Symposium Organizers
Dhananjay Kumar North Carolina A&T State University
Valentin Craciun University of Florida
Marin Alexe Max-Planck Institute of Microstructure Physics
Kaushal K. Singh Applied Materials Inc.
GG1: Nanostructured Functional Oxide Films I
Session Chairs
Tuesday PM, April 18, 2006
Room 2018 (Moscone West)
10:00 AM - **GG1.1
Multifunctional Complex Oxide Heterostructures
Ramamoorthy Ramesh 1
1 , University of California, Berkeley, Berkeley, California, United States
Show AbstractComplex perovskite oxides exhibit a rich spectrum of functional responses, including magnetism, ferroelectricity, highly correlated electron behavior, superconductivity, etc. There exists a small set of materials which exhibit multiple order parameters; these are known as multiferroics. Using our work in the field of ferroelectrics and ferromagnetics as the background, we are now exploring such materials, as epitaxial thin films as well as nanostructures. Specifically, we are studying the role of thin film growth, heteroepitaxy and processing on the basic properties as well as magnitude of the coupling between the order parameters. In single phase multiferroic perovskites, such as BiFeO3, we have found significant enhancements in magnetism and ferroelectricity compared to bulk. Detailed measurements indicate that the enhancement in magnetism is due to a mixed Fe+2/Fe+3 state in the films, while the ferroelectric polarization is reasonably commensurate with that predicted from first principles theory. A very exciting new development has been the discovery of the formation of spontaneously assembled nanostructures consisting of a ferromagnetic phase embedded in a ferroelectric matrix that exhibit very strong coupling between the two order parameters. This involves 3-dimensional heteroepitaxy between the substrate, the matrix perovskite phase and spinel phase that is embedded as single crystalline pillars in this matrix. This epitaxial coupling is critical and is responsible for the significantly higher magnetoelectric coupling and magnetic anisotropy in such vertical heterostructures compared to a conventional heterostructure.
10:30 AM - GG1.2
Ferrimagnetic CoCr2O4 and NiFeO4 Nanopyramids by Self-Assembled Growth
Florencio Sanchez 1 , Nico Dix 1 , Ulrike Luders 2 , Jean Francois Bobo 2 , Josep Fontcuberta 1
1 , ICMAB-CSIC, Bellaterra Spain, 2 , Onera, Toulouse France
Show AbstractNanoscale fabrication of multifunctional oxides can be done by self-assembled growth. It was demonstrated in multiferroic nanocomposites of ferrimagnetic spinel CoFe2O4 nanopillars embedded in a ferroelectric BaTiO3 matrix that were epitaxially grown. The nanostructured hybrid system showed coexistence of ferroelectricity and ferromagnetism, and displayed a remarkable coupling of magnetic and ferroelectric properties not observed in ordinary multilayer structures. Understanding the growth mechanisms of these nanocomposites is essential for its controlled fabrication and optimization of properties.The growth mechanisms of spinels have been much less investigated that those of perovskites. Here we report on the self-assembled growth of three-dimensional pyramidal objects in ferrimagnetic spinel, CoCr2O4 and NiFe2O4, epitaxial films. The spinel islands [2] have a shape very similar to the SiGe pyramids and hut clusters, but detailed characterization reveals important dissimilarities. They are {111} faceted pyramids and hut clusters, and thus have a very high aspect ratio, and moreover, they maintain the shape during growth. The objects are perfectly oriented along the <110> directions and have a certain positional order along the same direction. The growth progression was investigated: at early stages strained (dislocation free) small nanometric pyramids form, which is followed by a structural relaxation and a spectacular growth of some of the objects. We demonstrate that the size of the objects (from the nanometer to the micrometer) and area coverage (from isolated pyramids to fully faceted surfaces) can be controlled by the deposition time, growth temperature and substrate used. The driving forces for the observed {111} faceted objects and surfaces, and bi-modal or single-modal size distribution are discussed.Our demonstration of self-organized growth of ferrimagnetic spinel pyramids and hut clusters of controlled size and on different surfaces may open the possibility of controlled fabrication of hybrid systems combining these ferrimagnetic structures with other functional materials. References[1] H. Zheng et al., Science 303, 601 (2004); F. Zavaliche et al., Nano Letters 5, 1793 (2005)[2] U. Lüders et al., Phys. Rev. B, 70, 045403 (2004); Nanotechnology 16, S190 (2005)
10:45 AM - GG1.3
Self-selective Epitaxial Growth of BST Films: toward Nano-composite Structure for Microwave Tunable Devices.
Tomoaki Yamada 1 , Vladimir Sherman 1 , Andreas Noeth 1 , Paul Muralt 1 , Alexander Tagantsev 1 , Nava Setter 1
1 Laboratoire de Ceramique, Ecole Polytechnique Federale de Lausanne, Lausanne Switzerland
Show AbstractA composite structure of BaxSr1-xTiO3 (BST) films with improved characteristics for tunable applications was fabricated by a self-selective epitaxial growth process. The epitaxial growth of the film on the electrode surface was selectively achieved using patterned ultra-thin amorphous BST layer that prevented the epitaxial growth of upper BST. This self built-up mechanism resulted in a columnar composite structure with keeping the growing top surface flat. In this structure, epitaxial and quasi-amorphous components are electrically connected in parallel. The epitaxial BST showed a high permittivity and a high tunability as usually reported, whereas the quasi-amorphous BST showed a significantly lower permittivity and a non-tunable behavior. The effective permittivity of the composite capacitors decreased linearly upon increasing the concentration of quasi-amorphous BST while the tunability stayed fairly unchanged even when the concentration of quasi-amorphous BST exceeded 60%, meeting the conflictive demand in microwave application of a low permittivity and a high tunability. These results accord with the theoretical parallel composite model consisting of ferroelectric and dielectric components, suggesting the enhanced performance. The details of the structural and dielectric properties, and the attempt for the nano-scale structuring are addressed.
11:00 AM - GG1.4
Growth and Properties of a New Perovskite Thin Film – PbVO3.
Lane Martin 1 , Qian Zhan 1 , Miaofang Chi 2 , Wenkan Jiang 1 , Rajesh Chopdekar 3 1 , Tong Zhao 1 4 , Nigel Browning 2 5 , Yuri Suzuki 1 6 , R. Ramesh 1 4 6
1 Materials Science and Engineering, University of California, Berkeley, Berkeley, California, United States, 2 Chemical Engineering and Materials Science, University of California, Davis, Davis, California, United States, 3 Applied and Engineering Physics, Cornell University, Cornell, New York, United States, 4 Physics, University of California, Berkeley, Berkeley, California, United States, 5 National Center for Electron Microscopy, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 6 , Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractOver the past few decades, increasing attention has been given to investigating highly correlated electron systems, understanding the fundamental interactions between structure and properties in these systems, tailoring properties in such materials, and, recently, searching for new multiferroic materials. In this direction, vanadium-based perovskites have been widely studied and have been shown to exhibit interesting relationships between electronic properties and structure, are strong candidates for multiferroic behavior, and model systems for more fundamental studies of interactions between charge, orbital, lattice, and spin degrees of freedom. We report the growth of single phase, fully epitaxial thin films of a relatively new perovskite material, lead vanadate (PbVO3) [1,2], using pulsed laser deposition. This growth realizes the first production of PbVO3 outside of high-temperature and high-pressure techniques through growth of epitaxial thin films on LaAlO3 (001), (La0.18Sr0.82)(Al0.59Ta0.41)O3 (001), and SrTiO3 (001) substrates. Structural analysis of the PbVO3 thin films using transmission electron microscopy, x-ray diffraction, and Rutherford backscattering spectroscopy reveals films that are single phase, highly crystalline, and have a tetragonally distorted perovskite structure similar to that reported previously, with a = 3.79Å and c = 5.02Å (c/a = 1.32). The large structural distortion arises due to the presence of the lone pair of electrons of the lead atom and results in a layered structure with vanadium in square pyramidal coordination. Previous studies of vanadium-based perovskites have found interesting connections between B-site valence and properties, specifically d2 systems have shown Mott insulating behavior while d1 system have shown metallic properties. Electron energy loss spectroscopy and x-ray absorption spectroscopy were used to show the stabilization of vanadium in the V4+ state, thereby proving the creation of a new d1 system for intensive physical study. Additionally, the films exhibit semiconducting behavior in the plane of the film (ab-plane) with thermally activated behavior and distinctly different properties from other d1 AVO3 (A = Sr and Ca) thin films. Studies of the magnetism in PbVO3 revealed weak ferromagnetism and slight differences between magnetism in the plane of the film and out-of-plane of the film and studies are underway to understand the cause of this behavior. [1] Shpanchenko, R.V., et.al., Chem. Mater. 16, 3267-3273 (2004).[2] Belik, A.A., et.al., Chem. Mater. 17, 269-273 (2005).
11:15 AM - GG1:Nano
BREAK
GG2: Nanostructured Multifunctional Oxide Films I
Session Chairs
Tuesday PM, April 18, 2006
Room 2018 (Moscone West)
11:30 AM - **GG2.1
Functional Oxide Films Based on Multicomponent Assembly of Nanocrystals.
Stephen O'Brien 1 , Christopher Murray 2 , Elena Shevchenko 1 2 , Dmitri Talapin 2 , Limin Huang 1 , Zhuoying Chen 1
1 Applied Physics and Applied Mathematics, Columbia University, New York, New York, United States, 2 , IBM TJ Watson Research Center, Yorktown Heights, New York, United States
Show AbstractNanocrystals can be used as building blocks to form simple ordered arrays, called superlattices, which resemble the close-packed structures of atoms in crystals or hard spheres. The procedure can be described as a co-crystallization of nanocrystal dispersions following appropriate choice of solvents, substrates and conditions for self-assembly. The superlattices that result exhibit remarkable structural and compositional diversity, representing a variety of close packed structures reminiscent of binary alloy phases, and spanning a combination of magnetic and dielectric oxides, semiconductors and metals. The methodology can be thought of as a toolkit to assemble a wide range of structures intended for generating smart materials: thin films with enhanced functionality as a consequence of nanoscale manipulation. We outline our efforts to produce ferroelectric films based on nanocrystal assembly, and ferroic films based on multi-component assembly.
12:00 PM - GG2.2
Low Field Magneto-transport Properties of (La0.7Sr0.3MnO3)0.5:(ZnO)0.5 Nanocomposite Films.
Bo Soo Kang 1 , Haiyan Wang 1 , Yuan Li 1 , Quan Xi Jia 1 , Izabela Mihut 1 , Jonathan Betts 1 , Judith MacManus-Driscoll 2 1
1 Materials Science & Technology, Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 2 Department of Materials Science and Metallurgy, University of Cambridge, Cambridge United Kingdom
Show Abstract12:15 PM - GG2.3
Chemical Vapor Synthesis of Complex Nanocrystalline Oxides
Markus Winterer 1 , Vladimir Srdic 2 , Wei Jin 1 , Alexander Kompch 1 , Thomas Weirich 3
1 Department of Engineering, University of Duisburg-Essen, Duisburg, NRW, Germany, 2 Department of Materials Engineering, University of Novi Sad, Novi Sad, Serbia, , 3 Central Facility for Electron Microscopy, Rheinisch-Westfaelische Technische Hochschule (RWTH) Aachen, Aachen, NRW, Germany
Show AbstractFunctional materials such as ferroelectrics are often based on complex materials. The synthesis of such multinary, nanocrystalline oxides is highly demanding because it requires the control of composition / stoichiometry on the level of a few thousand atoms per particle. The challenge is especially difficult in case of chemical vapor synthesis (CVS) and chemical vapor deposition (CVD) of compounds such as perovskites where often only solid precursors with low volatilities are available. We will discuss several approaches to solve this problem and report on a novel flash evaporating method to produce stoichiometric, nanocrystalline strontium zirconate from tetramethylheptanedionates. This precursor delivery method may also be applied to the chemical vapor deposition (CVD) of thin films.
12:30 PM - GG2.4
Protective and Bio-compatible Nanostructured Surfaces by CVD Techniques: Controlled Modulation of Surface and Phase Structures
Sanjay Mathur 1 , Hao Shen 1 , Sven Barth 1 , Thomas Ruegamer 1 , Eva Hemmer 1 , Jessica Altmeyer 1 , Patrick Kuhn 1 , Christian Cavelius 1
1 , Leibniz Institute of New Materials, Saarbruecken Germany
Show AbstractThin film deposition by CVD techniques plays a dominant role in the development of both protective and functional coatings, important for their technological implications. Commonly, multi-component materials are prepared from a mixture of precursors; however the efficiency of such processes is hampered by the mis-match of chemical reactivity among the precursors species. As a consequence, phase separation and elemental segregation is commonly observed in CVD deposited materials.The de-mixing of elements in multi-component systems is thermodynamically driven and sensitive to the chemical behaviour of the precursors. Transformation of precursor compounds possessing bonding features inherent to the solid-state lowers the need of diffusion and counterbalances the thermodynamic impediments. Recently, we have designed several new metal-organic systems and demonstrated their suitability to deposit corrosion-resistant and bio-compatible coatings on metallic and non-metallic substrates. For instance, different Mg-Al alkoxides, [MgAl2(OPri)8], [MgAl2(OBut)8] and [MgAl2(OBut)4H4] were used as molecular precursors to deposit MgAl2O4 spinel films. The growth parameters and the application potential of the MgAl2O4 deposits as corrosion-resistance was found to be governed by the intrinsic chemical configuration of the precursors that determine the microstructure and protective properties of the barrier coatings. A novel precursor, [FeIIFe2III(OBut)8], containing both Fe(II) and Fe(III) centres in the ratio necessary for the magnetite composition was developed for selective growth of epitaxial magnetite films. The preservation of valence and stoichiometry was effectively enforced by employing a molecular scaffold with appropriate Fe(II): Fe(III) stoichiometry (1:2) and preformed FeII–O(R)–FeIII units. Nanostructured iron oxide coatings were examined towards their cell compatibility. The experimental findings suggest that cell differentiation is positively influenced by the nano-topography and phase structure of the films.This talk will focus on the controlled modulation of surface composition (both structural and chemical) to achieve enhanced performance and combination of functional properties.
12:45 PM - GG2.5
Magneto-Optical Characterization of Multiferroic Thin Film Nanostructures
Matthew Corbo 1 , H. Zheng 1 , V. von Hinten 2 , E. Marinero 3 , Y. Suzuki 1 , R. Ramesh 1
1 Materials Science & Engineering, University of California, Berkeley, Berkeley, California, United States, 2 Department of Technical Physics, University of Wurzburg, Wurzburg Germany, 3 , Hitachi San Jose Research Laboratory, San Jose, California, United States
Show AbstractWe have synthesized and characterized epitaxial thin films of BiFeO3-CoFe2O4 (BFO-CFO) and BaTiO3-CoFe2O4 (BTO-CFO) nanostructures on SrTiO3 (001) oriented substrates using pulsed laser deposition. The perovskite and spinel materials are highly immiscible and therefore the films spontaneously decompose into a composite multiferroic material with ferrimagnetic (CFO) nanopillars embedded in a ferroelectric (BFO, BTO) matrix during growth. We have observed that the size, aspect ratio and spatial density of nanopillars are strongly dependent on the growth parameters, namely temperature, growth rate and volume ratio of the two phases in the ceramic target. Magnetization measurements using a superconducting quantum interference device and a vibrating sample magnetometer reveal a large magnetic anisotropy with an easy axis along the CoFe2O4 nanopillar’s long axis. We have studied the magneto-optic properties of these thin films by performing magneto-optic kerr effect (MOKE) measurements in a polar geometry as a function of the size of the CFO nanopillars. In these thin films, the magnetization, and hence the MOKE signal increases as the size of the magnetic nanopillars increases to a maximum value for pure CFO films. In these multiferroic films, the magnetoelectric coupling between the ferrimagnetic CFO and ferroelectric BFO gives rise to changes in magnetization as a function of applied electric field as previously demonstrated [1]. Here we also report the observation of a corresponding reversal of the MOKE signal induced by an applied electric field. Spatially resolved maps of the Kerr rotation were completed over large areas (4 millimeters square) sampling both poled and unpoled regions of the sample in which a distinct change in the MOKE signal was observed. The impact of nanopillar size and film morphology on the magneto-optical properties of these thin films will be discussed.[1] Zavaliche, F., et. al., Nanoletters 5 (9), 1793-1795 (2005)
GG3: Nanostructured Multifunctional Oxide Films II
Session Chairs
Tuesday PM, April 18, 2006
Room 2018 (Moscone West)
2:30 PM - **GG3.1
Novel Chemical Growth Routes of Functional Oxide Nanostructures and Epitaxial Films
Judith MacManus-Driscoll 1 , Ming Wei 1 , Ying Liu 1 , Ahmed Kursumovic 1 , Li Chao 1 , Mei Li 1
1 Department of Materials Science and Metallurgy, University of Cambridge, Cambridge United Kingdom
Show AbstractA range of chemical growth routes is described to grow functional oxide nanostructures and epitaxial films. These include liquid-solid growth, ultrasonic assisted solution CVD, and electrodeposition in the presence of magnetic fields. Different nanostructure forms will be demonstrated including stars, rings, rods, cubes, wires, and faceted nano-crystals. The materials systems grown include Ta 2O5, ITO (transparent conducting), BiFeO3 (multiferroic), Mn-Cu2O (DMS), and Fe3O4 (ferromagnetic), gamma-Fe2O3/Fe3O4, Sr2FeMoO6 (ferromagnetic), and YBCO (superconducting).
3:00 PM - GG3.2
Self-organized SiO2/Si Nanostructures Formed by the Competing Process of Thermal Oxidation and Etching.
Kun Xue 1 , Jian Xu 1 , Ho Ho 1 , Lei Wang 1
1 Electronic Engineering department, The Chinese University of Hong Kong, Hong Kong Hong Kong
Show AbstractSelf-organized SiO2/Si nanostructures on Si(111) and Si(100) substrates have been fabricated by exploiting the competing process of thermal oxidation and etching in the transitional oxidation mode in an ultrahigh vacuum (UHV) system. UHV scanning tunneling microscope (STM) observation shows that the nanostructures are Si nano protrusions capped with SiO2 in a dimension of 3-10nm randomly distributed on the sample surface. The achievable density of the nanostructures can be as high as 1011/cm2. Scanning tunneling spectroscopy (STS) investigation on the nanostructures show that the threshold bias voltage existed for large current appearance in the I-V curves, indicating a Coulombic charging characteristic of nanosized Si capped by SiO2. With the high density and charging effect of the self-organized nanostructures, this technique is promising for nano-crystalline Si floating gate fabrication in flash memory applications.
3:15 PM - GG3.3
Ferromagnetic and Optic Properties of Transition Metal Doped Zinc oxide Nanoclusters above Room Temperature.
Jiji Antony 1 , David McCready 2 , Mark Engelhard 2 , Chongmin Wang 2 , Amit Sharma 1 , Joe Nutting 1 , Daniel Meyer 1 , Leah Bergman 1 , You Qiang 1
1 Physics, University of Idaho, moscow, Idaho, United States, 2 Environmental Molecular Science Laboratory, Pacific Northwest National Laboratory, Richland, Washington, United States
Show AbstractTransition metal(TM)-doped ZnO is an interesting area of current research due to its wide variety of spintronic applications. We prepared TM-ZnO nanoclusters by sputtering atoms of a mixed target of zinc and transition metal into an atmosphere of He, O2 and Ar gases to form the nanoclusters in an aggregation tube cooled by chilled water. The dilute ferromagnetic semiconductor nanoclusters are produced and characterized using transmission electron microscope (TEM), x-ray diffraction (XRD), x-ray photon spectroscope (XPS), photoluminescence (PL) and superconducting quantum interference magnetometer (SQUID). The TM-doped ZnO nanoclusters have the XRD pattern identical to the bulk ZnO wurtzite structure, even though small fluctuations in lattice parameters were observed and no element other than ZnO is detected. XPS showed the oxidation states of the transition metal. The oxidation states of the dopants indicated that these elements do not exist as independent aggregates but are incorporated into the wurtzite ZnO to form a solid solution. PL spectra was seen in ZnO doped with < 5% transition metal. The hysteresis loop of TM-ZnO is measured at various temperatures (5K to 400K) and these nanoclusters showed ferromagnetic behavior well above the room temperature (>400K). Saturation magnetization of the clusters varies very little with temperature, whereas the coercivity of the doped ZnO changed with the change in temperature. Financial support is provided by NSF-EPSCoR, DOE-EPSCoR, and Battelle-PNNL.
3:30 PM - GG3.4
Novel Approach for Fabrication of Single Crystalline Insulator/Si/insulator Double Barrier Nanostructures Using Cooperative Vapour-solid-phase Epitaxy.
Dirk Kuehne 1 , Andreas Fissel 2 , Eberhard Bugiel 1 , H. Joerg Osten 1 2
1 Institute of Electronic Materials and Devices, University of Hannover, Hannover Germany, 2 Information Technology Laboratory, University of Hannover, Hannover Germany
Show AbstractQuantum-effect devices based on silicon are promising for future nanoelectronic application due to their compatibility with mainstream technology. Here, double-barrier structures using epitaxial insulators as barriers and Si as quantum-well are particularly interesting. The fabrication of such an epitaxial insulator/Si/insulator heterostructure requires the growth of ultra-thin, atomically flat and defect-free insulator barriers on Si, and the growth of epitaxial Si quantum-well layers on the insulator. However, this can not be achieved straightforward because of the differences in the surface free energy between the insulator and silicon. Often, the surface free energy of the insulator is much lower than that of silicon leading to Si cluster formation on the insulator. This problem can be partly overcome using surfactants which suppresses island formation. However, the use of surfactants also introduces impurities into the epitaxial Si layer.We will present a new approach of nanostructure formation which is based on solid-phase epitaxy of the Si quantum-well combined with simultaneous vapour-phase epitaxy of the insulator on top of the quantum-well. In our experiments, we use the rare-earth oxide Gd2O3 as insulator, which has a large band gap of about 5.7 eV and a nearly equal valence-band and conduction-band offset, of 2.3 eV to Si respectively, as well as a low lattice mismatch of about 0.5 %. The structure consists of single crystalline Gd2O3/Si/Gd2O3 double barrier structure. It was grown on Si(111) by molecular beam epitaxy using electron beam evaporation of both silicon and granular stoichiometric Gd2O3. We will demonstrate that this new approach results in coherent and sharp interfaces between the underlying ultra-thin oxide layer and silicon as well as the ultra-thin silicon and the top oxide layer. The first Gd2O3 barrier was grown on Si at 670 °C. RHEED pattern obtained from the grown layer substantiates an epitaxial layer-by-layer growth in [111] orientation of the oxide layer. The oxide/Si(111) interface exhibits the known A/B twinning relationship where the B layer orientation is a twin related to the A substrate orientation obtained by a 180° rotation around the [111]-axis. Subsequent, an ultra-thin (2-4 nm) Si layer was deposited on top of the oxide under different conditions. Perfect double barrier structures were obtained as follows: Amorphous Si was deposited at low temperature. Then, the temperature was raised to 670 °C. During the temperature ramp-up, the deposition of the second oxide barrier was already started at medium temperature. This temperature was low enough to prevent the Si clustering. As revealed by RHEED, the second oxide barrier does not show significant differences compared to the first barrier layer. TEM investigation demonstrates that the Si quantum-well layer was also single-crystalline and contains only very few defects. The oxide/Si/oxide/Si(111) substrate interfaces were found to be atomically flat.
3:45 PM - GG3.5
Ga2O3 Nanoparticles Synthesized in a Low Pressure Flame Reactor.
Pascal Ifeacho 1 , Hartmut Wiggers 1 , Christof Schulz 1
1 Institute for combustion and gas dynamics, University of Duisburg-Essen, Duisburg Germany
Show AbstractCurrently, strong research interest exists in fully understanding the potentials of 1-D gallium oxide nanomaterials such as nanowires, nanorods and nanobelts. Special emphasis is however placed on β-Ga2O3 with a monoclinic crystal structure for application as a transparent conducting oxide (TCO). Furthermore, it has been reported that β-Ga2O3 has huge potentials as an optical emitter for UV, as well as for high temperature gas sensors. However, most of the synthesis methods employed involves multi-step processes culminating with a thermal operation lasting several hours. While these processes are employed on laboratory scale and are essential for obtaining required objectives, they are often cumbersome for industrial applications. In this study, a one step approach for the synthesis and characterization of Ga2O3 is presented with particular emphasis on its optical properties for TCO applications. The synthesis of Ga2O3 was achieved by doping a H2/O2/Ar premixed flat flame with diluted trimethyl gallium Ga(CH3)3 in a low pressure reactor. Material properties such as mean particle diameter of the resulting metal oxide is characterized in-situ with a particle mass spectrometer (PMS) embedded in the low pressure reactor. It was observed that depending on the residence time for particle growth, mean particle diameters dp ranging between 2.5 nm ≤ dp ≤ 6.5 nm are obtainable. This result was further collaborated by BET measurements, which yielded 200 m2/gm surface area, equivalent to a spherical diameter of 5 nm. XRD results show that the as-synthesized Ga2O3 nanoparticles are mostly amorphous, however, the observed broad reflexes can be ordered to the cubic crystal structure of Ga2O3. Consequently, by slightly reducing the overall oxygen concentration in the reactor, two new broad reflexes can be seen, indicating the presence of an additional phase. Using a pneumatic TEM sampling device, Ga2O3 nanoparticle were sampled on a TEM grid, whereby, image analysis indicated that the particles were agglomerated, but show spherical morphology. UV-VIS measurements show strong absorption in the UV range, which corresponds to the 4.8 eV direct band gap of bulk Ga2O3. The as-synthesized Ga2O3 nanoparticles were deposited on a silicon wafer for photoluminescence measurements. The deposited particles were excited with a 351 nm argon ion laser in vacuum, for excitation densities between 0.25 W/cm-2 and 1500 W/cm-2, as well as for temperatures between 4 K and 300 K. A broad emission band (blue light) ranging from 350 to 600 nm with a maximum at 460 nm was observed. The maximum corresponds to the 2.5 eV indirect band gap of Ga2O3, however, no significant shift in the photoluminescence spectrum was observed for increasing excitation density, but a slight red shift was observed at higher temperatures.
GG4: Nanostructured Multifunctional Oxide Films III
Session Chairs
Tuesday PM, April 18, 2006
Room 2018 (Moscone West)
4:30 PM - **GG4.1
Nanostructural Modification of High-Temperature Superconductors for Improved Properties.
David Christen 1
1 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractThe optimization of high-temperature superconductors (HTS) for potential high-current applications requires controlled manipulation of the nanostructure. This is so because of the intrinsic interactive force between a flowing electric current and the array of quantized supercurrent vortices that penetrate the material in the presence of a magnetic field. Since energy is lost by vortex motion under the influence of this force, it is necessary to introduce material inhomogeneities that “pin” the vortex array, thus allowing non-dissipative electrical transport up to a maximum critical current density, Jc. Ideally, the size and density of these lattice defects should match those of the natural, nanoscale vortex ensemble. Recent improvements in the processing of YBa2Cu3O7 (YBCO) epitaxial films have created both localized and extended nanostructures that mimic some of the best artificial defects and properties previously produced by methods such as ion irradiation. Approaches being used include inclusion and production of both random and self-assembled, aligned second-phase nanoparticles, and substrate surface decoration with nanodots that lead to various types of flux-pinning growth defects within the HTS coating. Nanostructure/superconducting properties correlations will be discussed within the context of previous and ongoing baseline studies on control systems, and considering applications requirements and the associated constraints that are imposed by the operational regimes of temperature, field, and orientation in field. The results are relevant to the performance requirements of emerging second-generation HTS wires, where epitaxial coatings of YBCO are applied to long-length, crystalline textured metal tape templates.
5:00 PM - GG4.2
Growth Mechanisms and Magnetotransport Properties of SrRuO3 Thin Films
Gervasi Herranz 1 , Florencio Sanchez 1 , Josep Fontcuberta 1 , Maria Victoria Garcia-Cuenca 2 , Cesar Ferrater 2 , Manuel Varela 2
1 , ICMAB-CSIC, Bellaterra Spain, 2 Fisica Aplicada i Optica, Universitat de Barcelona, Barcelona Spain
Show AbstractWe report on magnetotransport properties of nanometric epitaxial thin films of SrRuO3 (SRO) and its dependence on structural disorder. The films display prominent in-plane anisotropy of transport properties. The anisotropy is reduced as the film thickness increase, suggesting it comes from interface structural disorder. Moreover, an enhancement of resistivity is found at low temperatures. This enhancement typically occurs in conducting systems with a low mean free path, and thus is strongly dependent on film structural disorder. The film growth mechanisms have been investigated in details since they can have a dramatic impact on the structural disorder. Films below a certain thickness tc show a surface morphology consisting in finger-like structures formed from coalescence of 3D islands, which evolves into a smooth morphology of terraces and steps and a 2D growth mechanism for films having a thickness t > tc. This unique growth mode transition induces the formation of a well oriented pattern of disorder which is revealed by the appearance of in-plane anisotropy in the film resistance and low-temperature resistance enhancement.The strong dependence on structural disorder should allow tailoring magnetotransport properties via the controlled modification of the growth mode. The initial growth can be controlled by the miscut angle or by the substrate atomic termination. We demonstrate that the growth mode has an strong impact on the magnetotransport properties of SRO.
5:15 PM - GG4.3
Solution Processing of High Quality Oxide Buffer Layers for Coated Conductor Fabrication.
Srivatsan Sathyamurthy 2 1 , Shafiq Bhuiyan 1 , Tolga Aytug 2 1 , Mariappan Paranthaman 1
2 , University of Tennessee, Knoxville, Tennessee, United States, 1 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractOne of the main focus areas of research in high-temperature superconductivity (HTS) in recent years has been on the development of the second generation wires also known as coated-conductors. One of the leading textured-template approaches for the fabrication of coated-conductors is the rolling assisted biaxially textured substrates (RABiTS) approach. In this approach, cube textured nickel or Ni alloy substrates, obtained by cold rolling and recrystallization, function as a template for the epitaxial deposition of buffer layers and the YBa2Cu3O7-x (YBCO) superconductor. The buffer layers provide a structural template for the HTS layer, and also act as a chemical barrier between the metal substrate and the HTS coating. Using such architecture, sufficient biaxial texturing of the HTS layer has been obtained to avoid problems associated with weak-linked, high-angle grain boundaries. To date, in the processing of high current coated conductors using RABiTS, the best reproducible results have been obtained using three layer buffer architectures such as CeO2/YSZ/Y2O3/NiW, where Y2O3 serves as a seed layer which nucleates a well textured oxide layer, YSZ is a barrier layer which prevents the diffusion of Ni into the superconductor, and CeO2 is a cap layer which promotes good epitaxy of the superconductor. This multi-layered buffer architecture is being successfully used in scale-up to long length, however, the manufacturing process could be simplified and potentially be lowered in cost if one could achieve a buffer stack with fewer components and utilize a scaleable, non-vacuum technique such as solution deposition. Using solution deposition we have developed thin films of a variety of novel pyrochlore oxides. In this study rare-earth zirconates and niobates were used. By careful process optimization, very highly oriented dense films of these oxides can be processed at very high rates. These films have a very fine grained microstructure with grain size of 20-30 nm. Using atomic force Microscopy the surface roughness of the films were estimated to be about 2-3 nm. Critical currents over 200 A/cm-width have been obtained on textured Ni-W substrates using La2Zr2O7 as the primary barrier layer. Through this study we have demonstrated that the performance of lanthanum zirconium oxide films processed by solution deposition is comparable to that of vacuum processed yttria stabilized zirconia. In this paper, the effect of film chemistry on diffusion barrier properties and crystallographic texture will be discussed._________________Research supported by the Department of Energy, Office of Electric Transmission and Distribution. This research was performed at the Oak Ridge National Laboratory, managed by UT-Battelle, LLC for the USDOE under contract DE-AC05-00OR22725.
5:30 PM - GG4.4
Studies on Nb Substituion at Cu site in YBa2Cu3O7-x thin films.
Paul Barnes 1 , Srinivas Sathiraju 1 , G. Narasimharao 2
1 PRPG, Air Force Research Laboratory, Palm Coast, Florida, United States, 2 Ceramics Division, Advanced Research Center for Powder metallurgy, Hyderabad, Andhra Pradesh, India
Show Abstract5:45 PM - GG4.5
Mn2+ in ZnO thin films: Correlation Between Structural, Magnetic and Optical Properties.
Yves Dumont 1 , Ekaterine Chikoidze 1 , Hans Jurgen Von Bardeleben 2 , Jerome Gleize 3 , Francois Jomard 1 , Edouard Rzepka 1 , Ouri Gorochov 1
1 Laboratoire de Physique des Solides et Cristallogenese, CNRS-University of Versailles, Meudon France, 2 Institut des Nanosciences de Paris, CNRS-Universities of Paris VI et VII, Paris France, 3 Laboratoire de Physique des Milieux Denses, CNRS-University of Metz, Metz France
Show Abstract
Symposium Organizers
Dhananjay Kumar North Carolina A&T State University
Valentin Craciun University of Florida
Marin Alexe Max-Planck Institute of Microstructure Physics
Kaushal K. Singh Applied Materials Inc.
GG5: Spintronics I
Session Chairs
Wednesday AM, April 19, 2006
Room 2018 (Moscone West)
9:15 AM - **GG5.1
Functional Oxide Films and Heterostructures.
Neil Mathur 1
1 Materials Science, University of Cambridge, Cambridge United Kingdom
Show AbstractI will demonstrate diverse results in functional oxide systems, touching upon spin injection into molecules, strain control of superlattice periodicity, engines for heat pumps and multiferroic thin films.
9:45 AM - GG5.2
Magnetoresistance and Insulator-Metal Transition of EuO Thin Films Grown on YAlO3 and Si Substrates.
Andreas Schmehl 1 , Venu Vaithyanathan 1 , Alexander Weber 2 , Jochen Mannhart 2 , Darrell Schlom 1
1 Materials Science and Engineering, Pennsylvania State University, University Park, Pennsylvania, United States, 2 Center for Electronic Correlations and Magnetism, University of Augsburg, Augsburg Germany
Show AbstractWith its impressive electronic, magnetic, and optical properties, the ferromagnetic semiconductor EuO is a fascinating compound for basic studies and for possible electronic applications. In Eu-rich EuO single crystals the ferromagnetic transition is accompanied by an insulator–metal transition with a resistivity drop of up to 13 orders of magnitude. Further, in single crystals the Tc as well as the magnitude of this transition can be shifted over a wide range by applying external magnetic fields. These dramatic property changes, together with the low charge carrier density and a reported spin polarization of about 100% in the ferromagnetic state, make EuO a very promising material for possible applications in spintronic devices, provided comparable properties can be achieved in thin films. To assess the properties of epitaxial EuO films, we grew Eu-rich EuO films by reactive molecular beam epitaxy (MBE) and characterized their structural, magnetic, and transport properties. The films were grown either directly on (001) Si using 12 Å thick SrO buffer layers or on (110) YAlO3. As EuO is not stable in air the films were protected with capping layers of amorphous Al2O3. To make electric contact with the underlying EuO a novel process has been developed that combines in situ ion-milling and metal deposition. The structural properties were investigated using x-ray diffraction. For both substrate types these measurements indicate (001)-oriented, single-phase films, with [110] EuO being parallel to [110] YAlO3 and [001] EuO being parallel to [001] Si respectively. Rocking curve widths, measured on the EuO 004 reflections, show values better than 0.4° FWHM for both substrate types. Four-point transport and SQUID measurements show ferromagnetic transitions with Tcs of about 75 K and a resistivity drops at the insulator–metal transition of about seven orders of magnitude. Application of external magnetic fields up to 8 T perpendicular to the film plane suppress the resistance near Tc up to five orders of magnitude and shift the transition temperatures to ≈150 K. These samples reveal the most pronounced magnetoresistive effect reported in EuO films.
10:00 AM - GG5.3
Phonon Modes, Dielectric Constants, and Exciton Mass Parameters in Ternary MgxZn1-xO.
Carsten Bundesmann 1 , Ruediger Schmidt-Grund 1 , Daniel Spemann 1 , Michael Lorenz 1 , Marius Grundmann 1 , Mathias Schubert 2
1 Institut fuer Experimentelle Physik II, Uni Leipzig, Leipzig Germany, 2 Department of Electrical Engineering, University of Nebraska-Lincoln, Lincoln, Nebraska, United States
Show Abstract10:15 AM - GG5.4
Room-temperature Ferromagnetic Zn0.95Co0.05O Diluted Magnetic Semiconducting Thin Films by Pulsed Laser Deposition.
Yuebin Zhang 1 , Qing Liu 1 , Thirumany Sritharan 1 , Sean Li 2
1 School of Materials Science and Engineering, Nanyang Technological University, Singapore Singapore, 2 School of Materials Science and Engineering, The University of New South Wales, Sydney, New South Wales, Australia
Show AbstractCo-doped ZnO thin films with room-temperature ferromagnetism have been successfully synthesized on (001) Si substrates at 450 °C by pulsed-laser deposition using a Zn0.95Co0.05O ceramic target. Their microstructural properties are carefully studied using atomic force microscopy, x-ray diffraction and high-resolution transmission electron microscopy. The oxidation state of Co and the ratio of Co/Zn are examined by x-ray photoelectron spectroscopy, and magnetic measurements are performed using SQUID. The results show that a single-phase crystalline Co-doped ZnO film was grown with (002) preferential orientation and some edge dislocations formed during the film growth. The origin of room-temperature ferromagnetism is explored. The presence of nanoclusters of any magnetic phase can be ruled out. The dislocations, coupled with oxygen vacancy, may contribute to the ferromagnetic properties in the much diluted magnetic semiconductor.
10:30 AM - GG5.5
Development of CMR Manganite Sensors for Energy Measurement of the Linear Coherent Light Source Pulsed X-ray Laser.
Rajeswari Kolagani 1 , Grace Yong 1 , Stephan Friedrich 2 , Yong Liang 3 , David Cox 1 , Rajeh Mundle 1 , Owen Drury 2 , Zaheer Ali 2 , Vera Smolyaninova 1 , David Schaefer 1 , Anthony Davidson 1
1 Department of Physics, Astronomy & Geosciences, Towson University, Towson, Maryland, United States, 2 Advanced Detector Group, Lawrence Livermore National Laboratory, Livermore, California, United States, 3 , Motorola Labs, Tempe, Arizona, United States
Show AbstractWe are developing CMR manganite thin films for use as bolometric sensors for energy measurements of the Linear Coherent Light Source (LCLS) pulsed free electron x-ray laser (FEL) which produces ultra bright x-ray pulses in the energy range between 0.8 keV and 8 keV with ~ 10 12 photons per pulse and pulse repetition rate of ~ 120 Hz. The sensor functionality is based on the steep temperature dependence of the resistance accompanying the insulator-metal transition in the CMR manganites. The sensor array is to be fabricated on a low Z (atomic number) substrate capable of withstanding the pulse impact of 2 mJ in ~ 200 femtoseconds, without the thermal expansion exceeding the yield strength, when the back side of the substrate is irradiated with the FEL pulses. Si is a potential candidate substrate that is expected to meet this requirement though its stability for long term exposure is a concern that needs to be experimentally tested. The optimal operating temperature of the sensor has been estimated to be in the range 100 K-200 K, based on finite element simulations of the temperature evolution in the sensor pixel. Our initial work has identified in Nd1-x Srx MnO3 (NSMO) as the manganite material suitable for operation in this temperature range. We are developing thin films of NSMO on Si substrates by Pulsed Laser Deposition, employing several buffer and template layer schemes. We will present our materials development efforts towards meeting the LCLS sensor design and performance requirements. Effects of lattice mismatch and thermal strains on the structural properties as studied by 4-circle x-ray diffraction and the correlation of these with the electrical properties such as the insulator-metal transition and the temperature-coefficient of resistance will be discussed. We will also discuss our exploratory efforts on the growth of CMR manganite thin films on other potential low Z substrates such as BN which are intended to replace Silicon , in case Si proves to be unstable during long term exposure to the LCLS beam.
10:45 AM - GG5.6
Domain Formation in Nanoscale La0.7Sr0.3MnO3 Islands Patterned By E-Beam Lithography and Ion Implantation
Yayoi Takamura 1 , Rajesh Chopdekar 1 2 , Yuri Suzuki 1 , Alexander Liddle 3 , Bruce Harteneck 3 , Andreas Scholl 4 , Andrew Doran 4
1 Department of Materials Science and Engineering, University of California, Berkeley, Berkeley, California, United States, 2 School of Applied and Engineering Physics, Cornell University, Ithaca, New York, United States, 3 Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 4 Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractThe doped rare-earth manganite La0.7Sr0.3MnO3 (LSMO) has received renewed interest in recent years due to its wide range of technologically relevant properties, including novel magnetic and electronic properties. These properties depend strongly on parameters such as strain, oxygen stoichiometry, doping, and the presence of grain boundaries. From a fundamental perspective and for the development of device applications, understanding the relationship between the magnetic properties and the size of LSMO structures is of great interest. Geometric confinement increases the surface area to volume ratio and alters the strain state in epitaxial thin films. Previously, Wu et al.1 used optical lithography and ion milling to pattern pillars into LSMO thin films and used magnetic force microscopy (MFM) to image the domain patterns. The authors found that for pillars with diameters ≥ 500 nm, the magnetic properties are dominated by the compressive strain imposed from the LaAlO3 substrate. For structures below a critical dimension, the competition between magnetostatic energy and exchange energy are predicted to suppress magnetic domain formation, leading to single domain structures. In this work, we use photoemission electron microscopy (PEEM) and MFM to probe the magnetism in submicron LSMO islands within a non-magnetic matrix patterned by a novel approach of e-beam lithography and ion implantation. The samples consist of 60 nm thick epitaxial thin films deposited on (001)- and (110)-oriented SrTiO3 substrates by pulsed laser deposition. The choice of substrate orientation results in thin films with two- and four-fold in-plane anisotropy, respectively. A 500 nm thick resist pattern is used to define regions of varying shape and size that are/are not exposed to an Ar+ ion implantation at 100 keV with a dose of 1.0x1014 ions/cm2. By disrupting the ordering of the lattice, the implanted ions cause the degradation of the magnetic and transport properties of the LSMO film. PEEM and MFM images reveal that the domain structure in the islands depends predominantly on the shape of the islands, with the magnetocrystalline and magnetoelastic energies contributing secondary effects. 1 Y. Wu, Y. Matsushita, and Y. Suzuki, Phys. Rev. B 64, 220404 (2001).
11:00 AM - GG5:Spintronics
BREAK
GG6: Spintronics II
Session Chairs
Wednesday PM, April 19, 2006
Room 2018 (Moscone West)
11:30 AM - **GG6.1
Highly Conductive (Fe,Mn)3O4 Thin Films with Spin Polarization at Room Temperature and Their Application to Nano Spintronic Devices by AFM Lithography
Tomoji Kawai 1 , Hide Tanaka 1 , Mizue Ishikawa 1 , Yoshihiko Yanagisawa 1 , Issei Satoh 1 , Hidekazu Tanaka 1 , Luca Pellegrino 1 2
1 , ISIR, Osaka University , Ibaraki, Osaka, Japan, 2 , INFM-Lamia & Genova Universuty, Genova Italy
Show Abstract12:00 PM - GG6.2
Epitaxial Ilmenite-Hematite Films by Pulsed Laser Ablation
J. Dou 1 2 , L. Navarrete 1 2 , P. Padmini 3 2 , P. Kale 3 2 , R.K. Pandey 3 2 , R. Schad 1 2
1 Department of Physics , University of Alabama, Tuscaloosa, Alabama, United States, 2 Center for Materials for Information Technology, University of Alabama, Tuscaloosa, Alabama, United States, 3 Department of Electrical and Computer Engineering, University of Alabama, Tuscaloosa, Alabama, United States
Show AbstractSolid solutions of ilmenite (FeTiO3) and hematite (α-Fe2O3) have been investigated for various reasons since the 1950’s. By controlling the concentration, ferrimagnetic order can be established with high Curie temperatures above room temperature. The conduction type can also be varied from p- to n- type semiconducting as a function of composition. These unique ferromagnetic and semiconducting properties make it one of the candidates for application in spintronics.Bulk samples were prepared by solid-state reaction. Previously we have shown that proton irradiation can be used to increase the chemical ordering, resulting in an increase of the ferrimagnetic moments. Such bulk samples were used as targets for Pulsed Laser Deposition on α-Al2O3(001) and LiNbO3(001) substrates. X-ray diffraction and pole figures clearly show that films prepared under vacuum and Argon atmosphere have better crystal quality compared to films prepared under oxygen. Magnetometry shows that the films grown under vacuum with post annealing in oxygen have saturation moments as high as 50emu/cc. Band gap measurement by using Cary 5G UV-VIS-NIR spectrometer shows the films under oxygen atmosphere have a more narrow energy band gap (around 2.6eV) than the films grown in vacuum or Argon (around 3.3eV). Fitting the temperature dependence of the resistance, using Wilson’s formula, yields a value of the activation energy of about 0.16eV, which is very close to the reported bulk sample. Films grown in oxygen have a much higher resistivity than films grown in vacuum or Argon.
12:15 PM - GG6.3
A New Fundamental Limit of Ferroelectric Devices Set by Net Polarization Decay.
Jiyoung Jo 1 , D. J. Kim 1 , Y. S. Kim 1 , S. B. Choe 1 , T. K. Song 2 , J.-G. Yoon 3 , J. S. Chung 4 , T. W. Noh 1
1 , Seoul National University, Seoul Korea (the Republic of), 2 , Changwon National University, Changwon Korea (the Republic of), 3 , University of Suwon, Suwon Korea (the Republic of), 4 , Sungsil University, Seoul Korea (the Republic of)
Show AbstractWednesday, April 4/19New Presenter11:15 AM GG6.3A New Fundamental Limit of Ferroelectric Devices Set by Net Polarization Decay. D. J. Kim
12:30 PM - GG6.4
Femtosecond Pulsed Laser Deposition of Metal Oxide Thin Films
Bing Liu 1 , Arnold Alenic 2 , Zhendong Hu 1 , Yanbin Chen 2 , Yong Che 1 , Xiaoqing Pan 2 , Yuzuru Uehara 1
1 , IMRA America Inc., Ann Arbor, Michigan, United States, 2 Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan, United States
Show AbstractPulsed laser deposition (PLD) is a versatile technique capable of growing thin films of various compounds. Recently, femtosecond PLD (fs-PLD) began to attract much attention due to the possibility of droplet-free growth of high quality films. However, the growth mechanisms of fs-PLD are still not well understood, and reported growth results of several materials are inconsistent. In this work, we study fs-PLD of transition metal oxides, ZnO and NiO thin films. The films are characterized by scanning electron microscopy, x-ray diffraction, transmission electron microscopy, absorption spectroscopy, and Hall measurement. A Langmuir probe is used to analyze the kinetic energies of the laser ablation plume. In particular, the dependences of the ion kinetic energy and film qualities on various growth conditions such as laser fluence, background gas pressure, and growth temperature are investigated. Epitaxial ZnO and NiO thin films have been obtained with uniform surface morphologies and good optical properties. Our results suggest that fs-PLD can be a suitable technique for growth of high-quality metal oxide thin films with desired structural and surface qualities.
GG7: Ferroics and Device Applications
Session Chairs
Wednesday PM, April 19, 2006
Room 2018 (Moscone West)
2:30 PM - **GG7.1
Epitaxial Thin Films and Multilayers of Magnetocapactive and Multiferroic Double Perovskite Oxides
Arunava Gupta 1
1 MINT Center, University of Alabama, Tuscaloosa, Alabama, United States
Show AbstractOrdering of the B site cations in the double perovskite-type oxides, A2B’B’’O6, often results in novel electrical and magnetic properties due to the B’-O-B’’interaction. For example, a number of double perovskites are known that are either ferri- or ferromagnetically ordered with a magnetic Curie temperature (Tcm) close to or above room temperature, including A2FeMoO6 (A=Ba, Sr), A2CrWO6 (A = Ba, Sr), and La2NiMnO6. The latter (La2Ni2+Mn4+O6) is an ordered double perovskite that is a ferromagnetic semiconductor with a Tcm of 280 K. Recent studies of La2NiMnO6 in the bulk have revealed large magnetic-field induced changes in the resistivity and dielectric properties at temperatures close to Tcm [1]. This is a much higher temperature than previously observed for such a coupling between the magnetic, electric, and dielectric properties in a ferromagnetic semiconductor. Substitution at the A site can also lead to multiferroic behavior in the double perovskites. Azuma et al. have reported synthesizing the compound Bi2NiMnO6 in the bulk under high pressure (~ 6 GPa) and have established its multiferroic properties [2]. The presence of the 6s2 lone pairs of Bi3+ ions and the covalent Bi-O bonds results in ferroelectric properties with Tce of 485 K, while the -Ni2+-O-Mn4+-O-Ni2+- magnetic path leads to ferromagnetism with Tcm of 140 K. We have succeeded in growing high quality epitaxial films of both oxides on (100)-oriented SrTiO3 substrates using the technique of pulsed laser deposition (PLD). The magnetic and electric properties of the films are qualitatively similar to those observed in the bulk compounds, but with some differences resulting from the influence of strain. In addition, we have artificially layered these novel oxide thin films with other lattice-matched oxides and have been able to significantly alter their magnetocapactive and multiferroic properties. The details of the structure and property characterization of the single and multilayer films will be reported.1.N. S. Rogardo, J. Li, A. W. Sleight, and M. A. Subramanian, “Magnetocapacitance and magnetoresistance near room temperature in a ferromagnetic superconductor: La2NiMnO6”, Adv. Materials (in print).2.M. Azuma, K. Tanaka, T. Saito, S. Ishiwata, Y. Shimakawa, and M. Takano, “Designed ferromagnetic, ferroelectric Bi2NiMnO6”, J. Am. Chem. Soc. 127, 8889 (2005).
3:00 PM - GG7.2
Patterning of Hierarchical Multiferroic Oxide Nanostructures Using Soft Electron Beam Lithography (“Soft-eBL”).
Zixiao Pan 1 , Suresh Donthu 1 , Mohammed Aslam 1 , Vinayak Dravid 1
1 Materials Science and Engineering, Northwestern University, Evanston, Illinois, United States
Show AbstractMaterial systems exhibiting simultaneous ferroelectric and magnetic ordering have drawn significant interest in recent years due to their remarkable potential in diverse applications such as memory elements, field sensors, transducers, among many others. Recent experimental results[1] have shown that nanostructured multiferroic oxide composites exhibit a strong coupling between ferroelectric and ferromagnetic order parameters. On the other hand, theoretical calculations[2] have further substantiated that the three-dimensional (3D) geometry of such composites and the heteroepitaxy between the two oxides constrained by the substrate ultimately determine its coupled functionality. Therefore there is considerable interest in development of new strategies to fabricate, and particularly, to pattern 3D hierarchically stacked multiferroic nanostructures in order to investigate the coupling interactions in such system where the size and site of each phase are well-controlled. In our group we have developed an innovative soft electron beam lithography (“soft-eBL”) approach[3] which combines the high resolution eBL with deposition of liquid precursors for patterning nanostructures of variety of hard, soft and hybrid materials. We have further demonstrated that the soft-eBL approach can be utilized for patterning of radially stacked hierarchical structures composed of ferroelectric and magnetic ceramics in a facile two-step procedure[4]. For example, well-defined nanorings of lead zirconium titanate (PZT) are first fabricated on variety of substrates. The nanorings are then used as building block “containers” and filled with CoFe2O4 (CFO) to form radially stacked composite ceramic heterostructures. This approach circumvents the traditional bottlenecks of painstaking feature-realignment and etching for patterning of non-planar, multi-phase oxide structures. Such hierarchical PZT/CFO radial composites may serve as an interesting test bed to study the coupling effect by controlling the geometry and the microstructure of each phase.The presentation will cover the soft-eBL strategy for nanopatterning of functional inorganics, particularly to demonstrate the efficacy of this novel approach in fabricating hierarchical multiferroic oxide nanostructures, and emphasize the need to couple nanopatterning with control over microstructure and assessment of functionality of such structures.[1] Zheng, H. et al., Science 303, 661 (2004)[2] Liu, G. et al., J. Phys. D: Appl. Phys. 38, 2321 (2005)[3] Donthu, S. et al., Nano Lett., 5, 1710 (2005)[4] Pan, Z. et al., Small, accepted
3:15 PM - GG7.3
Electric Field-induced Magnetization Reversal in BiFeO3-CoFe2O4 Multiferroic Films.
Florin Zavaliche 1 2 , H. Zheng 1 2 , T. Zhao 1 2 , L. Mohaddes-Ardabili 1 , S. Y. Yang 1 , Q. Zhan 1 2 , M. P. Cruz 1 2 3 , P. Shafer 1 , D. Hao 1 , J. Zhang 4 , M. L. Scullin 1 , D. G. Schlom 4 , L. Q. Chen 4 , 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 , Centro de Ciencias de la Materia Condensada (CCMC)-UNAM, Ensenada, B.C., Mexico, 4 Materials Science and Engineering, Pennsylvania State University, University Park, Pennsylvania, United States
Show AbstractThe magnetoelectric coupling has been investigated in epitaxial BiFeO3-CoFe2O4 heterostructures with matrix-pillar morphology by scanning probe microscopy at ambient conditions. Such multiferroic nanostructures have been grown by pulsed-laser deposition on SrTiO3(001) substrates with SrRuO3 underlayers. The ferroelectric BiFeO3 matrix has been locally poled by applying an electrical bias to a conducting probe while scanning in contact mode. Subsequent magnetic force microscopy (MFM) images acquired in the tapping-lift mode reveal that magnetization reverses in most of the nanopillars. The quantitative analysis of the MFM images gives a perpendicular magnetoelectric susceptibility of ~1.0×10-2 G cm/V, which is in good agreement with the values obtained from the macroscopic experiments performed on test structures. By repeatedly switching the ferroelectric matrix at positive and negative biases, the reversibility of the electric field-induced magnetization reversal was observed in a large number of the nanopillars. Responsible for the observed effect is the onset of a strong elastic coupling between the two ferroic constituents as the result of the three dimensional heteroepitaxy. Such nanocomposites with matrix-pillar morphology open new avenues for microwave applications, energy conversion and data storage devices.This work has been supported in part by the ONR under a MURI program, SRC under a MARCO program, and by an LBL-LDRD program.
3:30 PM - GG7.4
Enhanced Electrical Properties of Hf-O-N Gate Dielectric Thin Films.
Karthik Ramani 1 , C.R. Essary 1 , V. Craciun 1 , R. K. Singh 1
1 Materials Science and Engineering, University of Florida, Gainesville, Florida, United States
Show Abstract3:45 PM - GG7.5
Potential Distribution and Domain Structure of Metal-ferroelectric-semiconductor-metal Heterostructures.
Rene Meyer 1 2 , Paul McIntyre 2
1 Materials Sciences and Engineering, Stanford University, Stanford, California, United States, 2 CNI, FZ Juelich, Juelich Germany
Show AbstractThe domain pattern of 180° domains is studied numerically for a metal-ferroelectric-semiconductor-metal structure. A 2-dimensional finite differences method is used to calculate the inner electric field, potential distribution and electrostatic energy under short circuit condition and for external electric fields. Based on empirical data, the domain size is estimated as a function of the screening efficiency of the electrodes and the applied field. Results of the 2-dimensional model are compared to a 1-dimensional approach, where a voltage dependence of the polarization, which originates from a formation or annihilation of 180° domains, is approximated by an effective polarization.
4:00 PM - GG7: Ferroics
BREAK
GG8: New Dielectrics
Session Chairs
Wednesday PM, April 19, 2006
Room 2018 (Moscone West)
4:15 PM - **GG8.1
Lattice Matched Dielectrics for Widebandgap Semiconductors.
B. Gila 1 , M. Hlad 1 , D. Stodilka 1 , S. Jang 2 , K. Allums 1 , A. Herrero 1 , A. Onstine 1 , J. Chen 2 , F. Ren 2 , Cammy Abernathy 1
1 Department of Materials Science and Engineering, University of Florida, Gainesville, Florida, United States, 2 Department of Chemical Engineering, University of Florida, Gainesville, Florida, United States
Show AbstractReproducible fabrication of high performance metal oxide semiconductor field effect transistors (MOSFETs) from widebandgap semiconductors will require both good interfacial electrical characteristics and good thermal stability. While the amorphous dielectric SiO2 has demonstrated low to moderate interface state densities on SiC, the low dielectric constant remains problematic. SiO2 has not proven to be as successful in the GaN system. As an alternative to amorphous dielectrics, we have investigated the crystalline MgO-CaO system. Crystalline dielectrics offer the potential for improved surface registry at the dielectric semiconductor interface, potentially resulting in better electronic behavior and reliability. This paper will discuss the growth by gas source molecular beam epitaxy of MgXCa1-XO alloys lattice matched to both SiC and GaN. Though Ca tends to segregate during growth, homogeneous alloys can be synthesized by using a digital alloy growth scheme. Films deposited in this fashion show superior surface passivation relative to mismatched dielectrics such as MgO and to amorphous dielectrics such as SiN. Similarly, lattice matched MgXCa1-XO produces lower values of Dit relative to MgO. Using the Terman method, Dit values of low 1011 have been achieved on both GaN and SiC, with typical breakdown fields of ∼ 3.5 MV/cm. XPS measurements indicate a valence band offset to GaN of ∼1eV and a conduction band offset of ∼3eV, both adequate for most device applications. Decomposition of the dielectric via formation of GaO, MgN and CaN is not thermodyamically favorable, resulting in thermally stable interfaces as measured by XRR after annealing at 800C. Prospects for use of these dielectrics in device technology will also be discussed.
4:45 PM - **GG8.2
Functional Oxides Grown by Molecular Beam Epitaxy.
Jean-Pierre Locquet 1 , A. Guiller 1 , C. Marchiori 1 , M. Sousa 1 , A. Ruefenacht 2 , B. Mereu 1 , D. Caimi 1 , H. Siegwart 1 , D. J. Webb 1 , R. Germann 1 , P. Martinoli 2 , C. Rossel 1 , J. W. Seo 3 4 , C. Dieker 4
1 , IBM Research GmbH, Rueschlikon Switzerland, 2 , Universty of Neuchatel, Neuchatel Switzerland, 3 , MosBeam Foundation, Lausanne Switzerland, 4 , EPFL, Lausanne Switzerland
Show AbstractIn this presentation an overview about the functional oxides we have grown by molecular beam epitaxy (MBE) in the past 15 years will be given. In particular, there has been a lot of progress in the preparation of high quality single crystal films as well as complete device structures. Our work has started with superconducting La2-xSrxCuO4 thin films. When deposited on the appropriate substrate, thin films with a large amount of compressive strain can be made, leading to a Tc ~ 50 K, a result which has not been reproduced by any other deposition method. Currently, this research has now expanded towards field effect structures using HfO2 as a dielectric. Another interesting system is the LaTiOx system which can easily be tuned from a metal to a dielectric (or ferroelectric) as a function of doping. Currently most of our activities focus on the different elements of the advanced gate stack. This includes high K dielectrics, metal gates as well as high mobility channels. We consider two type of dielectrics, amorphous (HfO2 based) and crystalline (SrTiO3). In both cases, the growth of the oxides on Si poses specific problems which will be reviewed. Functional field effect transistors with both type of materials have been made. Finally, another interesting application is the preparation of insulating graded oxide buffer-layers to allow the epitaxial growth of Ge (or GaAs) on Si.
5:15 PM - GG8.3
Metal-Organic-Chemical-Vapor Deposition of Amorphous Thin Sr-Ta-O and Bi-Ta-O Films for Incorporation in Backend Integration of High-k Capacitors.
Ludovic Goux 1 , Hans Vander Meeren 1 , Dirk Wouters 1
1 SPDT, IMEC, Leuven Belgium
Show AbstractDielectric layers with high dielectric constant, low leakage and high breakdown strength are of great interest for application in devices like Dynamic RAM, decoupling capacitors, or impedance matching capacitors. In particular, the need for high capacitances integrated on chip in the back-end-of-line interconnect is increasing. For these applications, process temperatures should be <400°C if Cu/low k interconnects are used.In this work, we prepared Pt/Sr-Ta-O/Pt and Pt/Bi-Ta-O/Pt capacitors on silicon, where dielectrics were deposited as amorphous layers at 360°C by metal organic chemical vapor deposition (MOCVD). All the films were dense and smooth. The thickness (t) of the dielectrics ranged between 5 and 100 nm. Both X-ray fluorescence (XRF) and scanning electron microscopy (SEM) were used to monitor the thickness of the dielectrics, while XRF gave access to their composition. After capacitor fabrication, current-voltage (I-V) was carried out using a conventional parameter analyzer, while capacitance and loss measurements (tgd) were made using a LRC analyzer.The effect of the temperature of the recovery anneal applied after Pt top electrode deposition was studied. For Bi-Ta-O (BT) -based capacitors, a 10min. long anneal at 300°C was sufficient to cure the plasma damage, while higher anneal temperature led to the increase of the leakage. For Sr-Ta-O (ST), leakage was minimized for annealing at 500°C.For both materials, the capacitance was well above 2 μF/cm2 for t ≤ 10 nm. Extrapolation to t = 0 indicated absence of a low-k interface layer. The extracted dielectric constant ε was 20 for ST, and 50 for BT. For both capacitors the capacitance did not vary from –3 to 3 V and tgd was kept within reasonable limits up to 1 MHz for t ≥ 20 nm.Leakage level around 2.10-8 A/cm2 at 3 V was achieved for 20 nm thin ST, that is at least 1 decade lower than reported for atomic layer deposited Sr-Ta-O. For 20 nm thin BT, leakage was ~3.10-8 A/cm2 at 3 V. For both ST and BT dielectrics, leakage levels were lower than typically reported for other dielectrics investigated for same applications.The breakdown voltage scaled with the thickness, and the extracted breakdown field was ~6 MV/cm for ST and ~3 MV/cm for BT.These results show that both types of dielectrics Sr-Ta-O and Bi-Ta-O are promising for incorporation in backend integrated high-k capacitors. Particularly, their leakage level is lower than reported for other dielectrics, which constitutes a significant advantage for memory application. The results also suggest that MOCVD is a suited technique to obtain very thin Sr-Ta-O and Bi-Ta-O films which are dense, smooth and with good interfacial quality.
5:30 PM - GG8.4
Characteristics of Lateral Capacitor Based High-K Materials
Thottam Kalkur 1
1 Dept. of ECE, University of Colorado, Colorado Springs, Colorado, United States
Show AbstractWith the advancement in VLSI line width geometries to submicron and deep submicron dimensions, large capacitors are implemented using lateral approach compared to conventional parallel plate configuration. In this proposal, we report the characteristics of lateral high capacitor implemented with barium calcium zirconate titanate (BCTZ) film and Pt/Ti electrodes. Pt-Ti electrode was deposited by DC magnetron sputtering. The lateral electrode structure was patterned by standard photolithography techniques and ion-milling. High-K BCTZ films of various thicknesses in range 100nm to 300 nm were deposited by spin-on MOD technique. The films were annealed at various temperatures (600 -800oC) and times by furnace and rapid thermal annealing. The lateral capacitors were characterized by current-voltage, capacitance voltage and capacitance vs frequency measurements.
5:45 PM - GG8.5
Reactive Deposition of Metal Oxide Films from Supercritical Carbon Dioxide.
Adam O'Neil 1 , James Watkins 1
1 Polymer Science and Engineering, University of Massachusetts, Amherst, Massachusetts, United States
Show AbstractRecently we reported that the deposition of device quality metal films within high aspect ratio features is enabled by supercritical fluid deposition (SFD). Here we discuss extensions of this technique to high purity, conformal metal oxide films, including cerium and hafnium oxides, using a novel approach that involves the hydrogen-assisted reduction of metal precursors and subsequent spontaneous oxidation to yield the target material. The films are prepared in a cold-wall pressure vessel using supercritical carbon dioxide as solvent.Supercritical fluids (SCFs) provide a means to conduct solution-based processes in a medium that behaves much like a gas. By comparison to liquids, SCFs offer lower viscosities, higher diffusivities, miscibility with gas phase reagents and the elimination of surface tension. Moreover, many organic and organometallic compounds, including a number of CVD precursors, are soluble in CO2 or other SCFs. This is an important advantage for reactive depositions because it eliminates precursor volatility constraints and can yield precursor concentrations several orders of magnitude greater than those realized during CVD deposition. H2-assisted SFD has been used to deposit conformal Cu, Co, Ru, Ni, Pt, Au metals in high aspect ratio features. Detailed kinetic studies demonstrate that conformal deposition for Cu facilitated by reaction-rate-limited film growth that is zero order in precursor at the elevated precursor concentrations accessible in SCFs. The SFD technique has now been adapted for the deposition of metal oxides including cerium and hafnium oxides. Films were deposited by the H2-assisted reduction of tetrakis(2,2,6,6-tetramethyl-3,5-heptanedionato) cerium and hafnium precursors. Spontaneous oxidation of the incipient films yields the target materials. Depositions were conducted on silicon test wafers in the presence of hydrogen and trace amounts of water at 200 - 300 °C, for cerium oxide and 250 - 350 °C, for hafnium oxide. No additional oxygen source was necessary. Planar films between 80 and 300 nm thick for cerium oxide and 40 and 90 nm thick for hafnium oxide were deposited and exhibited excellent adhesion to the substrate wafers. XPS analysis shows cerium oxide was deposited as a mixture to the cerous(III) and ceric(IV) forms, while hafnia was deposited solely as HfO2. Annealing at 600 °C reduced the mixed cerium oxide films to pure cerous oxide, while the hafnia films were unchanged. All films were free of carbon contamination within the detection limitations of our XPS instrument. SEM analysis indicated that conformal coverage and filling of via structures is readily accessible using SFD. AFM analysis revealed as-deposited RMS roughness of 3.1 nm for cerium oxide and 1.25 nm for hafnium oxide.
GG9: Poster Session: Multifunctinal Oxide films and Devices
Session Chairs
Thursday AM, April 20, 2006
Salons 8-15 (Marriott)
9:00 PM - GG9.1
Tuning Self-assembled Perovskite-spinel Nanostructures.
Haimei Zheng 1 , Qian Zhan 1 , Florin Zavaliche 1 , Matt Sherburne 1 , Florian Straub 1 , M. Cruz 1 , Long-Qing Chen 2 , Uli Dahmen 3 , R. Ramesh 1
1 Materials Science and Engineering, University of California, Berkeley, Berkeley, California, United States, 2 Materials Science and Engineering, Pennsylvania State University, University Park, Pennsylvania, United States, 3 National Center for Electron Microscopy, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractFormation of nanostructures through self-assembly has attracted increasing interest due to their potential applications in nanotechnology. The ability to predict and control the morphology of a nanostructure is critical for fabricating nanodevices. We report a discovery that the morphology of a nanostructure can be tuned by utilizing the intrinsic property of a crystal, the difference in surface energy. Multiferroic BiFeO3-CoFe2O4 nanostructures were grown on a SrTiO3 substrate using Pulsed Laser Deposition. We found that a (001) oriented substrate results in the formation of rectangular-shaped ferrimagentic CoFe2O4 nanopillars in a ferroelectric BiFeO3 matrix, a (111) oriented substrate leads to a dramatic inversion of pillar and matrix phases, i.e., the triangular-shaped ferroelectric BiFeO3 nanopillars embedded in a ferrimagentic CoFe2O4 matrix, irrespective of the volume fractions of the two phases. Such orientation dependence of the nanostructures is attributed to the difference in surface energy induced different growth mode of the matrix and nanopillars. It is expected that the same strategy can be explored to manipulate many other self-assembled two-phase nanostructures.
9:00 PM - GG9.10
Vanadium Adsorption and Vanadium Oxide Formation on Hematite(0001).
Donald Ellis 1 2 , Jianjian Jin 1 , C-Y Kim 3 , Xiaoyan Ma 4 2 , A. Escuadro 3 , Michael Bedzyk 3 1 2
1 Physics and Astronomy, Northwestern University, Evanston, Illinois, United States, 2 Institute of Environmental Catalysis, Northwestern University, Evanston, Illinois, United States, 3 Mat. Sci. Eng., Northwestern University, Evanston, Illinois, United States, 4 Chemistry, Northwestern University, Evanston, Illinois, United States
Show Abstract9:00 PM - GG9.11
Chemical Vapor Deposition of Titanium-doped Vanadium Oxide Thin Films for Bolometer Application.
Shan-Wei Fan 1 , Wei-Chang Yang Yang 1 , Tai-Bor Wu 1
1 Materials Science and Engineering, National Tsing-Hua University, Hsin-Chu Taiwan
Show AbstractVanadium dioxide is a well-known metal-insulator transition (MIT) material, accompanied by an abrupt resistivity change near room temperature (340 k). The vanadium oxide thin films were fabricated by metal organic chemical vapor deposition (MOCVD) from pure vanadium tri-isopropoxide oxide precursor. Furthermore, we used titanium as