symp. Proc., 966, T03-13 (2007)
Symposium Organizers
James F. Scott University of Cambridge
Venkatraman Gopalan The Pennsylvania State University
Masanori Okuyama Osaka University
Manuel Bibes Universite Paris-Sud
K4: Magnetoelectrics, Piezoelectrics and Strain effects
Session Chairs
Tuesday AM, November 27, 2007
Grand Ballroom (Sheraton)
9:00 AM - K4.1
Green's Function, Eshelby's Tensor, and the Effective Magnetoelectric Coefficient of Uniaixal Multiferroic Materials.
Jiangyu Li 1
1 , Univ of Washington, Seattle, Washington, United States
Show AbstractMultiferroic materials possess two or more types of orders simultaneously that couple the electric and magnetic fields, rendering them a rich variety of microstructural phenomena and macroscopic properties. By introducing a magnetoelectric potential function, we derive explicit closed-form expressions of magnetoelectric Green's functions for uniaxial multiferroic materials in the presence of point electric or magnetic charge. For the special cases when the electric and magnetic fields are uncoupled, our solutions recover the well-known solutions for a single-ferroic material, dielectric or magnetic. We then use these Green’s functions to determine the distribution of magnetoelectric fields in an ellipsoidal inclusion with spontaneous polarization and magnetization embedded in a multiferroic material, and study the polarization reversal by an external magnetic field, or vice versa. Numerical results show that for a typical multiferroic composite, it is easier to induce magnetic field by electric charge or spontaneous polarization, suggesting that it is probably easier to manipulate the electric polarization by a magnetic field in those composites. Such solutions should find a wide range of applications in the analysis of multiferroic materials, for example the evolution of domain configurations in a single-phase multiferroic material, and the effective properties of multiferroic composites. Indeed, we used these solutions to calculate the effective magnetoelectric coefficients in an electromagnetically annealed multiferroic polycrystal, which agree well with experiments.
9:15 AM - K4.2
Piezomagnetic Effect in Mn-based Antiperovskites.
Pavel Lukashev 2 3 , Renat Sabirianov 1 , Kirill Belashchenko 2 3
2 , University of Nebraska - Lincoln, Lincoln, Nebraska, United States, 3 Nebraska Center for Materials and Nanotechnology, University of Nebraska - Lincoln, Lincoln, Nebraska, United States, 1 Physics, University of Nebraska at Omaha, Omaha, Nebraska, United States
Show AbstractRecent experimental and theoretical studies of the magnetoelectric (ME) effect in the nanocomposite structures and in laminates show an enhanced ME coefficient. These materials combine piezoelectric properties of the paramagnetic phase and piezomagnetic properties of the magnetic phase. We propose to fabricate heterostructures formed by piezoelectric materials and magnetic antiperovskites (AP) as magnetoelectric materials. We show that the magnetic structure of antiperovskite, such as Mn_3GaN, can be changed by a small applied strain. The lowering of symmetry with the biaxial strain causes the local magnetic moments of Mn atoms to rotate from the trigonal D_3d structure with symmetric curl of spin density in the (111)-plane to an orthorhombic symmetry structure. As a result, an appreciable net magnetization appears in the strained system. The estimated piezomagnetic coefficient is 0.3nOe-1. We estimated the ME coefficient of proposed heterostructure to be 1 ns/m (assuming typical values of parameters in two phases), three orders higher than that that of the single-phase ME materials such as Cr2O3. The calculations are carried out using the projector augmented-wave method with its recent implementation in VASP code, within generalized gradient approximation.
9:30 AM - K4.3
Experimental Determination of the Magneto-electric Coupling Coefficient via Piezo-electric Measurements.
Markys Cain 1 , Marian Vopsaroiu 1 , Mark Stewart 1 , Tristan Hegarty 1 , Andres Muniz-Piniella 1 , Gopalan Srinivasan 2
1 , National Physical Laboratory, Teddington United Kingdom, 2 Physics Department, Oakland University, Rochester, Michigan, United States
Show AbstractMultiferroic materials exhibit a coupling between their intrinsic electric and magnetic fields known as the magneto-electric (ME) coupling. The ME coupling can be induced either magnetically or electrically and this effect is described by the ME coupling coefficient αH or αE, respectively. However, the experimental determination of the ME coupling coefficient is rather complex. In this paper we report a simple and convenient experiment for the measurement of the magnetically induced ME coupling coefficient, αH. Our experiment is based on the quasi-static piezoelectric coefficient measurement under applied magnetic field and can provide simultaneously the d33 piezo-coefficient of a multiferroic sample and the magnetically induced ME coupling coefficient αH as a function of both applied AC and DC magnetic fields.
9:45 AM - K4.4
Microfabrication and Characterization of Thin Film Magnetoelectric Sensors.
Peng Zhao 1 , Jason. Hattrick-Simpers 1 , Kyu-Sung Jang 1 , Shenqiang Ren 1 , Manfred Wuttig 1 , Ichiro Takeuchi 1 , Scott Mathews 2
1 Department of Materials Science and Engineering, University of Maryland, College Park, Maryland, United States, 2 Department of Electrical Engineering and Computer Science, Catholic University of America, Washington, District of Columbia, United States
Show AbstractWe have fabricated prototype high sensitivity magnetic field sensors operating at room temperature based on thin film magnetoelectric (ME) devices. The principle behind the high sensitivity detection of low frequency magnetic field is the elastic coupling of a thin magnetostrictive layer to a piezoelectric layer. Magnetoelectric devices with sensitivity as high as 10^-12 tesla have been demonstrated to date using bulk laminate samples by other research groups. The present work takes such devices into the regime of microfabricated multilayer thin film structures, which would readily facilitate future integration of the device with various electronic components as well as development of novel sensor array systems. The thin film devices are fabricated on micromachined Si cantilevers in order to minimize the clamping effect of the substrate which acts to reduce the magnetoelectric coupling of the bilayer. The ME layers to be used consist of a sol-gel derived Pb(Zr0.52Ti0.48)TiO3 (PZT) film and a sputter deposited magnetostrictive thin film. The laser cutting technique has been implemented to release and isolate the cantilever with patterned devices for optimization of the sensor performance. The ME interactions in bilayer structure of PZT and magnetostrictive layers has been investigated and the sensitivity of AC currents and the AC magnetic field detection will be reported.
10:00 AM - K4.5
Strain-Induced Magnetic Anisotropy in Highly Epitaxial COFE2O4 Thin Films.
Huang Wen 1
1 , University of Electronic Science and Technology of China, Chengdu China
Show Abstract10:15 AM - K4.6
Suppressed Dependence of Polarization on Epitaxial Strain in Highly Polar Ferroelectrics.
Ho Nyung Lee 1 , Serge Nakhmanson 2 3 , Matthew Chisholm 1 , Hans Christen 1 , Karin Rabe 3 , David Vanderbilt 3
1 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 Materials Science Division, Argonne National Laboratory, Argonne, Illinois, United States, 3 Department of Physics and Astronomy, Rutgers University, Piscataway, New Jersey, United States
Show AbstractBiaxial in-plane strain induced in epitaxial thin films due to lattice mismatch between the film and the substrate is known to result in a large enhancement of ferroelectric and dielectric responses as well as formation of new phases in certain ferroelectric perovskites. Therefore, it is tempting to assume that such strong sensitivity of physical properties to epitaxial strain is common to all perovskite compounds. However, our experimental and computational investigation of the coupling between polarization and epitaxial strain in the highest-quality ferroelectric PbZr0.2Ti0.8O3 (PZT) thin films grown by pulsed laser deposition indicates that such strong sensitivity of polarization to epitaxial strain is not universally true. A comparison of the properties of relaxed (tetragonality c/a ≈ 1.05) and highly-strained (c/a ≈ 1.09) films shows that the polarization, while being amongst the highest reported for PZT or PbTiO3 in either film or bulk forms (Pr ≈ 82 μC/cm2), is almost independent of epitaxial strain. In addition to these experimental results, first principles calculations illustrate why epitaxial strain induced in materials with already large ferroelectric atomic displacements, such as PZT and PbTiO3, does not have the same strong effect on the polarization as it does in less polar perovskites, for which it can lead to a substantial polarization increase. [Research sponsored by the Division of Materials Sciences and Engineering, Office of Basic Energy Sciences, U.S. Department of Energy, and by the Center for Piezoelectrics by Design (CPD) under ONR Grant N00014-01-1-0365.]
11:00 AM - **K4.7
Multiferroic Bi2NiMnO6 with a Double-Perovskite Structure: High-Pressure Synthesized Bulk and Epitaxially Grown Thin Films.
Yuichi Shimakawa 1
1 Institute for Chemical Research, Kyoto University, Uji, Kyoto, Japan
Show AbstractA new multiferroic compound, Bi2NiMnO6, was synthesized in both bulk and thin film forms. Bulk samples were prepared under high pressure at 6 GPa and 800 °C The crystal structure is a double perovskite in which Ni2+ and Mn4+ ions at the B-site are ordered in a rock-salt configuration. A significant distortion with noncentrosymmetric (C2) symmetry of the structure allows a spontaneous polarization at room temperature. The ferroelectric transition confirmed by a change in the dielectric constant occurs at 485 K. Ni2+-O-Mn4+ magnetic paths lead to ferromagnetic properties with a Curie temperature of about 140 K. Thin film samples, on the other hand, were successfully synthesized by a pulsed-laser deposition method. The films are epitaxially grown on SrTiO3 substrates and the rock-salt type arrangement of Ni2+ and Mn4+ ions are clearly confirmed by a (1/2 1/2 1/2) superstructure peak in synchrotron x-ray diffraction. The film shows multiferroic properties, both ferromagnetic behavior with a saturated magnetization of 4.5 μB/f.u. and ferroelectric behavior with a saturated polarization of about 5 μC/cm2. A coupling between the ferromagnetic and ferroelectric interactions in Bi2NiMnO6 exists, but it seems to be quite small. Other examples of multiferroic materials, such as Bi2CoMnO6 and Bi2CuMnO6 will also be reported.
11:30 AM - K4.8
Phase Transitions and Polarization Rotation in Anisotropically Strained Multiferroic SrTiO3.
Aravind Vasudevarao 1 , Sava Denev 2 , Michael Biegalski 3 1 , Yulan Li 4 1 , Long-Qing Chen 1 2 , Darrell Schlom 1 2 , Venkatraman Gopalan 1 2
1 Materials Science and Engineering, Pennsylvania State University, University park, Pennsylvania, United States, 2 Materials Research Institute , Pennsylvania State University, University Park, Pennsylvania, United States, 3 Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 4 MPA-STC, Los Alamos National Lab, Los Alamos, New Mexico, United States
Show AbstractSrTiO3 is a material not normally ferroelectric at any temperature. Recently we have grown epitaxial SrTiO3 film on (110) orthorhombic GdScO3 substrate in which SrTiO3 is subject to unequal in-plane biaxial strains with e1=1.61% and e2=1.84% along the [100]p and [010]p directions (where the subscript ‘p’ indicates pseudocubic unit cell) respectively. For this amount of strain, first principles calculation predicts a high temperature 4/mmm phase followed by a transition to a ferroelectric mm2 phase. Upon cooling the ferroelectric polarization is predicted to start along [010]p direction and then switch to <110>p directions. Upon further cooling the material is predicted to undergo a multiferroic transition with the existence of coupled ferroelectric and ferroelastic order parameters. We use optical second harmonic generation experiments to experimentally track these phase transitions, study the point group symmetry and directions of ferroelectric polarization in this material in the temperature range 4K-400K. We show that in this anisotropically strained film, indeed the polarization direction shows an intriguing switching behavior back and forth between <100>p and <110>p directions multiple times as the sample is cooled below the room temperature.
11:45 AM - K4.9
Structure and Origin of Polarity of Quasi-amorphous Pyro- and Piezo-electric Films of SrTiO3.
David Ehre 1 , Vera Lyahovitskaya 1 , Anatoly Frenkel 3 , Hagai Cohen 2 , Alexander Tagantsev 4 , Igor Lubomirsky 1
1 Materials & Interfaces, Weizmann Institute of Science, Rehovot Israel, 3 Physics Department, Yeshiva University, New York, New York, United States, 2 Chemcal Research Support, Weizmann Institute of Science, Rehovot Israel, 4 Department of Materials Science, Ecole Polytechnique Federale De Lausanne, New York Switzerland
Show AbstractWe have recently reported that SrTiO3 and BaZrO3 can be prepared in a non-crystalline phase, which is, nevertheless, pyro- and piezo-electric. This is the first instance that a compound that produces no polar crystalline polymorphs forms polar non-crystalline phases, called quasi-amorphous. The existence of quasi-amorphous phases of SrTiO3 and BaZrO3 was predicted by the theory developed for the earlier reported quasi-amorphous phase of BaTiO3. In the current study, we applied XAFS and XPS to explore the structure and origin of polarity of the quasi-amorphous phase of SrTiO3. Our data demonstrate that: a) Similar to the amorphous and quasi-amorphous phases of BaTiO3, their SrTiO3 counterparts contain a random network of local bonding units, TiO6 octahedra, which are asymmetrically distorted with strong Ti off-center displacements. Therefore, they possess dipole moment.b) In the random network, TiO6 octahedra are connected edge-to-edge and apex-to-apex.c) In the amorphous phases, Sr and Ba stabilize the peroxide-like chemical bonds between oxygen ions and, thereby, compensate for the local charge imbalance. d) Formation of the quasi-amorphous phase occurs via heat-induced severing of the peroxide-like bonds. If the severing of the peroxide-like bonds occurs in the presence of a strain gradient, then TiO6 octahedra may undergo partial alignment giving the films a macroscopic polarization.Our data suggest that the quasi-amorphous state may be observed in a large variety of oxide compounds containing: 1) a cation (M1) forming stable local bonding units that can be connected in multiple ways; 2) a cation (M2) that can stabilize peroxide-like oxygen-oxygen bonds and easily release them upon heating. As M1, one can choose Ti, Zr, Sn, Nb and Ta, because all of them form stable local bonding units (octahedral or tetrahedral). As M2, one can choose all metals that form stable peroxides: Ca, Sr, Ba, Na, K, Rb and Cs.Owing to the simplicity of their preparation, quasi-amorphous materials are very promising for future pyroelectric and piezoelectric devices that can be monolithically incorporated into integrated electronic circuits.
12:00 PM - K4.10
Strain Controlled Polarization in BaTiO3 Ferroelectrics with Planar Electrodes.
Chad Folkman 1 , Ho-Won Jang 1 , Chang-Beom Eom 1 , Yanbin Chen 2 , Xiaoqing Pan 2
1 Material Science, University of Wisconsin - Madison, Madison, Wisconsin, United States, 2 Material Science and Engineering, University of Michigan - Ann Arbor, Ann Arbor, Michigan, United States
Show AbstractEpitaxial strain has a large effect on the polarization in ferroelectric oxides such as tetragonal BaTiO 3, which have been pursued because of properties like large remnant polarizations and high non-linear dielectric constant. The response of the ferroelectric polarization in BaTiO3 has been shown to increase in magnitude when the c-oriented tetragonal structure is compressively strained by two smaller in-plane lattice parameters of the substrate. Biaxial tensile strain has been studied to a much lesser extent in this material due to the challenges involved manufacturing oxide single crystal substrates with lattice parameters larger than room temperature BaTiO3, a = 3.99Å and c = 4.036Å. Recently, we have shown larger lattice parameter oxide surfaces are obtained with single domain, strain relaxed templates or buffer layers of REScO3 (RE is a rare-earth element) grown on high miscut cubic or orthorhombic substrates. Purely a-oriented epitaxial BaTiO3 thin films were grown on (110) PrScO3 template (aP = 4.011Å and cP = 4.020Å) on (110) NdGdO3 by pulsed laser deposition. The rocking curve full width at half maximum of the BaTiO3 200 reflection was 0.075° indicating high crystalline quality. Since the polarization Ps lies along the c-axis, the polarization must reside in the plane of the film. To fully define the polarization vector Ps, we will present domain analysis from reciprocal space mapping performed with high resolution four circle x-ray diffraction, and polarization data from interdigit planar electrode capable of distinguishing the average in-plane orientational dependence of Ps. These two characterization methods can lead to highly engineered thin film ferroelectric materials where Ps is explicitly known in all three dimensions.
12:15 PM - K4.11
Dynamical Nonlinearities in Piezoelectric Materials.
Eira Seppala 1 , Matti Sarjala 2 , Virpi Korpelainen 3 , Mikko Alava 2 , Antti Lassila 3
1 , Nokia Research Center, Helsinki Finland, 2 Laboratory of Physics, Helsinki University of Technology, Espoo Finland, 3 , Centre for Metrology and Accreditation MIKES, Espoo Finland
Show AbstractProper understanding of dynamical nonlinearities in piezoelectric materials requires information about material properties also at the crystal level. This is especially important when it is desired to use piezoelectric components as precise actuators whose frequency dependence can be predicted. Many commercially available piezo sheets are ceramic, thus porous, and include randomness in various forms: dislocations, grain boundaries, pores, etc. [A.J. Moulson and J.M. Herbert, Electroceramics, 2nd ed. (John Wiley & Sons Ltd., 2003)]. In this study, the issues of nonlinearities during different time and frequency scales are studied by three different methods; measurements of the displacement of bulk material, measurements of nanometer scale surface structure of the material by an atomic force microscope (AFM), and numerical modelling of ferroelectric materials with quenched randomness.First, we have performed laser interferometer measurements of the deformations of piezoelectric materials, d31 type PZT and PMN-PT sheets, under voltage loading with different frequencies. This yields information about the dynamical hysteresis behavior, such as the area of the hysteresis loops as a function of the applied frequency ω. Difference between various samples, e.g. polycrystalline and single crystals, are investigated. Relaxation behaviors of the same materials have been measured by an AFM. Topography of the piezo sheets were measured before and after applied DC voltage. Local time dependent changes of crystal structure were detected, which allows for a comparison of the characteristics of the nonlinearities in the material.We have numerically used a Ginzburg-Landau-Devonshire (GLD) model for ferroelectric materials with a dilution type of quenched randomness. The dynamics of the hysteresis phenomenon, specifically the area of the hysteresis loop of the polarization in the material and the coercive electric field Ec as a function of the frequency ω, is investigated. The scaling behavior for the coercive field with respect to the frequency is modelled with and without a dipolar field and compared with two predictions: Ec ~ A0 + A1ω1/3 as in many magnetic materials [M. Rao, et al., Phys. Rev. B 42 (1990), 856], and Ec ~ A0 + A1[(1+A2ω1/2)-1] from the recently rediscovered scaling due to loss separation [F. Colaiori, et al., Phys. Rev. Lett. 97 (2006), 257203].
12:30 PM - K4.12
Piezoelectric Properties of Crosslinked Polypropylene Ferroelectrets.
Xiaoqing Zhang 1 , Jinfeng Huang 1 , Xuewen Wang 1 , Zhongfu Xia 1
1 Physics Department, Tongji University, Shanghai China
Show AbstractK5: Size Effects
Session Chairs
Tuesday PM, November 27, 2007
Grand Ballroom (Sheraton)
2:30 PM - K5.1
Finite Element Analysis of Ferroelectric Nanoscale Pattern.
David Albrecht 1 2 , Denis Aubry 1 , Laurent Bellaiche 3 , Brahim Dkhil 2
1 MSSMAT, Ecole Centrale Paris, Paris France, 2 SPMS, Ecole Centrale Paris, Paris France, 3 Dep. of Physics, The Univ. of Arkansas, Fayetteville, Arkansas, United States
Show AbstractBecause of their application in electronic, microwave or memory devices, thin ferroelectric films are widely studied. Thus it is of great interest to understand ferroelectric system at small scale, where boundary conditions strongly influence the behaviour and lead to unusual domain pattern like vortices and stripes. More precisely, ultra-thin film structure has been computed (Phys. Rev. Lett. 96, 137602 (2006)), showing that the pattern can switch from stripes to periodical bubble patterns when submitted to an applied electrical field. Simultaneously, stripes wavelength have been measured to be proportional to the square root of the film thickness (Phys. Rev. B 74, 024115 (2006)). Monte Carlo approach is often used for the first problem, but cannot be used for the second as it is a too large size problem. At microscale a microscopic Landau based model is more often encountered. Here we want to bridge the gap between those two approaches and to compute the size influence. Focus on a typical system like barium titanate is put forward here.We start from an effective Hamiltonian model (Phys. Rev. B 52, 13236 - 13246 (1995)) which represents a phenomenological description of the phonon behaviour. This model, based on first principle calculation, uses five different forms of interactions: long range electrostatic, short range elastic and electrostatic, mechanical and self interactions.Using the assumption of a mapping of the degrees of freedom taken from the effective Hamiltonian, the computation of the different forces acting on one cell provides a continuum description of the discrete model. In particular long range interactions can be described by the addition of a potential to a local self force. Similarly short-range forces can be described with gradient and self interactions. Finally as we focus on larger systems than the ones usually resolved by Monte-Carlo approach, finite elements have been used to compute the resulting partial differential equation system. The outcome is a continuum microscopic model with first principles related coefficients, and which can be directly connected to classical Landau based microscopical model. Another advantage of such a comparison is to achieve a complete set of natural free boundary conditions not often studied.Using the model, we can directly compare effective Hamiltonian calculation of a quantum dot and the corresponding finite element solution. We also discuss the influence of the mapping assumption and the approximation done by the continuum description. As an application we compute the Kittel’s law, and show that the structure exhibits three different types of patterns with respect to the thickness.
3:00 PM - **K5.3
Domains and Domain Walls in Ferroic Films and Nanostructures.
Gustau Catalan 1 , Alina Schilling 2 , Marty Gregg 2 , Manuel Bibes 3 , Stephane Fusil 5 , Patrycja Paruch 4 , Helene Bea 5 , Agnes Barthelemy 5 , Ard Vlooswijk 6 , Arjen Janssens 7 , Beatriz Barcones 7 , Beatriz Noheda 6 , James F. Scott 1
1 Department of Earth Sciences, University of Cambridge, Cambridge United Kingdom, 2 Department of Pure and Applied Physics, Queen's University of Belfast, Belfast United Kingdom, 3 Institut d'Electronique Fondamentale, Universite Paris-Sud, Orsay France, 5 Unité Mixte de Physique CNRS, Thales, Palaiseau France, 4 Laboratory of Atomic & Solid State Physics, Cornell University, Ithaca, New York, United States, 6 Zernike Institute for Advanced Materials, University of Groningen, Groningen Netherlands, 7 Institute for Nanotechnology, Twente University, Enschede Netherlands
Show AbstractFerroic (and multiferroic) materials generally display domains with the polar vector oriented along different energetically equivalent directions. Domains are separated by domain walls, the energy cost of which decreases as the dimensions of the sample get smaller. Consequently, ferroic nanodevices tend to have a high density of domain walls, which affects the functional properties. For thin films the size of the domains is normally proportional to the square root of the film thickness. While the constant of proportionality is different for different ferroics, we have found it to be “universal” once the domain width is renormalized by the wall thickness. New results will be also presented which extend the scaling laws to three-dimensional nano-columns and to systems in which the domains are not rectilinear, on one hand, and which establish limitations to domain scaling models for epitaxial thin films, on the other. Our results highlight the commonalities between different types of ferroic system, and the subtleties of domain scaling at small sizes.
4:00 PM - K5.4
Enhanced Pyroelectric Effect in Self-supported Nanocrystalline Films of BaTiO3.
Yachin Yvry 1 , Vera Lyahovitskaya 1 , Ilya Zon 1 , Ellen Wachtel 2 , Alexander Roytburd 3 , Igor Lubomirsky 1
1 Materials & Interfaces, Weizmann Institute of Science, Rehovot Israel, 2 Chemical Research Support Unit, Weizmann Institute of Science, Rehovot Israel, 3 Department of Materials and Nuclear Engineering, University of Maryland, College Park, Maryland, United States
Show AbstractWe have recently reported a hitherto unobserved phenomenon in self-supported, buckled films of nanocrystalline BaTiO3: a two orders of magnitude increase in the pyroelectric coefficient with respect to that of a single crystal. The value measured for the pyroelectric current (~ 1µC/(cm2×K)) is one of the highest ever reported for ferroelectric materials and is achieved in the range 20-60 oC. This is far below the temperature of the para-to-ferroelectric phase transition of BaTiO3, which fact clearly indicates that the origin of the enhanced pyroelectric effect is clearly different from that of standard pyroelectricity. In the present work, we will explain this phenomenon as being due to the contribution of polarization rotation (90o polarization switching) of some fraction of the nanocrystalline ferroelectric grains which constitute the film. In buckled, self-supported films of BaTiO3, grains self-organize into two types of polycrystalline macro-domains: 1) those for which the polarization (c-axis) of the grains is aligned predominantly perpendicular to the film (termed out-of-plane macro-domains); and 2) those for which it is aligned within the plane of the film (termed in-plane macro-domains). Due to the inhomogeneous strain imposed by buckling, these two types of macro-domains themselves arrange into two different geometric forms: wedge-ordered and linear. The contour of the wedge-ordered regions is that of a circular arc built by alternating wedge-(triangular)-shaped in-plane and out-of-plane macro-domains. The radius of the arc, R=D/(c/a-1), is fixed by the film thickness D and the crystallographic parameters c and a. The linear regions contain only out-of-plane macro-domains and remain flat. At equilibrium at a given temperature, the relative fraction of each type of geometric form is uniquely defined by the misfit between the dimensions of the film and those of the window that constrains its edges. Upon temperature variation, the crystallographic parameters change. As a result, the radius, R, of the wedge-ordered region changes, thereby modifying the equilibrium shape of the film. To accommodate this change, the polarization of grains at the boundaries between the linear and the wedge-ordered regions must reversibly switch from being in-plane to being out-of-plane, and vice versa, thereby producing the markedly enhanced pyroelectric current. To demonstrate the feasibility of this mechanism, we provide independent experimental confirmation of the fact that polycrystalline macro-domains are capable of fast (<10 µsec!) and reversible structural adaptation to changes in external conditions, which capability holds the promise of development of pyroelectric and piezoelectric devices with previously unattainable performance.
4:15 PM - K5.5
Ferroelectric Properties of BaTiO3 at Nanoscale Dimensions.
Aravind Vasudevarao 1 , Zixiao Pan 2 , Vinayak Dravid 2 , Venkatraman Gopalan 1 3
1 Materials Science and Engineering, Pennsylvania State University, University park, Pennsylvania, United States, 2 Materials Science and Engineering, Northwestern University, Evanston, Illinois, United States, 3 Materials Research Institute, Pennsylvania State University, University park, Pennsylvania, United States
Show AbstractBaTiO3, a well known perovskite material, remains a subject of considerable interest and study for a variety of applications involving piezoelectricity/ferroelectricity, photorefraction, non-linear optical effect, etc. In the process of studying the effect of interfacial strain on ferroelectric and multiferroic materials at nano scale, we have patterned BaTiO3 into line grid structures on a (100) SrTiO3 single crystal substrate using a facile approach termed soft electron beam lithography (“soft-eBL”). A combination of conventional e-beam lithography and versatile sol-gel chemistry, soft-eBL is an etch-free approach amenable to microstructural control of the patterned inorganic materials. BaTiO3 grid shows lateral dimensions of the order of 150-250nm and thickness of ~50nm. In this work we use Piezoresponse force Microscopy and Optical second harmonic generation to study the ferroelectric properties of BaTiO3 at such nano-scales. Variation of piezoresponse was observed in this material with temperature in the range of 290-400K. Optical second harmonic generation was employed to relate the observed changes in piezoresponse with temperature to possible ferroelectric phase transition.
4:30 PM - K5.6
Size-dependent Nanoscale Piezoelectricity due to the Flexoelectric Effect and Atomistic Investigation of Flexoelectric Properties of Various Dielectrics.
Pradeep Sharma 1 , Ravi Maranganti 1
1 , University of Houston, Houston, Texas, United States
Show Abstract4:45 PM - K5.7
Size Effects on Crystal Structure in Epitaxial PbTiO3 Nanoislands on Pt/SrTiO3 Substrates.
Masaru Shimizu 1 , Hironori Fujisawa 1 , Koichiro Honda 2 , Minoru Osada 3 , Yoshihiro Kuroiwa 4 , Osami Sakata 5 , Shigeru Kimura 5
1 Dept. of Elect. Eng. & Comp. Sci., University of Hyogo, Himeji, Hyogo, Japan, 2 , Fujitsu Lab. Ltd., Atsugi, Kanagawa, Japan, 3 , National Institute for Materials Science, Tsukuba, Ibaragi, Japan, 4 , Hiroshima University, Higashi-Hiroshima, Hiroshima, Japan, 5 , JASRI, Sayo-cho, Hyogo, Japan
Show Abstract5:00 PM - K5.8
Ferroelectric Stripe Domains and Polarization Reversal in Ultra-thin PbTiO3 Films.
R. Takahashi 1 , J. Grepstad 1 , Yuji Matsumoto 2 , Thomas Tybell 1
1 Department of Electronics and Telecommunications, NTNU, Trondheim Norway, 2 Materials and Structures Laboratory, Tokyo Institute of Technology, Yokohama Japan
Show AbstractA stripe domain ferroelectric ground state has recently attracted large interest, and extensively studied using XRD techniques. Here, we present high resolution XRD studies combined with AFM investigations, searching for possible surface contributions to the XRD signals. We also focus on the possibility to switch from a stripe domain state to a mono domain state by applying an electric field using a chemical technique. High quality PbTiO3 films, between 3 and 100 nm in thickness, were deposited on SrTiO3(001) and Nb-doped SrTiO3(001) substrates by off-axis radio frequency magnetron sputtering. All films showed atomically flat surfaces with a step and terrace structure of 1 unit-cell height. High resolution XRD profiles, recorded along the Qx direction, indicated a stripe domain state in the PbTiO3 thin films. The stripe width was confirmed to be proportional to the square root of the film thickness, in agreement with previous reports [1]. The thickness dependence of the satellite peak intensity was found to be proportional to the Bragg peak intensity. In order to rule out possible contributions from surface corrugations to those satellite peaks, we examined the thin film samples with high-resolution AFM. The data revealed an island structure superimposed on the smooth terraces. 2D fast fourier transforms of the AFM data gave a surface modulation of ~50nm, independent of film thickness. This, in combination with the thickness dependency of the satellite XRD intensity, demonstrates that a bulk effect is the cause to the XRD signals. Furthermore, the stability of the stripe domain state to electric fields was investigated. In order to apply an electric field over large areas a chemical technique was used. Linear Qx scans after the application of the electrical field revealed only the Bragg peak for the thinnest samples, indicating an effective switching from a strip- to a mono-domain state. Stability data of the induced mono domain state will also be presented. [1] S. K. Streiffer et al, Phys. Rev. Lett. 2005, 89, 067601
5:15 PM - K5.9
Size Effect of SrTiO3 Thin Films Probed with the Broadband Terahertz Time-domain Spectroscopy.
Ikufumi Katayama 1 , Hiroshi Shimosato 1 , Masaaki Ashida 1 3 , Iwao Kawayama 2 , Masayoshi Tonouchi 2 , Tadashi Itoh 1
1 Faculty of Engineering Science, Osaka University, Toyonaka, Osaka pref., Japan, 3 PRESTO, Japan Science and Technology Agency, Tokyo Japan, 2 Institute of Laser Engineering, Osaka University, Suita, Osaka pref., Japan
Show AbstractWe have measured the thickness dependence of the dielectric dispersion in SrTiO3 thin films by measns of broadband terahertz time-domain spectroscopy that can measure far infrared absorption spectra from 0.1 THz to 8 THz. The SrTiO3 thin films are fabricated by the pulse laser deposition technique on MgO substrates and LSAT substrates. The dispersions due to the TO1 soft mode in this material and the higher frequency TO2 mode at 5 THz are observed. We have confirmed that the resonant frequency and the damping constant of the TO1 soft-mode is strongly different from those of the bulk crystal, which is so-called size effect of the dielectric materials. In addition, the obtained thickness dependence of the dielectric dispersion in SrTiO3 thin films on MgO is strongly different from those on LSAT substrates. In the thin films deposited on MgO substrates, the dielectric constant at lower frequency keeps high value of about 500 even in 50 nm thin films. On the other hand, those films on LSAT have lower dielectric constant in 190 nm or 390 nm thin films. This can be understood that the mismatch of the lattice parameters in the case of MgO substrate is so large that the SrTiO3 fims cannot follow the lattice constant of the substrate resulting in the free grows of the SrTiO3 thin films. In the thin films deposited on LSAT, the SrTiO3 follows the lattice constant of substrate causing the strong stress inside the film to reduce the dielectric constant. These results suggest the strong effect of the substrate on the lattice dynamics of SrTiO3 thin films, and that the broadband terahertz time-domain spectroscopy is a powerful tool for studying the lattice dynamics of the thin films. In the presentation, we will also consider in detail the origin of the size effects of the ferroelectric soft-mode in SrTiO3 thin films.
5:30 PM - K5.10
Resolving Grain-to-grain Interactions in Nanostructured Ferroelectrics.
Samantha Wicks 1 , Michael Hambe 1 , Varatharajan Anbusathaiah 1 , Valanoor Nagarajan 1 , Sergei Kalinin 2
1 School of Materials Science and Engineering, UNSW, Sydney, New South Wales, Australia, 2 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractNanoscale domain mechanisms underpin the fundamental behaviour of ferroelectrics. This is particularly of vital importance in nanostructured polycrystalline ferroelectrics, where grain-to-grain interactions can no longer be neglected. Using an array of surface probes and advanced fabrication methods we show direct visual evidence of the complex interplay between electrical and mechanical fields in these polycrystalline samples. Isolated test devices without a top protective metal layer and with varying aspect ratios were created by a novel focussed ion beam (FIB) milling process which does not require post-mill annealing. This process, in conjunction with SPM and EBSD analysis, enables us to understand the switching behaviour of domains as a systematic function of texture, mechanical and electrical conditions. We demonstrate consequences of such grain-grain interactions that include correlated switching between the grain of interest and neighbouring grains, ferroelastic domain switching, inhomogeneous piezostrain profiles and domain pinning on very minute length scales. This work was funded by the Australian Research Council Discovery Program and the Australian Research Council Nano Network. A portion of this research was conducted at the Center for Nanophase Materials Sciences, which is sponsored at Oak Ridge National Laboratory by the Division of Scientific User Facilities, U.S. Department of Energy.
5:45 PM - K5.11
Complex Ferroelastic Nanodomains in Heterolayered Ferroelectric Thin Films.
Anbusathaiah Varatharajan 1 , Samantha Wicks 1 , Miryam Arredondo 1 , Mohammad Reza Mahjoub 1 , Fransiska Kartawidjaja 2 , John Wang 2 , Kaushik Bhattacharya 3 , Nagarajan Valanoor 1
1 School of Materials Science & Engineering, University of New South Wales, Sydney, New South Wales, Australia, 2 Department of Materials Science and Engineering, National University of Singapore, Singapore Singapore, 3 Division of Engineering and Applied Science, California Institute of Technology, Pasadena, California, United States
Show AbstractWe present a novel adaptive nanodomain structure in heterolayered Pb(Zr,Ti)O3 (PZT) thin films consisting of alternating PbZr0.7Ti0.3O3 and PbZr0.3Ti0.7O3 on Pt/Ti/SiO2/Si substrates. By constraining the top tetragonal (T) PbZr0.3Ti0.7O3 (only 70 nm thick) with an underlying rhombohedral (R) PbZr0.7Ti0.3O3 layer we create a complex ferroelastic domain hierarchy that is conventionally observed only in large grained bulk ceramics. These nanoscale microdomains resemble an adaptive ferroelectric state that is easily susceptible to external perturbation such as applied local DC bias. Piezoresponse force microscopy images demonstrate gross reconstruction of the domain orientations under local bias. This process creates giant piezoelectric properties confirmed by d33 measurements, where the heterolayered system shows values around 220 pm/V, which is nearly 300% of a constrained monodomain thin film. The observations are supported by a thermodynamic model, which predicts that a strong coupling between self-strains of the R and T phase should lead to such fine-twinned adaptive domain morphologies.
Symposium Organizers
James F. Scott University of Cambridge
Venkatraman Gopalan The Pennsylvania State University
Masanori Okuyama Osaka University
Manuel Bibes Universite Paris-Sud
K8: Characterization Techniques
Session Chairs
John Robertson
K. Uchiyama
Thursday AM, November 29, 2007
Grand Ballroom (Sheraton)
9:45 AM - K8.2
Spatially-Resolved Studies of Local Microstructure and Strain in Manganite Systems Using X-ray Microdiffraction.
John Budai 1 , D. Sarma 2 , Gopal Shenoy 3 , Jonathan Tischler 1 , Wenjun Liu 3 , Bennett Larson 1 , Sang-Wook Cheong 4 , Dinesh Topwal 2 , Wenge Yang 3 , Alexander Mukhin 5
1 , Oak Ridge National Lab, Oak Ridge, Tennessee, United States, 2 , Indian Inst of Science, Bangalore India, 3 , Argonne National Lab, Argonne, Illinois, United States, 4 , Rutgers University, Piscataway, New Jersey, United States, 5 , Russian Acad. of Sciences, Moscow Russian Federation
Show AbstractMicrostructural inhomogeneities in complex manganite systems are known to occur over a wide range of length scales and can strongly affect the magnetic and electronic properties. Spatially-resolved structural measurements are needed to help advance our understanding of the balance and interactions between competing phases, particularly in multicomponent materials. We have used 3D x-ray polychromatic microdiffraction to investigate domain formation, local lattice structure and interfaces in multicomponent, single-crystal manganite systems. Intense, focused synchrotron x-ray beams with submicron spatial resolution and ~0.01 degree angular resolution are used in scanning mode at the Advanced Photon Source (APS). X-ray Laue microdiffraction patterns are used to generate 3D spatially-resolved maps of the crystal structure, orientation and lattice parameters, while microfluorescence yields depth-integrated composition maps. Using directionally-solidified EuYMnO single-crystal samples, x-ray measurements reveal alternating lamella of Y-rich hexagonal (multiferroic) and Eu-rich orthorhombic phases with a self-organized periodicity of ~15 microns. In Lu(LaSr)MnO crystals, the phase-separated lamellar periodicity of the Lu-rich hexagonal and LaSr-rich rhombohedral phases is smaller (~ microns) and less regular. In both material systems, the phase domains maintain a well-defined long-range (~mm) average crystal orientation with respect to the growth direction and with respect to each other. In addition, particular preferred low-energy interfaces between phases are observed. However, small local variations in both orientation (i.e. mosaic) and lattice parameter (strain and composition) are also observed, and the possible origins and implications of these structural inhomogeneities will be discussed. With improved x-ray sources and optics, future measurements will probe the local structural origins of nanoscale phenomena. Support by the Division of Materials Sciences, DOE Office of Basic Energy Sciences under contract DE-AC05-00OR22725 with Oak Ridge National Laboratory, managed by UT-Battelle; UNICAT/XOR and APS supported by the DOE.
10:00 AM - **K8.3
The Hunt for a Snark: Spatially and Energy Resolved Imaging of Nucleation Centers in Ferroelectrics.
Sergei Kalinin 1 2 , Stephen Jesse 1 , Brian Rodriguez 1 2 , Ionela Vrejoiu 3 , Marin Alexe 3 , Y. Chu 4 , R. Ramesh 4 , Samrat Choudhury 5 , Long-Qing Chen 5 , Eugene Eliseev 6 , Anna Morozovska 7
1 Materials Sciences and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 The Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 3 , Max Planck Institute of Microstructure Physics, Halle Germany, 4 Department of Materials Science and Engineering, University of California, Berkeley, California, United States, 5 Department of Materials Science and Engineering, Pennsylvania State University, University Park, Pennsylvania, United States, 6 Institute for Problems of Materials Science, National Academy of Science of Ukraine, Kiev Ukraine, 7 V. Lashkaryov Institute of Semiconductor Physics, National Academy of Science of Ukraine, Kiev Ukraine
Show AbstractPolarization switching in ferroelectric and multiferroic materials is governed by nucleation centers that account for the experimentally observed low values of coercive fields. Despite 50 years of research, the microstructural origins of the Landauer paradox (switching fields corresponding to implausibly large nucleation activation energies) are still a mystery, as are mechanism for polarization switching in nanoscale systems. In this presentation, I will summarize recent advances in spatially resolved studies of polarization dynamics in nanoscale systems using Piezoresponse Force Spectroscopy in single-point and imaging modes. The mechanism of polarization switching on nearly-ideal surface is analyzed using combination of analytical theory and phase field modeling, and it is shown that the experimentally measured nucleation biases are within factor of ~2 from intrinsic thermodynamic switching. The role of long-range interactions on nucleation bias lowering is studied using phase-field models. Spatially resolved imaging of polarization dynamics in self-assembled multiferroic heterostructures and ferroelectric nanoparticles is illustrated, and the role of interfaces on switching is determined. The role of a single defect on polarization switching is analyzed, and the reconstruction of thermal and field disorder potential components from nucleation bias maps is illustrated for epitaxial PZT films. The hysteresis loops are shown to posses a rich fine structure, indicative of the interaction of growing domains with the electroelastic field of defect. Finally, spectroscopic measurements of polarization dynamics in systems with artificially-engineered defect structures, including bicrystal grain boundaries, are illustrated. These studies will ultimately allow atomistic understanding of polarization switching processes and role of defect on switching on a single-defect level. Research supported by the Division of Materials Science and Engineering, Basic Energy Sciences, U.S. Department of Energy at Oak Ridge National Laboratory, which is managed by UT-Battelle, LLC.
10:30 AM - K8.4
Detection of Ferroelectric Domain Boundaries with Lateral Force Microscopy.
Tobias Jungk 1 , Akos Hoffmann 1 , Elisabeth Soergel 1
1 Institute of Physics, University of Bonn, Bonn Germany
Show AbstractThe contrast mechanism for the visualization of ferroelectric domain boundaries with lateral force microscopy is generally assumed to be caused by the mechanical deformation of the sample due to the converse piezoelectric effect. A careful quantitative analysis of the measured lateral forces suggest, however, that the electrostatic interaction between the charged tip and the electric fields arising from the surface polarization charging dominates the contrast mechanism [1]. To sustain this explanation we performed comparative experiments with a specific test sample, thereby generating electric fields parallel to the surface which are similar to those of a periodically poled lithium niobate (LiNbO3) crystal. For the latter we calculated the field strength Ex along the x-axis which was found to be as large as Ex = 1011 V/m supposing an uncompensated surface polarization of σ = 0.71 C/m2. In the experiments we measured a lateral force of 6 nN acting on the tip which is consistent with a compensation of σ by a factor of 1000 (tip radius: 30 nm, applied voltage: 10 V) which is a reasonable assumption. For a further indication of the electrostatic origin of the lateral forces we carried out experiments with periodically poled potassium titanyl phosphate (KTP) crystals, where we found that the ratio between the vertical piezoelectric response and the lateral forces was smaller by a factor of 2.6 compared to LiNbO3. This agrees more likely with an electrostatic origin for the lateral forces as the surface polarization charge density for KTP is 3.5 times smaller than for LiNbO3.[1] T. Jungk, A. Hoffmann, E. Soergel, Appl. Phys. Lett. 89, 042901 (2006)Acknowledgments:The authors thank Boris Sturman for fruitful discussions. Financial support of the DFG research unit 557 and of the Deutsche Telekom AG is gratefully acknowledged.
11:15 AM - K8.5
A High Speed Piezo Force Microscopy Study of Nanoscale Ferroelectric Domain Switching Dynamics: Nucleation versus Domain Wall Motion Controlled Kinetics.
Ramesh Nath 1 , Nicholas Polomoff 1 , Ying-Hao Chu 2 , Ramamoorthy Ramesh 2 , Bryan Huey 1
1 Chemical, Materials and Biomolecular Engineering, University of Connecticut, Storrs, Connecticut, United States, 2 Materials Science and Engineering, University of California, Berkeley, Berkeley, California, United States
Show Abstract11:30 AM - K8.6
Piezoresponse Force Microscopy in Liquid Environments: Novel Opportunities for Ferroelectric Imaging.
Brian Rodriguez 1 2 , S. Jesse 1 , P. Rack 2 , K. Seal 2 , A. Baddorf 1 2 , S. Kalinin 1 2
1 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 The Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractIn this presentation, we discuss resent results on mapping static and dynamic polarization behavior by Piezoresponse Force Microscopy (PFM) in a liquid environment. These include high-resolution imaging, mapping nucleation centers and long-range correlations, and intermittent contact PFM. The interplay between frozen disorder and domain dynamics is addressed using solvents of varying conductivity. Under ambient conditions, the biased tip establishes a highly-localized electric field that decays rapidly with distance from the tip-surface junction, resulting in small, well-defined domains. For solvents with intermediate conductivities, the electric field is localized, but the characteristic length scale is significantly larger than the tip size and is mediated by pulse length via the mobile ion diffusion length. The switching in this case results in the formation of irregular fractal domains. In conductive solvents, the solution is uniformly biased, resulting in a homogeneous electric field across the film thickness and partial or complete uniform switching. Notably, high resolution imaging is possible even in polar solvents because of the high excitation frequencies, minimization of the diffusion paths, and high localization of the strain that transmit predominantly through the mechanical (rather than electrical) contact. The same screening effect in solution enables a mechanically modulated approach for intermittent contact PFM, In air, this mode is dominated by electrostatic forces, which are screened in solution, allowing the electromechanical signal to dominate. This method is demonstrated for PZT and PPLN systems. Future prospects for liquid PFM imaging and the fabrication and use of shielded probes are illustrated.Research sponsored by the Laboratory Directed Research and Development (BJR, SJ) and SEED (SVK) Programs of Oak Ridge National Laboratory, managed by UT-Battelle, LLC for the U. S. Department of Energy, and The Center for Nanophase Materials Sciences (PDR, KS, APB), at Oak Ridge National Laboratory, which is managed by UT-Battelle, LLC.
11:45 AM - K8.7
Limits of the Interface Sharpness in Perovskite Oxide Heterostructures.
Lena Kourkoutis 1 , Yasushi Hotta 2 , Harold Hwang 2 3 , David Muller 1
1 School of Applied and Engineering Physics, Cornell University, Ithaca, New York, United States, 2 Dep. of Advanced Materials Science, University of Tokyo, Kashiwa, Chiba, Japan, 3 , Japan Science and Technology Agency, Kawaguchi Japan
Show AbstractPerovskite oxides have attained considerable attention due to the wide variety of ground states available in closely lattice-matched crystal structures and the potential for combining these properties in heterostructures at the atomic scale. Advances in growth techniques, in particular molecular beam epitaxy and pulsed laser deposition, have allowed high quality materials with complex structures, such as quantum wells and superlattices, to be built, some of them with atomic-layer precision [1]. However, for most systems there are intrinsic limitations to the abruptness of an interface. Polar discontinuities which occur at many oxide heterointerfaces can drive electronic as well as atomic reconstructions at the interface [1, 2]. For traditional semiconductors, the perfection of heterostructures has been shown to be limited by surface segregation processes, which results in an interfacial composition gradient [3]. Well studied examples include In surface segregation during the growth of GaAs on InAs [3, 4] or Ga segregation in the AlAs/GaAs [3, 5] system. Here, we present a study of the microscopic structure of LaVO3/SrTiO3 superlattices and heterostructures by scanning transmission electron microscopy (STEM) in combination with electron energy loss spectroscopy (EELS). We find that depending on the growth sequence, LaVO3 on SrTiO3 or SrTiO3 on LaVO3, the interface is either diffuse or atomically sharp. Switching the SrTiO3 termination layer before the growth of the LaVO3 layer does not result in a sharp interface, which excludes the interface polarity as the driving force for the observed growth asymmetry. Instead, our measurements suggest that Sr surface segregation effects set the upper limit to the interface abruptness of this system. [6][1]A. Ohtomo, D. A. Muller, J. L. Grazul, and H. Y. Hwang, Nature 419, 378 (2002).[2]N. Nakagawa, H. Y. Hwang, and D. A. Muller, Nature Materials 5, 204 (2006).[3]J. M. Moison, C. Guille, F. Houzay, F. Barthe, and M. Van Rompay, Phys. Rev. B 40, 6149 (1989).[4]C. Guille, F. Houzay, J. M. Moison, and F. Barthe, Surf. Sci. 189-190, 1041 (1987).[5]R. A. Stall, J. Zilko, V. Swaminathan, and N. Schumaker, J. Vac. Sci. Technol. B 3, 524 (1985).[6] L.F.K. and D.A.M. acknowledge support by the Cornell Center for Materials Research (NSF No. DMR–0520404 and No. IMR-0417392), and under the ONR EMMA MURI. L.F.K. acknowledges financial support by Applied Materials.
12:00 PM - K8.8
Studying Electronic Structures of Thin Film Perovskite Vanadates by Electron Energy Loss Spectroscopy.
Miaofang Chi 1 2 , Lane Martin 3 , Teruyasu Mizoguchi 4 , John Bradley 2 , Ramamoorthy Ramesh 3 , Nigel Browning 1 2
1 , University of California, Davis, Davis, California, United States, 2 , Lawrence Livermore National Laboratory, Livermore, California, United States, 3 , University of California, Berkeley, Berkeley, California, United States, 4 Institute of Engineering Innovation, University of Tokyo, Tokyo Japan
Show Abstract12:15 PM - K8.9
Direct Observation of the Magnetoelectric Coupling Effect using Magnetic Force Microscopy and Lorentz Transmission Electron Microscopy.
Sung Hwan Lim 1 , Todd Brintlinger 1 , Yi Qi 1 , Shen Qiang Ren 1 , Manfred Wuttig 1 , John Cumings 1 , Ichiro Takeuchi 1 2 , Lourdes Salamanca-Riba 1
1 Materials Science and Engineering, University of Maryland, College Park, Maryland, United States, 2 Physics, University of Maryland, College Park, Maryland, United States
Show AbstractWe are pursuing direct observation of the magnetoelectric (ME) coupling effect in multiferroic thin film structures using a specially designed sample holder that allows the application of an external electric field in the Lorentz imaging mode in a transmission electron microscope. The thin film structures consist of a ferroelectric layer of PbZr0.5Ti0.5O3 (PZT) and a magnetostrictive layer of CoFe2O4 (CFO) that were deposited on either (001) MgO or SrTiO3 substrates by pulsed laser deposition. A 300 nm thick CFO layer was first deposited on the substrates followed by 100 nm thick PZT layer. To induce sufficient in-plane electric field on the PZT layer, an array of electrodes with 100 to 300 nm line pitch was patterned on the PZT layer. The direct observation of strain mediated ME coupling effect via the piezoelectric response of the PZT which in turn causes a strain and a change in the magnetic domain structure in the CFO layer will be discussed. Also, magnetic force microscopy was used to study the magnetic domain structure of the CFO layer and to observe the ME coupling effect directly. The switching of ferromagnetic domains with 200 nm in diameter in CFO layer was observed by applying a magnetic field along the out-of-plane direction of the film. The changes of ferromagnetic domains by applying an electric field along the normal direction of the film surface will be presented. Also, we are exploring the direct observation of ME coupling effect in BiFeO3 thin film which is known as intrinsic multiferroic material with antiferromagnetic and ferroelectric ordering at room temperature. To detect the evolution of the antiferromagnetic domains in BiFeO3 during the application of an electric field, a soft magnetic thin layer of Permalloy (Ni0.8Fe0.2) and an insulating layer were deposited on the BiFeO3 thin film.This work was supported by NSF MRSEC DMR 0520471, ONR N000140110761, ONR N000140410085, NSF DMR 0094265 (CAREER), NSF DMR 0231291 NSF DMR 0354740 and NSF 0095166. We acknowledge the use of the TEMs in the Nanoscale Imaging Spectroscopy and Properties (NISP) laboratory at the University of Maryland.
12:30 PM - K8.10
Studies of Dielectric, Electrical and Optical Properties of Pb(Fe2/3W1/3)1/2Ti1/2O3 Thin Films by Impedance and Raman Spectroscopy.
Ashok Kumar 1 , Nisit Murari 1 , Ram Katiyar 1
1 Department of Physics, University of Puerto Rico, San Juan, Puerto Rico, United States
Show AbstractWe have synthesized (1-x)Pb(Fe2/3W1/3)O3-xPbTiO3 (x=0.50)(PFWT) thin films on Pt/Si substrates by chemical solution deposition technique. The morphotropic phase diagram of PFWT solid solution indicates that it changes from natural relaxor to an ordered ferroelectric state above x = 0.33 of lead titanate concentration. The microstructure and films thickness were studied using secondary electron microscope (SEM). The dielectric spectroscopy studies in these films were carried out in the temperature range of 300K-650K, over a wide range of frequency (100Hz-1MHz). Real and imaginary parts of the dielectric constant indicated strong frequency dispersion in the low frequency region. The ferroelectric phase transition was found at 575K (Curie temperature) for all frequencies. The slope of the reciprocal of the dielectric constant is 2:1, matched well with the simplest Landau free energy model and it indicates continuous second order displacive ferroelectric phase transition. The Relaxation coefficient was estimated from a linear fit of the modified Curie-Weiss law and the results suggested a long range ordering (γ~1.30). The Non linear variation of the dielectric constant with applied bias voltage yielded 18% tunability indicating its utility in tunable device applications. The polarization hysteresis curve at room temperature illustrated a ferroelectric nature of the material. The impedance spectroscopy suggests two different relaxation mechanisms in the materials below and above the Curie temperature. The master modulus spectra revealed that the grain boundary capacitance plays a crucial role in conduction mechanism above the Curie temperature. The ac conductivity well behaves the Jonscher’s power law, which indicates that frequency independent conductivity above Curie temperature. Temperature dependent Raman spectra indicate that the crystal structure changes from tetragonal to cubic i.e. a ferroelectric phase transition at 575K.
12:45 PM - K8.11
Electric Field Effect on Photoluminescence in Er-doped LiNbO3 Films Prepared by Pulsed Laser Ablation.
Akiharu Morimoto 1 , Yuichi Susaki 1 , Takeshi Kawae 1 , Satoru Yamada 2 , Shigeru Ohtsubo 2 , Minoru Kumeda 1
1 Grad. School of Natural Science and Technol., Kanazawa Univ., Kanazawa, Ishikawa, Japan, 2 Department of Electrical Eng., Ishikawa National College of Tech., Tsubata, Ishikawa, Japan
Show AbstractFor the development of nonlinear optical devices, waveguide devices, or optical ICs, high quality LiNbO3 (LN) films are required. Furthermore, Er-doped LN waveguide are attracting much attention because Er-related 1.54 μm emission is a standard communications wavelength. The Er-related 1.54 μm photoluminescence (PL), which is originally a forbidden transition from 4I13/2 to 4I15/2, is known to be allowed by breaking the local inversion symmetry around Er ion. From this point of view, it is interesting to investigate the effect of applying the electric field on the PL properties in Er-doped LN crystals. The electric field of Er-doped LN crystals itself is expected to induce the local field of Er ion and/or local strain via piezoelectric or electrostrictive effect. In this paper, we report Er-doped LN film preparations on sapphire substrates and the first observation of 1.54μm PL modulation of the films by applying the electric field.We prepared Er-doped LN films on c-plane sapphire substrates at a substrate temperature of 500 °C in an oxygen pressure of 33 Pa by pulsed laser ablation (PLA) with a laser energy of 110 mJ and a repetition rate of 10 Hz. We used Er-doped Li1.2NbO3 (Er2O3: 1 mol.%) as a target. For characterization of PL properties, we employed an Ar+ ion laser with a laser power of 800 mW by two ways. One is the conventional lock-in amplification using a laser chopping frequency of 27 Hz with a constant applied voltage, and the other is special lock-in amplification using a voltage chopping frequency of 10 Hz with a CW laser excitation. For applying the electric field co-planar Au or Al electrodes with a gap of 0.5 mm were deposited by thermal evaporation. The applied voltage was mainly 700 V with on-off DC voltage or bipolar pulse of ±700 V with a frequency of 10 Hz, resulting in an applied filed of 14kV/cm in the c-plane of LN crystal. The X-ray diffraction and the pole figure measurements showed c-plane LN epitaxial growth on c-plane sapphire substrates. The result suggests that Er ions are incorporated into the LN host structure. All films prepared exhibited the characteristic Er PL spectra around 1.54μm, and the PL spectrum of the Er-doped LN film completely differed from that of the Er2O3 film. This result suggests that Er ions replace a peculiar site of LN crystal unlike that of Er2O3 crystal.In the conventional PL measurement, the PL intensity was found to be enhanced by 3 % by applying DC 700 V with an almost the same spectrum as one without the voltage. A sudden switching-off of the DC voltage was found to cause the PL intensity decrease with a decay constant of a few hundred ms. In the special PL measurement, a similar PL spectrum was observed also by the modulation with bipolar pulse of ±700 V instead of the conventional modulation of the excitation laser light. In summary, the electric field modulation effect was successfully observed for the PL spectra in Er-doped LN films.
K9: Theory
Session Chairs
Igor Lubomirsky
Alexander Roytburd
Thursday PM, November 29, 2007
Grand Ballroom (Sheraton)
2:30 PM - **K9.1
Theory on Spiral Magnetism and Multiferrocity.
Naoto Nagaosa 1
1 Applied Physics, The University of Tokyo, Tokyo Japan
Show Abstract3:00 PM - **K9.2
Theoretical Study on Electronic Structure and Material Design of Multiferroics by First-Principles Calculations.
Tamio Oguchi 1
1 ADSM, Hiroshima University, Higashihiroshima Japan
Show AbstractMultiferroic materials are characterized by the coexistence of spin, orbital and/or charge (electric-dipole) orders associated with the electronic degrees of freedom. A lattice degree of freedom is often coupled with them. Cross-term effects between the different degrees of freedom such as magnetoelectric effects are expected to give rise to novel properties and application potentiality. Several magnetic and ferroelectric oxides are known with perovskite-type crystal structure, often referred to as ABO3. We have recently applied our theoretical approach to such multiferroic perovskite oxides to clarify electronic mechanism for the coexistence of magnetic and ferroelectric orders. This talk covers a review on our first-principles study of multiferroic bismuth and lead transition-metal perovskite oxides: BiMnO3, PbVO3, BiCoO3, and double-perovskites BiBB'O6.
4:00 PM - K9.3
Band Gap and Phase Transitions of BiFeO3.
John Robertson 1 , Stewart Clark 2
1 Engineering Dept, Cambridge University, Cambridge United Kingdom, 2 Physics Dept, Durham University, Durham United Kingdom
Show AbstractBiFeO3 is a perovskite based multiferroic oxide. But its main interest at present is that it is a Pb-free ferroelectric with a large remnant polarisation, especially as a thin film [1]. The symmetry of the thin film form has been the matter of debate. Palai et al [2] have recently mapped the various phase transitions of BiFeO3 as a function of temperature, and suggest that BFO belongs to the class of displacive ferroelectrics like BaTiO3. However, BFO differs from typical perovskite ferroelectrics like BaTiO3 in that it is a correlated oxide with a partly filled Fe d shell. Its band gap and its origin are a matter of interest, both theoretically and practically, as leakage currents would inhibit is use as a practical storage device. Here, we present band structure calculations of BiFeO3 in its rhombohedral, tetragonal and cubic phase, assuming an antiferromagnetic local ordering, as a function of the off-center distortion of the Bi ion. We use the screened exchange method, which goes beyond LDA, in not suffering from the band gap problem [3]. Our band structure adheres to the model of correlated oxides of Sawatzky et al [4] and Boucquet et al [5]. In general, a band gap arises from both on-site Coulombic repulsion and one-electron interactions. In the case of BiFeO3, an off-center distortion is essential for the presence of a band gap.1. J Wang et al, Science 299 1719 (2003)2. R Palai, R S Katiyar, S J Clark, J Robertson, J F Scott, preprint 3. S J Clark, J Robertson, App Phys Lett 90 132903 (2007)4. J Zaanen, G A Sawatzky, J W Allen, Phys Rev Lett 55 418 (1986)5. A E Boucquet, et al, Phys Rev B 46 3771 (1992)
4:15 PM - K9.4
Electric-field Control of Weak-ferromagnetism from First Principles.
Craig Fennie 1
1 Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractWe have studied the interplay between structure and magnetism in a family of single-phase materialsusing first-principles density-functionalmethods. We find that a ferroelectric distortion induces a weak ferromagnetism that is forbidden in the paraelectric phase. Furthermore, the sign of theDzyaloshinskii-Moriya vector depends on the directionof the spontaneous polarization all of which strongly suggest that electric-field control of weak-ferromagnetismis possible in this class of compounds.
4:30 PM - **K9.5
Defects and Domain Walls in LiNbO3: Insights from Microscopic Simulation.
Haixuan Xu 1 , Donghwa Lee 1 , Jacob Piper 1 , Jun He 1 , Susan Sinnott 1 , Simon Phillpot 1
1 Department of Materials Science and Engineering, University of Florida, Gainesville, Florida, United States
Show AbstractWe use electronic-structure, density functional theory calculations integrated with thermodynamic calculations [1] to determine the structure and stability of point defects and point defect clusters in LiNbO
3. In particular, we identify the dominant defects at different temperatures, oxygen partial pressure, and compositions. In addition, we use classical molecular-dynamics simulation approaches to characterize the structure and energetic of domain walls in LiNbO
3. A discussion of the interaction of domain walls and point defects is presented. This work is supported by the National Science Foundation under awards DMR-0602986 and DMR-0303279.
[1] J. He, R.K. Behera, M.W. Finnis, X. Li, E.C. Dickey, S.R. Phillpot and S.B. Sinnott, Acta Materialia (in press).
5:00 PM - K9.6
First-principles Study of Point Defects in Barium Titanate: Thermodynamics and Electrical Conductivity.
Paul Erhart 1 2 , Karsten Albe 2
1 Chemistry, Materials and Life Sciences Directorate, Lawrence Livermore National Laboratory, Livermore, California, United States, 2 Institut für Materialwissenschaft, Technische Universität Darmstadt, Darmstadt Germany
Show AbstractThe thermodynamic and kinetic properties of mono and di-vacancy defects in cubic (para-electric) barium titanate are studied by means of density functional theory calculations. Depending on the thermodynamic boundary conditions either metal or oxygen vacancies prevail. The assumption that the vacancies occur in their nominal charge states throughout the band gap, which underlies the most widely employed defect models, is confirmed. Only within about 0.1 eV of the band edges transition levels are found. For the dominating range of the band gap the di-vacancy binding energies are constant and negative. The system, therefore, strives to achieve a state in which undermetal-rich (oxygen-rich) conditions metal (oxygen) vacancies are bound in di-vacancy clusters. Since oxygen vacancies readily migrate at typical growth temperatures, di-vacancies can be formed at ease. The formation and migration energies are employed to derive the dependence of the equilibrium Fermi level and the charge carrier concentrations on the chemical conditions and the temperature. Thereby, it is also possible to deduce the relation between the conductivity and the oxygen partial pressure which compares very well with experiments. Furthermore, we are able to demonstrate the correspondence between the Kröger-Vink analysis, widely applied in defect chemistry, and the equations of semiconductor physics.
5:30 PM - K9.8
Phase Field Modeling of Domain Structures of Confined Nanoferroelectrics.
Julia Slutsker 1 , Andrei Artemev 2 , Alexander Roytburd 3
1 , NIST, Gaithersburg, Maryland, United States, 2 , Carleton University, Ottawa, Ontario, Canada, 3 , University of Maryland, College Park, Maryland, United States
Show AbstractPhase field modeling of domain structures in ferroelectrics nanorods of different shape and sizes is presented. The vortex domain configurations in confined ferroelectrics have been explored by varying the ratio of the energies of electrostatic and elastic interactions. It is shown that a strong effect of the electrostatic interactions can cause the formation of 90o domain walls that do not satisfy the condition of strain compatibility. A good agreement between the results of phase field modeling and the results of atomistic calculations for nano ferroelectrics demonstrates that the phase field approach provides an effective tool for the analysis of domain structures in nano-ferroelectrics.
5:45 PM - K9.9
Association of Oxygen Vacancies with Impurity Metal Ions in Lead Titanate.
Paul Erhart 1 2 , Rüdiger-Albert Eichel 3 , Petra Traskelin 4 5 , Karsten Albe 2
1 Chemistry, Materials and Life Sciences Directorate, Lawrence Livermore National Laboratory, Livermore, California, United States, 2 Institut für Materialwissenschaft, Technische Universität Darmstadt, Darmstadt Germany, 3 Eduard-Zintl-Institut, Technische Universität Darmstadt, Darmstadt Germany, 4 Accelerator Laboratory, University of Helsinki, Helsinki Finland, 5 Department of Chemical Engineering and Material Science, University of California at Davis, Davis, California, United States
Show AbstractThe thermodynamic, structural, electronic and kinetic properties of isolated copper and iron atoms as well as their complexes with oxygen vacancies in tetragonal lead titanate have been investigated by means of density functional theory calculations. For both elements a strong chemical driving force for the formation of MTi-VO (M=Cu,Fe) associates is found. In the most stable configurations the defect dipole is aligned along the tetragonal axis parallel to the spontaneous polarization. The local spin moments are derived and the spin density patterns are employed to interpret recent electron paramagnetic resonance experiments. The calculations provide a simple and consistent explanation for the experimental findings.The energy landscape for oxygen vacancy migration is obtained which also dictates the reorientation process in the presence of oscillating electric fields. The migration barriers are used to model the kinetics of dipole reorientation under cyclic loading. The results are discussed in the context of models for degradation of ferroelectric materials.
K10: Poster Session: Ferroelectrics
Session Chairs
Helene Bea
Ratnakar Palai
Friday AM, November 30, 2007
Exhibition Hall D (Hynes)
9:00 PM - K10.1
Dielectric Nonlinearity of Barium Titanate-Based Ceramic Capacitors.
Ichiro Fujii 1 , Susan Trolier-McKinstry 1 , Craig Nies 2 , Michael Muir 2 , Youichi Mizuno 3 , Hirokazu Chazono 3
1 , Pennsylvania State University, University Park, Pennsylvania, United States, 2 , AVX Corporation, Myrtle Beach, South Carolina, United States, 3 , Taiyo Yuden Co., Ltd, Gunma Japan
Show AbstractAs BaTiO3-based capacitors utilize progressively thinner layers (now < 1 μm) due to demand for high capacitance at small sizes, the small signal dielectric properties cannot properly describe the observed dielectric response. In this study, the ac electric field dependence of the dielectric permittivity of BaTiO3-based dielectrics with X7R specifications in sub-switching conditions was investigated in both multilayer and disc capacitors. As the ac field amplitude continues to rise, the measured dielectric response increases sub-linearly. Thus, it is not possible to describe the field dependence as a pure Rayleigh-like response. However, it is clear that the high field behavior is dominated by domain wall motion. To investigate the factors that affect the domain wall mobility, the influence of grain size, dielectric thickness, dc bias, temperature, and oxygen partial pressure during firing was also investigated. The origin of the differences in the sub-linear and Rayleigh responses will be discussed.
9:00 PM - K10.10
Characteristics of BST Capacitors with Aluminum Electrode and Iridium Oxide Barrier Layers.
Thottam Kalkur 1 , Troung Troung 1
1 ECE, University of Colorado, Colorado Springs, Colorado, United States
Show Abstract9:00 PM - K10.11
Effect of Strain on the Tunability of Highly (100) Oriented Mn-doped Barium Strontium Stannate Titanate Thin Films.
Shengbo Lu 1 , Zhengkui Xu 1 , Ngai Wing Li 1
1 Department of Physics and Materials Science, City University of Hong Kong, Hong Kong China
Show AbstractHighly (100)-oriented Mn-doped barium strontium stannate titanate thin films of a nominal composition (Ba0.7Sr0.3)(Sn0.2Ti0.8-xMnx)O3 (Mn-BSSnT) (x=0%, 0.2%, 0.4%, 0.6% and 1%), were fabricated by pulsed laser deposition on (La0.7Sr0.3)O3/LaAlO3 substrates. Both elastic strain and inhomogeneous strain were measured by x-ray diffraction techniques. Relationship between the strain and the dielectric properties of the Mn-BSSnT thin films were systematically investigated as a function of the Mn content. Our results show that the tunability is dependent upon not only the elastic strain induced by thermal expansion coefficient and lattice mismatch between the thin film and the substrate but also inhomogeneous strain induced by Mn doping. The tunability decreases with increasing inhomogeneous strain and can be easily manipulated by changing Mn doping content, which is beneficial to real tunable device applications.
9:00 PM - K10.12
The Effect of Composition on the Microwave Performance of BaxSr1-xTiO3 Ferroelectric Films.
Andrei Vorobiev 1 , John Berge 1 , Spartak Gevorgian 1 2
1 Department of Microtechnology and Nanoscience, Chalmers University of Technology, Gothenburg Sweden, 2 Microwave and High Speed Electronics Research Center, Ericsson AB, Molndal Sweden
Show AbstractDue to the high dielectric permittivity/tunability and low intrinsic dielectric loss the BaxSr1-xTiO3 (BSTO) solid solutions have been widely considered for applications in microwave tunable devices. Both the permittivity/tunability and the dielectric loss increase with increasing Ba concentration (x). Typically achieving the best device performance requires selection of the right composition by trading the low losses against the high tunability. In this work thin film Au/Pt/BaxSr1-xTiO3/Pt/Au (x=0.25 and 0.75) structures have been fabricated on Si substrates using pulsed laser deposition of the ferroelectric films. Small signal dielectric properties were measured as a function of external dc field (up to 350 kV/cm), in the frequency range 1 MHz - 25 GHz and in the temperature range 50-450 K. The performance of BSTO films was characterized by the commutation quality factor K which takes into account both the tunability and the loss tangent. The temperature dependence of the apparent permittivity for x=0.25 reveals a sharp peak at 100 K with a room temperature permittivity of 280. The composition with x=0.75 reveals a broadened maximum around 250 K and a room temperature permittivity of 1200. The shift of the permittivity maxima to lower temperatures in comparison with that of bulk counterparts is explained by the contribution of the interfacial layer with reduced Curie temperature. The broadening of permittivity maximum is due to merging of three phase transitions. The room temperature permittivity is found to be rather frequency independent for both compositions. The relative tunability is n=1.8 for x=0.25 which is almost 2 times smaller than n=3.2 measured for the composition with x=0.75. The loss tangent of the device under test increases with frequency. The loss tangent measured at 25 GHz and zero dc field is tanδ=0.02 for x=0.25 which is 5 times smaller than tanδ=0.1 for x=0.75. The higher dielectric loss in the samples with higher Ba concentration can be explained by increasing of the intrinsic loss which is proportional to permittivity and loss associated with electrode series resistance which is proportional to the capacitance. The higher loss for x=0.75 results in lower K factor (400 at 25 GHz) in comparison with that for x=0.25 (1000 at 25 GHz).Thus the analysis of the measurements shows that the Ba0.25Sr0.75TiO3 composition offers a better trade-off between tunability and loss. On the other hand the Ba0.75Sr0.25TiO3 composition has better temperature stability of permittivity around room temperature due to broadening of the maximum in the temperature dependence of the permittivity.
9:00 PM - K10.13
Effect of Nanocrystalline Diamond Interlayer for BST Varactors.
Venkataramanan Gurumurthy 1 , Sathyaharish Jeedigunta 1 2 , Samuel Baylis 1 2 , Makoto Hirai 3 , Ashok Kumar 4 3 , Tom Weller 1 2
1 Department of Electrical Engineering, University of South Florida, Tampa, Florida, United States, 2 Centre of Wireless and Microwave Information Systems, University of South Florida, Tampa, Florida, United States, 3 Nanomaterials and Nanomanufacturing Research Center, University of South Florida, Tampa, Florida, United States, 4 Department of Mechanical Engineering, University of South Florida, Tampa, Florida, United States
Show AbstractTunable circuits are highly sought after for wireless communication applications as they offer a tool to counter the stringent frequency and power requirements of the industry. Barium strontium titanate (BST) is a ferroelectric material with composition-dependant Curie temperature and bias-dependant dielectric permittivity which enables its electrical properties to be changed over a broad range to meet the requirements of various electronic applications. In the varactors of metal-insulator-metal (MIM) structure, the bottom electrode lying on silicon dioxide (SiO2)/Si substrate should have good thermal stability, because insulator layer is usually deposited in the high-temperature range of 700 to 1000 K. Platinum (Pt) which is a thermally- and chemically stable material is widely used as the bottom electrode, whereas the diffusion of Pt layer into SiO2/Si interface has been a problem. Thus, in order to enhance the performance of BST varactors, this research has been performed to prevent Pt diffusion by inserting nanocrystalline diamond (NCD) layer between Pt layer and Si substrate. The NCD layer having average roughness (Rave) of approximately 10 nm was synthesized on Si substrate with a microwave plasma-enhanced chemical vapor deposition (MPECVD) method, and BST layer was deposited on Pt/NCD/Si substrate at 873 K by RF magnetron sputtering method. As a result, the BST layer consisted of the polycraystallines attributed to perovskite structure. The diffusion of the Pt layer was not observed in the cross section image of scannning electron microscope (SEM). Moreover, the BST varactors fabricated on the NCD layer as diffusion barrier displayed much better quality factors due to reduced overall losses, in comparison with the varactors without the NCD layer.
9:00 PM - K10.15
Influence of Induced Cation-Vacancies on the Dielectric Permittivity and Dielectric Relaxation of Pr–doped SrTiO3 Ceramics.
C. Ochoa 1 2 , A. Duran 2 , J. Diaz 2 , Jesus Siqueiros 2
1 Facultad de Ciencias, Universidad Autónoma de Baja California, Ensenada Mexico, 2 Centro de Ciencias de la Materia Condensada, Universidad Nacional Autónoma de México, San Ysidro, California, United States
Show AbstractThe effects of cation induced vacancies on the structural and dielectric properties of Sr1-xPr2/3x(Vac)1/3TiO3 (0≤x≤0.25) solid solution were studied. In this compound, the compensation of electrical charge when replacing a lower valence ion (Sr+2) by one of higher valence (Pr+3/+4) is achieved through the creation of cation vacancies. X-ray diffraction (XRD) shows that the samples are single structural phase belonging to the cubic pm-3m space group. Praseodymium appears in two states of oxidation in a proportion of 2:1 [Pr(III)/Pr(IV)] according to X-ray photoelectron spectroscopy (XPS) studies. Thermoelectric analysis performed between 450 and 750°C shows a wide relative dielectric permittivity peak with a maximum above 40,000 around 600°C. The dielectric response diminished with increasing frequency, an effect where cation induced vacancies played an important role. Dielectric relaxation with temperature was analyzed by fitting an Arrhenius law behavior to the experimental data and a value 0.67 eV was obtained for the activation energy for temperatures above 600°C. Here, it is suggested that the existence of A-site vacancies and the incorporation of Pr to the structure further distort the oxygen octahedron increasing the effect of the off-center Ti+4 site in the perovskite ABO3 lattice. The enhancement of the dielectric peak and the relaxor behavior are related to the thermal conduction associated to those alternative sites.We thank Dr. J. Mata and Dr. E. Martinez for advice and E. Aparicio, I. Gradilla, for technical assistance.
9:00 PM - K10.16
Piezoelectric and Dielectric Properties of Gd doped Pb(Zr0.53Ti0.47)O3.
Jesus Siqueiros 1 , Jorge Portelles 2 1 , Nelson Almodovar 2 1 , Oscar Raymond 1 , Jesus Heiras 1
1 Centro de Ciencias de la Materia Condensada, Universidad Nacional Autónoma de México, Ensenada, Baja California, Mexico, 2 Facultad de Fisica, Universidad de La Habana, La Habana Cuba
Show AbstractA study of poled and unpoled Pb(Zr0.53Ti0.47)O3 ceramics doped with 0.6% at. near the morphotropic region is presented. A shift of the transition temperature from 386 oC for PZT52/48 to 352 oC PZT53/47 doped sample is observed, taking this fact as proof of the incorporation of Gd to the crystal structure. Remarkable values of the relative permittivity as high as 42,000 with dielectric loss below 0.09 measured at 1 kHz are reported. Electrical conductivity studies to determine the role of the Gd dopant were performed. It is found that the material follows a Jonscher universal relaxation law in the 30-300 oC temperature interval in a wide frequency range. The observed behavior for the ac conductivity is consistent with a polaron hopping mechanism.From electromechanical resonance studies for samples poled at different electric fields, the fundamental parameters are determined. A value of Kp=0.5 is found for the electromechanical coupling factor. Values up to 26 μC/cm2 for the remanent polarization with coercive field of 17 kV/cm are obtained through hysteresis measurements. The overall behavior of the studied samples make the Gd doped PZT53/47 ceramic a good candidate for electromechanical based applications. This work was partially supported by DGAPA-UNAM Proj. No. IN116703, IN109305-3, and CoNaCyT Proj. No. 47714-F and 40604-F. Thanks are due to V. García, I. Gradilla, P. Casillas and E. Aparicio.
9:00 PM - K10.17
Structural Transitions in Electrostatic Fields and Ordered Stacking Faults in Ionic Crystals with Perovskite-type of Structure.
Dirk Meyer 1 , Alexandr Levin 1 , Emanuel Gutmann 1 , Torsten Weissbach 1 , Tilmann Leisegang 1 , Hartmut Stoecker 1 , Stefan Ritter 1 , Chris Elschner 1 , Manfred Bobeth 1 , Wolfgang Pompe 1
1 Physics, Dresden University of Technology, Dresden Germany
Show AbstractReversible structural changes of near -surface regions of strontium titanate (SrTiO3) single crystals under the influence of an electrostatic field are reported. The changes are mainly highlighted by means of wide-angle X-ray scattering (WAXS) and time-resolved measurements of the electric current. A comparable structural ordering, attributed to an excess of SrO complexes can be achieved by means of chemical solution deposition of nanometre films. A theoretical model, which describes all stages of the solid state reaction is presented, the results are compared to experimentally determined parameters. The ordered structures are interesting candidates for technical applications in adaptive optics and as substrates with tuneable dielectric properties at constant basal lattice parameters.
9:00 PM - K10.18
Influence of Oxygen Nonstoichiometry on the Transport Properties and Dielectric Loss of SrTiO3 Films and Single Crystals.
Bharat Jalan 1 , Roman Engel-Herbert 1 , Junwoo Son 1 , Susanne Stemmer 1
1 , University of California, Santa Barbara, Santa Barbara, California, United States
Show AbstractOxygen vacancies are believed to influence a large number of ferroelectric thin film device properties such as dielectric losses, leakage currents and Schottky barrier heights with electrodes. However, interpretation of measurements of films exposed to reducing atmospheres, such as forming gas, are often complicated by the presence of unintentional impurities, such as hydrogen. Hydrogen is belived to act as a shallow donor in many oxides. In this presentation, we will discuss the contribution of oxygen vacancies and hydrogen to the electrical conductivity and dielectric loss of SrTiO3 single crystals and films, which served as a model perovskite dielectric.SrTiO3 single crystals were exposed to different atmospheres to study the influence of hyrdrogen impurities and oxygen vacancies on electrical transport and dielectric loss. We combine four-point probe conductivity measurements with infrared transmission spectroscopy (IR) from 400 to 4000 cm-1 to monitor oxygen deficiency and OH bonds. Hydrogen concentrations were also monitored by secondary ion mass spectrometry (SIMS). IR showed that all as-received SrTiO3 crystals contained significant amounts of OH, which could be removed by oxidizing anneals but not by vacuum anneals. We show that mid-IR absorbance as well as phonon modes, in particular a narrow band at 1325 cm-1 were very sensitive to oxygen deficiency (vacuum versus oxidizing anneals) even for samples that appeared highly resistive, indicating the oxygen vacancies were either not shallow donors or compensated by other impurities. SrTiO3 films annealed with Pt top and bottom contacts under the same conditions show a large increase in leakage currents associated with a decrease in Schottky barrier height. Dielectric losses were unaffected by vacuum anneals, indicating the absence of a significant amount of charged defects. Only after large amounts of oxygen were removed by using Ti getter layers did the SrTiO3 crystals show metallic conduction behavior (~0.05 Ω/square ) coupled with strong mid-IR absorption.
9:00 PM - K10.19
Effects of Heat Treatments on Oxygen Vacancy Related Defects in SrTiO3 Substrates.
Mary Ellen Zvanut 1 , S. Jeddy 1 , G. Janowski 2
1 Physics, University of Alabama at Birmingham, Birmingham AL, Alabama, United States, 2 Materials Science and Engineering, University of Alabama at Birmingham, Birmingham , Alabama, United States
Show AbstractSrTiO3 is commonly used as a substrate for the deposition of thin film multiferroic and ferroelectric materials because of the compatibility of the lattice constant and availability of bulk material. However, the well-known thermal instability of charged defects in SrTiO3 will likely cause confusion when interpreting measurement results obtained from films grown on the substrate. Much of the concern focuses on oxygen vacancies (Vo). While most studies used to address this problem can only indirectly monitor the vacancies, the work reported here uses electron paramagnetic resonance (EPR) spectroscopy to detect a well-studied oxygen vacancy complex attributed to Vo. adjacent to a substitutional Fe3+ ion. X-band EPR was performed at room temperature before and after vacuum or O2 heat treatments between 200 and 800 oC. The results show that a series of 1 hr stepwise O2 anneals reduces the vacancy by an order of magnitude between 500 and 700 oC; while a subsequent vacuum treatment restores the Fe3+V0 EPR signal to approximately its original intensity by 400 oC. Time dependent O2 heat treatment at 700 oC demonstrates that the order of magnitude reduction in the vacancy concentration occurs monotonically over a period of one hour. The results of the study demonstrate that exposure to O2 at temperatures greater than 500 oC is required to remove oxygen vacancies, and processing in vacuum at temperatures as low as 400 oC can enhance the vacancy concentration. While these data appear straightforward, an isothermal heat treatment in O2 at 400 oC reveals that the vacancy complex actually increases by about 20% at this temperature, despite the O2 ambient. Collectively, the isothermal and isochronal heat treatment results demonstrate that movement of oxygen in SrTiO3 is a complex process, and that the complete time/temperature matrix used for SrTiO3film growth and device processing must be carefully considered.The work at UAB-Physics is supported by Dr. Colin Wood, ONR, and the NSF ADVANCE program.
9:00 PM - K10.2
Improved Epitaxy of Barium Titanate and Barium Strontium Titanate on Hexagonal Silicon Carbide Through the Integration of a Single Crystalline Magnesium Oxide Heteroepitaxial Template.
Trevor Goodrich 1 , Zhuhua Cai 1 , Mark Losego 2 , Jon-Paul Maria 2 , Katherine Ziemer 1
1 Chemical Engineering, Northeastern University, Boston, Massachusetts, United States, 2 Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina, United States
Show AbstractThere is a continued interest for the integration of functional oxides, such as ferroelectric barium titanate (BTO) and barium strontium titanate (BST), on wide bandgap semiconductors, such as hexagonal silicon carbide (6H-SiC), for next generation, multifunctional electronic devices. Initial attempts to integrate BTO by molecular beam epitaxy (MBE) on hydrogen cleaned 6H-SiC produced amorphous conformal films, likely due to the 6.2% compressive mismatch. Crystalline MgO(111), deposited by MBE on the 6H-SiC, was used as a heteroepitaxial template, which switched the lattice mismatch to 5.2% in tension between BTO and MgO and promoted epitaxial growth of BTO. BST was deposited by pulsed laser deposition (PLD) on MgO template layers as well as clean 6H-SiC. A similar epitaxial growth mechanism was observed for BST as with BTO, where the resulting BST films deposited on the MgO template layers were crystalline with only (111) orientations, while the BST deposited on bare 6H-SiC was amorphous. Crystalline MgO(111)-(1×1) was deposited by MBE at 140 °C on 6H-SiC(0001) that was cleaned ex-situ in a hydrogen flow furnace, which resulted in a √3×√3 R30° surface reconstruction. The MgO films were found to have a MgO(111)/6H-SiC(0001) epitaxial relationship where the {11-2} of the MgO(111) was aligned parallel with the {1-100} of the bulk 6H-SiC(0001). This indicates that the MgO prefers to grow in tension with a 3.4% mismatch. Subsequent MBE-grown BTO was carried out at 650 °C on heated-treated MgO(111) template layers, 2.5 nm thick, as well as hydrogen cleaned 6H-SiC(0001) without a MgO interlayer. Similarly, PLD-grown BST was deposited at 650 °C on hydrogen cleaned 6H-SiC, as well as two MgO/6H-SiC template layers that were 4 nm and 10 nm thick. In the absence of the MgO layer, both the BTO and BST were amorphous with no observed crystallographic orientation, as determined by x-ray diffraction (XRD) and reflection high energy electron diffraction (RHEED). However, when the BTO and BST were deposited on the MgO template layers, the resulting films were highly crystalline with clear (111) perovskite RHEED patterns and only (111) XRD peaks. Both the BTO and BST were found to have a {100}||MgO{100} epitaxial relationship. The improved epitaxy of the BTO and BST films is believe to be a result of the 5.2% and 6.1% tensile mismatches between BTO/MgO and BST/MgO, respectively. When deposited on bare 6H-SiC, BTO and BST have a minimum lattice mismatch of 6.2% compressive and 5.1% compressive, respectively. This indicates that the epitaxy growth mechanism of crystalline perovskites with (111) orientation favor tensile mismatch and cannot be epitaxially grown under compression, since the compressive mismatch of BST/6H-SiC is less than the tensile mismatch of BST/MgO. Ferroelectric characterization of the BTO and BST structures are currently under study.
9:00 PM - K10.20
Time Resolved In-Situ Diffuse X-ray Scattering Measurements of the Surface Morphology of Homoepitaxial SrTiO3 Films During Pulsed Laser Deposition.
John Ferguson 1 4 , Gokhan Arikan 2 4 , Arthur Woll 3 , Darren Dale 3 , Lena Fitting Kourkoutis 2 4 , Aram Amassian 1 4 , David Muller 2 4 , Joel Brock 2 4
1 Materials Science and Engineering, Cornell University, Ithaca, New York, United States, 4 Cornell Center for Materials Research, Cornell University, Ithaca, New York, United States, 2 Applied and Engineering Physics, Cornell University, Ithaca, New York, United States, 3 Cornell High Energy Synchrotron Source, Cornell University, Ithaca, New York, United States
Show AbstractHomoepitaxial SrTiO3 thin films were grown on SrTiO3 <001> using Pulsed Laser Deposition (PLD). The deposition process was monitored in-situ using x-ray reflectivity and scattering measurements in the G3 experimental station at the Cornell High Energy Synchrotron Source (CHESS). While it is known that film thickness and roughness can be monitored in real time using specular reflectivity using x-ray or RHEED, a wealth of information about the surface morphology can be obtained from the diffuse x-ray scattering around the (00L) Crystal Truncation Rod. For example, the average island size and spacing can be obtained by measuring the diffuse lobes of scattering generated by features on the surface. Using an area detector with approximately 200 ms time resolution, the PLD process and the subsequent surface evolution were both monitored over a wide range of parameters including substrate temperature, laser repetition rate, O2 partial pressure, and laser fluence. Additionally, time resolved x-ray diffuse scattering results will be shown for heteroepitaxial growth of LaAlO3 on SrTiO3 <001>. These data clearly indicate that the growth mechanism of the first layer is distinct from that of subsequent layers.
9:00 PM - K10.22
Leakage Behavior of Perovskite Oxide Film Capacitors Affected by Work function via Microstructure of Electrodes.
Tae young Kim 1 , Kentaro Kawasaki 1 , Takeshi Kawae 1 , Akiharu Morimoto 1 , Minoru Kumeda 1 , Satoru Yamada 2
1 Grad. School of Natural Sci. & Tech., Kanazawa Univ., Kanazawa , Ishikawa, Japan, 2 , Ishikawa National College of Technology, Tsubata, Ishikawa, Japan
Show AbstractPerovskite oxides such as SrTiO3(STO), (Ba1-xSrx)TiO3 and BaTiO3 with novel metal electrode such as Pt, Ru and Ir are the most promising capacitor materials in future DRAM applications. However, with decreasing the thickness of the perovskite film, the interface microstructure between the perovskite thin film and the electrode is becoming more important than the perovskite thin films themselves in a view of leakage currents. The microstructures affected by crystallinity of electrodes will be possibly related to the metal work function and the Schottky barrier heights of the oxide/metal interface. In the present paper, we will report a significant influence of the metal electrodes microstructure on the leakage behavior of dielectric STO films via work function. In order to prepare the metal electrode with various microstructures, Pt and Ru metal electrodes were deposited on c-plane sapphire, fused quartz, MgO and Gd3Ga5O12(GGG) by pulsed laser ablation (PLA) using a KrF excimer laser in vacuum at the temperatures in the range of 300 to 700°C. The STO films with 100-300 nm thickness were deposited on metal electrodes to prepare capacitors by PLA. Al top electrodes were deposited on the STO layers to investigate the electrical properties by vacuum evaporation. The θ-2θ XRD measurement showed the randomly orientated or (100)-oriented Pt film was grown on MgO substrate, and (111)-oriented Pt films were grown on c-plane sapphire, fused quartz and GGG substrates. On the other hand, (101)-orientated Ru film was grown on MgO substrate, and (002)-orientated Ru films were grown on c-plane sapphire, fused quartz and GGG substrates. The work function of metal electrodes measured by photo-electron spectroscopy in air was varied in a range of 4.8 to 5.1 eV depending on the crystal orientation and the crystallinity of electrodes on various substrates. The work function, however, was found to increase with decreasing the roughness value Rrms among the samples with the same orientation. It is well known that the leakage current is decreased by increasing the Schottky barrier height at the oxide/metal interface. In our experiment, the Schottky barrier height deduced from the I-V characterization was strongly enhanced by increasing the work function. The work function was found to be enhanced by decreasing the metal electrode roughness. Based on the present results, the leakage current characteristics of perovskite oxide thin film with metal electrode will be controlled by tuning of microstructures.
9:00 PM - K10.23
High Quality Deposition of STO (SrTiO3) Thin Films using Sol-Gel Method.
Kiyoshi Uchiyama 1 , Daiki Fukunaga 1 , Tadashi Shiosaki 1
1 School of Materials Science, Nara Institute of Science and Technology, Ikoma-shi, Nara, Japan
Show Abstract High quality deposition of STO (SrTiO3) thin films was demonstrated using a sol-gel method. The crystallinity of STO was improved above 1100 deg C sintering temperature and well crystallized at 1400 deg C. In addition, we revealed methanol addition into the sol-gel solutions affects the crystallinity of the STO thin films. Based on these basic experiments, we also examined doped STO depositions to realize conducting STO thin films. In order to achieve higher conductivity, sintering conditions with reduced atmosphere was also investigated. We consider this result will open the new window of the oxide thin films for electronic device applications.
9:00 PM - K10.24
Stress Influence on Dielectric Properties of Polycrystalline SrTiO3 Films.
Olena Okhay 1 , Alexander Tkach 1 , Aiying Wu 1 , Paula Vilarinho 1
1 Department of Ceramics and Glass Engineering, University of Aveiro, Aveiro Portugal
Show AbstractStrontium titanate (ST) is attractive for applications in tunable microwave devices due to the high dc-electric-field dependence of the dielectric constant. It is of particular practical interest if the low temperature (below ~80 K) tunability of ST is shifted towards high temperatures. ST is an incipient ferroelectric in which high dielectric constant monotonously increases with decreasing temperature, but no ferroelectric phase transition occurs. Among the ways to induce a polar state in ST, application of uniaxial stress was reported [1]. Recently through controlled substrate engineering, ferroelectricity and tunability were observed at room temperature in epitaxial ST films grown by molecular beam epitaxy with properties comparable to bulk ST at cryogenic temperatures [2]. The high dielectric constant at room temperature in these lead free films (nearly 7000 at 10 GHz) and its sharp dependence on electric field are extremely promising for these applications. However, this strain-induced enhancement in Tc is attained in epitaxially grown films and through the utilization of a particular (110) DyScO3 substrate. In addition to the tanδ values of 0.2 obtained for these films, the high costs associated with the use of DyScO3 substrate and molecular beam epitaxy equipment for deposition of the films are extremely high from the application point of view. However thin film properties exhibit a remarkable dependence on the preparation process. Different physical properties depending on structural and microstructural details, defects and stresses induced by the preparation procedure are expected.In this work ST thin films were prepared by sol-gel method and deposited on different substrates (Al2O3/Pt, SrTiO3/Pt and MgO/Pt) to evaluate the stress effect on dielectric properties of polycrystalline ST thin films. A structural and microstructural systematic study was conducted by XRD, Raman, and TEM. The analysis of the dielectric properties was carried out in a wide spectra of temperatures and frequencies. The relations between the stresses induced in the films and dielectric response is established. It was found that ST films deposited on MgO substrates are under compressive stress and demonstrate dielectric permittivity values (> 600) and high tunability (60%) and a Tc~-8K was calculated. On the other hand ST films deposited on Al2O3 substrates and prepared under identical conditions are under tensile stress and exhibit lower dielectric permittivity (~350) and tunability two times smaller (35%) than the films deposited on MgO substrates. For the films prepared on Al2O3 substrates a lTc~-100K was calculated. References:[1] Pertsev N.A., et al. (2000) Phys.Rev.B 61, R825[2] Haeni J.H., et al. (2004) Nature 430, 758
9:00 PM - K10.25
Anomalous X-ray Scattering from Strained SrTiO3 Films Grown on Si (001).
James Reiner 1 , Yaron Segal 1 , Frederick Walker 1 , Zhan Zhang 2 , Charles Ahn 1
1 Applied Physics, Yale University, New Haven, Connecticut, United States, 2 Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois, United States
Show Abstract9:00 PM - K10.26
Synthesis of the Ferroelectric Solid Solution, Pb(Zr1-xTix)O3 on a Single Substrate Using a Modified Molecular Beam Epitaxy (MBE) Technique.
Piers Anderson 1 4 , Samuel Guerin 1 , Brian Hayden 2 1 , Mikael Khan 3 , Andrew Bell 3 , Yisong Han 4 , Ashu Pasha 4 , Karl Whittle 4 , Ian Reaney 4
1 , Ilika Technologies Ltd, Southampton, Hampshire, United Kingdom, 4 Dept. of Engineering Materials, University of Sheffield, Sheffield, Yorkshire, United Kingdom, 2 School of Chemistry, University of Southampton, Southampton, Hampshire, United Kingdom, 3 School of Process, Environmental and Materials Engineering, University of Leeds, Leeds, Yorkshire, United Kingdom
Show AbstractHigh-throughput synthesis of the ferroelectric solid solution Pb(Zr1-xTix)O3 (PZT) on single Pt/Ti/SiO2/Si substrates was demonstrated using a modified molecular beam epitaxy (MBE) system. The PZT films exhibited a phase transition from rhombohehdral (R) to tetragonal (T) symmetry as a function of Zr:Ti ratio, across the substrate diagonal. This was consistent with the presence of a morphotropic phase boundary (MPB) at a Zr:Ti ratio of 0.64:0.36, different from the value of 0.53:0.47 observed for bulk ceramics. All points on the films exhibited ferroelectric hysteresis loops. The results demonstrate the feasibility of high-throughput MBE for deposition of complex ferroelectric oxides, and pave the way for further materials discovery, in particular Pb-free piezoceramics.
9:00 PM - K10.27
Effect of Growth Conditions on Structural and Electrical Properties of Pb(ZrxTi1-x)O3 Layers Grown by Peroxide MBE.
Natalia Izyumskaya 1 , Vitaliy Avrutin 1 , Xing Gu 1 , Bo Xiao 1 , Serguei Chevtchenko 1 , Lin Zhou 2 , David Smith 2 , Jong-Gul Yoon 1 3 , Hadis Morkoç 1
1 Department of Electrical and Computer Engineering, Virginia Commonwealth University, Richmond, Virginia, United States, 2 Deptartment of Physics, Arizona State University, Tempe, Arizona, United States, 3 Department of Physics, University of Suwon, Kyunggi-do Korea (the Republic of)
Show AbstractFerroelectric Pb(ZrxTi1-x)O3 (PZT) films have attracted considerable interest owing to their potential applications in nonvolatile random access memory devices, ferroelectric field effect transistors, motion sensors, infrared detectors, surface acoustic wave devices, etc. Harnessing PZT, however, requires high quality single-crystal PZT films. PZT thin films have been prepared by various methods such as sol-gel and hydrothermal techniques, metal-organic chemical vapor deposition, rf magnetron sputtering, and pulsed laser deposition. Recently, we reported epitaxial growth of high-quality PbTiO3 and PZT layers by molecular beam epitaxy (MBE) [1-3]. Here, we focus on the effect of growth conditions, structure, and phase composition (presence of second-phase inclusions) on electrical properties of PZT films grown on (001) SrTiO3 substrates by MBE, with the use of hydrogen peroxide as an oxidant. Phase composition and electrical properties of PZT films were studied by high-resolution x-ray diffractometry (HRXRD), transmission electron microscopy (TEM), conductive atomic force microscopy (C-AFM), piezoelectric force microscopy (PFM), and electrical (I-V and polarization-field) measurements. Peroxide pressure was found to control the phase composition of the films. Excess peroxide leads to PbO inclusions in PZT layers, whereas deficiency results in TiO2 or ZrO2 phase. The second-phase inclusions can be responsible for high leakage current in the films, deteriorating their electrical characteristics. Therefore, a precise control over the peroxide pressure is imperative for single-phase PZT films with good ferroelectric properties.1.X. Gu, N. Izyumskaya, V. Avrutin, H. Morkoç, T.D. Kang, and H. Lee, Appl. Phys. Lett., 89 122912 (2006). 2.N. Izyumskaya, V. Avrutin, Xing Gu, Ü. Özgür , Bo Xiao, T.D. Kang, H. Lee, and H. Morkoç, Ferroelectrics and Multiferroics , edited by V. Gopalan, J-P. Maria, M. Fiebig, C-W. Nan (Mater. Res. Soc. Symp. Proc. 966E , Warrendale, PA , 2007), 0966-T11-17. 3.N. Izyumskaya, V. Avrutin, Xing Gu, Ü. Özgür , T.D. Kang, H. Lee, D.J. Smith, and H. Morkoç, ibid, 0966-T07-04.
9:00 PM - K10.28
The Role of SrTiO3 Seed Layer on Low-temperature Crystallization of Pb(Zr, Ti)O3 Films Prepared by Metalorganic Chemical Vapor Deposition.
Ji-Won Moon 1 , Naoki Wakiya 2 , Takanori Kiguchi 3 , Tomohiko Yoshioka 1 , Junzo Tanaka 1 , Kazuo Shinozaki 1
1 Metallurgy and Ceramics Science, Tokyo Institute of Technology, Tokyo Japan, 2 Department of Materials and Chemical Engineering, Shizuoka University, Hamamatsu, Shizuoka, Japan, 3 Center for Advanced Materials Analysis (CAMA), Tokyo Institute of Technology, Tokyo Japan
Show Abstract Lead zirconate titanate (PZT) is widely used for capacitor materials in ferroelectric random access memory (FeRAM). However, the crystallization temperature of PZT film with good ferroelectricity is usually above 550 oC and there are several problems such as reliability degradation and interdiffusion at the uncompatibility point of view with CMOS process. Therefore, the low-temperature crystallization of PZT films has been issued with development of deposition process, introduction to seed layers and modification of PZT sources. We also suggested that SrTiO 3 could be used as a seed layer because of relatively small lattice mismatch with Pt bottom. We also reported that crystallized PZT films using SrTiO3 seed layer can be prepared around 290-300 oC by MOCVDs. However, the role of SrTiO3 seed layer on low-temperature crystallization of PZT films has not been cleared yet. In this study, we demonstrated the role of seed layer on the low-temperature crystallization of PZT films. The pulsed laser deposition (PLD) and metalorganic chemical vapor deposition (MOCVD) were used to prepare SrTiO3 seed layer and 100 and 200 nm-thick PZT films, respectively. The surface morphology, composition and coverage, crystalline phase of SrTiO3 seed layer were examined as the function of deposition temperature and deposition time by atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction meter (XRD), wavelength dispersive spectroscopy (WDS) and transmission electron microscope (TEM), respectively. We found that the crystal structure, phase orientation and coverage of seed layer were important parameters for low-temperature crystallization of PZT films. The role of SrTiO3 seed layer on low-temperature crystallization included initial nucleation and growth mechanism of PZT films will mainly discussed. Ferroelectric properties of low-temperature crystallized PZT films prepared around 300 oC will be discussed.
9:00 PM - K10.29
Monoclinic Phase and Ferroelectric Properties in Pb(Zr0.52Ti0.48)O3 Epitaxial Thin Films on (110) Oriented SrTiO3 Substrates.
Li Yan 1 , Jiefang Li 1 , Hu Cao 1 , Dwight Viehland 1
1 Materials Department, Virginia Polytechnic Institute and State University, Blacksburg, Virginia, United States
Show Abstract9:00 PM - K10.3
Structural Characterization and Transport Properties of BaTi1-xNbxO3 Thin Films.
Yang Shao 1 2 , Christian Maunders 1 2 , Declan Keogh 1 , Antoni Dabkowski 2 , Robert Hughes 2 , Jim Britten 3 , John Preston 2 4 , Gianluigi Botton 1 2
1 Materials Science and Engineering, McMaster University, Hamilton, Ontario, Canada, 2 Brockhouse Institute for Materials Research, McMaster University, Hamilton, Ontario, Canada, 3 Chemistry, McMaster University, Hamilton, Ontario, Canada, 4 Engineering Physics, McMaster University, Hamilton, Ontario, Canada
Show AbstractPerovskite oxides, such as BaTiO3, have demonstrated a variety of fascinating properties. Recently there has been increased interest in perovskite conducting oxides for use as an electrode material in thin film devices, with doped barium titanate being a promising candidate. To this end, the pulsed laser dopostion was used to deposit a series BaTi1-xNbxO3 thin films on (001) MgAl2O4 substrate. Unlike many commonly used substrates, MgAl2O4 offers the excellent lattice match needed for epitaxial growth. The θ-2θ X-ray results indicate that all these films were single phase and strongly oriented in the [001] direction. More detailed X-ray work, however, indicated that there were eight other minor orientations around the major one. Since Nb substitudes for Ti, cation ordering and changes to the valence become a concern as they could cause alterations to the conducting network. This, however, does not appear to be an issue as electron diffraction patterns from the [001], [011] and [111] directions show Nb substitudes randomly on the Ti site. Temperature dependent resistivity measurements as a function of Nb doping indicate a metal-insulator transition near x=0.2, with x>=0.5 films showing significant metallic conductivity. Room temperature Hall effect data showed that the charge compensation mechanism switched from holes to electrons between x=0.002 and x=0.02. Consistent with the resistivity results was that, as the Nb content increased, the charge density underwent a change from decreasing to increasing after the compensation point. Magnetic susceptibility measurements on the x=0.05, x=0.2 and x=0.5 film showed an abnormal increase from 200K-300K, which may indicate that a bipolaron spin singlet is forming at low temperature and dissolving into two isolated polarons at higher temperatures. In an effort to determine valence information, the Ti-L2,3 edge spectra was recorded using a FEI Tecnai 200 FEG microscope equipped with a monochromator and a high-resolution energy-loss spectrometer. The spectra were analyzed using a multiplet calculation that changed the Ti valence in the octahedral crystal field. The analysis revealed that the valence of Ti gradually transformed from tetravalent to trivalent as the Nb content increased, and completely converted to trivalent for x=0.5. Thus, in order to maintain the charge balance the valence of Nb is expected to change from pentavalent to tetravalent.
9:00 PM - K10.30
Internal Fields in PZT Thin Films.
Pu Yu 1 , Nina Balke 1 2 , Ying-Hao Chu 1 2 , Qing He 1 , Li-Peng Wang 3 , Long-Qing Chen 4 , Ramamoorthy Ramesh 1 2
1 Department of Physics, University of California, Berkeley, California, United States, 2 Department of Material of Science and Engineering, Univeristy of California, Berkeley, California, United States, 3 Novel Memory Technology, CTM/Flash Memory Group, Intel Corporation, Santa Clara, California, United States, 4 Department of Material of Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania, United States
Show AbstractFerroelectric thin films are attracting considerable attention for potential use in nonvolatile memory applications, such as a FRAM and more recently in probe based data storage systems. Among the various phenomena, fatigue, imprint and retention loss are key issues to understand and solve. Imprint, which is due to the built-in bias voltage of the thin films, results in an asymmetric hysteresis loop and thus make one of the states (the as-grown preferred state) more stable over the other. So far, research work on the imprint effect has mostly focused on the structures with both top and bottom electrodes, which is of relevance to FRAM applications. We are exploring the development of internal fields in epitaxial PZT thin films in the 2-50nm thickness range using a combination of controlled epitaxial growth and theoretical calculations. Annealing processes as a function of time, oxygen pressure, and temperature were systematically studied to understand the source of the internal field. Our studies show that the film defect chemistry can be appropriately tuned to control and even negate the effects of the polarization field driven internal field.
9:00 PM - K10.31
Structural and Dielectric Properties of PZT Thin Films Prepared on ZrO2 Buffered Silicon Substrate Using the Sol-gel Method.
Feng Chen 1 , Xiaoyan Yang 1 , Jinrong Cheng 1 , Shengwen Yu 1 , Dengren Jin 1 , Zhongyan Meng 1
1 Electronic Information Material, Shanghai University, Shanghai China
Show Abstract9:00 PM - K10.32
Effects of Na+-Dopants on the Dielectric and Tunable Properties of Ba0.6Sr0.4TiO3 Ceramics.
Jia Gong 1 , Jinrong Cheng 1 , Shengwen Yu 1 , Wei Tao 1 , Wenbiao Wu 1 , Zhongyan Meng 1
1 School of Material Science and Engineering, Shanghai University, Shanghai China
Show Abstract9:00 PM - K10.33
Domain Relaxation in PZT Thin Films.
Nina Balke 1 , Pu Yu 2 , Li-Peng Wang 3 , Ramamoorthy Ramesh 1 2
1 Department of Materials Science and Engineering, University of California Berkeley, Berkeley, California, United States, 2 Department of Physics, University of California Berkeley, Berkeley, California, United States, 3 Novel Memory Technology, CTM/Flash Memory Group, Intel Corporation, Santa Clara, California, United States
Show AbstractFerroelectric materials have been investigated for many years because of their application possibilities. Pb(Zr,Ti)O3 (PZT) thin films are the most promising candidate for FeRAMs because of their desirable ferroelectric properties. The advantages of ferroelectric materials are a very fast response of ferroelectric domains to an applied field and the possibility to write very small domains which results in a very high write velocity and a high storage density, respectively. Because of this the investigation of domain relaxation is of fundamental interest when it comes to the question of the smallest writable domain size. The domain relaxation behavior is mainly influenced by the local ferroelectric properties of the sample which is determined by the growth conditions of the PZT film. Usually the local ferroelectric hysteresis loops are shifted along field and signal axis which leads to a preferred polarization direction. This results in different stabilities of patterns written with positive and negative fields. This presentation focuses on the domain relaxation of small ferroelectric domains in the nm range and shows ways of changing ferroelectric properties of as grown PZT samples to design a suitable domain relaxation behavior for memory applications.
9:00 PM - K10.34
The Effect of Microstructure on the Ferroelectric Switching of Polycrystalline PZT Films.
Eva Anton 2 , R. Edwin Garcia 1 , John Blendell 1 , Keith Bowman 1
2 Materials Science and Engineering, Darmstadt Technical University, Darmstadt Germany, 1 Materials Engineering, Purdue University, West Lafayette, Indiana, United States
Show Abstract9:00 PM - K10.35
Strained-relaxed Novel Domain Structure of Epitaxially Grown Pb(Zr,Ti)O3 Thick Films by Metal Organic Chemical Vapor Deposition.
Hiroshi Funakubo 1 , Hiroshi Nakaki 1 , Rikyu Ikariyama 1 , Shintaro Yokoyama 1 , Yong Kwan Kim 1 , Ken Nishida 1 2 , Keisuke Saito 3 , Osami Sakata 4 , Shigeru Kimura 4
1 Department of Innovative and Engineered Materials, Tokyo Institute of Technology, Yokohama Japan, 2 Department of Communications Engineering, National Defense Academy, Yokosuka Japan, 3 Application Laboratory, Bruker AXS, Yokohama Japan, 4 Materials Science Division, Japan Synchrotron Radiation Research Institute/Spring-8, Hyogo Japan
Show AbstractThe domain structure of ferroelectric materials is known to be strongly contributed to the ferroelectric and piezoelectric properties. The domain structure of epitaxially grown tetragonal Pb(ZrxTi1-x)O3 films below 400 nm in thickness have been widely investigated last 20 years. However, the research on them above 500 nm has been hardly investigated in spite of the fact that these thick films are important for MEMS applications. In the present study, we show the novel and complicated domain structure, which was not observed below 400 nm. These consisted of three types of (100) orientation together with one types of (001) one and were observed irrespective x value within the x range from 0 to 0.45. In addition, it was observed not only oxide single crystal substrates, such as (100)SrTiO3 and (100)MgO, but also on buffered-(100)Si substrates. These indicate that this domain structure is a common one for the thick epitaxail films. Moreover, this shows the more relaxed structure than the observed domain structure for the films below 400 nm in thickness as already predicated by Roytburd et al.[1]In addition, this novel domain structures play an important role to the large piezoreponse by the domain switching under electric filed. [1] A.Roytburd et al., Ferroelectrics, 144, 137 (1993).
9:00 PM - K10.36
Screening of Weak Cells in A High Density Ferroelectric Random Access Memory.
YoungMin Kang 1 , Jai-Hyun Kim 1 , SongYi Kim 1 , HanKyoung Ko 1 , EunSun Lee 1 , DoYeon Choi 1 , JuYoung Jung 1 , JinYoung Kang 1 , WooSong Ahn 1 , WonWoong Chung 1 , HwiSan Kim 1 , SeungKuk Kang 1 , YoungKi Hong 1 , HyunHo Kim 1 , DongJin Jung 1 , SungYoung Lee 1 , HongSik Jung 1
1 Technology Development Team 2, Samsung Electronics Co., Ltd., Yongin, Gyeonggi, Korea (the Republic of)
Show Abstract9:00 PM - K10.37
Comparative Study of Thin PZT Sol-gel Films Deposited on Pt and GaN Substrates.
Serguei Chevtchenko 1 , Francisco Agra 1 , Hadis Morkoc 1 2
1 Electrical Engineering, Virginia Commonwealth University, Richmond, Virginia, United States, 2 Physics, Virginia Commonwealth University, Richmond, Virginia, United States
Show AbstractOver the last few years, ferroelectric-semiconductor structures attracted considerable interest due to a variety of potential applications in optoelectronic, piezoelectric, and microwave devices. The integration of ferroelectric materials with III-nitride semiconductors, GaN in particular, is one of the promising directions owing to the several advantages of GaN, which are include thermal, chemical and mechanical stability. It is well known that the boundary conditions applied to thin ferroelectric films influence piezoelectric and ferroelectric properties of these films. The theoretical limits predict, for example, that piezoelectric response is diminished due to the strain associated with substrates, known as the “substrate clamping” effect. The remarkable properties of GaN surface, namely, a strong surface potential of about 1.0 eV and high concentration of surface states, may result in unexpected changes of piezo- and ferroelectric properties.In this work we provide comparative study of piezoresponse and remanent polarization in thin Pb(ZrxTi1-x)O3 (PZT) films (~200 nm) deposited onto GaN/sapphire and Pt/Ti/SiO2/Si substrates using the sol-gel process. Wurtzite Si doped GaN (~2 μm) layers used in this study were grown on c-plane sapphire substrate by low-pressure organometallic vapor phase epitaxy (OMVPE). The [0001] oriented GaN films used in experiment had Ga-terminated surfaces. Properties of PZT films have been characterized by Piezoresponse Force Microscopy (PFM) in amplitude and phase modes. Our preliminary results indicate a stronger piezoresponse, or higher piezocoefficient, for PZT films deposited on GaN as compared to the film on metal substrate. The experiments show a difference up to 2.5 times. These results contradict to the expected stronger “substrate clamping” effect of GaN compare to Pt due to higher value of Young’s modulus of GaN. Despite the reported low values of remanent polarization for PZT/GaN heterostructures obtained from polarization-voltage measurements we observed clear phase contrast in PFM of the regions previously polarized by applying dc voltage to the sample in contact mode of AFM. It is possible that the aforementioned properties of GaN surfaces are responsible for our experimental observations.
9:00 PM - K10.38
Enhanced Photocurrent in Transparent Lead Zirconate-Titanate Thin Film Capacitors Under Sun Light Illumination.
Krishna Uprety 1 2 , Leonidas Ocola 1 , Orlando Auciello 1 2
1 Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois, United States, 2 Materials Science Division, Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractA report will be presented on research focused on developing transparent Pb(ZrxTi1-xO3) (PZT)–based capacitor for photovoltaic device applications. The transparent PZT-based capacitors exhibit high photocurrents when exposed to Xenon (Xe) light that has wavelengths from visible to infrared (i.e. 200-2000 nm), stimulating sunlight. Ferroelectric thin film-based structures PZT/LNO (LaNiO3)/ITO (InO2 90% and SnO2 10%)] produced on glass substrates exhibits 59% transmittance, while a PZT/ITO capacitor grown on the same glass structure exhibits 69% transmittance, both within the visible light range. However, the PZT capacitors including the LNO layer have a highly (001) oriented PZT layer induced by the close lattice matching of LNO with PZT, as opposed to the polycrystalline PZT based capacitors with the ITO electrode layer alone. These transparent PZT-based structures maintain excellent transmission properties even for far infrared wavelengths. The broad bandwidth-efficient transmission of light through the in the transparent PZT-based structures, provides the basis for potentially efficient ferroelectric-based photovoltaic devices. Preliminary measurements of photocurrents in the transparent PZT capacitors showed enhanced photovoltaic properties under Xe light illumination. The current voltage (I-V) curve showed four orders of magnitude increase in photocurrent upon sunlight illumination. The transparent ITO/LNO/PZT/LNO/ITO capacitor exhibits an increase in photovoltaic current from 2.6 ×10-6 A to 1.4×10-2 A, at ~ 1V, and from 3.7 ×10-11 A to 3.9 ×10-5 A at ~ 7V. The changes in photocurrent as a function of applied voltage for the transparent PZT capacitors upon sunlight illumination can be interpreted in terms of defects and associated electron excitation in the PZT layer, combined with rapid separation of electron-hole pairs created by the sunlight photons.
9:00 PM - K10.39
Quantitative Measurements of the Frequency-Dependent Complex Permittivity of PbTiO3 and Pb(Zr0.52Ti0.48)O3 Thin Films to 40 GHz.
Nathan Orloff 1 2 , Makoto Murakami 3 , Jordi Mateu 4 , James Booth 2 , Ichiro Takeuchi 1 3
1 Department of Physics, University of Maryland, College Park, Maryland, United States, 2 EEEL, National Institute for Standards and Technology, Boudler, Colorado, United States, 3 Department of Material Science and Engineering, University of Maryland, College Park, Maryland, United States, 4 , Universitat Politecnica de Catalunya, Campus Nord, Barcelona, Spain
Show AbstractThe electromagnetic response of ferroelectric thin-films at microwave frequencies is fundamental to the understanding of the dynamics of these materials, as well for their potential applications in electronics and communications. We explore the high frequency response (60 MHz-40 GHz) of lead titanate (PbTiO3) and lead zirconium titanate (Pb(Zr0.52Ti0.48)O3) thin films using swept-frequency measurements of patterned coplanar transmission lines. These measurements are combined with those of interdigitated capacitors at lower frequencies (100 Hz-100 MHz) to directly measure the frequency dependence (100 Hz-40 GHz) of the complex permittivity of the thin films. Measurements on PbTiO3 and Pb(Zr0.52Ti0.48)O3 at room temperature show a systematic decrease in εr′ at the highest measurement frequencies, which is accompanied by an increase in the εr ″. For PbTiO3, we find that εr′ is approximately 180 below 4GHz, and decreases to 110 at 40GHz.[1] These measurements allow us to probe both the effects of temperature and electric field bias on the frequency-dependent permittivity of PbTiO3 and Pb(Zr0.52Ti0.48)O3 thin films, as a means to quantitatively describe the dynamical response of these material systems.[1] N. Orloff, J. Mateu, M. Murakami, J. C. Booth, and I. Takeuchi, "Broadband Characterization of Multilayer Dielectric Thin Films," IEEE MTT-S International Microwave Symposium Digest, pp. 1177 - 1180 (2007).
9:00 PM - K10.4
Deposition Rate Effect on Critical Thickness of BaTiO3 Epitaxial Thin Film Grown on SrTiO3(001).
Masanori Kawai 1 , Daisuke Kan 1 , Seiichi Isojima 1 , Hiroki Kurata 1 , Seiji Isoda 1 , Osami Sakata 2 , Shigeru Kimura 2 , Yuichi Shimakawa 1
1 , Institute For Chemical Research, Kyoto University, Uji, Kyoto, Japan, 2 , JASRI/SPring-8, Sayo, Hyogo, Japan
Show AbstractBaTiO3 thin films epitaxially grown on SrTiO3 (001) substrates (BTO/STO(001)) are prepared with a pulsed laser deposition technique and the heterostructures are evaluated by synchrotron X-ray diffraction (SXRD) measurements and cross-sectional HAADF-TEM observations. We found that a deposition rate significantly affects the structure of the BTO/STO(001) heterointerface. In a SXRD reciprocal space map around the (301) reflection for a film grown at a low deposition rate (0.10 Å/sec.), the position of the Bragg peak from the BTO thin film is different from that of the STO substrate, suggesting the lattice strain due to the lattice mismatch (2.2 %) between the BTO and STO is completely relaxed. The cross-sectional HAADF-TEM images near the interface also reveal that edge-type misfit dislocations are located at a very close region of the BTO/STO interface. On the other hand, a BTO film grown at a high deposition rate (0.39 Å/sec.) consists of lattice-strained and relaxed structures. A broad SXRD peak originating from the lattice-strained BTO is clearly observed at a low L-index region of the (301) Bragg peak from STO. In this heterostructure, many misfit dislocations are found in a region about 6 nm away from the interface. Thus, the 6 nm-thick BTO structure is under strained and the in-plane lattice constant completely matches to that of the STO(001) substrate. The results imply that critical thickness of BTO/STO(001) can be controlled by the growth rate. We will also discuss differences in physical properties between the strained and relaxed BTO structures.
9:00 PM - K10.40
Phase Transition and Dielectric Tunability of (Pb0.35Sr0.65) (Zr0.5Ti0.5)O3 Thin Films.
Naba Karan 1 , Reji Thomas 1 , Marilin Perez 1 , Rafael Pagan 1 , Ram Katiyar 1
1 Department of Physics, University of Puerto Rico, San Juan, Puerto Rico, United States
Show AbstractPb0.35Sr0.65Zr0.5Ti0.5O3 (PSZT) films were grown on Pt/ZrO2/SiO2/Si substrates by chemical solution deposition (CSD). A two-step pyrolysis followed by rapid heat treatment yielded polycrystalline crack-free films. Thicknesses of the annealed films were in the range of 310-290 nm, that were slightly reduced with annealing temperatures (550°C-750°C). Structural, morphological properties have been studied as a function of annealing temperatures. As-deposited (pyrolysed at 500°C) films were amorphous and the onset of crystallization started at 600°C and single phase films were formed at temperature as high as 700°C. Circular Pt electrodes of area 3.14X10-4 cm-2 were sputter deposited on top of the films to form Metal-Insulator-Metal (MIM) capacitors. Capacitance-voltage (CV), capacitance- frequency (CF), and current-voltage(IV) were measured as a function of temperature in the range 100 K to 550 K. Dielectric constant of the PSZT films increased with increasing annealing temperature. The transition temperature (ferroelectric to paraelectric) for the 750 oC annealed film was 238 K. Dielectric constant and loss tangent of the 750°C annealed films at room temperature were 317 and 0.022, respectively at 100 kHz. At room temperature the film showed 45% tunability at 500kV/cm and at 100kV/cm the leakage current density was 4X10-7A/cm-2. Low dielectric loss, low leakage current, high values of tunability along with almost temperature independent tunability around room temperature make the material a suitable candidate for tunable microwave device applications. Comparison of annealing effect on the electrical and dielectric properties of the thin films will be presented.
9:00 PM - K10.41
Index-guiding Thin Films of PLZT, Epitaxially Integrated with Silicon.
Ornulf Nordseth 1 , Arne Royset 2 , Thomas Tybell 1 , Jostein Grepstad 1
1 Dept. of Electronics and Telecommunications, Norwegian University of Science and Technology, Trondheim Norway, 2 , SINTEF Materials and Chemistry, Trondheim Norway
Show AbstractThe ferroelectric perovskite lead-lanthanum zirconate-titanate (PLZT) offers several functional properties attractive to optical device applications, such as low propagation losses and a large electro-optic coefficient. The case for integration of epitaxial PLZT thin films with silicon has drawn considerable interest in recent years [1-3] and is essential to application of this material in microelectromechanical systems (MEMS) and integrated optics.Thin films of Pb0.92La0.08Zr0.4Ti0.6O3 were deposited on CeO2/YSZ buffered Si(100) by on-axis radio frequency magnetron sputtering, with and without a SrRuO3 electrode layer intercalated between CeO2 and PLZT in the multilayer thin film structure. The surface topography and structural properties of the different oxide layers were examined with atomic force microscopy and x-ray diffraction (XRD) analysis. The XRD measurements show epitaxial growth of PLZT and SrRuO3 with a full width at half maximum of approximately 0.3 degrees for rocking curves taken around the respective 00l peaks, thus indicating films of good crystalline quality. The films exhibit smooth surfaces with a measured root-mean-square roughness of less than 5 nm.Finite difference time domain (FDTD) simulation of light propagation in PLZT films grown on this buffered silicon substrate suggests that optical absorption in the semiconductor is considerably reduced when thick CeO2 buffer layers are adopted. The low-index buffer layer results in index guided in-plane transmission for waveguides defined in PLZT. The optical properties of the ferroelectric films were experimentally investigated using rutile prism coupling of red and infrared light into such waveguiding structures. [1] R. Ramesh et al., Appl. Phys. Lett., 63, 3592 (1993). [2] S. G. Ghonge et al., Appl. Phys. Lett., 64, 3407 (1994). [3] M. Kondo et al., Fujitsu Sci. Tech. J., 38, 46 (2002).
9:00 PM - K10.42
Ferroelectric Thin Films Grown on Base-Metal Foils for Embedded Passives.
Beihai Ma 1 , Dokyun Kwon 1 , Manoj Narayanan 1 , U. (Balu) Balachandran 1
1 Energy Sysytems Division, Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractDevelopment of electronic devices with greater performance and smaller size requires passive components to be embedded in a printed wire board (PWB). The “film-on-foil” approach is the most viable method. We have deposited high-permittivity ferroelectric thin films on base metal foils by chemical solution deposition to form film-on-foil capacitor sheets. These capacitors could be embedded into PWBs. However, the formation of a parasitic low-permittivity interfacial oxide layer during thermal processing of the ferroelectric material significantly reduced the capacitance density. Two approaches were taken to overcome this problem. In the first, a conductive oxide buffer layer acting as a bottom electrode was inserted between the ferroelectric film and the metal foil to hinder formation of the deleterious interfacial oxide. In the second, high-temperature processing was done under low oxygen partial pressures such that no interfacial oxide was formed. We have grown high-quality ferroelectric (Pb,La)(Ti,Zr)O3 thin films on Ni and Cu foils. Capacitance densities as high as 1.5 µF/cm2 were obtained with breakdown fields >1.2 MV/cm. Scaling of the ferroelectric film permits operating voltages of 600 V. Dielectric properties as a function of foil electrode, fabrication method, and thickness will be discussed.Work was supported by the U.S. Department of Energy, Office of FreedomCAR and Vehicles Technology Program, under Contract DE-AC02-06CH11357.
9:00 PM - K10.43
Occurrence of Anti-Ferroelectric Phase in Fe Modified PLZT (8/65/35).
Ahamad Mahamad 1 , Yadav Kanhayya Lal 1
1 Physics, Indian Institute of Technology, Roorkee, Uttaranchal, India
Show Abstract9:00 PM - K10.45
Investigation of Electrical and Optical Properties of Pb1/2Sr1/2TiO3 Nano-ceramics.
Iris Rivera 1 , Ashok Kumar 1 , Frank Mendoza 1 , Ganpat Sharma 1 , Ram Katiyar 1
1 Department of Physics, University of Puerto Rico, San Juan, Puerto Rico, United States
Show AbstractPb1/2Sr1/2TiO3 (PST) nano-ceramics have been prepared with solid-state reaction technique using high-energy ball mill. PST shows low dielectric constant, sharp ferroelectric phase transition with very low dielectric loss above room temperature. These low dielectric loss behaviors continued in the paraelectric phase. We observed soft mode behavior below ferroelectric phase transition and breaking in the local symmetry in paraelectric regions. We studied frequency and temperature dependence of the impedance, electric modulus and ac conductivity of PST in the range of 100 Hz to 1 MHz and 100 to 650 K respectively. We observed two distinct electrical responses attributed to the grain effects and grain boundary effects in the investigated temperature regions. The role of grain boundary becomes more prominent with increase in temperature. In the paraelectric regions, the local symmetry breaking was associated with the polar clusters localized at the grain boundaries. The master modulus spectra showed active role of the grain boundary capacitance in conduction mechanism above the Curie temperature. The frequency dependent conductivity data were fitted in the Jonscher`s power law, , and the results showed evidence of two types of conduction process at elevated temperatures i.e. the low frequency conductivity is due to long range ordering (frequency independent) and high frequency conduction is due to the localized hopping mechanism.
9:00 PM - K10.46
Microstructure and Strain Relaxation of Epitaxial PrScO3 Thin Films Grown on (001) Vicinal SrTiO3 Substrates.
Yanbin Chen 1 , Michael Katz 1 , Xiaoqing Pan 1 , Chad Folkman 2 , Rasmi R Das 2 , Chang Beom Eom 2
1 Department of Materials Science and Engineering, University of Michigan, Ann Arbor, 48109, Michigan, United States, 2 Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, 53706, Wisconsin, United States
Show AbstractRecently, rare-earth scandates (such as GdScO3, DyScO3) have been utilized as substrates on which to grow ferroelectric perovskites (such as BaTiO3). BaTiO3 thin films have been grown coherently on GdScO3 and DyScO3 substrates, which induce compressive strains in the BaTiO3 films. These strained BaTiO3 thin films show enhanced remnant polarization and ferroelectric transition temperature. When using PrScO3, another rare-earth scandate, as a template, BaTiO3 thin films are under biaxial tensile strain because the pseudo-cubic lattice parameter of PrScO3 is slightly larger than that of BaTiO3. The strained BaTiO3 thin films have a-axis domains, as predicted by thermodynamic calculation. In this work, we studied the microstructure and strain relaxation of epitaxial PrScO3 films grown on miscut (001) SrTiO3 substrates by transmission electron microscopy. PrScO3 films grown on highly miscut (>1 degree) SrTiO3 substrates are single domain films, fully strain-relaxed via interfacial misfit dislocation formation, small angle tilt boundaries, and antiphase boundaries bounded by partial dislocations. In contrast, strain in PrScO3 films on low miscut (<0.2 degree) SrTiO3 substrates is relaxed by misfit dislocation formation as well as the formation of six different crystallographic domains. The formation of single domain PrScO3 films on high angle miscut substrates could be due to interfacial strain-energy minimization.
9:00 PM - K10.47
Structural and Dielectric Studies of La Modified Lead Scandium Niobate Ceramics.
Margarita Correa 1 , Ashok Kumar 1 , Ram Katiyar 1
1 Physics, University of Puerto Rico, San Juan, Puerto Rico, United States
Show AbstractRelaxor materials posses remarkable properties with potential applications in MEMS and energy storage devices. Although these have been extensively studied, the fundamental physics is still poorly understood. Disordered Lead Scandium Niobate (PSN) is a typical relaxor that undergoes a relaxor to ferroelectric phase transition on decrease in temperature. However we have found that even a small substitution of Pb by La atoms changes drastically their dielectric properties. On 5% substitution by La, the temperature variation of dielectric constant corresponds to a canonical relaxor at zero electric field. In case of such substitution, the dielectric peaks are broad and there is strong frequency dependence with Tm varying from about 320 to 365 K. On the other hand, the freezing temperature is close to Tm (Tf=315 K) indicating a rapid frozen of polar nanoregions into a nonergodic state. The TEM studies on FIB prepared ceramic samples revealed single-phase material with nano constrant regions up to 10 nm apparent sizes. Raman spectra showed a shift to lower frequencies of F2g mode and changes in intensities and linewidths of the dirty modes on increase in La substitution. We have also studied microstructure-property relationship for up to 20 % La substitution on PSN using dielectric, TEM, and Raman spectroscopy and the results will be presented.
9:00 PM - K10.48
Preparation and Characterization of Pb(Fe1/2Ta1/2)O3 (PFT).
Ricardo Martinez 1 , Ratnakar Palai 1 , Ram S. Katiyar 1
1 Physics, University of Puerto Rico, San Juan PR, Puerto Rico, United States
Show Abstract9:00 PM - K10.5
Substrate Defect-induced Inhomogeneity and its Effect on Ferroelectric Properties of Strained BaTiO3 Thin Films.
Ho Won Jang 1 , Chad Folkman 1 , Ying-Hao Chu 2 , Ramamoorthy Ramesh 2 , Chang-Beom Eom 1
1 Materials Science and Engineering, University of Wisconsin-Madison, Madison, Wisconsin, United States, 2 Physics and Materials Science & Engineering, University of California-Berkeley, Berkeley, California, United States
Show Abstract9:00 PM - K10.50
Electronic States in Bi4-xLaxTi3O12 Thin Films and Film/Si Interfaces.
Atsushi Kohno 1 2 , Takayuki Tajiri 1
1 Department of Applied Physics, Fukuoka University , Fukuoka Japan, 2 SEAS, Harvard University, Cambridge, Massachusetts, United States
Show AbstractFerroelectric Bi4-xLaxTi3O12 (BLT) thin films have been formed directly on silicon substrate at 550 °C by sol-gel and spin-coating techniques. However, in capacitance-voltage characteristics of as-fabricated Au/sub-100 nm-thick BLT/p-Si (metal-ferroelectric-semiconductor) structures we had seen the flat-band voltage shift caused by undesirable positive charges and the frequency dispersion by the interface fast states at the BLT/Si interfaces. A low-temperature post-annealing at 400 °C improved the film properties and the electron-trap states at the interface in the Au/BLT/p-Si structures. X-ray photoelectron spectroscopy (XPS) has indicated that the oxygen vacancies were diminished by the low-temperature post-annealing. By repeating of Ar+ etching and low-temperature annealing we analyzed the interfacial oxide and the electronic states near the interface without the increase of the interfacial oxides. The changes in the valence band and O1s loss spectra were observed near the interface.
9:00 PM - K10.51
An Improvement in C-V Characteristics of the Metal-ferroelectric-insulator-semiconductor (MFIS) Transistor Using a Pt/Bi3.15Nd0.85Ti3O12/SrTiO3/Si Structure.
Yongyuan Zang 1 , Dan Xie 1 , Yong Ruan 1 , Tianling Ren 1 , Litian Liu 1
1 Institute of Microelectronics, Tsinghua Univeristy, Beijing China
Show Abstract9:00 PM - K10.52
Effective Thickness and Dielectric Constant of Interfacial Layers of Pt/Bi3.15Nd0.85Ti3O12/SrRuO3 Capacitors.
Hao Yang 1 , N. Suvorova 1 , M. Jain 1 , M. Hawley 1 , P. Dowden 1 , R. DePaula 1 , C. Lu 2 3 , Q. Jia 1
1 Superconductivity Technology Center, Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 2 Department of Materials Science and Engineering, Hubei University, Wuhan China, 3 Department of Physics, Qingdao University, Qingdao China
Show AbstractEpitaxial c-axis-oriented Bi3.15Nd0.85Ti3O12(BNT) thin films with thickness ranging from 150 to 350 nm were deposited on conductive SrRuO3 (SRO) on (001) SrTiO3 substrates by pulsed laser deposition. The top Pt electrode was deposited by sputtering to construct a capacitor Pt/BNT/SRO. We have evaluated the effective thickness (ti) and dielectric constant (εi) of interfacial layers at the Pt/BNT and BNT/SRO interfaces based on the optical refractive index of the BNT layer and the capacitance-frequency as well as the current-voltage characteristics of the capacitors. Using a series capacitor model, we have found that the dielectric constant of bulk BNT and the ti/εi ratio are 586 and 1.46 nm, respectively. Knowing the optical dielectric constant (εopt) and the product of εoptti of BNT thin films, we have estimated that the effective thickness and dielectric constant of the interfacial layers are 20.1 nm and 13.7, respectively.
9:00 PM - K10.53
Structural and Ferroelectric Properties of Bi4-xCoxTi3O12 Thin films by Sol-Gel process
Ricardo Melgarejo 1 , Maharaj Tomar 1 , Segundo Jauregui 1 , Ram Katiyar 2
1 Physics, University of Puerto Rico, Mayaguez, Puerto Rico, United States, 2 Physics, University of Puerto Rico, San Juan, Puerto Rico, United States
Show AbstractCobalt-substituted Bi4Ti3O12 (i.e., Bi4-xCoxTi3O12) were synthesized by sol-gel process for different compositions. Thin films were deposited on Pt (i.e., Pt/TiO2/SiO2/Si) substrate by spin coating. Materials were characterized by x-ray diffraction and Raman spectroscopy. This study indicates that the material makes a solid solution for the compositions: x = 0.00, 0.05, 0.10, 0.15, and 0.20, where a Co ion replaces the Bi site. The prominent effect of Co substitution is observed in low-frequency Raman modes. Sol-gel derived thin films of Bi4-xCoxTi3O12 on a Pt substrate and post annealed at 700°C were tested for ferroelectric response which showed remnant polarization (Pr = 16µC/cm2 for x = 0.10).The dielectric constant and the dissipation factor (tan δ) of the Bi3.90Co0.10Ti3O12 film capacitor measured at 25 0C are 431 and 0.051 respectively at a frequency of 1 MHz. These results indicate the potential application of Co substituted bismuth titanate films in non-volatile ferroelectric memories.
9:00 PM - K10.54
Ferroelectric and Dielectric Properties on Nanometric Powders of Bi4-xPrxTi3O12 and Bi4-xEuxTi3O12 Studied by HRTEM.
Abril Munro 1 4 , Eduardo Martinez 2 , Jorge Mata 3 , Jesus Siqueiros 4
1 Postgrado en Física de Materiales. Apdo. Postal 2732, CICESE-CCMC-UNAM, Ensenada, Baja California, Mexico, 4 Centro de Ciencias de la Materia Condensada., Apdo. Postal 2681, Universidad Nacional Autónoma de México, Ensenada, Baja California, Mexico, 2 Centro de Investigación en Materiales, DIP-CUCEI. Apartado Postal 2-638, CP 44281, Universidad de Guadalajara., Guadalajara, Jalisco, Mexico, 3 Departamento de Fisica. Facultad de Ciencias. Km 106 Carretera Tijuana-Ensenada, Universidad Autonoma de Baja California, Ensenada, Baja California, Mexico
Show AbstractThe stoichiometric Bi4-xRExTi3O12 (RE= Pr and Eu) ceramic system was obtained for different concentrations (x=0, 0.25, 0.5, 1.0). Crystallographic and surface morphological studies were carried out by the powder x-ray diffraction and scanning microscopy techniques. Differences in the microstructure, crystallographic features, densities and grain size were observed as functions of RE content. Measurements of dielectric constant and dielectric loss were made as functions of temperature from room temperature (RT) to 750 °C, at different frequency values. This study shows that rare earth presence in the structure modifies the transition temperature Tc and dramatically increases the dielectric constant values. This behavior is well explained in terms of the distribution of space charge. The frequency response study was carried out by means of the analysis of the complex impedance (Cole-Cole diagrams) in the RT to 750 °C temperature range for each composition. The results lead us to establish an appropriate microstructural model capable of explaining the local and non-local conduction processes that provoke the disruption of the long-range ferroelectric order by clamping effects of the domain walls due to the thermally activated diffusion of oxygen vacancies. The relaxation processes are very much conditioned by the grain and domain sizes, the degree of deformation of the lattice and the crystallites, as well as the potential barriers at the grain boundaries. Values of the activation energy corresponding to the different relaxation processes were determined from an Arrhenius law fitting of experimental data, identifying thus the involved mechanisms in excellent agreement with those obtained from the temperature response. Well defined BIT nanostructures produced as a consequence of the synthesis method were observed. The nanostructured complexes were analyzed by high-resolution transmission electron microscopy (HRTEM) and electron diffraction to determine the crystallographic changes and their influence on the electrical properties. This work is partially supported by CONACyT Mexico, projects 47714-F and 40604-F and DGAPA-UNAM projects IN116703 and IN100903.
9:00 PM - K10.55
Measurement of the Dispersion of the Electrooptic Coefficient in Sillenite Crystals.
Nikolaos Deliolanis 1 , Anastasios Efraimidis 1 , Evaggelos Vanidhis 1
1 Physics, Aristotle University of Thessaloniki, Thessaloniki Greece
Show Abstract9:00 PM - K10.56
Effect of B Site Substitution in Perovskite Layers of Bismuth Layered Structured SrBi4Ti4O15.
Guduru Prasad 1 , M.Lakshmipathi Rao 1 , G.Subrmanya Kumar 1 , K. Madhavi 1
1 Department of Physics, Osmania University, Hyderabad, Andhra Pradesh, India
Show Abstract9:00 PM - K10.58
Phase Field Modeling of Ferroelectric Thin Films with Space Charge.
Nathaniel Ng 1 , Rajeev Ahluwalia 2 , Haibin Su 1 , Freddy Boey 1
1 Materials Science & Engineering, Nanyang Technological University, Singapore Singapore, 2 , Institute of Materials Research & Engineering, Singapore Singapore
Show Abstract9:00 PM - K10.6
Distribution of Oxygen Vacancies in BaTiO3 based MLCC Probed by Raman Spectroscopy.
Ken Nishida 1 , Hiroshi Kishi 2 , Hiroshi Funakubo 3 , Takashi Katoda 4 , Takashi Yamamoto 1
1 Department of communications Engineering, National Defense Academy, Yokosuka Japan, 2 General R&D Laboratories, TAIYO YUDEN Co., Ltd., Gunma-gun Japan, 3 Department of Innovative and Engineered Materials, Tokyo Institute of Technology, Yokohama Japan, 4 Department of Electronic and Photonic Systems Engineering, Kochi University of Technology, Kami Japan
Show AbstractMulti-layer ceramics condenser (MLCC) is one of the most widespread electronic devices. Therefore, it has been required to performance and reliability, which are affected by defects in the MLCC. MLCC is fired in reductive atmosphere or in the vacuum during device process and it is speculated that the oxygen vacancy is generated in BaTiO3. Since this oxygen vacancy moves in device under applying the DC bias, which might depredate the insulation property of MLCC so that it is pointed out to be one of the important issues in the reliability and in the life.However, it is very difficult to evaluate the amount and the distribution of oxygen vacancy. Then, we propose Micro-Raman spectroscopy as the evaluation method for oxygen vacancy in the MLCC. The MLCC with Ni internal electrode was used as the sample and its composition was 100BaTiO3-0.3MnO-3.5MgO-0.75Ho2O3-1.5BaSiO3. Raman spectra were measured using the Ar+ laser with 514.5 nm line for excitation source. Its irradiation power and beam spot was ~1mW and 1-µm-diameter on the sample surface. The measurement time was fixed at 150 sec.The Raman spectra of BaTiO3 in MLCC showed the typical tetragonal structure in the MLCC. Then we focused on the local structural changing to the oxygen ions site. The Raman peak related to lattice vibration of oxygen ions (the B1-mode) was observed around 305 cm-1. The peak of B1-mode was hardened and broadened near the Ni electrodes compared to the median center between Ni electrodes. It shows that the oxygen vacancies were localized near Ni electrodes. In order to reveal the behavior of oxygen vacancy under DC bias, a highly-accelerated life testing (HALT) was applied to MLCC. After HALT, the peak of B1-mode with harden and broaden was observed neat Ni electrode that was applied positive voltage. It was indicated that the oxygen vacancies were moved and concentrated around the plus electrode after DC bias applying. This would be first direct observation of oxygen vacancies moving in MLCC and it seems that it was mechanism for depredation of the insulation property of MLCC under DC bias.In addition, these observations clearly show that Raman spectroscopy has remarkable potential to evaluate the residual strain and oxygen vacancy in MLCC devices.
9:00 PM - K10.60
Damage-free Focused Ion Beam (FIB) Milled Ferroelectric Nanostructures as Building Blocks for Self-assembly.
Michael Hambe 1 , Samantha Wicks 1 , Nagarajan Valanoor 1 , Liwu Chang 2 , Marty Gregg 2
1 School of Materials Science, University of New South Wales, Sydney, New South Wales, Australia, 2 Centre for Nanostructured Media, IRCEP, School of Maths and Physics, Queen's University Belfast, Belfast, BT7 1NN UK, United Kingdom
Show AbstractFocused ion beam (FIB) milling has emerged as a powerful tool which enables ferroelectric test structures on nanometer scales to be developed. Inherent in the FIB process is the tendency for ion beam damage to occur, which can manifest as a disruption of crystal symmetry or implantation of gallium ions, which leads to the formation of non-ferroelectric– gallium oxides. Both of these effects were found to reduce if not destroy ferroelectricity. Traditionally either a top protective hard mask, which also doubles as an electrode or post-mill annealing has been used to recover the ferroelectric properties. However a fundamental limitation of such processes is that the metal overlayer severely limits nanoscale visualization of the ferroelectric domain structure by SPM techniques and annealing destroys the virgin domain state. We present a novel “protection followed by etch” method allowing nanoscale test structures to be developed without gallium implantation, thereby obviating the need for post-mill anneals. PFM images show that even grains at the walls of the milled devices are fully switchable and local strain loops confirm that the milled-grains have a higher piezoresponse magnitude as compared to clamped grains. We show how this method can be further extended to use ferroelectric patterns as templates for nanoelectronics and self-assembly.
9:00 PM - K10.61
Contrast Mechanism for the Detection of Ferroelectric Domains on the Non-Polar Faces of LiNbO3 using Piezoresponse Force Microscopy.
Tobias Jungk 1 , Akos Hoffmann 1 , Elisabeth Soergel 1
1 Institute of Physics, University of Bonn, Bonn Germany
Show Abstract9:00 PM - K10.62
Ozone Gas Generator Using Uniaxially Polarized LiTaO3 Single Crystal.
Nakanishi Yoshikazu 1 , Junko Ide 2 , Jun Kondo 2 , Shinji Fukao 1 , Katsumi Handa 2 , Tatunori Tochio 3 , Yoshiaki Ito 2 , Akikazu Tanaka 4 , Shinzo Yoshikado 1
1 Electronics, Doshisha University, Kyotanabe, Kyoto, Japan, 2 Institute for Chemical Research, Kyoto University, Kyoto Japan, 3 , Keihanna Interaction Plaza Incorporated, Kyoto Japan, 4 , Sumitomo Metal Mining Co. Ltd., Tokyo Japan
Show Abstract9:00 PM - K10.63
Dielectric Properties of Single Crystal Ln2Ti2O7 (Ln = Rare Earth Elements Ln3+ and Y3+) Pyrochlores.
Samantha Yates 1 2 , Christopher Stanek 1 , Maria Sandoval 1 , Ken McClellan 1 , Juan Nino 2
1 Structure/Property Relations, Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 2 Materials Science and Engineering, University of Florida, Gainesville, Florida, United States
Show AbstractSingle crystals permit more precision in structure determination and anisotropic material property measurements. This work investigates the effect of composition on the crystal structure and dielectric properties among a series of single crystal Ln2Ti2O7 (Ln = rare earth elements Ln3+ and Y3+) compounds. Single crystals of the Ln2Ti2O7 compounds were synthesized using the optical float zone technique and the resulting crystal structures were analyzed. Although compounds Lu2Ti2O7 through Sm2Ti2O7 crystallize in the typical pyrochlore structure (space group Fd3m) the Ln:Ti cationic mismatch becomes large enough at Nd:Ti that a monoclinic distortion occurs for compounds Nd2Ti2O7 through La2Ti2O7 (space group P21). Dielectric measurements were then performed on harvested samples over the frequency range of 1 kHz to 1 MHz and the temperature range of 115 K to 475 K. Finally, the variation in dielectric constant as a function of composition has been predicted by atomic scale simulation techniques. The calculations complement experimental values as well as provide insight into the non-intuitive atomic scale phenomenon. By integrating single crystal growth, experimental characterization, and atomic scale simulation, we are able to formulate a systematic statement on the variation of dielectric constant as a function of composition in Ln2Ti2O7 pyrochlores.
9:00 PM - K10.64
SrNbO3/Nb2O5 Laminated Thin Films for Gigabit DRAM Capacitor Cell.
Yamato Masaki 1 , Hara Hikaru 1 , Tanioku Masami 2 , Kikkawa Takamaro 1
1 , Hiroshima Univ., Higashi-hiroshima Japan, 2 , Elpida Memory Inc., Higashi-Hiroshima Japan
Show AbstractFor future Gigabit DRAM capacitor application, it is necessary to reduce capacitor cell area and increase its dielectric constant. The physical thickness can not be reduced less than 7 nm due to the increase of leakage current under a constant electric field. The requirements of DRAM capacitors are higher dielectric constant εr > 30, larger energy band gap Eg > 3.5 eV, lower leakage current density j < 10-8 A/cm2 and lower equivalent oxide thickness (EOT) < 0.8 nm. It has been reported that Nb2O5 has large dielectric constant (εr=60) but small energy bandgap (Eg=3.4eV). On the Other hand, SrO has larger energy bandgap (Eg=5.3eV) but lower dielectric constant (εr=13). We investigate SrxNb1-xOy as a candidate for larger bandgap and higher dielectric constant material. We also investigate the effect of laminated structures of SrNbO3 and Nb2O5 on the electrical characteristics. SrNbO3 and Nb2O5 thin films were deposited on a platinum electrode on an oxidized silicon substrate by RF magnetron sputtering. The sputtering power was 50 W and sputtering gas pressure was 2.5 Pa (Ar / O2 = 35 / 35 sccm). The laminated films are annealed in a furnace at the temperature ranging from 500°C to 800°C in O2 ambient for 5 min. SrNbO3 amorphous thin films were obtained by 700°C annealing. From XPS energy loss spectra of deconvoluted SrNbO3 O1s peak, the band gap of SrNbO3 was determined as 3.8 eV. Leakage currents of SrNbO3, whose thicknesses were 10~60 nm, were less than 10-8 A/cm2@1V. Dielectric constant of a single layer SrNbO3 annealed at 700°C was 40 and the minimum value of EOT was 1.12 nm. The refractive indices calculated from leakage current density using the Schottky and Poole-Frenkel equations were 0.92 and 2.02, respectively. The refractive index measured by spectroscopic ellipsometry was 1.95, so that the leakage current mechanism of the SrNbO3 was Poole-Frenkel emission. Leakage current of Nb2O5 single layer films with thicknesses of 20~60 nm were larger than 10-8 A/cm2@1V. In order to reduce the leakage current, amorphous films of SrNbO3 and Nb2O5 are formed. SrNbO3 (5nm) / Nb2O5 (10nm) / SrNbO3 (5nm) and Nb2O5 (5nm) / SrNbO3 (10nm) / Nb2O5 (5nm) laminated thin films annealed at 700°C were investigated. The SrNbO3 / Nb2O5 / SrNbO3 shows lower leakage current less than 10-8 A/cm2@1V. The EOT of SrNbO3 / Nb2O5 / SrNbO3 and Nb2O5 / SrNbO3 / Nb2O5 laminated thin films were 1.15 nm and 1.20 nm, respectively. Consequently, thinner laminated films of SrNbO3 (4 nm) / Nb2O5 (2 nm) / SrNbO3 (4 nm) annealed at 700°C achieved the leakage current less than 10-8 A/cm2@1V and the minimum EOT of 0.77 nm. It is also found that stoichiometry of Sr/Nb does not affects the EOT but leakage current. The leakage current could be reduced by decreasing Nb2O5 ratio of the SrNbO3 / Nb2O5 / SrNbO3 laminated structure.
9:00 PM - K10.65
Characteristics of TiO2/Al2O3/TiO2 Sandwich Structures for Next Generation DRAM Capacitor Cell.
Hikaru Hara 1 , Masami Tanioku 2 , Masaki Yamato 1 , Takamaro Kikkawa 1
1 , Hiroshima University, Higashi-Hiroshima Japan, 2 , Elpida Memory, Inc., Higashi-Hiroshima Japan
Show AbstractRecently, it becomes very difficult for gigabit dynamic random access memories (DRAM’s) to keep sufficient capacitance per unit cell for refresh requirement and tolerance to noises. Therefore, high dielectric constant materials play an important role in the development of DRAM cell. To satisfy the requirements for both high dielectric constants and low leakage current, we focus on two dielectric materials such as Al2O3 having lager bandgap but lower dielectric constant and TiO2 having larger dielectric constant but smaller bandgap. We also investigate Al2O3-TiO2 mixed film, Al2O3/TiO2/Al2O3 and TiO2/Al2O3/TiO2 sandwich structures. Metal-Insulator-Metal (MIM) capacitor was deposited on SiO2/Si substrates. Platinum (Pt) was deposited as both top (φ=1.6 mm) and bottom electrodes. Al2O3/TiO2/Al2O3 and TiO2/Al2O3/TiO2 sandwich films were deposited by RF magnetron sputtering by use of Al2O3 and TiO2 targets. The gas mixture ratio of Ar and O2 was Ar:O2=1:1. The substrate temperature was 300°C. RF powers of sputtering for Al2O3 and TiO2 were 50 W and 150 W, respectively. The post-deposition annealing in O2 ambient was performed at the temperature of 600°C. When films contain 30% Al2O3 for these three film structures with physical thickness of approximately 10 nm, equivalent oxide thickness (EOT) of Al2O3-TiO2 mixed film and TiO2/Al2O3/TiO2 sandwich film were 1.16 and 1.33, respectively, which were 65-75% of Al2O3/TiO2/Al2O3 sandwich film. The measured voltages applied to the TiO2/Al2O3/TiO2 sandwich film at the current density of 1×10-8 A/cm2 was 1.95 V, which was 1.6 times as large as the other film structures. We also investigate the difference between Al2O3/TiO2/Al2O3 and TiO2/Al2O3/TiO2 sandwich film structures for different percentage of Al2O3 of 30%, 20% and 10% with the same physical thickness of approximately 7.5 nm. The EOT of TiO2/Al2O3/TiO2 sandwich films were 0.96-0.67, which are smaller than that of Al2O3/TiO2/Al2O3 sandwich films. The applied voltages at the leakage current density of 1×10-8 A/cm2 of TiO2/Al2O3/TiO2 sandwich films were 1.36-1.4 times larger than that of Al2O3/TiO2/Al2O3 sandwich films. The EOT of 0.67 nm and the leakage current of 1×10-8 A/cm2 at 1 MV/cm were obtained for TiO2/Al2O3/TiO2 sandwich film with 10% Al2O3 whose physical thickness of 7.5 nm.
9:00 PM - K10.66
A Low Leakage Dielectric Oxide (Ti, Dy)xOy Prepared by Two Sputter Deposition Techniques.
S. Barron 1 , D. Ruebusch 1 , J. Hevey 1 , R. van Dover 1
1 Department of Materials Science and Engineering, Cornell University, Ithaca, New York, United States
Show AbstractAdvances in thin film dielectric oxides will be critical over the next few years as demands increase for thinner and more robust dielectric layers in electronic circuits. The first criteria for thin film dielectrics are often a high dielectric constant and low electron leakage currents in an applied electric field. Amorphous titania, TiO2, may meet the first criterion, with a dielectric constant of 60-80 depending on density and processing conditions, but it often displays unacceptably high leakage currents. We report on TiO2 with a 30% Dy2O3 substitution, Ti0.7Dy0.3O1.85, with a dielectric constant ~ 35 and low leakage ~ 10-6 A/cm2 at 1 MV/cm. This material is prepared by reactive RF sputtering from a metallic alloy target in an Ar/O2 atmosphere. The device structure is a metal-insulator-metal (MIM) capacitor with evaporated platinum electrodes. We have also explored metal-oxide-semiconductor capacitor structures by sputtering the Ti0.7Dy0.3O1.85 on silicon; an oxide thickness equivalent to 2.88 nm of SiO2 has a leakage of 5 x 10-6 A/cm2 at Vg=2 V. An adventitious SiO2 layer can form on Si when sputtering in an oxygen atmosphere, however; so we have additionally explored the properties of Ti0.7Dy0.3O1.85 MIM capacitors formed by sputtering the metals in an inert atmosphere, followed by post-deposition in-situ oxidation. A thin metal layer is sputtered in an argon atmosphere on an unheated substrate; after deposition, the film is heated to 200 - 500 °C and exposed to flowing O2 at a moderate pressure (1 Torr). A 60 nm film is fully oxidized at 450 °C in 20 minutes. The post-deposition oxidized films have properties almost identical to the reactively sputtered ones and, in fact, support a charge of 5 μC/cm2 with a leakage of ~ 1 mA/cm2. We anticipate that thinner films may be fully oxidized at lower temperatures in less time, and that by tuning this process we may be able to deposit a thin (Ti, Dy)xOy film on silicon with minimum SiO2 interfacial layer.
9:00 PM - K10.67
Growth and Evaluation of Magnetoelectric Cr2O3 Single Crystal Thin Films.
Nobuyuki Iwata 1 , Takeshi Asada 1 , Shunpei Ootsuki 1 , Hiroshi Yamamoto 1
1 Electronics & Computer Science, College of Science & Technology, Nihon University, Chiba Japan
Show AbstractCr2O3 is the most representative magnetoelectric (ME) material, the ME properties of which are investigated in detail. The magnitude of ME effect generally depends on crystallinity and crystallographic axis, hence single crystal Cr2O3 film growth was studied on sapphire single crystal substrate which has a same crystal structure to that of Cr2O3 with approximately +4% lattice mismatch for application to oxides devices. Used substrates were (1-102) (R-)sapphire, (11-20)(a-)sapphire and (0001)(c-)sapphire.Cr metal target was sputtered using DC-RF magnetron sputtering method. Substrates were etched with HF : H2O = 1 : 7 solution, immediately annealed at 1000 degree C for 12 h. Growth conditions of substrate temperature, DC current, RF power, total pressure, the ratio Ar to O2 flow were 575±10 degree C, 0.04 A, 100W, 0.26 Pa, Ar : O2 = 4 : 1 sccm. On R-sapphire approximately 200×500 nm2 rectangle grains grew with a step-terrace structure. Almost all of those grains were coalesced, and except for the coalesced grains grain boundaries appeared with deep pits. The depth was 15 nm at most. Average roughness Ra was 1.3 nm. On a-sapphire two-dimensional growth was observed with the bunching steps less than five lattice constant. Terrace size was 50×200 nm2. The Ra was 1.1 nm. Precipitates were also observed with 50 nm in diameter . On c-sapphire protrusions, the figure of which was rectangle, appeared on a flat film surface. The rectangle protrusions were supposed to have a crystal face and aligned along the six-fold directions. The Ra was 2.9 nm. The surface morphology was distinct as comparing that on R-, a- with that on c-sapphire. The film step-terrace structure was derived from that of the substrate on R- and a-sapphire, however not on c-sapphire, even though surface structures of each substrate were almost same with 100-500 nm terrace width, 0.2-0.35 nm step height, and a lattice mismatch of +3.86 % ~ +4.47%. It is expected that the different morphology is caused by a different surface potential. The surface is terminated with oxygen on R- and a-sapphire and then total charge is zero. On c-sapphire the surface is terminated with aluminum atom and the surface is charged with plus. Therefore the film surface is expected to be different. The ME effect and film growth will be discussed more.
9:00 PM - K10.68
Surface Chemistry Approach to the Heteroepitaxy of Alkaline Earth Oxide Layers on Si(100)-2x1.
Brian Willis 1 , Dimitri Skliar 1
1 Chemical Engineering, University of Delaware, Newark, Delaware, United States
Show AbstractCrystalline oxide-perovskite layers integrated with semiconductors are promising materials for novel electronic and optical device applications. To date, the highest quality materials have been grown using molecular beam epitaxy methods, but these methods have disadvantages for practical application of crystalline oxide device technologies. There is interest in the development of new processing methods for the integration of crystalline oxides with semiconductors. Homoepitaxy of crystalline oxide thin films can be achieved with chemical vapor deposition methods, but integration with semiconductors requires a level of control over the surface chemistry that has not yet been demonstrated. In this paper, we explore the surface chemistry aspects for a chemistry-based approach such as chemical vapor deposition or atomic layer deposition to the nucleation of crystalline oxides directly on the semiconductor surface. Previous surface science data in the literature has demonstrated that alkaline earth oxides are good templates for the heteroepitaxy of oxide layers on silicon, and the focus of this paper is the growth of strontium oxide layers (SrO) on Si(100)-2x1. Three unique strategies have been investigated for the chemistry-based growth of crystalline oxides including: (1) direct reaction of the metal bearing precursor with the Si(100)-2x1 surface, (2) reaction of the precursor with a water templated surface, H2O-Si(100)-2x1, and (3) alkaline earth catalyzed oxide desorption with a chemical vapor deposition/ atomic layer deposition grown SrO layer. Single molecule resolution UHV-STM investigations of the adsorption of the precursor ligand demonstrate an unfavorable interaction for the first approach, but the other two approaches are promising. Reflection high-energy electron diffraction, Rutherford backscattering spectrometry, and X-ray photoelectron spectroscopy data show that a dimer-ordered layer of ¼ monolayer metal oxide coverage with an atomically abrupt oxide/semiconductor interface is achieved on water templated Si(100)-2x1. Computational chemistry models show the coverage to be limited by adsorbate-adsorbate interactions, but strategies to overcome these limitations are presented. The catalytic oxide desorption is also a promising route to heteroepitaxy. Auger electron spectroscopy, Rutherford backscattering spectrometry, and low energy electron diffraction data are presented to demonstrate the successful growth of a 3x reconstructed Sr/Si(100) interface via chemistry-based deposition. Issues related to the surface chemistry of the alkaline earth metal precursors will also be discussed.
9:00 PM - K10.7
Active Plasmonic Devices on Barium Titanate Thin Films.
Matthew Dicken 1 , Henri Lezec 1 , Luke Sweatlock 1 , Harry Atwater 1
1 Applied Physics, California Institute of Technology, Pasadena, California, United States
Show AbstractIntegration of electro-optic materials with integrated silicon photonics will allow for active control of devices (cavity resonant frequency, photonic crystal waveguide dispersion) to be developed in a manner compatible with CMOS processes, e.g, similar to those that currently employ barium strontium titanate capactors in front-end processing. Ferroelectric perovskite oxides, such as barium titanate (BTO), are interesting candidates for thin film optical devices because of their large electro-optic coefficients and electrically switchable structural and optical properties. The ability to electrically modulate the refractive index of BTO thin films has previously yielded electro-optic waveguide modulators and interferometers fabricated on bulk MgO oxide substrates. We have extended the idea of electro-optic materials integration to include plasmonic devices.It has been known for some time that metal/insulator interfaces support propagating plasmon modes. It is possible to couple light into and out of these modes using slits and grooves as diffraction gratings. We have incorporated these ideas with thin films of optically active materials in an attempt to modulate guided plasmons at the interface. Using barium titanate thin films deposited on a conductive substrate we can design devices that will modulate the optical index at the metal/insulator interface. We will present results for active optical devices such as slit-slit pairs and periodic hole arrays in gold films on barium titanate.Optical engineering using modal analysis and FDTD simulations has been used to design the mode profile and predict the electro-optic response of Au/BTO/SRO plasmonic structures. We will discuss measurements of loss and dispersion in BTO optical and plasmonic waveguides and the potential for creating tunable photonic crystal resonators in these optically active oxides.
9:00 PM - K10.70
Thin Layer Multilayer Capacitors Fabricated by Chemical Solution Deposition.
Song Won Ko 1 , Hajime Nagata 1 , Clive Randall 1 , Susan Trolier-McKinstry 1 , Mike Randall 2 , Pascal Pinceloup 2
1 , Pennsylvania State University, University Park, Pennsylvania, United States, 2 , KEMET Electronics Corporation, Fountain Inn, South Carolina, United States
Show Abstract9:00 PM - K10.71
Ferroelectric Polarization and Switching Response of CsNO3: PVA Composite Films.
Koppole Sekhar 1
1 Physics, IIT Roorkee, Roorkee India
Show Abstract9:00 PM - K10.72
Ferroelectric Polymers with Tunable Permittivity for Electric Energy Storage.
Jason Claude 1 , Yinying Lu 1 , Qing Wang 1
1 Department of Materials Science and Engineering, Pennsylvania State University, University Park, Pennsylvania, United States
Show AbstractHigh permittivity polymers are attractive materials for electric energy storage for a wide range of applications. Ferroelectric polymers based on vinylidene fluoride (VDF), trifluoroethylene (TrFE), and chlorotrifluoroethylene (CTFE) exhibit some of the highest permittivities among polymers. Our work has demonstrated, for the first time, the ability to precisely control the polymers’ permittivity from 10 to 50 through a unique synthetic approach.The maximum energy density of a dielectric polymer is controlled by the polymers’ permittivity and electrical breakdown strength with higher values of both producing a higher energy density. With the goals of improving energy density, the influence of molecular weight on the electrical breakdown strength of poly(vinylidene fluoride - chlorotrifluoroethylene) P(VDF-CTFE) is explored. Multiple possible breakdown mechanisms are examined and related to the polymers’ electrical, mechanical, and structural properties.Four different ferroelectric polymers with number average molecular weights (Mn) ranging from 136 to 294 kg/mol of composition 78.4 mol% VDF and 21.6 mol% CTFE were suspension polymerized with polydispersities ranging from 1.10 to 1.72. The use of suspension polymerization showed a five-fold increase in Mn over a solution based method allowing a greater range of molecular weights to be explored. The thermal and low electric field dielectric properties of the polymers were nearly identical with a melt temperature of 113C and permittivity of 9.3 at 1 kHz. The calculated degree of crystallinity and crystallite sizes from x-ray diffraction are also nearly identical for all the polymers with values of 7.81% and 2.71 nm respectively. Differences between the polymers were seen in the mechanical properties at both low and high strains with the mechanical properties improving as Mn increases. The DC electrical breakdown strength was measured and analyzed using a Weibull distribution with the resulting data having coefficient of determination (r^2) parameter of at least 0.89. The breakdown strength in general was found to increase with increasing Mn and decreasing temperature. The breakdown mechanism is hypothesized to be mainly electromechanical resulting from the compressive force of the parallel electrodes on the polymer. The breakdown strength was found to scale with the polymers’ measured modulus and yield stress. Quantitative calculations at room temperature accurately predict the Weibull characteristic electrical breakdown field with an error of less than 11% based on knowledge of the polymers’ low frequency permittivity and yield stress.
9:00 PM - K10.73
Storage and Decay of Charges for Polypropylene Ferroelectret Films with Macroscopy Dipoles.
Zhongfu Xia 1 , Feipeng Wang 1 , Xiaoqing Zhang 1 , Jinfeng Huang 1
1 Physics Department, Tongji University, Shanghai China
Show Abstract9:00 PM - K10.76
Effect of Diamagnetic A2+ Substitution on the Magnetic and Ferroelectric Properties of the Bi1-xAxFeO3 Multiferroics.
V. Khomchenko 1 , D. Kiselev 1 , Y. Pogorelov 2 , J. Vieira 1 , A. Kholkin 1
1 Department of Ceramics and Glass Engineering & CICECO, University of Aveiro, Aveiro Portugal, 2 IFIMUP/ Department of Physics, University of Porto, Porto Portugal
Show Abstract9:00 PM - K10.77
The Origin of Photocurrent in Polycrystalline PZT Films.
Lyuba Delimova 1 , Valentin Yuferev 1 , Anatolii Petrov 2 , Valentin Afanasjev 2 , Igor Grekhov 1
1 Solid-State Electronics Division, Ioffe Physicotechnical Institute of the Russian Academy of Sciences, St-Petersburg Russian Federation, 2 Microelectronics Department, St-Petersburg Electrical Engineering University "LETI", St-Petersburg Russian Federation
Show AbstractAn effect of interfaces on the properties of submicron ferroelectric M/Pb(ZrTi)O3(PZT)/M capacitors is usually explained by the existence of thin defective layers adjacent to electrodes. In this case, the M/PZT/M capacitor is a sandwich, where the low- and high-permittivity PZT layers are connected in series. In many experiments, however, the same polycrystalline PZT film prepared with Pb excess shows good ferroelectric (FE) properties despite high dielectric losses and leakage. These facts are poorly consistent with the series scheme of the capacitor. We have measured steady-state short-circuit photocurrent Iph in polycrystalline Pt/PZT/Ir structures with Pb excess generated by light with wavelengths λ > 0. 4 μm. The measured photocurrent was controlled by the magnitude of FE polarization and always was directed opposite to polarization. It was shown however, that Iph was not a depolarization current of the FE. To explain these observations, we assume that Pt/PZT/Ir capacitor is heterogeneous medium consisting of PZT grains and semiconductor PbO phase segregated on PZT grain boundaries during the PZT formation. The PZT and PbO phases are connected in parallels between the electrodes, and we propose that the FE properties of the structure are controlled by PZT grains, while the PbO phase is responsible for carrier transport. Due to vacancies of both types, PbO can be considered as a strongly compensated intrinsic semiconductor with the forbidden energy gap ~2 eV. Far from electrodes, the current channel formed by PbO phase has a 2D configuration surrounding a PZT grain from all sides, the channel thickness is ~5 nm. Due to imperfect shape of PZT grains, the FE polarization charge of the grains can be compensated by a metal electrode only partly. Within this model, the uncompensated polarization charge of PZT grains creates electric field acting on the carriers in the PbO channels. This field is directed opposite to the FE polarization and responsible for the observed photocurrent in the film. Calculations show that in a 100-nm-thick PZT film with the remnant polarization ~20 µC/cm2, the field is ~2*103 V/cm. Photoexcited electrons and holes drift in the field of the channel towards the top and bottom electrodes, respectively. Near the electrodes, the carriers overcome a potential barrier, which is less than kT and reach the metals producing in the external circuit the photocurrent. The carrier transit time through the channel is ~10-8 s for the carrier mobility of 0.1 cm2/V*s. In the stationary mode, the carriers never can compensate the polarization charge of the grains, since they are exported from the channel to the electrodes by the current with the rate of their excitation. The developed model allows us to study a contribution of polarization charge into current-voltage characteristics of M/PZT/M structures. The effects of the PbO content, channel geometry, electrode materials on the conduction of polycrystalline PZT films are discussed.
9:00 PM - K10.78
Dielectric Properties of Mn-doped CaCu3Ti4O12 Ceramics.
Ming Li 1 , Antonio Feteira 1 , Derek Sinclair 1 , Anthony West 1
1 , The University Of Sheffield, Sheffield United Kingdom
Show Abstract9:00 PM - K10.79
Composition, Cation ordering, Conductivity and Dielectric Loss Relationships in BaCo1/3Nb2/3O3 Microwave Dielectric Ceramics.
Ming Li 1 , Antonio Feteira 1 , Derek Sinclair 1
1 , The University Of Sheffield, Sheffield United Kingdom
Show Abstract9:00 PM - K10.8
Influence of A-site Substitution on the Microstructure and Dielectric Properties of BaZr0.1Ti0.9O3 Ceramics.
Bhaskar Reddy Sudireddy 1 2 , Prasad Rao Kalvala 3 , Mamidanna Rao 1 2
1 Physics, Indian Institute of Technology, Chennai, TamilNadu, India, 2 Materials Science Research Centre, Indian Institute of Technology, Chennai India, 3 Metallurgical and Materials Engineering, Indian Institute of Technology, Chennai India
Show Abstract9:00 PM - K10.80
Low Temperature Growth of Epitaxial Multiferroic BiFeO3 Films by Metalorganic Chemical Vapor Deposition.
Guoren Bai 1 , Orlando Auciello 1 2
1 Materials Science Division, Argonne National Laboratory, Argonne, Illinois, United States, 2 Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois, United States
Show Abstract9:00 PM - K10.9
Structural, Dielectric, and Electrical Properties of Relaxor BaZrxTi1-xO3 Thin Films Grown by Polymer Assisted Deposition Technique.
Menka Jain 1 , E. Bauer 1 , H. Yang 1 , H. Lou 1 , A. Burrell 1 , T. McCleskey 1 , R. DePaula 1 , Q. Jia 1
1 Materials Physics and Applications Division, Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Show AbstractThere is an increased interest in BaZrxTi1-xO3 (BZT), a lead-free dielectric material for applications in dynamic random access memory, tunable microwave devices, and microelectromechanical systems. For Zr substitutions of 27% or greater, the phase transition becomes diffuse and relaxor like. Thin films of BZT have been studied by the sol-gel technique; however, it is very hard to prepare a stable solution as precipitates within few hours of preparation. Using polymer assisted deposition; we have successfully prepared stable solutions of BZT with various Zr contents. Highly c-axis oriented films of BZT (Zr= 27%) were deposited on LaNiO3 buffered LaAlO3 (LAO) and SrTiO3 (STO) substrates. The phi-scans on BZT (202), LAO (202), and STO (202) showed that the films were of good epitaxial quality. The orientation relationship is determined to be (001)BZT||(001)LAO and [100]BZT||[100]LAO for the film on LAO substrate. The structural, dielectric, and electrical properties of these films will be presented in detail. Successful preparation of these films with stable solution offer unique advantage over other solution techniques.