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 a dopant in the MOCVD process. The correlations between the crystal structures and the growth recipes were investigated by x-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM) and x-ray photoelectron spectroscopy (XPS). Also, the electrical characteristics of vanadium oxide thin film resulted from the crystal structures and phase changes were measured by four-point probe equipment. Compared with pure vanadium oxide thin films, titanium-doped vanadium oxide thin films obviously showed a higher temperature coefficient of resistance (TCR) and lower resistivity for bolometer application.
9:00 PM - GG9.12
Low Resistance Ohmic Contact to p-ZnO Using Pt/Ni/Au.
Ji-Myon Lee 1 , Kyoung-Kook Kim 2 , Hitoshi Tampo 2 , Akimasa Yamada 2 , Shigeru Niki 2
1 Materials Science and Metallurgical Engineering, Sunchon National University, Chonnam Korea (the Republic of), 2 Thin Film Compound Semiconductor Team, Institute of Advanced Industrial Science and Technology(AIST), Tsukuba Japan
Show Abstract9:00 PM - GG9.13
Comparative Analysis of VO2 Thin Films Prepared on Sapphire and SiO2/Si Substrates by the Sol-gel Process.
Byung Gyu Chae 1 , Hyun-Tak Kim 1 , Sun-Jin Yun 1 , Bong-Jun Kim 1 , Yong-Wook Lee 1 , Kwang-Yong Kang 1
1 , ETRI, Daejeon Korea (the Republic of)
Show AbstractVO2 thin films were successfully grown on sapphire and SiO2/Si substrates by the sol-gel process. The VO2 phase was well formed during simplified low pressure annealing in oxygen over a relatively wide range of processes. The films prepared on sapphire directly crystallized to the VO2 phase without passing through intermediate phases with increasingthe annealing temperature, resulting in highly [010]-oriented films on Al2O3(1010) substrate. In contrast, the polycrystal films grown on SiO2/Si reached the final VO2 phase with passing through several phases. Mixed phases existed at the interface between the film and substrate due to interdiffusion of the elements, especially vanadium diffusion into the substrate. For the films on sapphire, the phases with low-valent vanadium appeared drastically at the interface region along the depth, whereas the phase of the polycrystal film slowly changed into a low valence state at the initial stage of the interface and then returned to a high value. An abrupt change in resistivity of 3-4 orders of magnitude occurred at a transition temperature, and these properties were investigated in detail with the crystallization of the film.
9:00 PM - GG9.14
Development of Devices based on a-InGaO3(ZnO)x filmsDeposited by Pulsed Laser Deposition
Arun Suresh 1 , Anuj Dhawan 1 , Praveen Gollakota 1 , John Muth 1
1 Electrical and computer engineering, NC State University, Raleigh, North Carolina, United States
Show AbstractTransparent amorphous oxide semiconductors (AOS) have high potential for being useful in optoelectronic applications because uniform and smooth depositions are achievable at room temperature with reasonable conductivities. AOS based on ternary-quaternary oxides are thought to exploit their intrinsic structure which gives them unique transport properties and high conductivities compared to other amorphous materials. In this study, InGaO3(ZnO)x system based highly transparent and conductive films were deposited using Pulsed Laser Deposition (PLD). Various techniques were used to characterize the films, including x-ray, AFM, profilometry, transmission etc. The effect of the deposition ambience on the physical, optical and electrical properties of the films was studied. Post deposition annealing studies on the films will be discussed including the effect of the onset of crystallization on the electronic transport properties and associated changes in surface morphology.
9:00 PM - GG9.15
Vapor-Phase Functionalization of Nanostructured Gradient-Index Titanium Dioxide Thin Films
Andy van Popta 1 , John Steele 1 , Shufen Tsoi 1 , Enrico Fok 2 , Jonathan Veinot 2 , Michael Brett 1 , Jeremy Sit 1
1 Electrical and Computer Engineering, University of Alberta, Edmonton, Alberta, Canada, 2 Chemistry, University of Alberta, Edmonton, Alberta, Canada
Show AbstractChemical treatments, when applied to nanostructured oxide thin films, can be used to generate added functionality for devices. In this study, nanostructured thin films were prepared by glancing angle deposition (GLAD) of rutile titanium dioxide, and functionalized with a monolayer of 3,3,3-trifluoropropyl-trichlorosilane to render the films insensitive to variable humidity conditions.GLAD is a form of physical vapor deposition that combines in situ substrate motion with low adatom mobility to create engineered thin-film nanostructures with high porosity. In the past, GLAD has successfully been applied to both inorganic and organic compounds to create columnar thin films composed of helices, chevrons, vertical posts, and various heterostructures. We will present experimental results detailing how GLAD was used to fabricate a defect-mode rugate filter through careful manipulation of the substrate tilt angle. At large tilt angles, the effective refractive index is low because the thin-film layer is primarily composed of air-filled pores. At small substrate tilt angles, the effective refractive index is high because the thin-film layer is very dense. By oscillating the deposition angle between 30° and 80°, the desired sinusoidal refractive-index profile can be created. A defect-mode, in the form of a narrow-bandpass, was added to the filter by integrating a π phase-shift into the index profile of the film. Like many porous optical materials, the gradient-index TiO2 filter is sensitive to humid environments. At high humidity levels, water adsorption within the thin-film pores causes the effective refractive index to increase, producing a large red-shift in the optical transmission spectrum. The defect-mode experiences a 40 nm wavelength-shift as the relative humidity is increased from 0% to 90%. In order to stabilize the optical properties, the porous films were placed in an oxygen plasma reactive ion etch to saturate the TiO2 surface in hydroxyl groups, and then functionalized with 3,3,3-trifluoropropyl-trichlorosilane (TFP-SiCl3). Application of TFP-SiCl3 reduces the shift in the defect-mode wavelength by more than six times over a large range of humidity levels. Aqueous contact angle measurements show that the originally hydrophilic TiO2 films become hydrophobic when functionalized (films exhibit advancing contact angles as large as 118°), and capacitance measurements are used to confirm these results. The goal of applying a siloxane-based chemistry is to eliminate sensitivity to water vapor; however, the basic techniques involved can easily be adapted to alternative chemical reagents in order to create functionalized optical devices for use in a variety of gas sensors and nano-biosensors.
9:00 PM - GG9.17
Microwave Properties of Magnetron Sputtered Ba0.5Sr0.5TiO3 Thin Films on (0001) Sapphire Substrates
Ernest Fardin 1 , Anthony Holland 1 , Geoffrey Reeves 1 , Patrick Reichart 2
1 School of Electrical and Computer Engineering, RMIT University, Melbourne, Victoria, Australia, 2 School of Physics, University of Melbourne, Melbourne, Victoria, Australia
Show AbstractMany studies of Barium Strontium Titanate (BST) thin films for RF / microwave applications have employed MgO, LaAlO3 or Pt/Si as the substrate material for BST deposition. However, there have been relatively few reports of BST films grown on sapphire, despite the excellent microwave properties of this material. In this investigation, BST thin films were deposited by RF magnetron sputtering on c-plane sapphire substrates. Deposition was performed in a gas mixture of Ar/O2 9:1 at 5, 10, 20, 30 and 40 mTorr, in order to investigate the effect of the process pressure on the film stoichiometry. Interdigital capacitors patterned on the film surface were used to measure the dielectric tunability and loss tangent from 40 MHz to 20 GHz. Thick Au conductors were electroplated to minimize conductor losses. Post deposition annealing in air was found to significantly improve the tunability of the sputtered films.
9:00 PM - GG9.18
Structuring of Low Firing Temperature PZT Thick Films by Photolithography.
Stefan Schimpf 1 , Erik Ansorge 1 , Bertram Schmidt 1
1 IMOS, Otto-von-Guericke-University , Magdeburg, Sachsen-Anhalt, Germany
Show AbstractSummaryStructured piezoelectric PZT thick films were fabricated on silicon wafers. Different supplements, like lead oxide and different glasses, were added to the PZT to enhance the sintering. The films were structured by doctor blading on an epoxy based photoresist (SU8) mask. This allows very accurate micro patterns of high quality piezoelectric material. A multi-step firing process was developed to gain PZT structures more than 100µm thick and smaller than 100µm in lateral size. The structures were electrically contacted, poled and characterized.MotivationPZT (Lead Zirconate Titanate) is a cost-efficient and readily available piezoelectric material. Generally it is used by sintering powder into macro-sized electroceramics. Micro-Electro-Mechanical Systems often require forces or torques that could be generated by microstructured PZT films. This is a simple, flexible and low-cost way to drive MEMS. Conventional PZT thick films are produced by screen printing PZT with a lead oxide supplement [1]. These films are virtually impossible to be produced and aligned in microscale, since the screen printing process is very inaccurate. They have to be fired at temperatures of about 900°C-1000°C. This leads to a degradation of the platinum electrodes [2] and will prevent the use of any temperature sensitive structures along with the PZT. Additionally the lead oxide tends to leak out of the PZT structure. Apart from being poisonous and harmful to the environment this lead oxide can interfere with other structures on the substrate.ResultsThe epoxy based photoresist SU8 was used as a mask for printing PZT paste. The accuracy of the fabricated structures was limited by the photolithography and the grain size in the paste only. Test patterns were designed and the limitations of possible geometries were investigated. Different glasses were used as supplements to promote the sintering at reduced firing temperatures. The results were compared to conventional lead oxide containing PZT films in terms of mechanical stability and electromechanical behavior. Since the glasses have different softening points different firing profiles were used and compared. References[1] Ferrari V., Marioli D., Taroni A., Ranucci E., Multisensor array of mass microbalances for chemical detection based on resonant piezo-layers of screen-printed PZT, Sensors and Actuators B, Vol. 68, No. 1, August 2000, pp. 81-87(7)[2] Firebaugh S., Jensen K. Schmidt M., Investigation of High-Temperature Degradation of Platinum Thin Films with an In Situ Resistance Measurement Apparatus, J. Microel. Sys., Vol. 7, No. 1, March 1998
9:00 PM - GG9.2
Ruddlesden-Popper-type Heterostructures in AO-doped SrTiO3 (A=Sr2+,Ca2+,Ba2+): Structural and Compositional Analysis at the Atomic Level.
Saso Sturm 1 , Miran Ceh 1
1 Department for nanostructured materials, Jozef Stefan Institute, Ljubljana Slovenia
Show AbstractPerovskite-based thin films have been extensively studied in recent years, mainly due to their excellent ferroelectric, dielectric and optical properties. For instance, SrTiO3, an ideal perovskite, reveals a wide range of electrical behavior. In its undoped form it is a paraelectric with a high dielectric constant, while doping with various elements transforms it into superconductor. However, the desired properties of perovskite-based thin films can be suppressed by the formation of defects, which are often initiated during film deposition. Misfit dislocations, formed due to the lattice mismatch between substrate material and the thin film, are such commonly observed defects. In order to reduce the formation of misfit dislocations in perovskite films a variety of uniformly structured buffer layers can be used between the substrate and thin films. In our study, we propose a perovskite-based heterostructred buffer layer, in which the misfit strain would be gradually reduced. A promising candidate for heterostructred perovskite-based buffer layer is a Ruddlesden-Popper-like structure, which we produced by an accommodation of surplus AO in SrTiO3 (A= Sr2+, Ca2+, Ba2+ ). It is known, that the non-stoichiometry in perovskites (ABO3) caused by an AO-excess is commonly accommodated by formation of rock-salt type planar faults, also called Ruddlesden-Popper (RP) faults. The resulting heterostructure is composed by alteration of a few unit cells thick perovskite layers (ABO3) with one layer of an AO-rich rock-salt type structure (RP-faults). By combining quantitative high-resolution transmission electron microscopy (HRTEM) and quantitative high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) of these heterostructures in AO-doped SrTiO3, we were able to reconstruct their structure and the composition at the atomic level. We found that the structure of RP-faults in the heterostructure remains unchanged regardless of different ions added to SrTiO3. On the contrary, the composition of these planar faults, as well as the degree of lattice distortions in the perovskite layers and RP-faults, are related to the ion sizes of added ions. Therefore, by introducing A-type cations with different ionic sizes, such as Ca2+ and Ba2+, the lattice parameters of the heterostructure can be modified, depending on the desired structural properties of a buffer layer between the substrate and various perovskite-based thin films.
9:00 PM - GG9.20
Deposition of Fluorine Doped Tin Oxide Thin Films on Polymers by Plasma Enhanced Chemical Vapor Deposition.
Jerome Pulpytel 1 , Marie Jubaulta 1 , Mickael Redolfi 2 , Hubert Cachet 3 , Farzaneh Arefi-Khonsari 1
1 LGPPTS, Universite Pierre et Marie Curie, Paris France, 2 LIMHP, Universite Paris, Paris France, 3 LISE, Universite Pierre et Marie Curie, Paris France
Show Abstract9:00 PM - GG9.21
Photoelectrical Properties Presented by Indium Zinc Oxide Thin Films and TTFTs.
Goncalo Goncalves 1 , Rodrigo Martins 1 , Elvira Fortunato 1
1 Materials Science, FCT-UNL, Caparica Portugal
Show Abstract9:00 PM - GG9.22
Studies of Strains in (Pb,Sr)TiO3 Films on NdGaO3 Substrates.
Yuan Lin 1 , Y. Wang 1 , X. Chen 2 , C. Chen 2 , A. Bhalla 3 , Q. Jia 1
1 Material Science & Technology Division, Los Alamos National Lab, Los Alamos, New Mexico, United States, 2 Texas Center for Superconductivity and Advanced Materials, and Department of Physics , University of Houston, Houston, Texas, United States, 3 Materials Research Lab. , Penn. State University, University Park, Pennsylvania, United States
Show Abstract9:00 PM - GG9.23
Annealing Behavior of (HfO2)x(Al2O3)1-x Nanolaminates: Changes in Film Morphology and Structure.
Ramarajesh Katamreddy 1 2 , Ronald Inman 2 , Axel Soulet 2 , Gregory Jursich 2 , Christos Takoudis 1
1 Chemical Engineering, University of Illinois at Chicago, Chicago, Illinois, United States, 2 , American Air Liquide, Countryside, Illinois, United States
Show Abstract9:00 PM - GG9.24
Decreasing Splitting of LO-TO Phonons in BaTiO3 Nanoparticles Due to Unit-cell Volume.
Tung-Ching Huang 1 , Wen-Feng Hsieh 1
1 Department of Photonics and Institute of Electro-Optical Engineering, National Chiao Tung University, Hsinchu Taiwan
Show Abstract9:00 PM - GG9.3
Preparation and Characterization of Ce(1-x)TxO2,(T=Mn,Cr, x = 0.05) by Chemical and Solid State Method.
J Sarala Shanthi 1 2 , M Kottiasamy 2 , K Sethupathi 1 , Mamidanna Ramachandra Rao 1 2
1 Department of Physics, Indian Institute of Technology Madras, Chennai, Tamil Nadu, India, 2 Materials Science Research Centre, Indian Institute of Technology Madras, chennai, Tamilnadu, India
Show Abstract9:00 PM - GG9.4
Design of Single-Source Mixed Acetylacetonate Precursors for Group 13 Oxide Thin Film Growth
Bradley Fahlman 1 , Dan Denomme 1
1 Department of Chemistry, Central Michigan University, Mount Pleasant, Michigan, United States
Show AbstractA plethora of work has focused on the use of metal acetylacetonate (acac) compounds for metal and metal oxide thin film growth by chemical vapor deposition (CVD). It has been found that precursor volatility generally follows the order: M(hfac)x > M(tfac)x >> M(acac)x. However, to date, no studies have employed mixed complexes such as M(acac)x(tfac)y or M(acac)x(hfac)y. Herein, we report the synthesis/characterization of these complexes, along with volatility studies and preliminary thin film growth.
9:00 PM - GG9.5
Low-Temperature Densification and Grain Growth of Bi2O3 - Doped Ceria Gadolinia Ceramics
Jesus Tartaj 1 , Vanesa Gil 1 , Carlos Moure 1
1 Electroceramics, CSIC, Ceramic and Glass institute, Madrid Spain
Show AbstractSolid oxide fuel cells, SOFCs, have several advantages as, among others, it can operate not only on hydrogen but also on hydrocarbons and, given that the operating temperatures are sufficiently elevated (800-900C), without using an external reformer, i.e., the reforming of the fuels is carried out within the fuel cell (internal reforming). From a point of view of its commercialization, the above described SOFC present more problems that advantages, as for example, the use of metals as interconnects is not possible at such operating temperature and, therefore, a decrease in the same up to about 550-700C would be desirable. In such operating conditions a wider choice of interconector materials would be possible leading, thus, to a lower cost, higher mechanical strength and, finally, to a longer lifetime of the cell. However, being this so, a device operating in such thermal conditions, i.e., at intermediate temperatures and currently designated as IT-SOFCs, would need the availability of an electrolyte having an ionic conductivity at such temperature range as high as that of YSZ at 850-1000C, and no many ceramic materials are known so far as the most potential candidate for the alternative. Rare earth oxide doped-ceria (RDC) ceramics where R is mainly Y2O3, Gd2O3, and Sm2O3, i.e., YDC, GDC, and SDC, are considered as the best candidate due to their higher ionic conductivity (4 to 9 S/m at 700C). However, two main disadvantages have to be considered as extremely important difficulties before making a final decision for using RDC as the only alternative for electrolyte in IT-SOFCs. One of them is the high electronic conductivity at the reducing side leading to a lower open circuit voltage, along with higher electrochemical oxygen permeation than YSZ. Another one, and the most important, is the difficulty of RDC ceramics to sinter at a temperature reasonably low (1350 to 1400C) with a density level of at least 95-98 % of theoretical density. The use of nanosized GDC powders as an alternative has the strong inconvenient of its rapid shrinkage at low-temperature, becoming this raw material as incompatible with other ceramic components of the SOFC in a co-firing process. Besides this, such nanosized powders are too expensive.We report in this paper, at our best knowledge for the first time in the case of GDC ceramics, the preparation of dense (≥ 98 % of theoretical density) Ce0.9Gd0.1O1.95 ceramic electrolytes sintered at 1200 to 1400C for 4 h, starting from a commercial submicronized powder by using bismuth oxide as a sintering aid. The effect of Bi2O3 additions on the grain-growth process of these dense GDC ceramics will also be reported.
9:00 PM - GG9.6
Thin Film Solid Oxide Fuel Cells on Nanoporous Substrates.
Yong-il Park 1 , Pei-Chen Su 2 , Gug Ho Yoon 1 , Eun Hyung Kim 1 , Yuji Saito 2 , Fritz Prinz 2
1 School of Materials & System Engineering, Kumoh National Institute of Technology, Gumi, Kyungbuk, Korea (the Republic of), 2 Rapid Prototyping Laboratory, Stanford University, Stanford, California, United States
Show AbstractLow-temperature solid oxide fuel cells were fabricated using yttria stabilized zirconia (YSZ) thin films having submicrometer thickness. 30nm~300nm-thick YSZ films were obtained by oxidizing Y-Zr alloy thin films deposited onto anodic nanoporous alumina substrates having pore diameter of 20nm and 200nm using dc-magnetron sputtering at room temperature. During the thermal oxidation, the alloy films were successfully transformed to defect-free oxide thin films. Volume expansion induced from the oxidation of the alloy resulted in dense oxide thin films that are free from hydrogen permeation. Conductivity of YSZ thin films at room temperature was also measured and compared with the reported conductivity of YSZ ceramics. Fuel cell operation test was performed using the fabricated thin film fuel cell at low temperature from 300 to 400 degrees Celsius.
9:00 PM - GG9.7
Atomic Layer Deposition of Thin-Film Yttria-Stabilized Zirconia Nanolaminates for Ultra-Thin Solid Oxide Fuel Cell Electrolyte.
Cynthia Ginestra 1 , Paul McIntyre 1
1 , Stanford University, Stanford, California, United States
Show AbstractSolid oxide fuel cells (SOFCs) are interesting as an energy conversion technology with potential applications in transportation systems. A major disadvantage of current SOFC technology, however, is the relatively high operating temperatures (800 – 1000 °C), limiting their range of practical use to large power systems. Reducing operating temperatures can be achieved by making the SOFC electrolyte membrane thinner, thereby making it easier for oxygen ions to move across the membrane at lower temperatures. In an effort to further the development of ultra-thin SOFCs, nano-structured laminates of ZrO2 and Y2O3 (total thickness ≤ 20 nm) were grown via atomic layer deposition (ALD) in order to prepare yttria-stabilized zirconia films for electrolytic property studies. Maximum oxygen diffusivity in bulk YSZ occurs in concentrations of 8 molar percent yttria. Therefore, as a starting point in studying the oxygen diffusion characteristics of nanoscale thin film YSZ, multilayer structures of yttria (Y2O3) and zirconia (ZrO2) were deposited onto silicon substrates via ALD in a nominal 1:12 layer thickness ratio. The precursors tris(cyclopentadienyl)yttrium, zirconium tetrachloride and water were used in the ALD process. Post-deposition annealing and low angle x-ray diffraction were used to investigate the interdiffusion kinetics of Y2O3 and ZrO2 as a function of temperature and time. The crystallinity and phase evolution of the annealed films were also examined in order to probe for the cubic phase of YSZ.
9:00 PM - GG9.8
Highly Near-Infrared Transparent In2O3 Thin-Film Electrodes for Precision Teng-Man Electro-Optic Measurements.
Lian Wang 1 2 , Yu Yang 1 2 , Tobin Marks 1 2 , Zhifu Liu 2 3 , Seng-Tiong Ho 2 3
1 Department of Chemistry, Northwestern University, Evanston, Illinois, United States, 2 the Materials Research Center, Northwestern University, Evanston, Illinois, United States, 3 Department of Electrical and Computer Engineering, Northwestern University, Evanston, Illinois, United States
Show AbstractA series of highly near-infrared (NIR) transparent conducting oxides, In2O3 thin films, has been grown by ion-assisted deposition (IAD) at room temperature, and their optical and electrical properties characterized. The NIR transparency and the plasma edge frequency can be engineered through control of the film deposition conditions. Owing to great compatibility with both inorganic and organic electro-optic (EO) materials, the as-deposited In2O3 thin films were employed as transparent electrodes for direct EO characterization measurements via the Teng-Man technique. Using LiNbO3 as the standard, the relationship between the degree of electrode NIR transparency and Teng-Man EO measurement accuracy was evaluated. It is found that In2O3 electrodes can be tailored to be highly NIR transparent with considerable condcutivities, thus providing far more accurate Teng-Man EO coefficient quantification than traditional ITO (tin-doped indium oxide) electrodes. In addition, the EO coefficients of an organic EO material, namely stilbazolium-based self-assembled superlattice (SAS) thin film, was directly determined for the first time by the Teng-Man technique using an optimized In2O3 electrode. EO coefficients r33 of 42.2, 13.1, and 6.4 pm/V are obtained at 633, 1064, and 1310 nm, respectively. Importantly, the current highly NIR transparent In2O3 films should have many other applications in NIR-sensitive opto-electronic devices and measurements.
9:00 PM - GG9.9
Defect Luminescence from N-doped ZnO Thin Films.
Hui Wang 1 , Kwong-Chung Lo 1 , Ho-pui Ho 1
1 Electronic Engineering, The Chinese University of Hong Kong, Hong Kong China
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.
GG10: Oxide Films for Magnetic and Optical Applications
Session Chairs
Thursday AM, April 20, 2006
Room 2018 (Moscone West)
9:15 AM - **GG10.1
Effect of Nonmagnetic Doping on Magneto-Transport Properties of Oxide-Based Zn1-x(Co,Mn)xO Dilute Magnetic Semiconductors.
kartik Ghosh 1 , Govind Mundada 1 , Srikanth Manchiraju 1 , Theodore W Kehl 1 , Sandhya Pulugam 1 , Pawan Kahol 1
1 Physics,Astronomy, and Materials Science, Missouri State University, Springfield, Missouri, United States
Show AbstractRecently, oxide-based dilute magnetic semiconductors (DMS) have attracted an immense research interest to the scientists due to the possibility of inducing room temperature ferromagnetism and potential uses in novel spintronic devices. Zinc Oxide (ZnO), a high frequency transparent opto-electronic material, is an interesting prospect for spintronics due to its unique electrical, magnetic, and optical properties. ZnO, doped with a transition metal like cobalt or manganese and non magnetic metals such as Ti, Al, and Cu, is a DMS which has strong exchange interaction between localized s-p band carriers and d band electrons. High quality epitaxial thin films of nonmagnetic doped oxide-based DMS materials have been grown by pulsed laser deposition technique on various substrates such as single crystal of sapphire (001), silicon (100), and quartz at 600C in 5x10-5 Torr of oxygen. The effect of non magnetic doping on the structural and electro-magnetic properties of these films has been studied using various techniques such as Raman Spectroscopy, X-Ray Diffraction, Scanning Electron Microscopy, and Magneto-Transport. X-Ray Diffraction and Raman spectra confirm the epitaxial nature of the thin films. Detailed temperature and magnetic field dependent resistivity, magnetoresistance, and Hall effect data will be presented. This work is supported by the National Science Foundation (award number DMR-0321187) and Research Corporation (award number CC6166).
9:45 AM - GG10.2
Improved Photoluminescence Yield by Controlling Erbium Doping Level and Its Distribution in Yttrium Oxide Thin Films.
Trinh Van 1 , John Hoang 1 , Jane Chang 1
1 Chemical & Biomolecular Engineering, University of California, Los Angeles, Los Angeles, California, United States
Show Abstract Miniaturizing the erbium-doped optical fiber amplifier (~20 m in length) into a small, compact planar optical amplifier that can be integrated with other optical and electronic devices on a single chip (optoelectronics) offers great promise in optical communication as an alternative to the electronic technology. Though SiO2 has been widely used as a host material for Er-doped optical amplifiers, its low solubility for Er ions limits its application in miniaturized devices. Another limiting factor in miniaturizing these amplifiers is that, while a high concentration of Er ions are desired to achieve the necessary gain of the device, the conventional method for Er incorporation, ion implantation followed by a high temperature annealing, typically results in Er clustering and precipitate formation and quenches the Er luminescence. In this study, we synthesized yttrium oxide (Y2O3) as the host material since it has an identical crystal structure and a very similar lattice constant to that of erbium oxide (Er2O3), allowing for a much higher Er concentration to be incorporated, compared to that in the SiO2 host. We demonstrated radical-enhanced atomic layer deposition (RE-ALD) as a superior method for Er incorporation with spatial control. With an appropriate choice of precursor chemistry, we were able to synthesize Er-doped Y2O3 thin films at temperatures below 400 °C. In addition, the Er doping level and its distribution in the Y2O3 lattice were effectively controlled by combining RE-ALD of Y2O3 and Er2O3 in an alternating fashion, confirmed by X-ray photoelectron spectroscopy and extended X-ray absorption fine structure. Incorporation of optically active Er3+ in the Y2O3 host with concentration that is at least three orders of magnitude higher than the Er solubility limit in SiO2 was achieved, thus making it possible to observe significant photoluminescence (PL) at room temperature for a fairly thin film (~50 nm). Specifically, the room-temperature PL at 1.54 micron characteristic of the Er intra 4f transition showed various well resolved Stark features, indicating the proper incorporation of Er in the Y2O3 host. The result is promising, since the film is fairly thin and no annealing at high temperature is needed to activate the Er ions. The effective absorption cross section for Er3+ ions incorporated in Y2O3 was determined to be ~ 10-18 cm2, about three orders of magnitude larger than the direct optical absorption cross section reported for Er3+ ions in the SiO2 host.[1] Direct measurement of the Er absorption cross section by cavity ringdown spectroscopy was recently performed to further assess the luminescence mechanism responsible for this enhanced PL efficiency.[2][1] T.T. Van and J.P.Chang, Appl. Phys. Lett. 87, 011907 (2005).[2] W.M.M. Kessels, B. Hoex, I.M.P. Aarts, T.T. Van, J.P. Chang, H. Mertens, A. Polman, and M.C.M. van de Sanden, abstract submitted to MRS 2006 Spring meeting.
10:00 AM - GG10.3
Studies of Interfacial Optical and Electrical Properties on Transparent Dielectrics/ZnO Systems.
Ran Shi Wang 1 , Jin An 1 , H.C. Ong 1
1 Physics, The Chinese University of Hong Kong, Hong Kong Hong Kong
Show Abstract10:15 AM - GG10.4
Combinatorial Study on In-Ga-Zn-O Semiconductor Films as Active-channel Layers for Thin-film Transistor.
Tatsuya Iwasaki 1 , Naho Itagaki 1 , Tohru Den 1 , Hideya Kumomi 1 , Kenji Nomura 2 , Toshio Kamiya 2 3 , Hideo Hosono 2 3
1 Canon Research Center, CANON INC., Tokyo Japan, 2 ERATO-SORST, Japan Science and Technology Agency, Tokyo Institute of Technology, Yokohama Japan, 3 Materials and Structures Laboratory, Tokyo Institute of Technology, Yokohama Japan
Show Abstract Thin-film transistors (TFTs) using oxide semiconductors are promising devices for flat-panel displays and system-on-glass due to their good device performance, high optical transparency, and low process temperature. Recently, great interest has been directed toward TFTs with amorphous-InGaZnO4 channel layers since they can be fabricated at room temperature on flexible substrates and exhibit high saturation mobility of 6-9cm2V-1sec-1 [1]. Here we report the chemical composition dependence of In-Ga-Zn-O film properties and the device characteristics using these films as the TFT channel layers. The In-Ga-Zn-O films were prepared by radio-frequency magnetron sputtering method at room temperature in mixed-gas atmosphere of argon and oxygen. The combinatorial synthesis technique was adopted to study compositional dependence of In-Ga-Zn-O films efficiently. The newly developed co-sputtering equipment with three kinds of cathodes (In2O3, Ga2O3 and ZnO), which makes the compositionally graded film with uniform thickness across the 4-inch substrate, was effectively utilized. The chemical composition, the crystallinity, the electrical conductivity and the optical transmission spectrum were evaluated for the compositional libraries of In-Ga-Zn-O films. Further, we investigated the device characteristics of TFTs having the In-Ga-Zn-O channel layers with various compositions. In order to study the In-Ga-Zn-O chemical composition dependency in the channel layer of TFTs, we applied the combinatorial scheme to the device production. The TFT libraries, having various In-Ga-Zn-O layers as the channel layer, were fabricated by using above compositionally graded films and photolithography techniques. Over 10000 kinds of TFTs were fabricated on a substrate at a time and compared with each other. The TFT libraries enabled us to systematically survey the device characteristics of TFTs in wide compositional range of channel material. It is found that the TFT characteristics are very sensitive to the chemical composition ratio of In:Ga:Zn and oxygen partial pressure during deposition. Some devices exhibited good performance of the field-effect mobility of ~10 cm2V-1sec-1 and on-to-off current ratio of ~108. The relationship between the device characteristics and the film properties for various chemical compositions of In-Ga-Zn-O are discussed. Finally, based on the experimental results, we propose a favorable composition of In-Ga-Zn-O films for active channel layers of transparent TFTs.[1] K.Nomura, H.Ohta, A.Takagi, T.Kamiya, M.Hirano and H.Hosono, Nature, 432, 488-492 (2004).
10:30 AM - GG10.5
Characterization of Glancing Angle Deposition Thin Film Optical Filters with Engineered Index Profiles.
James Gospodyn 1 , Peter Hrudey 1 , Michael Brett 1 , Jeremy Sit 1
1 Electrical and Computer Engineering, University of Alberta, Edmonton, Alberta, Canada
Show AbstractThe thin film fabrication technique glancing angle deposition (GLAD) produces porous, columnar films by exploiting highly oblique angle deposition. Central to the GLAD technique is in situ control of the substrate orientation which allows the growing columns to be sculpted into various morphologies including helices and tilted or vertical columns. By using a rapid rotation in the substrate, the films are composed of isolated columns oriented normal to the substrate. Subsequently, by introducing an exponential decrease in the incoming flux angle as the film grows, we can achieve a second layer but of a higher film density. Thus a film grown in this case is composed of a low-index layer of vertical isolated columns, which is capped-off by a high-index, solid layer of the same material. In our method, by repeating this sequence, we can form a multiple-period high-low dielectric stack. By using this technique, we have a one deposition process for achieving a high-low dielectric stack. Furthermore, we can engineer the thickness and periodicity of the films, as well as the form of the periodicity from abrupt high-low (dielectric stacks), to a sinusoidal index variation (rugate filters).In this study, we examine both high-low index and rugate filter films composed of SiO2, a simple inorganic optical material, and Eu-doped Y2O3, an inorganic phosphor. We characterize the index profile of the films using spectroscopic Mueller matrix ellipsometry and examine the morphology of the columns throughout the growth of the film through scanning electron microscopy studies. This leads to a complete description of the optical properties of these films as a function of wavelength. We also examine how modifying the index profile of Y2O3:Eu films affects their photoluminescence output – studies here include the effect the differences between high-low stacks compared with sinusoidal index variation, the emissive output dependence on the number of periods for a given periodicity, as well as the effect that the periodicity has on the luminescence output.
10:45 AM - GG10.6
Novel Low-Driving-Voltage Organic Electro-Optic Modulators using Transparent Conducting Oxides as Electrodes.
Lian Wang 1 2 , Yu Yang 1 2 , Tobin Marks 1 2 , Guoyang Xu 2 3 , Zhifu Liu 2 3 , Boyang Liu 2 3 , Seng-Tiong Ho 2 3
1 Department of Chemistry, Northwestern University, Evanston, Illinois, United States, 2 the Materials Research Center, Northwestern University, Evanston, Illinois, United States, 3 Department of Electrical and Computer Engineering, Northwestern University, Evanston, Illinois, United States
Show AbstractA novel device structure for organic electro-optic (EO) modulators using transparent conducting oxides (TCOs) as electrodes was demonstrated to achieve the low driving voltage (Vπ) for the first time. In contrast to the conventional EO modulation structure, this new TCO electrode structure is compatible with organic EO materials, and can in principle decrease Vπ 4-6 times lower by diminishing the electrode distance. Two series of TCO electrodes include ZnO bottom electrodes grown by metal-organic chemical vapor deposition (MOCVD) from 400 to 475 oC and In2O3 top electrodes grown by ion-assisted deposition (IAD) at room temperature, and their electrical and optical properties were further characterized. Through deliberated control of carrier concentrations, TCO electrodes are capable of exhibiting considerable conductivities and very low optical absorption coefficients in near-IR region, and thus promise the efficient EO modulation in 1300~1550 nm wavelength range. Using optimized TCO electrodes and an organic EO material (poled guest-host chromophore/polymer material AJL8/APC), the organic EO modulators shows a very low driving voltage Vπ = 2.8 V on an 8-mm device at 1310 nm. This corresponds to Vπ = 1.1 V for a 1-cm device in a push-pull configuration. In addition to organic EO modulators, the present TCO electrode structure was also successfully integrated into BaTiO3-based inorganic EO modulators revealing the generality of this novel TCO electrode strategy.
11:00 AM - GG10:Magneto
BREAK
GG11: ZnO Oxide Films for Optoelectronic Applications
Session Chairs
Thursday PM, April 20, 2006
Room 2018 (Moscone West)
11:30 AM - **GG11.1
Synthesis of ZnO Based Exotic Nanostructures Using a Novel Sol-gel Technique.
Michael Snure 1 , Ashutosh Tiwari 1
1 Materials Science & Engineering, university of utah, Salt Lake City, Utah, United States
Show AbstractIn this presentation we will show some of our very exciting results on the growth of ZnO based diluted magnetic semiconducting nanostructures using a novel sol-gel nanofabrication technique. Imprtant aspects of this technique will be discussed. Various different kinds of nanostructures such as nanodots, nanorods and nanorings, prepared during this work will be described. A detailed study of structural, electrical, magnetic and optical properties of these systems will be presented.
12:00 PM - GG11.2
Trace Detection and Related Solubility Issues in MOCVD Grown Pure and Mixed-phase ZnO Films
Laxmikant Saraf 1 , Zheming Wang 1 , V Shutthanandan 1 , Scott Lea 1 , S Heald 1 , M Engelhard 1 , C Wang 1 , P Nachimuthu 1 , J Swoboda 1 , S Thevuthasan 1 , S Chambers 1
1 , Pacific Northwest National Laboratory, Richland, Washington, United States
Show AbstractPure and doped ZnO is a multifunctional oxide with applications in thermoelectrics, UV detectors, wide-band gap ferromagnetic semiconductors, dielectrics and environmental sensors. Attempts to modify the physical properties of ZnO by incorporating new elements are an important factor, which may provide fundamental insights and strength of adaptability in ZnO. Excellent optical emission properties of ZnO can be used to detect the effect of dopants in it and can have applications as trace detectors. The structural anisotropy in hexagonal ZnO drives the natural growth in out-of-plane c-axis orientation on most of the substrates except single crystal r-Al2O3, where an epitaxial growth would be in (110) direction. Here we discuss our results related to barium traces and chromium phase mixing in oriented ZnO films grown by MOCVD on Si (100) and single crystal r-Al2O3. The analysis was carried out by AES, XPS, XRD, HRTEM, EXAFS, PL, RBS and PIXE techniques. Optical emission results at liquid helium temperatures indicate features corresponding to traces of barium. Upon chromium phase mixing, it was observed that chromium prefers to stay in an octahedral environment than tetrahedral environment. XPS depth profiling and RBS experiments reveal the segregating nature of chromium at the interface. We will discuss the overall results in the context of modification of physical properties in ZnO in order to gain a wider acceptance of ZnO as a truly multifunctional oxide.
12:15 PM - GG11.3
Preparation of Atomically Smooth ZnO layer on GaN Template by Laser Deposition.
Takeshi Okato 1 2 , Minoru Obara 1 , Menno Kappers 2 , Mark Blamire 2
1 Electronics and Electrical Engineering, Keio University, Yokohama Japan, 2 Materials Science and Metallurgy, University of Cambridge, Cambridge United Kingdom
Show Abstract12:30 PM - GG11.4
Formation Of Impurity Complexes During The Growth Of Undoped And Nitrogen Doped Zinc Oxide.
Norbert Nickel 1 , Felice Friedrich 1 , Pierre Galtier 2 , Jean-Francois Rommeluere 2
1 , Hahn-Meitner-Institut Berlin, Berlin Germany, 2 , CNRS-LPSC, Meudon France
Show AbstractGG12: Transparent Conducting Oxide Films
Session Chairs
Thursday PM, April 20, 2006
Room 2018 (Moscone West)
2:30 PM - **GG12.1
Optimization of Transparent Conducting Amorphous In-Zn-O (a-IZO) Thin Films
John Perkins 1 , Maikel van Hest 1 , Matthew Dabney 1 , Lynn Gedvilas 1 , Brian Keyes 1 , Bobby To 1 , David Ginley 1 , Matthew Taylor 2 , Dennis Readey 2
1 , National Renewable Energy Lab., Golden, Colorado, United States, 2 , Colorado School of Mines, Golden, Colorado, United States
Show AbstractAmorphous In-Zn-O (a-IZO) transparent conducting oxide (TCO) thin films are increasingly becoming the TCO of choice for applications such as flat panel displays. The published nominal standard composition for this application is 10 wt. % ZnO in In2O3 (InxZn1-xOy with x = 0.84). When deposited by sputtering in Ar at low substrate temperatures (TS < 100 °C), such films are typically smooth, conducting and transparent. Using a sputtering based composition spread combinatorial approach to make IZO thin films over nearly the full composition range (x ~ 0.05 to 0.95), we have found that IZO films deposited in Ar at 100 °C are amorphous for x = ~ 0.65 to ~ 0.85, with a maximum conductivity of ~ 3000 Ω-1-cm-1 at x ~ 0.80 and an RMS roughness ~ 0.4 nm. Subsequent sequential annealing experiments in both Ar and air show that a-IZO films are structurally, electrically and optically quite robust for anneals up to ~ 500 or 600 °C. In this work, we discuss two recent results. First, that the In/Zn ratio for maximum conductivity depends upon the amount of O2 in the sputtering gas and second, the coupled substrate temperature and metals composition bounds for the deposition of amorphous IZO thin films.
3:00 PM - GG12.2
Band Structure and Optical Properties of n-type and p-type Transparent Conducting Oxides.
Suhuai Wei 1
1 , National Renewable Energy Laboratory, Golden, Colorado, United States
Show AbstractTransparent conducting oxides (TCOs) are a group of unique materials that are transparent and at the same time conductive, thus are suitable for optoelectronic device applications. Using first-principles method, we have studied the band structure and optical properties of n-type TCOs SnZn2O4, SnCd2O4, and CdIn2O4 [1] and p-type TCOs CuAlO2, CuGaO2, and CuInO2 [2]to investigate the reasons for the combined transparency and conductivity. For the n-type TCOs, we analyzed the atomic and orbital characters of the band edge states and explained the general trends observed in the fundamental band gap, the optical band gap, the energy difference between the first and the second conduction bands, and the electron effective mass. General rules for designing more efficient n-type TCOs are proposed. For the p-type TCOs, we find that the observed band gap anomaly, that is the band gap increases from CuAlO2 to CuGaO2, and to CuInO2, can be explained by the large differences in terms of the energy and dipolar optical transition matrix element between the fundamental direct band gap and the apparent optical band gap. This finding, therefore, provides a new avenue to achieve bipolar doping in wide-gap materials. [1] D. Segev and S.-H. Wei, Phys. Rev. B 71, 125129 (2005).[2] Nie, S. B. Zhang, and S.-H. Wei, Phys. Rev. Lett. 88, 066405 (2002); Phys. Rev. B 65, 075111 (2002).Work is supported by U.S. DOE/BES.
3:15 PM - GG12.3
Some Studies on Molybdenum Doped Indium Oxide Thin Films rf Sputtered at Room Temperature.
E. Elamurugu 1 , P Barquinha 1 , A Pimentel 1 , R Martins 1 , E Fortunato 1
1 Department of Materials Science, University of New Lisbon, Monte de Caparica, Setubal, Portugal
Show AbstractAn important application of thin film technology is the fabrication of transparent thin film transistors (TTFTs). The challenging prerequisite for this is to develop transparent and conducting oxides (TCOs) that serve as an active element. These TCOs are also being employed successfully in solar cells, stable resistors, touch-sensitive switches, digital displays, electro-chromic displays and gas sensors. Novel materials have been tried apart from the conventional TCOs viz. tin oxide, zinc oxide and indium tin oxide to improve the device performance. Although, the recently developed high mobility molybdenum- doped indium oxide (IMO) is very attractive it requires further research especially regarding processing at room temperature. Toward this, characterization of IMO thin films rf sputtered at room temperature is reported in this study. The films were sputtered from an In2O3 (95 wt. %): Mo (5 wt. %) target (2” diameter) at a constant power mode of 100 W on to glass substrates (100 × 100 × 1 mm3). Partial pressure of oxygen varied from 1.9 × 10-5 to 2.0 × 10-4 mbar with flow between 0.5 and 3.0 sccm, whereas, argon partial pressure was fixed at ~1.5 × 10-3 mbar (20 sccm). The pressure was maintained at ~1.7 × 10-3 mbar during sputtering. The sputtered films were characterized for their structural, electrical and optical properties. The x-ray diffraction spectra showed that the films were amorphous in nature with thickness varying between 177 nm and 259 nm. The transmittance spectra were found to be in the range of 77 to 89 %. The optical band gap calculated from the absorption coefficient of transmittance spectra was around 3.9 eV. The negative sign of Hall coefficient from electrical measurements confirmed that the films were n-type conducting; however the films were having high sheet resistance in the order of several kΩ. Further experiments to improve the conductivity as well as the transmittance of these films are underway.
3:30 PM - GG12.4
Surface States and Segregation of Tin on tin-doped Indium Oxide Surfaces.
Yvonne Gassenbauer 1 , Andreas Klein 1
1 Materials Science, Darmstadt University of Technology, Darmstadt Germany
Show AbstractIn this contribution we will demonstrate photoelectron spectroscopy (PES) in combination with in-situ sample preparation as a powerful tool to examine the correlation between electronic and chemical properties of oxide surfaces. Tin-doped indium oxide (ITO) as an example, is a degenerate semiconductor showing high transparency in the visible region and a high electrical conductivity. It is widely used as electrode material in optoelectronic devices, for example in organic light emitting diodes (OLEDs), flat panel displays or thin film solar cells. The ITO electronic surface properties strongly correlate with chemical and structural properties. While optical measurements showed a strong Burstein-Moss shift indicating a Fermi level above the conduction band minimum in the bulk of the material, it can be shown using PES that the surface Fermi level is located inside the forbidden band gap at the surface. Hence a surface depletion layer is present having its origin in a high density of surface states around the Fermi-level. This is most likely related to not fully coordinated In or Sn atoms at the surface. The electrostatic potential drop at the surface leads to segregation of Sn dopants, which are obviously mobile enough to change their concentration on the time scale of 1 hour at temperatures as low as 300°C. The surface properties of ITO can be modified by changing preparation conditions using magnetron sputtering or by applying post-deposition treatments. Under reducing preparation conditions, or by exposure to reducing atmospheres after deposition, the density of surface states can be increased which in turn leads to an increase of Sn content at the surface. Electronically, the treatments change the position of the Fermi-level with respect to the band edges with an associated change of work function of the same magnitude. No change of the surface dipole is observed. In contrast, ozone treatment, which is a common method to clean ITO surfaces for organic LEDs, results in a change in Fermi level position and in surface dipole.
3:45 PM - GG12.5
Boron Doping Effects on the Electro-optical Properties of Zinc Oxide Thin Films Deposited by Low-Pressure Chemical Vapor Deposition Process.
Steinhauser Jerome 1 , Seung Yeop Myong 1 , Sylvie Fay 1 , Romain Schluchter 1 , Evelyne Vallat 1 , Alain Rufenacht 2 , Arvind Shah 1 , Christophe Ballif 1
1 PV-Lab, Institute of Microtechnology, Neuchatel Switzerland, 2 , Institute of Physics, Neuchatel Switzerland
Show Abstract4:00 PM - GG12:Transparent
BREAK
GG13: Growth and Characterization of Oxide Films
Session Chairs
Thursday PM, April 20, 2006
Room 2018 (Moscone West)
4:15 PM - **GG13.1
Study of Oxide Film Growth and Interface Processes Using Integrated Physical Vapor Deposition and In Situ Ion, Electron, and Photon-Based Spectroscopy Techniques.
O. Auciello 1 , L. Zhong 1 , B. Kabius 1 , J.P. Allain 2 , A. Hassanein 2 , M. Nieto 2 , V. Titov 2 , E.A. Irene 3
1 Materials Science Division, Argonne National Laboratory, Argonne, Illinois, United States, 2 Energy Technology Division, Argonne National Laboratory, Argonne, Illinois, United States, 3 , University of North Carolina, Chapel Hill, North Carolina, United States
Show AbstractWe have developed unique combinations of in situ and ex situ analytical techniques capable of providing information about thin film growth and interface processes at the atomic scale. The in situ techniques include time-of-flight ion scattering (TOF-ISARS) and mass spectroscopy of recoil ions (MSRI), angle resolved XPS, Auger analysis and extreme ultraviolet photoelectron spectroscopy (EUPS), soft X-ray reflectometry, and spectroscopic ellipsometry. These techniques are not only powerful for understanding fundamental thin film science, but are also useful for establishing composition-microstructure-property relationships critical for the development of film-based micro and nanodevices. We will discuss examples of application to understanding ferroelectric and high-k dielectric film growth and interface processes and using this knowledge for developing integration of ferroelectric capacitors with silicon microcircuits for non-volatile ferroelectric random access memories (FERAMs), high-frequency devices, and the next generation of nanoscale CMOS gates with high-K dielectric layers. This presentation will include a review of studies of a unique TiAl layer that can be used as a material with a double diffusion barrier / bottom electrode functionality for integration of ferroelectric capacitors with CMOS devices for fabrication of FeRAMs, high-K dielectric layers with Cu electrodes for high frequency devices, and as a new high-K dielectric for the next generation of nanoscale CMOS devices. We will discuss results from systematic studies designed to understand TiAl film growth and oxidation processes using sputter-deposition in conjunction with complementary in situ characterization techniques mentioned above and ex situ transmission electron microscopy and electrical characterization. * This work was supported by the US Department of Energy, BES-Materials Sciences, under Contract W-13-109-ENG-38.
4:45 PM - GG13.2
Adsorption of Methane on the MgO(100) Surface: Insight from Inelastic Neutron Scattering and First-Principles Calculations
Michael Drummond 1 , Bobby Sumpter 1 , William Shelton 1 , John Larese 2 3
1 Computer Science & Mathematics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 Chemistry Department, University of Tennessee, Knoxville, Tennessee, United States, 3 Chemical Science Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractThe adsorption of individual molecules onto the surface of an extended solid is a phenomenon with important ramifications in areas such as catalysis, corrosion, and electronics. We have used plane-wave, psuedopotential-based density functional calculations, in conjunction with inelastic neutron scattering (INS) data, to study methane on the MgO(100) surface, a model system for adsorption. At monolayer coverage, methane assumes a dipod-down orientation above magnesium atoms, in a square lattice commensurate with the surface. However, due to CH4-CH4 interactions, each methane is found to be rotated 90 degrees with respect to its nearest neighbors. These interactions are responsible for determining the relative stabilities of possible monolayer arrangements. Likely structures for adsorbed methane bilayers and higher order adlayers will also be discussed, aided by comparisons of calculated and experimental INS spectra. On the whole, the combination of high-resolution INS and high-quality calculations has proven extremely useful for the elucidation of the adsorption of weakly bound particles on a solid surface.
5:00 PM - GG13.3
Spectroscopic Study of Titanium Oxide Thin Films at Low Temperatures by X-ray Diffraction, Raman Scattering, Fourier Transform Infrared Spectroscopy and Photoluminescence.
Beng Kang Tay 1 , Zhiwei Zhao 1
1 School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore Singapore
Show AbstractTitanium oxide thin films were prepared by filtered cathodic vacuum arc (FCVA) at low temperatures ranged from room temperature to 330oC. Spectroscopic study of the deposited films is carried out by X-ray diffraction (XRD), Raman Scattering, Fourier transform infrared spectroscopy (FTIR) and photoluminescence (PL), respectively. The films are amorphous up to substrate temperature of 230oC. Nanocrystalline titanium oxide thin films with anatase phase occur at 330oC and the strongest peak intensity is from (101) plane, and the grain size is around 20 nm. Observation of various Raman allowed vibrational frequencies (e.g. 152, 199, 399, 640 cm-1) and the peak of 436 cm-1 in FTIR spectrum denote the presence of anatase phase in the films at 330oC. Moreover, the peak at 379 nm in PL spectrum is also observed at room temperature. The results obtained from XRD, Raman scattering, FTIR and PL evidently verify the existing of nanocrystalline films with anatase phase at 330oC.
5:30 PM - GG13.5
Correlations between Microstructure and Resistive Switching in Pt/TiO2/Pt Thin Film Capacitors – An Approach by TEM Investigations
Herbert Schroeder 1 , Doo Seok Jeong 1
1 IEM / IFF and CNI, Forschungszentrum Juelich GmbH, Juelich Germany
Show AbstractResistive non-volatile memories are serious candidates for substituting conventional charge-based DRAMs in future ultra-large scale-integrated memory chips in a simple cross-bar architecture. A large variety of material candidates is presently under discussion such as magnetic RAM, phase change materials, single molecules, polymers and other organic insulating materials, but also functional oxides, e.g. ferroelectric and paraelectric oxide thin films. There are numerous experimental (leakage) current data published in the literature for each material class demonstrating the switchable memory effect but there is no agreement on the working mechanism, especially for the oxides. To a large extent this is due to the lack of microstructural information on the changes during formation and switching of the devices. Among the suggested mechanisms the creation and destruction of highly conductive paths, so-called filaments, is favored by many groups. If these effects are connected with microstructural changes these may be observable in a transmission electron microscope (TEM) and correlated to resistance changes.Therefore, in this contribution we present a rather seldom used approach for a TEM experiment to observe the microstructure of a metal/insulator/metal (MIM) capacitor structure before and after (ex-situ) as well as during (in-situ) resistive switching due to an applied external voltage or current. A special TEM sample holder has been developed allowing controlled application of temperature (RT to 300°C) with a heating stage and of voltage (current) as a part of a 4-point resistance measurement set-up for ex- and in-situ experiments. This is combined with a special TEM sample preparation method, the so-called window-technique, for which the silicon substrate is etched away from the backside, so that no thinning of the MIM thin film structure is necessary at all (which is an advantage as the oxides are known to be very sensitive to damage introduced by methods such as ion-milling). Special electrode configurations have been designed to allow nearly undisturbed TEM observation of the switching insulator. Identical samples are also investigated ex-situ in conventional switching experiments to identify the influence of the special TEM environment (high vacuum, irradiation with energetic electrons). Examples for first microstructural observations in a (Pt/amorphous TiO2 thin film/Pt) stack on the resistive switching will be presented.
5:45 PM - GG13.6
Laser Heating, A Challenging New Technology For Small Substrates In Oxide Deposition Processes.
W. Stein 1
1 , SURFACE System & Technology GmbH &CoKG, Huckelhoven Germany
Show AbstractThe growth of high quality oxyde layers is strongly related to a properly heated substrate under oxygen atmosphere. Such heating of substrates can be done in different ways, using conventional ways like radiation or conductive heaters or new techniques like laser heating. Laser heating offers a lot of interesting features, that is not possible with the conventional way of heating. High power diode lasers are very usefull tools for such applications. They are now available in a power range to heat up 10x10 mm substrates to higher temperatures like 1300°C and above. The usage of such heaters offers especially for the LaserMBE a lot of advantages. For clean UHV conditions this heating technique is the optimal solution, be-cause the substrate itself is the hottest spot in the process. Outgasing effects from heaters at higher temperatures are no more possible, the dynamic of the heat transfer can be very fast for the heating up and cool down periode. Such conditions can be used to moderate the thin film deposition in several ways – the .process engineering offers new possibilities to influ-ence the layer grows. The different absorbtion conditions of substrate and layer in coordina-tion with the high speed temperature controll can be used to modify the interfacing of films and the film grows. The temprature control runs 10 kHz sample rate and controls directly the laser output and allows very fast variation in the energy transfer, which is finally limited by the substrate behaviour. Controlled temperature ramps up to 700 °C/sec are possible, Temperature stabilities of +/-0,1 °C at 1200 °C are typical.This now available clean and high speed technique offers a lot of interesting features for small substrates.
GG14: Poster Session: Multifunctional Oxide Films and Devices
Session Chairs
Friday AM, April 21, 2006
Salons 8-15 (Marriott)
9:00 PM - GG14.1
TiO2 Film Formation Behavior in Micro Arc Processed Ti and Ti-6Al-4V Alloys.
Young-Keun Shin 1 , Anatoli Mamaev 2 , Vera Mamaeva 2 , Seung-Young Park 3 , Yun-Mo Sung 3
1 Mater. Sci. & Eng., Daejin Univ, Pochun Korea (the Republic of), 2 Ceramic Coating Lab, ISPMS, Tomsk Russian Federation, 3 Materials Sci. & Eng., Korea University, Seoul Korea (the Republic of)
Show Abstract9:00 PM - GG14.10
Electrical Characteristics of BaxSr1-xTiO3(BST) Capacitors Implemented with Ti-Al Electrodes
Thottam Kalkur 1
1 Dept. of ECE, University of Colorado, Colorado Springs, Colorado, United States
Show AbstractHigh-Dielectric constant based ferroelectric films such as BST have wide applications in the implementation of on-chip decoupling capacitors as well as tunable devices. Platinum is the most common electrode material used as electrodes for BST capacitors. Recently, Aluminum Titanium alloys have been used as barrier layers for ferroelectric memories. In this paper, we are reporting results of BST capacitors fabricated with Ti-Al electrodes. Ti-Al electrodes were deposited on thermally oxidized (100 ) silicon wafers by electron beam evaporation. 100 nm BST films were deposited by RF magnetron sputtering in Ar environment at a substrate temperature of 450 oC. The top electrode Ti-Al was also deposited by electron beam evaporation. Parallel plate capacitor structures were fabricated by standard photolithographic technique and ion-milling. The structural characterization of BST films have been performed by x-ray diffraction. The electrical characterization of BST capacitors were performed by capacitance-voltage (C-V), capacitance-frequency(C-f), capacitance-temperature (C-T) and current-voltage (I-V) measurements.
9:00 PM - GG14.11
Orientation Dependence of Strontium-doped Lead Zirconate Titanate (PSZT) Thin Films on RF Magnetron Sputtering Conditions.
Sharath Sriram 1 , Madhu Bhaskaran 1 , Anthony Holland 1 , Geoffrey Reeves 1
1 Microelectronics and Materials Technology Centre, School of Electrical and Computer Engineering, RMIT University, Melbourne, Victoria, Australia
Show AbstractThis paper discusses the effects of sputter deposition conditions on the orientation of thin films of Pb0.92Sr0.08(Zr0.65Ti0.35)O3, where strontium is an A-site dopant in 65/35 lead zirconate titanate (PZT). RF magnetron sputtering of 8/65/35 PSZT thin films was conducted on a variety of substrate surfaces which included metal (platinum, gold, and nickel) coated silicon and glass substrates and bare lithium niobate, lithium tantalate, and langasite substrates. Undoped and doped PZT thin films are known to exist in one or a mixture of the following phases – amorphous, pyrochlore, and perovskite (single crystal). The presence of the perovskite phase in deposited thin films is essential for pronounced piezoelectric and ferroelectric properties exhibited by PSZT. The paper shows how deposition temperature and post deposition heat treatments affect the film orientation, and presents optimal conditions for perovskite thin film deposition. The effect of sputtering duration and sputtering temperature on the nano-sized grains of the thin films, and the variation in grain size is reported. Observed non-linear increases in thickness of deposited thin films are described. All thin films deposited were analyzed using Scanning Electron Microscopy (SEM) and X-Ray Diffractometry (XRD). The composition of the sputtering target and resulting thin films were determined using X-Ray Photoelectron Spectroscopy (XPS). Deposited thin films were etched by Ion Beam Etching (IBE) with an etch rate of about 19 nm/min.
9:00 PM - GG14.12
HRTEM Observation in Cr-doped SrZrO3 Perovskite Thin Films.
Hwan-Soo Lee 1 , David Laughlin 2 , Paul Salvador 2 , James Bain 1
1 Electrical and Computer Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania, United States, 2 Materials Science and Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania, United States
Show AbstractIn recent years, films of Cr-doped SrZrO3 (Cr:SZO) perovskite oxides1, along with other oxide systems,2 have attracted significant interest as potential memory materials for cross-point non-volatile memory. In this geometry, a film of the material would be sandwiched between two conducting electrodes, (often with SrRuO3 [SRO] as the bottom electrode to permit epitaxial film growth of the Cr:SZO). In this work, epitaxial Cr:SZO thin films deposited directly on (001) SrTiO3 (STO) substrates were studied by transmission electron microscopy (TEM). The SRO bottom electrode was eliminated to simplify the analysis, but, due to the structural similarities of the SRO layers (a = 0.393 nm) and STO substrates (a = 0.3905 nm), it is expected that the observations for films directly on STO may apply to films on SRO bottom electrodes as well.Undoped SZO is stable at room temperature in the orthorhombic (Pnma) phase, with the following lattice parameters: a=0.5814, b=0.8196, and c=0.5792 nm.3 This phase is sometimes described using a pseudo-cubic set of basis vectors, having a lattice parameter, a'=0.409 nm, and with the a and c axes of the orthorhombic unit corresponding to the < -101 > and < 101 > in the pseudo-cubic reference frame. In TEM plan view images, lattice plane fringes associated with an in-plane period of ~0.82 nm were observed, indicating two variants of this Pnma phase in the Cr:SZO films, with domains having the b axis parallel to either the [100] or the [010] in-plane directions of the substrate. Consistent with this, reflections at half-integral reciprocal points of the pseudo-cubic Cr:SZO a'(100) lattice planes were observed in the corresponding electron diffraction pattern. However, the fact that there are no reflections at half-integrals of a'(110) planes indicates that the b axes lie only in the film plane, not out of the plane. This lack of normal b orientation is attributed to a minimization of lattice mismatch, since a larger lattice mismatch (5.3 %) between the Cr:SZO and the STO substrate is expected along the a direction than those (4.9%) in b and c directions.In addition to these orientational features, high-resolution TEM (HRTEM) images of the cation columns projected along the viewing direction a' [001] at a higher magnification reveal a consistent displacement of the cations by 0.03-0.04 nm along the pseudo-cubic a' [010] direction (which corresponds to the orthorhombic b [010] direction). Additionally, in some regions, periodic cation displacements along the pseudo-cubic [110] direction were observed. This last feature structure could indicate oxygen/vacancy ordering but more detailed structural examinations are needed to make this determination.References1A. Beck et al., Appl. Phys. Lett., 77, 139 (2000).2A. Baikalov et al., Appl. Phys. Lett., 83, 957 (2003).3A. Ahtee et al., Acta Cryst. B32, 3243 (1976).
9:00 PM - GG14.13
High Temperature Ferromagnetism in Transition Metal doped Lanthanide Oxides
Ashutosh Tiwari 1
1 Materials Science & Engineering, university of utah, Salt Lake City, Utah, United States
Show AbstractHere we will report the observation of room temperature ferromagnetism in highly insulating oxides of lanthanide group. We have found that when a small amount of certain transition metal elements is doped in these oxides, several of them start exhibiting high tempertaure ferromagnetism while retaining their insulating and tranparent character. Method of preparation and various intersting experimental results will be presented. These experimental results will be explained using most recent theoretical models.
9:00 PM - GG14.14
WITHDRAWN 4/7/06 Low Resistivity ZnO-Based Thin Films On Aluminum Nitride Substrates.
Yeon Hwa Jo 1 , Dong joo Shin 1 , Hyun Jae Kim 2 , Yong S Cho 1
1 School of Advanced Materials Engineering, Yonsei Univ., Seoul, 120-749, Korea (the Republic of), 2 Department of Electrical and Electronic Engineering, Yonsei Univ., Seoul, 120-749, Korea (the Republic of)
Show AbstractThursday 4/20withdrawnposterGG14.14
9:00 PM - GG14.17
Thermoelectric Properties of Nano-structure Controlled Sm2-xCexCuO4 Thin Films.
Yusuke Ichino 1 , Koji Yamazaki 1 , Yutaka Yoshida 1 , Yoshiaki Takai 1
1 Dept. of Energy Engineering and Science, Nagoya University, Nagoya Japan
Show AbstractWe have studied an improvement of thermoelectric properties of RE2-xMxCuO4 (RMCO; RE=light rare earths, M=Ce, alkaline earths) materials so far. Although the RMCO is well known as the superconductor, the excellent thermoelectric properties of RMCO have also been reported. In order to enhance the thermoelectric properties of RMCO, we have prepared the RMCO thin films and controlled the crystallographic orientation, carrier concentration and introduction of nano-structures. In particularly, we expect the decrease of thermal conductivity due to the phonon scattering at crystalline defects introduced by nano-structure. In this report, we will discuss the effect of substrate with nano-structure in Sm2-xCexCuO4 (SCCO) films on the thermoelectric properties.The SCCO films and nano-structures were fabricated using the pulsed laser deposition (PLD) method on SrTiO3 (STO) single crystalline substrates. In order to form the nano-structure on STO, thin CeO2 layer was deposited, and then, annealed at 900~1000°C in O2 gas flow. After this heat treatment, the nano-dotted and nano-porous structures, which were made of CeO2, were appeared on the STO substrates with a height of less than 50 nm. The SCCO films were prepared on the nano-structural substrate under the conditions of growth temperature 840°C, oxygen pressure 0.4 Torr and laser energy 1.0 J/cm2. Orientation and crystalline phases were checked by x-ray diffraction. Surface morphologies of films were observed by atomic force microscopy (AFM). Carrier concentration and mobility of films was confirmed by Hall effect measurement.We measured the nano-structural effect on the power factors (PF) of SCCO films. As a result, PF showed a maximum at a certain height of the nano-structures, and the value was 0.66×10-3 W/K2m. This improvement of PF occurs by the high conductivity in the SCCO film due to the high mobility of carrier. From the SCCO thickness dependence of mobility, we found that the mobility of thin film was higher than that of thick film. Because the mobility of SCCO films tends to be improved with increase of Ce content, we argued that the high mobility was achieved by a formation of high Ce concentration layer at film-substrate interface.This research was partially supported by the Ministry of Education, Science, Sports and Culture, Grant-in-Aid for Scientific Research (B), 16360479, 2005.
9:00 PM - GG14.18
Current Percolation in Two-dimensional Vanadium Dioxide Thin Films.
John Rozen 1 , Rene Lopez 2 , Richard Haglund 2 1 , Leonard Feldman 2 1
1 Institute of Nanoscale Science and Engineering, Vanderbilt University, Nashville, Tennessee, United States, 2 Department of Physics and Astronomy, Vanderbilt University, Nashville, Tennessee, United States
Show Abstract9:00 PM - GG14.19
Effect of Polyvinylpyrrolidone Molecular Weight on the Critical Thickness, Densification and Properties of PLZT Films.
Zehui Du 1 , Jan Ma 1
1 school of materials science and engineering, Nanyang Technological University, Singapore Singapore
Show Abstract Lanthanum-substituted lead zirconate titanate(PLZT) films around 1µm thick are very promising in developing advanced electro-optical (EO) and waveguide-based devices. However, when sol–gel coating technique is used to fabricate such PLZT films, crack formation is likely to occur on the gel films during heat treatment. The critical thickness i.e. the maximum thickness achieved without crack formation via nonrepetitive deposition is often <0.1µm. Thus to prepare the films around 1µm, tens of rounds of coating and pyrolysis treatment are needed. The work is time-consuming and the optical properties of the films tend to be deteriorated due to the multi-coating structure. In this work, a stress-relaxing agent of polyvinylpyrrolidone(PVP) with the molecular weight of 40000,360000 and 630000 were used to modify sol gel precursor solution for preparing PLZT 9.5/65/35 thin films around 1µm thick. The effect of PVP molecular weight on the critical thickness, crystallization behavior, morphology, electric and optical properties of the PLZT films have been investigated and characterized by surface profiler, XRD, FESEM and Ferroelectric test system etc. It is found that PVP40000 can increase the critical thickness up to 0.22µm(compared with the critical thickness of 0.077µm in case of without PVP) and the PLZT films are well-crystallized and dense in microstructure. PVP360000 and PVP630000 can increase the critical thickness of the films up to 0.49µm and 0.93µm individually, but they suppress the perovskite formation and the morphology of the films tends to be nano-porous. The films modified by PVP360000 can be densified by optimizing the annealing conditions. When heated at 600°C for 30mins, the films are dense and exhibit a transmittance of about 60%~80% in the wavelength above 500nm and a very slim P-E hysteresis loop with remanent polarization of 1.00uC/cm2 and coercive field of 26.42kV/cm.
9:00 PM - GG14.2
Effects of Sputtering Power and Annealing Temperature on the Properties of Sc-doped ZnO Thin Films.
Ming Hua Shiao 1 , Cheng-Chung Jaing 2 , Yu-Jia Huang 3 , Chien-Ying Su 1 , Chih-Jung Lu 4
1 , Instrument Technology Research Center, Hsinchu Taiwan, 2 Department of Optoelectronic System Engineering, Ming Hsin University of Science & Technology, Hsinchu Taiwan, 3 Department of Electronic Engineering, Ming Hsin University of Science & Technology, Hsinchu Taiwan, 4 Department of Materials Engineering, National Chung Hsing University, Taichung Taiwan
Show AbstractSc-doped ZnO thin films were deposited on Corning 1737 glasses by using r.f. magnetron co-sputtering system with Sc2O3 and ZnO targets. Different sputtering powers (100-200W) of Sc2O3 target and post annealing temperatures (400-550°C) were investigated to understand the optical and electrical properties of Sc-doped ZnO thin films. From X-ray diffraction (XRD) results, the Sc-doped films have (002) preferential orientation, and the Sc2O3 (222) diffraction intensity increases with increasing the Sc2O3 sputtering power. Atomic force microscopy (AFM) surface measurement also shows that the roughness of the films was smoother when the Sc2O3 sputtering power increased from 100W to 200W. The optical transmission of these Sc-doped films in the visible region all exceeded 80%. The X-ray diffraction peaks did not change with different annealing temperatures, but the optical transmission was increased about 2-3%. Electrical resistivity measurement reveals that the as-deposited Sc-doped ZnO thin films had lowest resistivity of 0.97 Ω cm when the Sc2O3 sputtering power was 125W, and decreased to 9.85 × 10-2 Ω cm after annealing at 550°C.
9:00 PM - GG14.21
Reversible Tunability of Crystalline Perovskite-like Structures and Physial Properties in Strontium Titanate.
Dirk Meyer 1 , Alexandr Levin 1 , Tilmann Leisegang 1 , Emanuel Gutmann 1 , Marianne Reibold 1 , Peter Paufler 1 , Reiner Dietsch 2
1 Physics, Dresden University of Technology, Dresden Germany, 2 , AXO Dresden, Dresden Germany
Show Abstract9:00 PM - GG14.22
Growth Mechanisms in the Epitaxy of Manganite Films and Control of Surface Roughening
Ingrid Infante 1 , Florencio Sanchez 1 , Ulrike Luders 1 , Llibertat Abad 1 , Josep Fontcuberta 1
1 , ICMAB-CSIC, Bellaterra Spain
Show AbstractUnderstanding the growth mechanisms in the epitaxy of a material is critical to control its (nano)microstructure and its surface morphology. The great efforts that have been done to this research in the field of semiconducting materials are in sharp contrast with the reduced attention paid to the growth of oxides. In the particular case of manganites, enormous efforts are concentrated to investigate their properties and to use them to fabricate magnetic tunnel junctions. These devices require two-dimensional (2D) growth of epitaxial films and ultra-flat surfaces, but paradoxically little is known about the growth processes. Moreover, it is commonly observed that three-dimensional islands appear above a relatively low thickness of the manganite films. Clearly, understanding and controlling growth of manganites, and of complex oxides in general, is a necessary step towards its funcionalization.We have investigated the growth mechanisms and surface morphology of La0.67Ca0.33MnO3 epitaxial films on SrTiO3(001) substrates. It is found that at early growth stages, in nanometric films, a layer-by-layer mechanism dominates, which results in step and terrace surface morphology. Upon further growth, the flat surface becomes unstable when large 2D islands form. A step-edge energy barrier induces an anisotropic adatom kinetics that reduces downhill adatom current and thus favours 2D nucleation on top of the islands. As a result, there is an evolution with growth to mound-like structures of increasing height. Critical thickness for mound formation and average mound separation can be tuned by substrate miscut angle and growth temperature. We demonstrate that mounds do not appear if the growth is by step flow mechanism, although there is a marked step meandering. We analyze the results and we discuss on methods to obtain stable two-dimensional growth in thicker films. In addition, knowing the influence of the growth mechanism into film nanostructure and its properties, we present detailed characterization of the strain state and the magnetic properties of films of varied thickness. The structural and magnetic data are discussed in connection with the morphology and the roughness transition.
9:00 PM - GG14.23
Epitaxial Pt(111) Thin Films on Si(111) Substrates with γ-Al2O3(111) as Buffer Layer.
Mikinori Ito 1 , Kazuaki Sawada 1 , Makoto Ishida 1
1 Electrical and Electronic Engineering, Toyohashi University of Technology, Toyohashi Japan
Show Abstract(111)-oriented epitaxial Pb(Zr,Ti)O3 (PZT) films around morphotropic phase boundary composition on SrRuO3(111)/SrTiO3(111) substrates exhibit larger piezoelectric response more than other orientations and compositions[1]. Therefore, (111)-oriented epitaxial PZT films are attracting much attention for micro-electro-mechanical systems (MEMS) and sensor applications. However, there have been hardly any reports realized such PZT films on Si substrates. For this achievement, it is required (111)-oriented epitaxial bottom electrode on Si substrates. In addition, the electrical and physical properties of the PZT films are strongly affected by the surface roughness and crystal quality of bot