Symposium Organizers
Alp T. Findikoglu Los Alamos National Laboratory
Judy Z. Wu University of Kansas
Ruben Huehne Leibniz-Institute for Solid State and Materials Research (IFW)
Institute for Metallic Materials
Toshihiro Shimada Hokkaido University
DD1: Inorganic Nanostructures
Session Chairs
Tuesday PM, November 30, 2010
Room 104 (Hynes)
9:30 AM - **DD1.1
From Texture Control to Single Crystals in Thin Metal Films by Ion Bombardment.
Matteo Seita 1 , Daniel Muff 1 , Annika Baier 1 , Ralph Spolenak 1
1 Department of Materials, ETH Zurich, Zurich Switzerland
Show AbstractThe reliability of microelectronic devices and microsystems depends critically on the microstructure of thin metal layers, which ideally is single crystalline. The current paper presents two strategies to achieve this goal by ion bombardment. One, selective grain growth and texture rotation is triggered by high energy (MeV) post deposition ion irradiation, whereas, two, low energy (keV) ion bombardment leads to selective sputtering of thin films, resulting in nanometric islands of identical orientation. These can then be used for homoepitaxial growth of oriented thin films. Texture evolution is characterized by electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). The interpretation of the underlying mechanisms is supported by in-situ irradiation inside a TEM (Jannus facility in France) and ab-initio modeling. Two novel processes for crystalline alignment are presented, where the second process holds promise for industrial application.
10:00 AM - **DD1.2
Nanostructured Optical Thin Films Fabricated by Oblique Angle Deposition.
Chang Kwon Hwangbo 1 , Kim Jin Joo 1 , You Suk Shin 1 , Yong Ho Lee 1
1 Physics, Inha Univ., Incheon Korea (the Republic of)
Show AbstractStudying the optical properties of nanostructured thin films is one of major focuses in nanotechnology research, motivated by the ability to controllably alter the optical behavior. The main goal of this research field is to study the improvement of the optical and physical properties of optical thin films by controlling their structures at nanoscale and, hence, the application in multilayer optical components. To control the structures at nanoscale, optical thin film layers are fabricated in an electron-beam evaporation system by using an oblique angle deposition (OAD) technique. Recently, the oblique angle deposition (OAD) is a sophisticated technique to fabricate engineered nanostructured thin films for next generation optical nanodevices. In this technique, oblique angle deposition and substrate rotation are employed to control the columnar and helical nanostructures of thin films. The films deposited by this technique show the optical anisotropy, the porosity, or the chirality, depending on the controlled morphologies at nano-scale. These controls can be utilized to engineer thin films for specific applications such as three-dimensional photonic crystals, gradient index optical filters, broadband antireflection coatings, circular Bragg reflector, gas sensor, and linear polarizer, etc. In this study, the nanostructural effects on the optical and the structural properties of the thin films deposited by using OAD techniques are investigated. The nanostructured optical thin film devices, such as the linear and circular polarization handedness inverters, the broadband Bragg reflector, the R-G-B color filter, the bilayer circular filter, selective coatings, and the wide band antireflection coatings, are fabricated by electron beam evaporation using OAD technique and their optical and structural properties will be described.
10:30 AM - DD1.3
Mechanism for the Evolution of Vertically Aligned Biaxial Textured Tungsten Nanorods.
Rahul Krishnan 1 , Yu Liu 2 , Churamani Gaire 2 , Thomas Parker 2 , Liang Chen 2 , Gwo-Ching Wang 2 , Toh-Ming Lu 2
1 Materials Science & Engineering, Rensselaer Polytechnic Institute, Troy, New York, United States, 2 Physics, Applied Physics & Astronomy, Rensselaer Polytechnic Institute, Troy, New York, United States
Show AbstractRecently there has been keen interest in creating biaxial metal or dielectric films as a substrate for further growth of functional materials such as high Tc superconductors and semiconductors. Oblique angle deposition is one convenient approach to grow biaxial films. However, so far for oblique angle deposition of biaxial metal films, often the out-of-plane crystal orientation is not normal to the substrate but with an angle leaning towards the incident flux. Here we report vertical biaxial textured tungsten nanorods (A15 crystal structure) that have been grown by oblique angle (α = 85° from the surface normal) DC magnetron sputtering using a novel substrate rotation mode called ‘two-step rotation’ [1]. In this mode, the substrate is given a fast rotation through 180° at 90 rpm followed by a rest period of 30 seconds. As a result of this rotation mode, the flux is incident from two diametrically opposite directions on the sample at an oblique angle, averaging out the growth into vertical columns that retain the in-plane texture. These nanorods of thickness ~390 nm have a [002] out-of-plane orientation along with a [110] in-plane texture as shown by X-ray pole figure analysis. The in-plane texture is selected so as to obtain maximum capture area. In contrast, the tungsten nanorods of thickness ~390 nm obtained without substrate rotation are slanted with an angle of ~45° towards the flux. In this case, the [002] texture axis is tilted ~17° away from the substrate normal (towards the flux) and the selection of a [031] in-plane texture does not maintain maximum in-plane capture area. The vertical nanorods with different thicknesses (10 nm, 25 nm, 50 nm and 100 nm) were also grown and analyzed for biaxial texture evolution using a highly surface sensitive Reflection High-Energy Electron Diffraction (RHEED) pole figure technique [2]. The initial polycrystalline film begins to show the inception of biaxial texture with a fiber background between 10 and 25 nm. Biaxial texture development is eventually completed between 50 and 100 nm thicknesses of the film. Scanning Electron Microscopy and Atomic Force Microscopy show that the vertical tungsten nanorods have a (112) crystal habit which is a minimum surface energy plane for the cubic A15 crystal structure. References[1] R. Krishnan, T. Parker, S. Lee, T-M. Lu, Nanotechnology 2009, 20, 465609[2] F. Tang, T. Parker, G-C. Wang, T-M. Lu, J. Phys. D: Appl. Phys. 2007, 40, R427
11:15 AM - DD1.4
Rational Synthesis and Crystalline Alignment of Self-assembled Silicide Nanomaterials.
Tom Wu 1
1 , Nanyang Technological University, Singapore Singapore
Show AbstractRational synthesis of nanomaterials with desired morphology, alignment, and structure is the foundation for nanosciences and nanotechnologies. Researchers strive to achieve controls in nanomaterials on crystalline structure, shape, size, orientation, assembly, doping, and so on, which in return determine the properties of the nanomaterials and the functionalities of the nanodevices. Here I use self assembled growth of nanoscale silicides as examples to illustrate some unique approaches to obtain advanced nanomaterials with tailored morphology and physical properties. As the first example, nanoscale Cu3Si triangles, squares, and wires have been grown on Si(111), (100), and (110) substrates, respectively, through a template-free Au-nanoparticle-assisted vapor transport method. The sides of triangles and squares and the growth direction of the nanowires are all aligned along the Si <110> directions, giving rise to long-range ordering of the nanostructures. Down a similar line, we report the fabrication of micro/nanoscale pits with facile shape, orientation and size controls on Si surface via an Au-nanoparticles-assisted vapor transport method. Based on this understanding of the mechanism and the morphological evolution of the pits, we manage to estimate the diffusion coefficients of Co in bulk Si along <100> and <111> directions. As the final example, in-plane growth of Mg2SiO4 nanowires on Si substrates is achieved by using a vapor transport method. The self-assembly of the as-grown nanowires shows dependence on the substrate orientation, i.e., they are along one, two, and three particular directions on Si (110), (100), and (111) substrates, respectively. Furthermore, using these nanowires, a lithography-free method is demonstrated to fabricate nanowalls on Si substrates by controlled chemical etching. These self assembled growth of nanoscale silicides with crystalline alignment hinges on the intimate interactions between substrates, nanoparticles, and nanowires, and our studies may help to advance the developments of novel nanomaterials and functional nanodevices.References:1. Z. Zhang, L. M. Wong, H. G. Ong, X. J. Wang, J. L. Wang, S. J. Wang, H. Y. Chen, and T. Wu, "Self-assembled shape- and orientation-controlled synthesis of nanoscale Cu3Si triangles, squares, and wires." Nano Letters 8, 3205 (2008).2. Huatao Wang, Zhou Zhang, Lai Mun Wong, Shijie Wang, Zhipeng Wei, Gong Ping Li, Guozhong Xing, Donglai Guo, Dandan Wang, and Tom Wu, “Shape-controlled fabrication of micro/nanoscale triangle, square, wire-like, and hexagon pits on silicon substrates induced by anisotropic diffusion and silicide sublimation” ACS Nano 4, 2901 (2010).3. Zhou Zhang, Lai Mun Wong, Hou Xiao Wang, Zhi Peng Wei, Wei Zhou, Shi Jie Wang, and Tom Wu, “Self-assembled in-plane growth of Mg2SiO4 nanowires on Si substrates catalyzed by Au nanoparticles” Advanced Functional Materials (in print).
11:30 AM - DD1.5
Atomic Structure of Au-Pd Bimetallic Alloyed Nanoparticles.
Yong Ding 1 , Fengru Fan 1 2 , Zhongqun Tian 2 , Zhong Lin Wang 1
1 MSE, Georgia Institute of Technology, Atlanta, Georgia, United States, 2 Department of Chemistry, Xiamen University, Xiamen China
Show AbstractUsing a two-step seed-mediated growth method, we synthesized Au octahedron core and Pd epitaxial shell bimetallic nanoparticles with controlled Pd-shell thickness. The mismatch-release mechanism between the Au-core and Pd-shell of the nanoparticles was systematically investigated by high-resolution transmission electron microscopy. In the single Pd atomic layer coated nanoparticles, the strain built between the surface Pd layer and the Au core is released by the formation of Shockley partial dislocations accompanied by stacking faults. With more layers of Pd coated (> 2 nm), the stacking faults still exist, but no Shockley partial dislocations are found. Possibly, it is dues to the diffusion of the Au atoms into the Pd shell layers to eliminate the Shockley partial dislocations. At the same time, a long-range ordered L11 AuPd alloy phase has been identified in the interface area, supporting the assumption of the diffusion of Au into Pd to release the interface mismatch. With increased Pd shell layers, the shape of the Au-Pd nanoparticle transferred from truncated-octahedron to cube step by step. Annealing the bimetallic nanoparticles at 523 K for 10 minute, the Shockley partial dislocations at the surface of the single Pd atomic layer coated nanoparticles disappear due to the Au atoms diffused into the surface layer, while the stacking faults and the L11 AuPd alloyed structure still stable. With annealing temperature increased to 800 K, electron diffraction patterns and diffraction contrast images reveal that the nanoparticles become a uniform Au-Pd alloy, and most of the stacking faults disappear due to the annealing effect. Even so, some clues still support the existence of the L11 phase, which suggests the L11 phase is a stable long-range ordered structure in Au-Pd bimetallic nanoparticles. For more information, please visit: http://www.nanoscience.gatech.edu/zlwang
11:45 AM - DD1.6
Ultrafast Laser Alignment of Carbon Nanotubes.
Ryan Murphy 1 3 , Huanan Zhang 2 , Ben Torralva 3 , Nicholas Kotov 2 , Steven Yalisove 3 1
1 Applied Physics Program, University of Michigan, Ann Arbor, Michigan, United States, 3 Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan, United States, 2 Chemical Engineering, University of Michigan, Ann Arbor, Michigan, United States
Show AbstractOrganized nanostructures are formed after irradiation of a monolayer of randomly aligned single-walled carbon nanotubes by a Ti:Sapphire 800 nm laser with a 150 fs pulse at fluences near 0.1 J/cm2. At varying peak fluences morphology is seen where the tubes are ejected from the substrate or formed into “nanohair” structures. Nanohair has been created on both silicon substrates and carbon grids. These structures are typically 400 nm long and 5 nm wide, crystalline, and are arranged such that they are aligned towards the middle of the crater. Transmission Electron Microscopy analysis of crystalline and electronic properties as compared to randomly aligned tubes will be discussed. A possibility of unzipping of the tubes into graphene ribbon is also discussed.
12:00 PM - DD1.7
Epitaxial Control of Cu2O Nanostructures via Pulsed Laser Deposition.
Sungki Lee 1 , Chen-Wei Liang 1 , Lane Martin 1
1 Materials Science and Engineering and Materials Research Laboratory, University of Illinois, Urbana-Champaign, Urbana, Illinois, United States
Show AbstractCuprous oxide (Cu2O) has long been studied because of the unique properties manifested in this material, including the observation of Bose-Einstein condensation of excitons. More recently Cu2O has been investigated as a candidate material for photovoltaics and photocatalysis because it is a non-toxic, widely abundant, stable, relatively cheap to produce p-type semiconductor with a direct band gap of ~2.1 eV. Additionally, Cu2O has a relatively high hole mobility for oxide materials (typically 50-100 cm2/V-s at room temperature) and a large minority carrier diffusion length (~1 μm in some cases). Essential to next generation applications based on such oxide materials – especially photocatalytic applications – is the ability to synthesize and control nanostructures of this material. In this spirit, we will discuss our ability to deterministically control the nanostructure shape, exposed crystal facets, epitaxial alignment, and overall feature density of nanostructures of the widely studied and exciting oxide semiconductor Cu2O. Using pulsed laser deposition and lessons learned from thin film epitaxy we can generate Cu2O nanostructures with different shapes, sizes, alignments, and geometries – from boxes to pyramids to huts. By varying the thin film growth process – especially the material flux per laser pulse – we have established a pathway to tune not only the nature of nanostructure geometry in this exciting material, but also the total density of features and the relative surface area to volume ratio of the sample. We will report on the evolution of nanostructure alignment relative to the underlying substrate, the ability to generate nanostructures with highly polar surfaces, and routes to deterministically tune the exposed crystal surface to be (001)-, (110)-, (111)-, or mixed-type directly from the vapor phase. We will also present studies of the various routes to control local ordering and alignment of the nanostructures – including self-assembly of nanostructures into 3- and 4-nanosturcure clusters, a study of the electronic and optical (i.e., transport, transmission-absorption, photoluminescence, etc.) properties of these nanostructures, and first generation devices based on these materials. Such control of these materials will open up new pathways to study exotic exciton and photocatalytic behavior in this exciting material.
12:15 PM - DD1.8
Holes and Hillocks, Thermal Instabilities and Pattern Formation of Pt Thin Films on Dielectric Substrates.
Henning Galinski 1 , Thomas Ryll 1 , Lukas Schlagenhauf 1 , Jennifer Rupp 1 , Anja Bieberle-Huetter 1 , Ludwig Gauckler 1 , Patrick Stender 2 , Guido Schmitz 2
1 Department of Materials, ETH Zurich, Zurich Switzerland, 2 Institute of Materials Physics, WWU Muenster, Muenster Germany
Show AbstractMetals and dielectrics have due to their differing electronic structures distinct diametric bonding characteristics. The stability of a metal thin film on dielectric substrates is conditioned by the magnitude of interactive forces at the interface. In the case of a non-reactive interface and weak adhesion the minimization of free surface energy gives rise to decomposition and agglomeration of thin films. In order to study these effects, Pt thin films with thicknesses up to 180 nm were deposited via magnetron and ion-beam sputtering on yttria stabilized zirconia single crystals. All films have been subjected to heat treatments up to 1173 K for 2 h. In the case of ion beam sputtering the single crystal has been pre-cleaned in the ion-beam before deposition. The morphological evolution of Pt thin films has been investigated by means of scanning electron microscopy (SEM) , atomic force microscopy (AFM) and standard image analysis techniques. Three main observations have been made: i) the pre-cleaning has an impact on the morphological evolution of the film during annealing. Instead of holes which immediately break the symmetry of the system, triangular hillocks are formed on top of the film. It is shown by comparing the hillocks' aspect ratio with FEM simulations that the hillock formation can be assigned to a stress relaxation process inside the thin film.ii) the morphological evolution as function of time has been analyzed by means of statistical measures (Minkowski functionals). It is shown that hole formation and hillock formation possess different statistical signatures and therefore can be regarded as different agglomeration regimes.iii) The hole growth in case of the uncleaned film is in agreement with Brandon and Bradshaw's theory of surface energy driven diffusion.
12:30 PM - DD1.9
Crystallographic Orientational Control of Nb-doped Anatase TiO2 Thin Films on Glass Substrates with Inorganic Nanosheets.
Kenji Taira 1 2 3 , Yasushi Hirose 1 2 3 , Shoichiro Nakao 1 2 , Naoomi Yamada 5 , Toshihiro Kogure 1 3 , Tatsuo Shibata 3 4 , Takayoshi Sasaki 3 4 , Tetsuya Hasegawa 1 2 3
1 Chemistry School of Science, Univ. Tokyo, Bunkyo-ku, Tokyo, Japan, 2 , KAST, Kawasaki, Kanagawa, Japan, 3 , CREST, Chiyoda-ku, Tokyo, Japan, 5 , Univ. Chubu, Kasugai, Aichi, Japan, 4 , NIMS, Tsukuba, Ibaragi, Japan
Show AbstractInorganic nanosheet, which are ultrathin sheet-like oxide nanostructures exfoliated out of the oxides with layered structures, have been demonstrated to be quite useful as seed layers for controlling crystallographic orientation of thin film materials on amorphous substrates, such as glass (T. Shibata et al., Adv. Mater. 20 (2008) 231.). Recently, we also succeeded in fabricating (001)-oriented Nb-doped anatase TiO2 (TNO), being an indium-free transparent conducting oxide, on lattice-matched Ca2Nb3O10- nanosheets. A unique feature of inorganic nanosheets as seed layers is that they can be deposited on substrates by room temperature wet processes, such as electrostatic deposition or Langmuir-Blodgett (LB) method. Thus, the technique is free from thermal damage on substrate during seed-layer deposition. Meanwhile, nanosheets must cover a large area of substrate surfaces, typically coverage ratio of > 90%, in order to obtain highly oriented films on them. It is of practical importance to develop a process to grow epitaxial-like films on substrates with low coverage of nanosheets. Here, we propose an idea of lateral epitaxial growth and successfully fabricated (001)-oriented TNO films on the glass substrates even with low coverage ratio of ~ 40 % of Ca2Nb3O10- nanosheets. TNO films were fabricated by the solid phase crystallization procedure, in which amorphous TNO films were first deposited on glass with nanosheet seeds and then crystallized by annealing in H2 atmosphere. The crystallographic structure and orientation of TNO films were characterized by X-ray diffraction (XRD) measurements. Most of the crystallized TNO films were in the form of randomly oriented polycrystals. However, (001)-oriented films were obtained when thin anatase layers, which would serve small nuclei of anatase, were formed at substrate temperature ~ 140°C prior to the deposition of amorphous film. It was also found that bulky organic cations on the nanosheets, which adhered through exfoliation process, prevent the solid phase epitaxy. We conducted microscopic observation of each crystal grain by AFM and SEM with Electron Back-Scattered Diffraction (EBSD). These observations directly confirmed that the nucleation of (001)-oriented TNO grains starts from the nanosheets and that the grains grow in the lateral direction in a micrometer-scale. The lateral growth proceeds over the boundaries of nanosheets and finally (001)-oriented grains cover almost the entire region of substrate surface. This demonstrates that highly oriented films can be obtained even on the substrates with low nanosheet coverage by using the nanosheet seed layer technique combined with solid state epitaxy.
DD2: Organic Nanostructures
Session Chairs
Gen Sazaki
Toshihiro Shimada
Tuesday PM, November 30, 2010
Room 104 (Hynes)
2:30 PM - **DD2.1
Directed Self-assembly in Thin Films.
Ting Xu 1 2
1 Department of Materials Science and Engineering, Department of Chemistry, University of California, Berkeley, Berkeley, California, United States, 2 Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractA key to future technologies is the design and fabrication of hierarchical materials having structures ordered down to the molecular level with built-in functionalities. Block copolymer, composed of two homopolymers covalently linked together, self-assembles into well ordered arrays of microdomains that are typically tens of nanometer in size. In thin films, both the lateral ordering and the macroscopic alignment of microdomains can be readily tailored. I will discuss recent efforts in two areas. One is to achieve long-range order of block copolymer microdomains in thin films using a faceted substrate. The other is to direct nanoparticle assemblies in thin films with inter-particle ordering. Both processes are amenable to solution processing to fabricate various functional devices.
3:00 PM - **DD2.2
Micromolding in Capillary of Crystalline Organic Systems Showing Strong Fluorescence Emission and Switching.
Soo Young Park 1
1 Mat. Sci. Eng., Seoul National University, Seoul Korea (the Republic of)
Show AbstractMicromolding in capillary (MIMIC) is one of the soft lithographic methods which is most beneficial for the fabrication of crystalline organic solids, if the material characteristics could be fine tuned to the processing variables. Recently, we have synthesized a unique class of ‘torsion spring’ type π-conjugated organic molecules which hold a strong and specific self-assembly tendency into highly fluorescent and semiconducting supramolecular nanostructures. [1-3] We could grow these functional nanostructures in the MIMIC mold to give the aligned stripe patterns showing excellent semiconducting and polarized light emission properties.[4] Moreover, we could fabricate highly fluorescent reticular coordination polymer in a MIMIC mold through the solvent-mediated reconfigurable polymerization.[5] Many other functional materials including those showing reversible optical switching could be patterned via MIMIC process, once combined with appropriate molecular design and synthesis. References1. B.–K. An, S.-K. Kwon, S.-D. Jung, S. Y. Park, J. Am. Chem. Soc., 124, 14410 (2002).2. B.–K. An, D.-S. Lee, J.-S. Lee, Y.-S. Park, H.-S. Song, S. Y. Park, J. Am. Chem. Soc., 126, 10232 (2004).3. B.–K. An, S. H. Ghim, J. W. Chung, C. R. Park, S.-K. Kwon, S. Y. Park, J. Am. Chem. Soc., 131, 3950 (2009)4. J. H. Kim, Y. Jung, J. W. Chung, B.-K. An, S. Y. Park, Small, 5, 804 (2009)5. Y. You, H. Yang, J. W. Chung, J. H. Kim, Y. Jung, S. Y. Park, Angew. Chem. Int. Ed., 49, 3757 (2010)
3:30 PM - DD2.3
Crystal Grain Alignment in Vacuum Deposition of Organic Semiconductor Molecules onto Liquid Films.
Toshihiro Shimada 1
1 Materials Chemistry, Hokkaido University, Hokkaido Japan
Show AbstractWe study the vacuum deposition of organic molecules onto various substrates covered by liquid with low vapor pressure, aiming at obtaining large single crystalline films. We found that organic semiconductor "rubrene" crystallizes in different ways depending on the substrate materials. It indicates that the nucleation occurs on the substrates. Epitaxial growth was observed on some substrates. The domain size was far larger than the ordinary vacuum deposition and reached to the substrate size in one direction. ReferencesT.Shimada et al., J. Cryst. Growth 311, 163(2008)Y.Ishii et al., Langmuir 23,6864(2007).
DD3: Modelling and Charcterization of Nanostructures
Session Chairs
Diederik Depla
Vladimir Matias
Tuesday PM, November 30, 2010
Room 104 (Hynes)
4:15 PM - **DD3.1
Development of the Grain Size Distribution During the Crystallization of an Amorphous Solid.
Andreas Bill 1 , Ralf Bergmann 2
1 Physics & Astronomy, California State University Long Beach, Long Beach, California, United States, 2 , Institute for Applied Beam Technology (BIAS), Bremen Germany
Show AbstractThe microstructure of a solid impacts in important ways its electronic, optical or magnetic properties. A quantitative characterization of a material’s granularity is thus essential for tailoring its functionality. The grain size distribution provides such characterization as an amorphous solid undergoes crystallization. We present an overview of the theory we developed in recent years to describe the grain size distribution. Our analytical description applies to isotropic and anisotropic growth rates and allows for the analysis of different stages of crystallization, from early to full crystallization. We show how the time-dependence of nucleation and growth rates affect the final distribution and discuss under what conditions a lognormal type distribution is obtained. Applications of the theory to semiconductors will be presented.This work is supported by the Research Corporation, the DAAD and SCAC at CSU Long Beach.[1] R.B. Bergmann and A.Bill, J. Cryst. Growth 310, 3135 (2008).[2] A.V. Teran, R.B. Bergmann and A.Bill, Phys. Rev. B 81, 075319 (2010).
4:45 PM - DD3.2
Electronic Structure of Grain Boundaries in Crystalline Si.
Rajamani Raghunathan 1 , Engin Durgun 1 , Jeffrey Grossman 1
1 Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractWe present results from density functional theory calculations of the electronic and structural properties of multi-crystalline silicon with different types of grain boundaries. A comparison of the impact of different grain boundaries on electronic and optical properties in these systems will be presented, with the aim towards predicting “grain boundary engineered” materials with tailored properties.
5:00 PM - DD3.3
A Phase-field Model for Polycrystalline Thin Film Growth.
Frank Wendler 1 , Christian Mennerich 1 , Britta Nestler 1
1 Institute of Materials and Processes, Karlsruhe University of Applied Sciences, D-76133 Karlsruhe, Baden-Württemberg, Germany
Show AbstractThin polycystalline films are of major technical importance in a broad range of applications due to the preferential chemical, mechanical and electrical properties as compared to bulk materials. As an example, we study hydrothermally grown zeolite films used as molecular sieves and catalytic supports. These applications involve the transport of species through internal nanosized pores, strongly depending on orientation and boundary morphology of the grains. Hence, controlling the resulting film texture is of great importance.We extend a multi-phase-field model (PFM) [1] to describe the process in a continuum picture in 2D and 3D, based on the formulation of a free energy functional including interface and bulk contributions [2]. Each growing grain and the aquaeous solution phase are represented by individual order parameters, evolved according to Allen-Cahn dynamics. The coupling of the model to the underlying nanoscale process - oriented attachment growth of silicate building blocks - is given.The objective of the simulation study is to find possible process variables controlling the competitive growth behaviour, the formation of undesired mesoscale porosity and the resulting mechanical properties of the thin film. First, the focus is directed towards a description of single crystals, which typically form hexagonal platelets in MFI zeolite. When choosing appropriate models for the anisotropy of both surface tension and kinetic coefficient, different crystal aspect ratios as well as an observed transition between both growth shapes emerge. The dependance of the growth shape on the reaction environment gives one degree of freedom for texture optimization. In simulation starting from small random seeds a fibre texture evolves during competitive growth, related to the fastest growing crystalline direction. As another parameter to control preferential orientation and texture in the simulated film growth the use of patterned substrates is studied. Incorporating polycrystalline elasticity contributions in the PFM, the distribution of elastic energy under strained substrate is investigated. This allows for an evaluation of film stability under thermal expansion.[1] B. Nestler, H. Garcke and B. Stinner, Phys. Rev. E 71 (2005) 041609.[2] F. Wendler, C. Mennerich and B. Nestler, (2010) submitted to J. Cryst. Growth.
5:15 PM - **DD3.4
In-situ Observation of Crystal Growth Processes by Advanced Optical Microscopy.
Gen Sazaki 1 2 , Yoshinori Furukawa 1
1 Institute of Low Temperature Science, Hokkaido University, Sapporo, Hokkaido, Japan, 2 PRESTO, Japan Science and Technology Agency, Kawaguchi, Saitama, Japan
Show AbstractTo control the orientation of thin film crystals and their growth behavior, in-situ observation of crystal growth processes is essential. To perform such in-situ observation, many microscopy techniques are available. Among them, we have been focusing on one of the advanced optical microscopy techniques, laser confocal microscopy combined with differential interference microscopy (LCM-DIM) [1]. Since LCM-DIM has a high detection sensitivity and is not affected by the observation environment, we were able to visualize elementary steps of protein crystals (several nm in height) even in gel [2] and under high pressure [3]. Hence such in-situ observation will be successfully utilized for the growth of organic thin film crystals, in particular from solutions, under which conditions other microscopy technique, such as TEM, SEM, etc. cannot be available. Non-invasiveness of the observation is also very important. The growth rate of elementary steps on a protein crystal measured by AFM was much faster than that measured by LCM-DIM, since the scan of a cantilever significantly disturbed the solute concentration distribution around a growing crystal [4]. Now we are focusing on the in-situ observation of elementary steps on an ice crystal, which is one of the most abundant materials on earth and then its crystal growth governs a wide variety of phenomena, such as weather, environment-related issues, life in a cryosphere, cosmic evolution, etc. We further improved our LCM-DIM, and succeeded in visualizing elementary steps (0.37 nm in height) at ice-air interfaces (reflectivity 1.8%). We found that a basal (0001) face did not show the roughening transition up to 0°C, in contrast a prism (10-10) face roughened at -1.7°C with increasing temperature. We could also observe the surface melting process directly, and found that two types of quasi-liquid layer appeared at ice-air interfaces. Now we are trying to improve LCM-DIM further in order to visualize the 0.37-nm-thick elementary steps at ice-water interfaces that have much smaller reflectivity of 0.007%. 1) G. Sazaki, et al., J. Crystal Growth, 262, 536-542 (2004). 2) A.E.S. Van Driessche, et al., Crystal Growth & Design, 8, 3623-3629 (2008).3) Suzuki, et al., Crystal Growth & Design, 9, 4289-4295 (2009).4) A.E.S. Van Driessche, et al., Crystal Growth & Design, 8 , 4316-4323 (2008).
5:45 PM - DD3.5
Analysis of the Microfibril Organization Modes Emerging in Plant Cell Walls of Variable Curvature.
Yogesh Kumar Murugesan 1 , Alejandro Rey 1 , Damiano Pasini 2
1 Chemical Engineering, McGill University, Montreal, Quebec, Canada, 2 Mechanical Engineering , McGill University, Montreal, Quebec, Canada
Show AbstractThe cell wall of different plant species possesses enhanced mechanical properties due to their highly ordered 3-D structural organization[1]. The knowledge of the underlying principles governing this micro-structural development is essential in the design and fabrication of lightweight biomimetic materials. The paper presents the theory and modeling of the fiber organization emerging on membranes of variable curvature, as pertinent to the cellulose fibrillar organization in plant cell walls.The plant cell wall is a biological fiber composite reinforced with cellulose microfibrils. During cell wall morphogenesis, these microfibrils self-assemble over a curved cell surface. A mechanical model describing the self-assembly of rigid fibers on an arbitrarily curved fluid membrane has been developed[2]. Depending on the relative strength of the fiber-membrane interactions and membrane curvature, one of the three fiber orientation modes appears on a circular cylindrical membrane (constant curvature): 1) line, 2) helix, 3) ring. In nature, plant cells have different shapes and sizes depending on their type. The shape of these cells can be generalized as polyhedral cylinders of variable curvature[3]. In this work, a model for self-assembly of rigid rods over a polyhedral cylindrical membrane is presented. The model is based on a free energy function that takes into account fiber-fiber interactions (Landau-de Gennes Q-tensor model), membrane bending energy (Helfrich bending-torsion model), and fiber-membrane interactions (extended 2D Maier-Saupe model to curved surfaces) that include competing curvo-philic and curvo-phobic effects. The polyhedral shape of the cell is mathematically defined by using the class of superellipses, namely Lamé curves. Graded-fiber orientation textures, which may contain line, helical, and ring modes, are obtained by solving numerically the model developed for fiber-laden membranes in Lamé-shaped cylinders.The presented model takes into account new mechanisms of cellulose-matrix interactions in the presence of variable curvature, and it contributes to the understanding of cell wall morphogenesis. The knowledge gained in this study can inspire novel material processing methods to fabricate thin films and structures with graded-fiber orientation. References:1.U. Kutschera, The growing outer epidermal wall: Design and physiological role of a composite structure, Ann.Botany 101 (2008) 615-621.2.Y.K.Murugesan, A.D.Rey, Mechanical Model for Fiber-laden Membranes, arXiv:0906.4266.3.R.W. Korn, The Changing Shape of Plant Cells: Transformations During Cell Proliferation, Ann. Bot. 46 (1980) 649-666
Symposium Organizers
Alp T. Findikoglu Los Alamos National Laboratory
Judy Z. Wu University of Kansas
Ruben Huehne Leibniz-Institute for Solid State and Materials Research (IFW)
Institute for Metallic Materials
Toshihiro Shimada Hokkaido University
DD7: Poster Session
Session Chairs
Wednesday PM, December 01, 2010
Exhibition Hall D (Hynes)
DD4: Biaxial Texturing
Session Chairs
Wednesday PM, December 01, 2010
Room 104 (Hynes)
9:30 AM - **DD4.1
Understanding the Deposition of Biaxially Aligned Thin Films by Magnetron Sputtering.
Diederik Depla 1 , Stijn Mahieu 1
1 Solid State Sciences, Ghent University, Ghent Belgium
Show AbstractTaking TiN as an example, the paper first discusses the intimate relationship between the thin film properties and the particle fluxes towards the substrate. The total energy flux towards the substrate is defined by several processes. These will be discussed in detail, and the total energy flux will be related to the resulting crystallographic orientation and the microstructure of the thin TiN film. What can we learn from it related to biaxially aligned thin films? Biaxially aligned thin films can only be grown under specific conditions. This is not only true for TiN but also holds for other materials such as MgO, YSZ, InN and Cr. The paper looks for a simple explanation for this behaviour which results in a simple analytical model. The combination of experimental evidence with a Monte-Carlo based single particle trajectory code, SIMTRA, enables to support this analytical model, giving general conclusions about the structure evolution of biaxially aligned thin films deposited by magnetron sputtering.
10:00 AM - **DD4.2
RHEED Pole Figure Measurements of Biaxial Thin Film Growth Front Evolution.
Gwo-Ching Wang 1 , Wen Yuan 1 , Yu Liu 1 , Toh-Ming Lu 1
1 Physics, Rensselaer Polytechnic Institute, Troy, New York, United States
Show AbstractRecently there has been increasing interests in artificially induced crystal texture orientation during film growth. This is driven by a number of applications such as high Tc superconductors, solar cells, and displays. In particular, artificially induced biaxial texture formation has been a focus of research. The most frequently used characterization technique for biaxial texture formation in thin films is x-ray pole figure analysis. However, x-ray interacts weakly with matter and can penetrate few micron deep into the film. The texture obtained by x-ray is therefore an average texture from the entire thickness of the film. As the texture of a film often changes during growth, information on the basic mechanisms that control the final texture is often lost. Recently we have developed a reflection high energy electron diffraction (RHEED) surface pole figure technique [1,2] to measure quantitatively growth front texture evolution during film growth. Electrons interact strongly with matter and they have very limited penetration and escape depths of few nm. Therefore our RHEED pole figure technique is a surface-sensitive technique that would allow us to obtain unprecedented and rich information on the dynamic behavior of texture evolution of the growth front during film deposition. In this talk we will show how we can use RHEED surface pole figure technique to probe the surface texture evolution of the growth front from the initial stage (nm thick) to the later stage (microns thick). We shall explain the principle, measurement, and construction of such RHEED surface pole figures. An example of the measurement of surface texture evolution during the oblique angle growth of unusual Mg nanoblades (hydrogen storage material) using in situ RHEED surface pole figure will be presented. We will also discuss our ex situ RHEED surface pole figure measurements of CaF2 biaxial film evolution (buffer layer for semiconductor energy conversion materials) using oblique angle deposition technique. Information on the onset of biaxial formation under atomic shadowing effect in the oblique angle deposition during the growth of these films will be presented and discussed.Work partially supported by the NSF 0853562 and 0506738.Refs.1. F. Tang, G.-C. Wang, and T.-M. Lu, "In situ RHEED surface pole figure study of biaxial texture evolution in anisotropic Mg nanoblades during shadowing growth”, J. of Appl. Phys. 102, 014306 (2007).2. F. Tang, T. Parker, G.-C. Wang, and T.-M. Lu, “Surface texture evolution of polycrystalline and nanostructured films: RHEED surface pole figure analysis”, J. Appl. Phys. D: Appl. Phys. 40, R427 (2007).
DD5: Ion Beam Assisted Deposition
Session Chairs
Alp Findikoglu
Randy Groves
Wednesday PM, December 01, 2010
Room 104 (Hynes)
11:00 AM - **DD5.1
Studies of Texture Evolution in IBAD-MgO under Various Growth Conditions.
Vladimir Matias 1 , Alp Findikoglu 1
1 MPA-STC, Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Show AbstractWe examine crystalline-texture evolution during ion-beam assisted deposition (IBAD) of MgO thin films. To perform these experiments we developed an experimental methodology based on linear combinatorics. This technique allows us to fabricate film-thickness wedges that maximize data collection and allow us to easily and systematically obtain texture evolution plots for MgO. MgO texture evolution can be separated into three different regions. During initial ion beam assisted deposition an amorphous layer is formed that is crucial for obtaining <100> grain alignment. Onset of texture appears in the first 1-2 nm of film deposit when MgO crystallizes. We separate out-of-plane <100> fiber texture that appears first, followed by in-plane grain alignment along the ion-beam assist direction. Texture improves with continued ion beam bombardment. Further improvement is seen with growth of a homoepitaxial overlayer. We have studied texture evolution under different ion beam incidence angles and for combinations of different angles. We have developed an empirical quantification of the texture evolution in both IBAD and homoepitaxial layers. The best texture attained thus far in the MgO template layer on polished metal tape has an in-plane FWHM of 1.6°. This work is supported by the Department of Energy Office of Electricity Delivery & Energy Reliability.
11:30 AM - DD5.2
The Effect of Nucleation Layers on Biaxial Texture Development in IBAD MgO.
James Groves 1 3 , Robert Hammond 2 , Vladimir Matias 3 , Raymond DePaula 3 , Liliana Stan 3 , Bruce Clemens 1
1 Materials Science and Engineering, Stanford University, Stanford, California, United States, 3 Superconductivity Technology Center, Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 2 Geballe Laboratory for Advanced Materials, Stanford University, Stanford, California, United States
Show AbstractLow-energy ion-beam irradiation (≤ 1 keV) during the concurrent deposition of magnesium oxide results in the growth of a biaxially textured film. Typically, this template is used for the heteroepitaxial deposition of materials with texture dependent properties such as high temperature superconductors, tunable microwave materials, and ferroelectrics. We have shown in previous work that the initial nucleation of biaxial texture in this system textures at a thickness of ~2 nm. Using a previously reported technique combining an in situ quartz crystal microbalance (QCM) substrate with in situ reflection high-energy electron diffraction (RHEED), we have correlated the mass uptake with the RHEED images of the growing surface. Our research has shown that the development of biaxial texture in this materials system occurs in several stages. The initial stage shows the onset of texture occurs quickly, and the combination of in situ RHEED imaging and ex situ TEM observations has been used to further elucidate the mechanism of growth at the initial stage of texture formation. We have found that we can influence the in-plane texture quality by varying the initial nucleation surface using different nucleation layers. The nucleation depends upon the surface energy and the susceptibility of the layer to amorphization. By selecting the optimum nucleation layer and optimizing the ion beam, we can improve the in-plane texture of IBAD MgO by 1° to 2° and further reduce the grain-to-grain misorientation. This improvement is directly applicable to industrial processes that rely on template layers to improve materials properties through orientation.
11:45 AM - DD5.3
Solution Deposition Planarization for Ion Beam Texturing of Long-length Flexible Substrates.
Chris Sheehan 1 , Yehun Jung 1 , Terry Holesinger 1 , Cynthia Edney 2 , Jon Ihlefeld 2 , Paul Clem 2 , Vladimir Matias 1
1 Superconductivity Technology Center, Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 2 , Sandia National Laboratories, Albuquerque, New Mexico, United States
Show AbstractWe present the results of a study of solution deposition planarization (SDP) for preparing smooth flexible substrates in long lengths. Roll-to-roll fabrication of electronic and power devices with single-crystal properties are desired for inexpensive production. Using the SDP process we have achieved 0.5 nm RMS roughness from a starting roughness of over 20 nm on 5 µm areas. We model the surface roughness reduction as governed by the amount of film shrinkage during solution deposition, number of coatings, solution composition and a residual roughness based on film thickness. This process is extremely well suited for ion beam texturing of MgO. By utilizing solution deposition of a-Y2O3 to planarize the substrate we create the required surface for in-plane MgO texturing using assisted ion-beam deposition. We have achieved in-plane texture FWHM of 4° on the SDP substrates. Using an appropriate simple layer architecture for superconducting coated conductors we attained critical currents in excess of 3 MA/cm2 at 75 K for 1-1.2 µm thick YBa2Cu3Oy films.
12:00 PM - DD5.4
Developing Bi-axially Textured MgO Templates on Flexible Substrates using Ion Beam Assisted Texturing Process.
Judy Wu 1 , Alan Elliot 1 , Rongtao Lu 1 , Ronald Vallejo 1
1 Department of Physics and Astronomy, University of Kansas, Lawrence, Kansas, United States
Show AbstractEpitaxial growth technologically important materials on flexible and transparent substrates is demanded for many optoelectro applications including photovoltaic devices and various photo sensors. Ion beam assisted deposition (IBAD) may provide a practical scheme in generating a thin and transparent bi-axially textured template on these substrates. This work investigates the feasibility of IBAD MgO on polyimide films on Si substrates and polyimide tapes. It has been found that the organic film surface roughening occurs at the initial stage of IBAD MgO process, resulting in poor nucleation of textured MgO layer. To resolve this issue, an ultra thin buffer layer of less than 1nm has been developed using a two-step process. Bi-axially textured MgO template of 10-12 nm has been obtained on polyimide films with in-plane full-width-at-half-maximum less than 10 degree. The effect of substrate bending on the mechanical and optical properties of the templates will be discussed.
12:15 PM - DD5.5
Ion Beam Assisted Deposition of Textured Transition-metal Nitride Films.
Ruben Huehne 1 , Ronald Gaertner 1 , Martin Kidszun 1 , Konrad Gueth 1 , Ludwig Schultz 1 , Bernhard Holzapfel 1
1 , IFW Dresden, Dresden Germany
Show AbstractIon beam assisted deposition (IBAD) is a suitable approach to provide biaxially textured templates for functional materials like superconductors or ferromagnets. As an example, highly textured MgO films were prepared within this approach on arbitrarily textured substrates by applying an amorphous or nanocrystalline bed layer. In this case, the ion beam influences already the nucleation. Consequently, a strong cube texture is achieved within the first 10 nanometres. More recently it was found that transition-metal nitrides with a rocksalt structure, as for example TiN, might be textured in a similar way. Therefore, a reactive IBAD process was applied using pulsed laser deposition of pure metals in combination with a nitrogen-containing ion beam. The results on the in-plane textured growth of TiN are promising for the development of simplified buffer architectures for superconducting YBCO films on metallic tapes. Furthermore, the IBAD approach was successfully used to prepare thin highly textured superconducting transition-metal nitride films as NbN or ZrN. Detailed measurement on the structural properties of the prepared layers will be discussed in order to clarify the mechanism of texture formation during nucleation.
12:30 PM - **DD5.6
Ion Beam Assisted Deposition for Photovoltaic Thin Film Absorber Layers.
Bruce Clemens 1 , James Groves 1 , Garrett Hayes 1 , J. Alfonso Caraveo Frescas 1 , Joel Li 1 , Alberto Salleo 1 , Robert Hammond 2 , Charles Teplin 3
1 Materials Science , Stanford University, Stanford, California, United States, 2 Geballe Laboratory for Advanced Materials, Stanford University, Stanford, California, United States, 3 , National Renewable Energy Laboratory, Golden, Colorado, United States
Show AbstractHigh solar cell efficiency requires efficient harvesting of photo-induced minority carriers. Defects in the absorber layer. Currently, thin film crystalline Si solar cells have reduced efficiency relative to their single crystalline or large grain multicrystalline counterparts. This reduced efficiency is due at least in part to recombination of minority carriers at the high angle grain boundaries in the untextured polycrystalline absorber layers. Here we discus the use of ion beam assisted deposition (IBAD) to create crystallographically textured template layers for controlling the grain boundary angle distribution in solar cell absorber layers. IBAD has been used for deposition of materials with orientation-dependent properties in a number of materials systems. Low energy ion irradiation is used during vapor deposition to produce polycrystalline thin films with biaxial alignment very near that of single crystal. Our approach is to use IBAD to deposit a lattice-matching template layer, of either CaF2 or YSZ and then deposit highly-aligned Si heteroepitaxially. Here, we present data on the deposition of CaF2 and YSZ using the IBAD technique to develop a lattice-matching template for subsequent Si hetero-epitaxy. Our data includes in-situ film growth monitoring with reflected high-energy electron diffraction, x-ray diffraction and Hall mobility measurements. We conclude with characterization using photothermal deflection spectroscopy to study the distribution of gap-states, and our work on modeling grain boundaries to describe the effect of grain boundary alignment on carrier mobility.
DD6: Other Alignment Methods
Session Chairs
Wednesday PM, December 01, 2010
Room 104 (Hynes)
2:30 PM - DD6.1
Fabrication of Single Crystal-like Thin Films on Glassy Materials by the Crystal Imprint Epitaxy.
Yasushi Hirose 1 2 , Kenichi Kimura 1 , Tetsuya Hasegawa 1 2
1 Department of Chemistry, School of Science, University of Tokyo, Tokyo Japan, 2 , Kanagawa Academy of Science and Technology, Kawasaki Japan
Show AbstractWe propose a new technique to fabricate biaxially-oriented single crystal-like thin films on glassy materials. The technique, referred to as the crystal imprint epitaxy (CIE), is a kind of solid phase epitaxy assisted by close contact of lattice-matched single crystalline plate (template). In the CIE process, an amorphous precursor film of product material is deposited on a glass substrate first. Then the single crystalline template was pressed on to the film and heat-treated. When the sample is heated at a temperature sufficiently higher than glass transition point of the substrate, the substrate becomes softer and the template firmly contacts with the precursor film in an atomic scale like usual thermal imprint processes. This close contact triggers solid phase epitaxy of the precursor film from the template side, and the epitaxial film was obtained on glass after removing the template.As a demonstration of the CIE process, we fabricated typical oxide films with perovskite structures, LaAlO3 (LAO) and SrTiO3 (STO), on soda glass substrates. The amorphous precursor films of these materials were fabricated by pulsed laser deposition method. (001) face of LaSrAlO4 (LSAO) single crystalline plates were used as templates, and temperature of heat-treatment (TCIE) was varied in a range of 500 - 700 oC.In the case of LAO, (100)-oriented single crystal-like films were successfully grown at TCIE ≥ 650 oC. From pole figure measurements, it was confirmed that the LAO films were epitaxially grown from LSAO (001) templates with perfect alignment in both out-of-plane and in-plane direction. The FWHM of the rocking curve and phi-scan of the LAO film fabricated at TCIE ≥ 700 oC were 0.8o and 1.2o, respectively. The surface of the LAO film was as smooth as that of LSAO template. In contrast to the LAO films, the STO films obtained after annealing were of polycrystalline form consisting of randomly oriented grains regardless of TCIE. This is because that nucleation temperature of STO (~ 350 oC) is much lower than transition point of the glass substrate (550 oC), and nucleation inside the film starts before the close precursor/template contact. These results indicate that atomic scale contact of single crystalline template realized by thermal imprint process is a key to the present CIE technique.
2:45 PM - DD6.2
Formation of Dense and Aligned Planar Arrangements of Pb Nanoparticles at Silica/Silicon Interface.
Flavia Luce 1 , Felipe Kremer 1 , Dario Sanchez 1 , Zacarias Fabrim 1 , Shay Reboh 1 3 , Fernando Zawislak 1 , Paulo Fichtner 1 2
1 Instituto de Física, UFRGS, Porto Alegre Brazil, 3 Groupe nMat, CEMES-CNRS, Toulouse France, 2 Escola de Engenharia, UFRGS, Porto Alegre Brazil
Show AbstractThe combination of room temperature Pb ion implantation into the center of a silica film, submitted to a low temperature ageing treatment (573 K, 100 h) followed by high temperature annealings (T>1000 K, 1 h), characterizes an alternative method for the formation of dense bi-dimensional arrays of aligned Pb nanoparticles (NP) exclusively at the silica/silicon interface. The samples are investigated by Rutherford Backscattering Spectrometry and Transmission Electron Microscopy. The experimental results demonstrate the formation of very small Pb clusters during the ageing treatment. These clusters seems to be thermal stable, dissociating only at high temperatures (T>1000 K), thus inducing Pb migration towards the silica/silicon interface without particle coarsening in the silica. The resulting bi-dimensional NP system is characterized by epitaxially aligned particles with a mean diameter of 8 nm and a number density of 4e11 cm-2, presenting a order degree as characterized by a well defined pair correlation function peak. The NP formation is discussed in terms of a Pb segregation process from solute atoms inside a strained silicon layer at the interface region.
3:00 PM - DD6.3
Growth of Complex Oxide Nanostructures by Diffusion Driven Self Organization on Different Chemical Terminations.
Bouwe Kuiper 1 , Jeroen L. Blok 1 , Gertjan Koster 1 , Guus Rijnders 1 , Dave H.A. Blank 1
1 Faculty of Science and Technology and MESA+ Institute for Nanotechnology, University of Twente, Enschede Netherlands
Show AbstractThin film deposition techniques that allow for atomic control of perovskite-type oxides, have been used to build artificial crystal structures bottom up by stacking mono-layers of different materials on top of each other. These layered structures result in new or enhanced functionality, for example when creating a superconducting superlattice of BaCuO2/(Sr,Ca)CuO2[1] or create a conducting interface between to insulating materials[2]. These perovskite crystals all share a common oxygen backbone structure, this ABO3 (001) structure can be represented by a stacking of alternating AO and BO2 planes. Both of these stacking layers can be present at the surface, however the ideal starting point for thin film growth is a single terminated crystal surface, typically achieved by wet chemical etching. A less studied scenario is a case where both terminations are present at the surface and show an ordered distribution of AO and BO2 termination. These different chemical terminations will have a different interaction during growth with material applied by thin film deposition techniques like Pulsed Laser Deposition (PLD). For example, metallic and ferromagnetic SrRuO3 is sensitive to the surface termination during PLD. Growth of such a material results in patterns which resemble the substrate termination distribution, either random or ordered along the step edges[3]. We provide a Solid-On-Solid (SOS) model to explain the selective growth of SrRuO3 on ScO2 terminated DyScO3. The selectivity is driven by a difference in diffusivity, resulting in preferential epitaxial growth on only ScO2 terminated areas. When the substrate shows ScO2 termination ordered along the step edges, growth of SrRuO3 results in conducting nanowires parallel to step edges of, typically 8 nm high, 100 nm wide, spaced by 100 nm and several micrometers long. Controlling the size and shape of the ordered areas of different surface termination could allow for the fabrication of combined lateral and vertical hetrostructures. For example by using a chemical treatment to create single terminated DyScO3 [4] and subsequently applying a controlled amount of DyO, one could control the termination template. By combining this with tuning the SrRuO3 growth conditions using the SOS model one could control the dimensions of the SrRuO3 structures. Since these structures are coherently grown, they allow us to study intrinsic structure to property relationships.[1] Koster, G Physica C 2001, 353, 167–183 [2] Ohtomo, A.; Hwang, H. Y. Nature 2004, 427, 423–6. [3] Bachelet, R. Chem. Mater. 2009, 21, 2494–2498 [4] Kleibeuker, J.E. Adv. Funct. Mater. (accepted)
3:15 PM - DD6.4
Defect and Surfactant Mediated Growth of Electrodeposited Thin Films
Stephen Farias 1 , Lei Tang 2 , Karl Sieradzki 2 , Robert Cammarata 1
1 Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland, United States, 2 , Arizona State University, Tempe, Arizona, United States
Show AbstractElectrochemical deposition has become an established and important method in modern industry as a method of producing metallic thin films for such applications as coatings, electrical interconnects, and magnetic devices. While this technique is widely used, it often produces polycrystalline films with small grain sizes and high intrinsic stresses, characteristics that can adversely affect the performance of the devices produced. In order to overcome these limitations, the technique of defect mediated growth has been developed [Sieradzki et al., Science 284, 138 (1999)]. In this approach, the primary metal that is to be grown is co-deposited with a reversibly deposited mediator metal. The mediator is periodically deposited and stripped from the surface, resulting in an increase in the density of two-dimensional islands of the principal metal, which in turn promotes layer-by-layer growth to form a single crystal that is atomically flat. Results characterizing the interrelationship among the electrochemistry, microstructure, and stress of the films produced by this process will be presented with particular attention given to single crystal Ag deposition using Pb as the intermediary species. Extension of this approach to other surfactant/single crystal thin film systems will also be discussed. This work was supported in part by the National Science Foundation, award number DMR 0706178.
3:30 PM - DD6.5
Tilting of Precipitation Patterns in Carbon-transition Metal Nanocomposite Thin Films by Hyperthermal Ion Deposition.
Gintautas Abrasonis 1 2 , Thomas W. Oates 3 , Gyorgy Kovacs 1 , Mark Tucker 2 , Joerg Grenzer 1 , Per O. Persson 3 , Karl-Heinz Heinig 1 , Andrius Martinavicius 1 , Nicole Jeutter 1 , Carsten Baehtz 1 , Marcela M. Bilek 2 , Wolfhard Moeller 1
1 Institute of Ion Beam Physics and Materials Research, Forschungszentrum Dresden-Rossendorf, Dresden Germany, 2 School of Physics, The University of Sydney, Sydney, New South Wales, Australia, 3 , Linköpings University, Linköping Sweden
Show AbstractThe structure control, especially at the nanoscale, is of the primary importance in the field of the materials science of thin films. Here, the hyperthermal ion induced self-organization caused by phase separation during the carbon-transition metal (Ni, Cu) thin film growth is reported. The films have been grown by ionized physical vapour deposition using filtered cathodic vacuum arc. Influence of the metal type, film composition, ion energy and incidence angle is studied. The film morphology has been determined by transmission electron microscopy and grazing incidence small angle x-ray scattering. At these growth conditions, atomic displacements are caused solely by impacting energetic ions, resulting in phase separation in an advancing surface layer. If the metal amount surpasses some critical value, this layer switches to an oscillatory mode and a nanoscale precipitation pattern emerges. The results show that for the perpendicular incoming depositing ion incidence the C:Ni film structure consists of alternating self-organized nickel carbide and carbon layer oriented parallel to the film surface. Moreover, the ion induced atomic mobility is not random, as it would be in the case of thermal diffusion, but conserves to a large extent the initial direction of the incoming ions, resulting in a tilting of the periodic precipitation structures for the oblique ion incidences. The metal nanopatterns no longer align with the advancing surface, but with the incoming ions. While both type of films show tilted structures, for C:Cu films the ‘tilted-lying’ transition is observed when increasing Cu content.We establish a dependence of the nanopattern morphology on the growth parameters and demonstrate a method for controlling the nanopatterning. The results are discussed on the basis of the interplay between thermodynamically driven phase separation and energetic ion induced ballistic effects. Application of this concept opens new ways for the bottom-up nanostructure control for composite materials.
3:45 PM - DD6.6
Low-Temperature Growth of Epitaxial Semiconductor Nanostructures and Films.
Alp Findikoglu 1 , Daniel Perea 1 , S. Picraux 1
1 Materials Physics Applications, Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Show AbstractThe growth of epitaxial semiconductor nanostructures and films at low temperatures is important for semiconductor technology because it allows the possibility of monolithically integrating different high-performance single-crystalline semiconductor structures directly onto low cost technologically important substrates. At sufficiently low temperatures this can enable, for example, Si or Ge device fabrication on flexible substrates such as plastics. We have studied the reduced-temperature liquid-mediated growth of Ge nanostructures and films on crystalline template layers on non-single-crystalline substrates in a low pressure chemical vapor deposition (LPCVD) system. The heteroepitaxial process is implemented by the Au seeded vapor-liquid-solid (VLS) catalytic growth technique with germane below 400°C. Crystalline template layers were prepared with ion-beam-assisted-deposition (IBAD) texturing and electron-beam evaporation on glass substrates. A thin layer of e-beam evaporated Au forms the catalyst layer, upon which we grew Ge films at 386°C. Scanning electron microscopy and x-ray diffraction results indicated that both Ge islands and nanowires grew heteroepitaxially on the crystalline template layers on glass substrates with good alignment over large areas. Considerations for optimizing thin film morphology while maintaining good heteroepitaxial growth will be presented.
DD7: Poster Session
Session Chairs
Thursday AM, December 02, 2010
Exhibition Hall D (Hynes)
9:00 PM - DD7.1
Application of Simplified Buffer Architectures Based on IBAD-TiN for YBCO Coated Conductors.
Ruben Huehne 1 , Ronald Gaertner 1 , Rainer Kaltofen 1 , Tom Thersleff 1 , Steffen Oswald 1 , Ludwig Schultz 1 , Bernhard Holzapfel 1
1 , IFW Dresden, Dresden Germany
Show AbstractIon Beam Assisted Deposition (IBAD) is one of the major approaches to provide biaxially textured templates for REBCO coated conductors. Whereas IBAD-MgO layers are already in use for long-length production, other materials like TiN might be applied in the same way as they show a similar strong cube texture at a thickness of less than 10 nm, if an amorphous or nanocrystalline bed layer is used. Accordingly, cube textured IBAD-TiN layers have been deposited reactively using pulsed laser deposition on polished metal tapes as Hastelloy or stainless steel. The influence of different amorphous or nanocrystalline bed layers as well as of the roughness of the used metal tape on the in-plane texture has been studied. An amorphous metallic TaxNi1-x bed layer was tested successfully for the IBAD-process leading to highly textured TiN films with an in-plane orientation below 10°. Furthermore, SrZrO3 buffer layers were used afterwards directly on TiN. As a result, biaxially textured YBCO layers were obtained showing an in-plane alignment down to 6° and critical current densities of more than 2 MA/cm2.
9:00 PM - DD7.10
Strain-induced Mophotropic Phase Boundary of Multiferroic BiFeO3 Thin Film on Silicon Substrate(2010).
Wen-I Liang 1 , Chih-Hung Wang 1 , Chun-Yen Peng 1 , Heng-Jui Liu 2 , Wei-Chen Kuo 3 , Tai-Bor Wu 2 , Li Chang 1 , Jenh-Yih Juang 3 , Ying-Hao Chu 1
1 Department of Materials Science and Engineering, National Chiao Tung University, Hsin Chu Taiwan, 2 Department of Materials Science and Engineering, National Tsing Hua University, Hsin Chu Taiwan, 3 Department of Electrophiscs, National Chiao Tung University, Hsin Chu Taiwan
Show AbstractMultiferroic BiFeO3 (BFO) is known to have strain-induced coexistence of two-phases across a morphotropic phase boundary (MPB). These MPBs exhibit pronounced piezoelectricity and ferroelectricity, which can be utilized for the next generation device architecture. However, it is without doubt that silicon industry rules technology market in the past decades, and how to turn BFO thin film into a practical alternative in applications raises extensive discussions currently. Driven by this concept, we demonstrate the integration of BFO thin film on silicon substrate and delve into novel properties in detail, such as ferroelectricity and magnetic response, that have great potential ushered in new era of technology.In this study, we have successfully grown epitaxial BFO thin films on LaAlO3 coated Silicon substrates by using reflective high energy electron diffraction-assisted pulsed laser deposition. X-ray Diffraction and reciprocal space mapping as a function of film thickness and temperature are measured to understand the structural evolution of this phase boundary while the atomic structure has been studied in detail via high-resolution transmission electron microscopy. Moreover, topography and ferroelectric domain structure have been probed by scanning probe microscopy to study the electrostatic and elastic boundary conditions. Meanwhile, we have also used superconducting quantum interface device to investigate magnetic properties. The correlation between structure, surface topography, ferroelectric domain pattern, and magnetic phenomena will be addressed to understand the behaviors of BFO thin film grown on LAO/Si substrates. A model will be proposed to illustrate the formation of this MPB boundary. Such results demonstrate a new pathway to integrate strain induced MPB on Si substrates for future applications.
9:00 PM - DD7.11
Magnetic Properties of Orientation Controlled CoFe2O4 in Heteroepitaxial CoFe2O4-BiFeO3 Nanostructure.
Pei-Yu Tsai 1 , Sheng-Jie Liao 2 , Heng-Jui Liu 2 , Tai-Bor Wu 2 , Chih-Huang Lai 2 , Ying-Hao Chu 1
1 Materials Science and Engineering, National Chiao Tung University, Hsinchu Taiwan, 2 Materials Science and Engineering, National Tsing Hua University, Hsinchu Taiwan
Show AbstractMagnetoelectric effects in materials provide a great opportunity to use an electric field to control ferromagnetism. Magnetoelectric coupling between electric and magnetic order parameters has been theoretically predicted, and there is intense interest in its implementation in device architectures taking advantage of these properties. Single-phase remain elusive as most exhibit mulitferroicity only at low temperatures. Alternatively, magnetoelectric materials can be synthesized as a composite system, e.g. as a product property of a composite phase consisting of a magnetostrictive and a piezoelectric material. Magnetoelectric materials could also be fabricated in a nanostructured columnar fashion. By selecting materials that spontaneously separate due to immiscibility, such as spinel and perovskite phases, one can create nanostructured phases made of pillars of one material embedded in a matrix of another. Such structures were shown to exhibit strong magnetoelectric coupling. These nanostructures, in which the interface is perpendicular to the substrate, remove the effect of substrate clamping and allow for better strain-induced coupling between the two phases. These structures have been shown to be very versatile and offer an excellent opportunity for electrically controlled magnetic storage. However, the independent orientation control of multiphase is still lack, in this study, a method was proposed to solely control the orientation of CoFe2O4 in hetero-epitaxial CoFe2O4-BiFeO3 columnar nanostructures. We showed that CoFe2O4-BiFeO3 heterogeneous thin film deposited on various perovskite substrates would induce CoFe2O4 to form (100), (110), and (111) orientations respectively with (100) epitaxial BiFeO3 films. A growth model accompanied with Xray diffraction and TEM will be shown to understand the formation and the control of these nanostructures. The detailed magnetic properties of CoFe2O4 nanopillars are studied by using VSM and FMR to map out the magnetic anisotropy, and magnetoelectric coupling is also studied to understand the orientation effects on coupling mechanism. With this new method, we could control the interfaces between CoFe2O4 and BiFeO3 and gain more opportunity to tune magnetoelectric coupling in multiferroic CoFe2O4-BiFeO3 nanostructures for future applications.
9:00 PM - DD7.12
Preparation of Heteroepitaxial SrRuO3 Thin Film on Si Substrate and Microstructure of BaTiO3-NiFe2O4 Epitaxial Composite Thin Film Deposited on the SrRuO3 Bottom Electrode by PLD.
Naoki Wakiya 1 , Naonori Sakamoto 1 , Shigeki Sawamura 1 , Desheng Fu 1 , Kazuo Shinozaki 2 , Hisao Suzuki 1
1 , Shizuoka Univ., Hamamatsu Japan, 2 , Tokyo Tech., Tokyo Japan
Show AbstractCrystal structure and microstructure of epitaxial BaTiO3-NiFe2O4 multiferroic composite thin film was examined by x-ray diffraction and cross sectional TEM observation. Prior to deposit BaTiO3-NiFe2O4 multiferroic composite thin, heteroepitaxially grown SrRuO3 on Si(001) substrate was achieved using a (La,Sr)CoO3/CeO2/YSZ triple buffer layer. This multi-layer electrode structure enabled to realize high thermal stability, high electrical conductivity and heteroepitaxial growth on Si. Cross sectional TEM observation revealed that the BaTiO3-NiFe2O4 multiferroic composite thin film deposited on the SrRuO3 had “0-0” type composite that granular BaTiO3 and NiFe2O4 crystals are mixed together 3-dimensionally with keeping heteroepitaxial relations each other. The BaTiO3-NiFe2O4 multiferroic composite thin showed both ferroelectricity and ferromagnetism at the same time.
9:00 PM - DD7.13
Textured Nanocrystalline Magnetic Ni0.5 Zn0.5 Fe2O4 Ferrite Particles Produced by Chemical Route.
Raul Valenzuela 1 , Raul Ortega-Zempoalteca 1 , Gabriela Vazquez 1 , Nader Yaacoub 2 , Jean-Marc Greneche 2 , Anna Slawska-Waniewska 3 , Frederic Herbst 4 , Souad Ammar 4
1 Materials Science, National Autonomous University of Mexico, Mexico City, DF, Mexico, 2 , Université du Maine, Le Mans France, 3 Institute of Physics, Polish Academy of sciences, Warsaw Poland, 4 ITODYS, Universite de Paris 7-Diderot, Paris France
Show AbstractFerrite nanoparticles (NPs) of composition Zn0.5Ni0.5Fe2O4 were prepared by forced hydrolysis in a polyol (polyol process) from the corresponding iron, nickel and zinc acetates. The solution was heated slowly (sample A) or quickly (sample B) up to boiling and maintained under reflux for about 1 hour under mechanical stirring. The recovered dark brown powders after centrifugation exhibited specific microstructures. The former are constituted by non aggregated single-crystals of about 5 nm in size as inferred from low and high resolution Transmission Electron Microscopy (TEM) image analysis, while the latter are constituted by polycrystalline particles of about 22 nm in size with an average crystal size of about 5 nm. In this case, the nanocrystals have the same orientation and form textured polycrystalline particles. The interplanar distance is estimated to be 4.86 Å. This distance is in good agreement with the {111} planes of nickel-zinc ferrite. The fast Fourier transformation (FFT) pattern of each of these particles showed a Laüe-like pattern, demonstrating that the polycrystalline particles are effectively textured. Both types of samples showed a superparamagnetic behaviour at room temperature, and a ferrimagnetic ordering at low temperatures, but significant differences were observed in their magnetic properties in relation with their microstructure. The magnetization as a function of magnetic field H and temperature T for zero-field cooled (ZFC) and field-cooled (FC) conditions, exhibited clear differences; blocking temperature, TB, is about 36 K for sample A, while it increases up to ~85 K for sample B; additionally, a kind of kink-discontinuity at T ~ 58 K can be observed for this sample. Henkel plots performed on both type of samples evidenced a net deviation from the Stoner-Wolharth model of non-interacting uniaxial magnetic single domain. This deviation agreed with the occurrence of exchange interaction in the textured polycrystals (magnetization increase) and dipolar ones in the single crystals (magnetization decrease). These results were corroborated by a Mossbauer spectrometry study at different temperatures. These results are very interesting since they open the possibility of producing textured powdered nanostructures by chemical route, acting judiciously on the synthesis conditions.
9:00 PM - DD7.14
High Quality ZnO Thick Film Grown by Low Temperature Chemical Bath Deposition.
Chen-Chun Lin 1 , Christophe Couteau 1 , Corinne Sartel 2 , Vincent Sallet 2 , Yue-Han Wu 3 , Jing-Chie Lin 4 , Gilles Lerondel 1
1 Laboratoire de Nanotechnologie et d'Instrumentation Optique / ICD , Université de Technologie de Troyes, Troyes France, 2 Groupe d'Etude de la Matière Condensée, CNRS - Université de Versailles Saint-Quentin en Yvelines, Meudon France, 3 Department of Materials Science and Engineering, National Chiao-Tung University, Hsinchu Taiwan, 4 Institute of Materials Science and Engineering, National Central University, Jhongli Taiwan
Show AbstractWell-oriented, dense and thick zinc oxide (ZnO) films were synthesized by using chemical bath deposition (CBD) method on the c-plane sapphire coated with a ZnO buffer layer previously deposited by metal-organic chemical vapor deposition (MOCVD). The buffered substrate was immersed in an aqueous solution consisting of zinc nitrate and diethylenetriamine (DETA) and the aqueous solution was heated and refluxed at 98oC in an oil bath. The thickness of the ZnO films deposited by CBD linearly increased from 0.3 to 2.6 um with the increasing concentration of zinc nitrate from 0.01 to 0.05 M. X-ray diffraction analysis showed both the ZnO thick films and the ZnO buffer films were highly oriented along the c-axis and the rocking scan around (002) position of ZnO thick films showed narrower full width at half maximum (FWHM) than the buffered ZnO film. From the transmission electron microscopy observation, many dislocations found in the ZnO buffer layer due to the lattice mismatch between the ZnO and the c sapphire and the density of the dislocations were reduced in the CBD ZnO film. These results demonstrated that CBD method could also be used to deposit high quality ZnO thick films in combination with physical method. The optical properties of the ZnO thick films have also been studied and will be presented.
9:00 PM - DD7.2
Effects of Electric Field on Molecular Orientation in Electrospun Polymer Fibers.
Xiaoqian Ma 1 , Bruce Chase 1 , John Rabolt 1
1 Materials Science and Engineering, University of Delaware, Newark, Delaware, United States
Show AbstractPoly (vinylidene fluoride) (PVDF) fibers were collected between two counter electrodes separated by an air gap. Scanning electron microscopy (SEM) images showed that PVDF fibers were macroscopically aligned. Polarized Fourier transform infrared (FTIR) spectra demonstrated PVDF fibers were also aligned at molecular level. The degree of molecular orientation was evaluated using dichroic ratio (DR) calculated from the polarized IR spectra. Meanwhile, macroscopical misalignment and thickness effect were also taken into consideration. Fibers between the negatively charged counter electrodes had higher degree of orientation than those between the grounded ones. That indicated electric field affected the molecular orientation during electrospinning process. Both the intensity and distribution of applied electric field were investigated in this work.
9:00 PM - DD7.3
Crystalline Alignment and In-plane Texture Improvement of Buffer Layers Deposited on NiW Tapes.
Yijie Li 1 , Linfei Liu 1 , Huaran Liu 1 , Xiaokong Song 1 , Dan Hong 1 , Ying Wang 1 , Da Xu 1
1 Department of Physics, Shanghai Jiao Tong University, Shanghai, Shanghai, China
Show AbstractIn order to deposit YBCO coated conductor with high critical current density on rolling assisted biaxially textured Ni-W tapes, the influence of deposition conditions on the orientation, in-plane texture, and surface morphology of buffer layers and superconducting layers have been systematically studied. It was found that crystalline alignment and in-plane texture of cerium oxide cap-layers were well improved by optimizing deposition parameters. The full width at half maximum of phi-scan x-ray diffraction peak was reduced from original value of 7-8 degrees to 4-5 degrees. High Critical current density of 5×10<6>A/cm<2> has been achieved on optimized buffer layers. This value is comparable with the critical current density of YBCO thin films deposited on single crystalline substrates.
9:00 PM - DD7.4
Growth of GaN on Sapphire with Ga2O3 as a Sacrificial Layer by Metal Organic Vapor Phase Epitaxy.
Tsung-Yen Tsai 1 , Ming-Tsung Hung 1 , Po-Rung Lin 1 , Chun-Ting Pan 1 , Dong-Sing Wuu 1
1 Material sciences and engineering, National Chung-Hsing University, Taichung Taiwan
Show AbstractChemical lift-off (CLO) technique has drawn much attention since no damages will be exerted to GaN epi-layer during the process. This study has presented the MOVPE growth of GaN epi-layer on sapphire substrates with Ga2O3 as a sacrificial layer for the subsequent CLO process. At first, the 150nm-thick (-402)-oriented Ga2O3 with RMS of 1.77 nm was fabricated on sapphire at 400 celisus by pulsed laser deposition. The well-crystallised wurtzite GaN was then grown on Ga2O3 template by MOVPE at N2 ambient throughout because the degradation of Ga2O3 was remarkably at H2 ambient. The FWHM of (002) reflection and PL spectrum for GaN/Ga2O3/Al2O3 were 1670 arcsec and 74.8 meV, respectively. This unsatisfactory quality can be dramatically improved by optimizing the regular GaN growth at N2 environment. The CLO process of mesa-less GaN epi-layer from sapphire was successfully conducted with the lateral etching rate of 53.8 micrometers per hour.
9:00 PM - DD7.5
Defect Structure and Gas Sensing Properties of Hetero-epitaxial SnO2 Thin Films Depending on O2 Plasma Time.
Daihong Kim 1 , Seong-Hyeon Hong 1
1 Department of Materials Science and Engineering, Seoul National University, Seoul Korea (the Republic of)
Show AbstractTin dioxide (SnO2) is an n-type wide-band-gap semiconductor and an important material in electronic devices such as transparent electrodes and gas sensors. The performance of these SnO2-based devices is strongly influenced by internal defects such as dislocations and stacking faults. Especially, defects are performed as the role of oxygen adsorption sites in gas sensors. Recently, epitaxial films have been interested to study their electrical and electro-chemical property isolating from the grain boundary effects. The epitaxial SnO2 films have been fabricated using various techniques. Although many studies about epitaxial SnO2 films have been reported, little attention has been paid to the defect structure during hetero-epitaxial growth. In particular, no investigations about effect of defect structures on gas sensing property have been conducted.ALD is one of powerful technique to produce ultra-thin films through a self-limiting surface reaction. Therefore, epitaxial films can be easily acquired with accurate thickness control and good conformality. Moreover, the deposition of oxide films using plasma enhanced atomic layer deposition (PEALD) can occur in a reactive atmosphere with adjusting oxygen plasma, which allows the formation of stoichiometric oxides. For the epitaxial growth of SnO2 film, the commonly used substrates are sapphire (Al2O3) and TiO2. Among these substrates, (100) TiO2 substrate is a good candidate due to the large lattice mismatch between SnO2 c-axis and TiO2 c-axis, which introduces misfit-induced stress. Therefore, the defect structure of SnO2 thin films is easily varied by deposition conditions.In this study, we developed the epitaxial SnO2 films on (100) TiO2 substrates with different O2 plasma time by PE-ALD. As a Sn precursor, Dibutyltindiacetate (DBTDA) was used and the deposition was conducted with rf power of 100 W at 240 mTorr for 1000 cycles. All the films were post-deposition annealed at 600 oC in air to enhance their crystallinity. The out-of-plane orientation and crystallinity was investigated by x-ray diffraction with double-crystal monochromator, and (100) orientations were grown on (100) TiO2 substrates. However, the film peaks are slightly shifted toward substrate peaks and sharpened with decreasing plasma time. Increasing plasma time, the misfit-induced compressive stress was almost fully relaxed to yield the high density interfacial misfit dislocations identified as {101} planar defects, which were confirmed by X-ray pole figure, X-ray reciprocal space mapping and transmission electron microscopy. The H2 and EtOH gas sensing properties were determined by measuring the changes in electric resistance between sample gas and pure air. Most films exhibited the maximum gas response at 400 oC, and SnO2 thin film deposited with 6 sec and 4 sec plasma exhibited the highest gas response toward H2 and EtOH gas, respectively. We also discuss effect of defect structure on gas sensing properties.
9:00 PM - DD7.6
Ferroelectricity Induced by Broken Symmetry and Weak Ferromagnetism in Epitaxial Stabilzed Hexagonal LuFeO3 Films.
Youngkyu Jeong 1 , Jung-Hoon Lee 1 , Suk-Jin Ahn 1 , Sangwoo Ryu 1 , Hyun Jang 1
1 MSE, POSTECH Korea, Pohang Korea (the Republic of)
Show AbstractWe have studied the nature of multiferroic properties of hexagonal LuFeO3 thin films. In bulk state, LuFeO3 possesses an orthorhombic perovskite structure with space group of Pnma, and it consists of three-dimensional networks of FeO6 octahedra. By adopting hexagonal templates and pulsed-laser-deposition method, however, it can be modified artificially into a two-dimensional layered hexagonal structure. These artificial hexagonal phases are turned out to have not only room temperature ferroelectricity (TC~570K), which is not expected for the bulk RFeO3 orthoferrite where R is one of the rare earth ions, but also weak ferromagnetic behavior under the magnetic field normal to the film surface below Neel temperature (TN~120K).Our first principle calculations support that the spontaneous electric polarization induced by a broken symmetry (P63cm) exists along the direction normal to the film surface even at room temperature. In addition, the residual moment is revealed to be come from the canted spin structure whereas a geometrical spin frustration within a film plane, where the net moment is almost zero, is preserved.
9:00 PM - DD7.7
Oriented Thin Films of Poly(tetrafluoroethylene) on Uniaxially Polished Substrate.
Koji Okudaira 1 , Kunihiro Hotta 1 , Nobuo Ueno 1
1 Graduate School of Advanced Integration Science, Chiba University, Chiba Japan
Show AbstractFabrication of oriented structure such as uniaxially oriented crystallites is important to obtain the oriented growth of materials as a substrate. Thin poly(tetrafluoroethylene) (PTFE) films obtained by friction transfer can be used as orienting media onto various substrate.[1] Since the friction transfer process needs the high substrate temperature of about 300°C and was done in the atmosphere, the contamination would introduce to the PTFE surface. In this study, we show the uniaxially oriented PTFE thin films are obtained by evaporation onto the uniaxially polished Cu plate and determine the molecular orientation of these films by near-edge x-ray absorption fine structure (NEXAFS) spectroscopy. PTFE was deposited on uniaxially polished polycrystal Cu plate by polishing paste (alumina particles with mean radius of about several μm). The deposition was performed in 10-4 Pa at room temperature. NEXAFS measurements were performed at Photon Factory (BL13A). We observed the incidence angle dependence of carbon (C) K-edge NEXAFS spectra of PTFE(5nm)/Cu where the electrical vector of incidence photon is parallel (parallel condition) and perpendicular (perpendicular condition) to the polishing direction of Cu plate. In the NEXAFS spectra three main peaks appear at photon energy of 292 eV, 295eV and 298.5 eV, which are assigned to the transition from C1s core state to σ*(C-F), σ*(C-C), and σ*(C-F), respectively. [2] In the case of parallel condition, the three peaks in the C1s NEXAFS spectra show the remarkable incidence angle dependence. The transition intensity of σ*(C-F) at a grazing incidence is larger than that at normal incidence, on the other hand the transition intensities of σ*(C-C) show the opposite incidence angle dependence With the perpendicular condition, NEXAFS spectra do not show the incidence angle dependence apparently. At low (room) temprature, PTFE forms a helix structure which results in long straight rod-like molecules, where the direction of C-F bonds is perpendicular to the direction of the C-C main chain (molecular axis of the rod-like molecule). [4] From the incidence angle dependence of C1s NEXFS spectra with two different conditions and the molecular structure of PTFE, it was concluded that PTFE molecules uniaxially align, where the C-C main chains are parallel to the polishing direction of Cu substarte. [References][1] J. C. Wittmann et al., Nature, 352(1991) 414[2] T. Ohta et al., Physica Scripta, 41 (1990) 150.[3] K. Nagayama et al., J. Electron Spectrosc. Rel. Phenom., 78 (1996) 375.[4] C. W. Bunn et al., Nature, 174 (1954) 549
9:00 PM - DD7.9
Interplay Between The Crystal And Liquid Crystalline Ordering Of IPP And Carbon Nanotube Composites Under Melt-shear.
Georgi Georgiev 1 2 , Robert Judith 1 , Erin Gombos 2 , Michael McIntyre 2 , Peggy Cebe 2
1 Natural Sicences, Assumption College, Worcester, Massachusetts, United States, 2 Physics and Astronomy , Tufts University, Medford, Massachusetts, United States
Show AbstractIsotactic polypropylene (iPP) exhibits a smectic liquid crystalline phase under melt-shear. This phase acts as a precursor to an oriented fabrillar crystal structure along the direction of shear flow. Multi-walled carbon nanotubes (MWCNTs) align under shear stress in polymer melts and induce oriented crystals perpendicular to their surface. MWCNTs also enhance the crystallization kinetics of iPP. IPP/MWCNT films at concentrations up to 5% were sheared at 200○C for two seconds and cooled to room temperature. The samples were then analyzed using differential scanning calorimetry (DSC), wide angle X-ray scattering, polarized optical microscopy (POM) and transmission ellipsometery. The MWCNT’s aid the alignment of the polymer chains causing an increase of ordering of the smectic phase and of the subsequently formed crystals.Research supported by: Assumption College Faculty Development Grant, funding for students’ stipends, instrumentation and supplies. The NSF Polymers Program of the DMR, grant (DMR-0602473), NASA grant (NAG8-1167) and the MRI Program under DMR-0520655 for thermal analysis instrumentation.