Symposium RR: Artificially Induced Grain Alignment in Thin Films

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Artificially Induced Grain Alignment
in Thin Films
December 2 - 3, 2008




Chairs  

Vladimir Matias
Materials Physics and Applications Division
Los Alamos National Laboratory
MS T004
Los Alamos, NM 87545
505-663-5564

   

Robert Hammond
Geballe Laboratory for Advanced Materials
Stanford University
476 Lomita Mall
Stanford, CA 94305-4045
650-723-0169

Seung-Hyun Moon
SuNAM Co. Ltd.
65-10 Daeyadong, Siheungsi
Gyeonggido, 429-807 Korea
82-50-2558-9662

 

 

Ruben Huehne
Institute for Metallic Materials
Leibniz-Institute for Solid State
and Materials Research (IFW)
Helmholtzstr. 20
Dresden, D-01069 Germany
49-351-4659-716

Symposium Support
Bruker HTS
k-Space Associates Inc
Superconductivity Technology Center -Los Alamos National Laboratory
Staib Instruments Inc

Proceedings to be published online
(see Proceedings Library at www.mrs.org/publications_library)
as volume 1150E
of the Materials Research Society
Symposium Proceedings Series.
 


* Invited paper
 

SESSION RR1: Milestones in IBAD Texturing
Chairs: Ruben Hühne and Vladimir Matias
Tuesday Morning, December 2, 2008
Room 111 (Hynes)


8:30 AM *RR1.1
Inducing Grain Alignment in Metals, Compounds and Multicomponent Thin Films. James M.E. Harper, Physics, University of New Hampshire, Durham, New Hampshire.

Several methods to induce grain alignment in polycrystalline thin films will be discussed, in which directional effects can dominate over the normal evolution of fiber texture during thin film growth. Early experiments with ion beam assisted deposition showed the importance of channeling directions in selecting grain orientations with low sputtering yield or low ion damage energy density. Examples of this approach include the formation of biaxial fiber textures in bcc Nb, fcc Al and hexagonal AlN. Grain orientations may also be selected by the controlled release of stored energy in the form of abnormal grain growth (electroplated Cu), solute precipitation (Cu-Co) or phase transformation (TiSi2). Other energy sources such as mechanical deformation, crystallization or compound formation may also be manipulated to produce desired grain alignments. Prospects for combining several of these mechanisms will be discussed.


9:00 AM *RR1.2
Development of IBAD Process for Biaxial Texture Control of RE-123 Coated Conductors. Yasuhiro Iijima, Materials Technology Lab., Fujikura Ltd., Sakura-Shi, Chiba, Japan.

Ion-Beam-Assisted Deposition (IBAD) is a quite sophisticated technique to deposit in-plane textured thin films with concurrent off-normal ion beam bombardment directly on non-textured substrates. It is a key technology for long, high-performance REBa2Cu3O7-x (RE-123) superconducting wires, which are now available for various practical applications operating around liquid nitrogen temperature. RE-123 superconducting wire, with the largest Ic performance ever available, requires “biaxially aligned structure” (single crystal like structure without large-angle grain boundaries) even in flexible conductors, in order to eliminate so sensitive intergranular weaklinks that should interrupt macroscopic transporting current. IBAD had realized choice of non-textured metal substrate with strong mechanical durability, low magnetism, low cost, etc., favorable in both conductor manufacturing and winding process, and their operations in practical applications. The concept of biaxial alignment by off-normal IBAD was proposed in 1985, in Nb films on fused silica. In 1991, sharply textured films were first observed in oxide films (Yttrium stabilized Zirconia (YSZ)) grown on non-textured Ni-Cr alloy, which result in biaxially aligned, flexible high-Jc RE-123 film tapes, epitaxially grown on the IBAD-textured template. Good textured films were observed in many fluorite, pyrochlore, rare earth C, and rock salt type oxide or nitride films. One of <111>, <110>, or <100> axis is aligned to Ar+ ion bombarding direction where another <100> or <111> axis is aligned normal to substrate. Biaxial (triaxial) aligned structure was obtained with the optimized angle of ion beam, which was determined by the combination of indexes of the alignment axes if symmetrical requirement was cleared. In early 90s, low energy ion source technology was still elemental and frequent filament exchange must be required in oxygen gas flow, which prevented concurrent reel-to-reel IBAD processing. Now large area RF discharged ion sources were developed which allow long continuous operation over 500h, even in pure oxygen. Long IBAD template films near 1km were routinely obtained by using such ion sources. The process throughput of fluorite type IBAD template was so low which caused high cost. The peculiar thickness dependent growth evolution was observed in fluorite like type oxide films, which requires thickness around 1000 nm. On the other hand, rock salt type materials as MgO, et. al., found in 1997, needs only 10-30nm for sharp textured films. The technique to use thin MgO templates was drastically improved in recent years, and quite low cost process was constructed for coated conductors. Now process throughput reached over 100m/h for MgO templates. This paper reviews development of both materials and vacuum technology, which contributed the drastic advancement of long length, high-performance, and cost effective RE-123 coated conductor, achieved in this two decades.


9:30 AM RR1.3
From IBM (Harper) to Stanford, from IBAD-YSZ to ITaN-MgO. Robert H. Hammond, GLAM, Stanford University, Stanford, California.

The seed of the ITaN (Ion Texturing at Nucleation) MgO was planted at IBM in the summer of 1979. In1994 a facility had been built at Stanford to grow the seed, with the essential RHEED which was the key to the discovery. The arrival of the need for HTSC on Coated Conductor gave the impetus for improvement in biaxial texturing over the existing IBAD-YSZ method. Khiem Do was central in establishing the thin film research facility and the ITaN-MgO initial observation of biaxial texturing using RHEED, as well as further research that lead to a thesis by Connie Wang. This work was made possible by the foresight of Paul Grant of EPRI. The knowledge was transferred to Paul Arendt and James Groves at LANL, who made further improvements, and then transferred to SuperPower. More recently with funding from the Korea Electrotechnology Research Institute and Seoul National University a new dedicated research facility and program has been started at Stanford, as will be described by Groves in his talk.


 

SESSION RR2: IBAD Texturing
Chair: James Harper
Tuesday Morning, December 2, 2008
Room 111 (Hynes)


10:30 AM *RR2.1
Ion Damage Anisotropy Investigations of MgO Crystals. Paul Arendt1, Igor Usov1, James R Groves1,2, Liliana Stan1 and Raymond DePaula1; 1MPA-STC, Los Alamos National Laboratory, Los Alamos, New Mexico; 2Stanford University, Stanford, California.

P. N. Arendt, I. O. Usov, J. R. Groves, R. F. DePaula, and L. Stan MgO single crystals with (100), (110) and (111) orientations were implanted with 100 keV Ar + ions at doses ranging from 1X1014 to 1X1017/cm2. The resulting lattice damage was characterized using Rutherford Backscattering Spectrometry combined with Channeling (RBS/C). For a dose range 10E15 to 10E16 ions/cm2, the differences in damage accumulation for the three orientations varied according to the relation: (110) < (100) <(111). Rapid thermal annealing experiments were performed in a range of 600 to 1300 °C. The annealing of defects occurred most effectively for the (110) oriented crystals according to the relation: (110) > (100) > (111). The anisotropy observed in the damage accumulation and annealing data also provides a possible explanation for the orientations that are empirically observed when MgO films are deposited under ion-assist conditions.


11:00 AM *RR2.2
Investigation of Early Nucleation Events During the Ion Beam Assisted Deposition of Magnesium Oxide. James Groves1,2, Raymond F DePaula2, Robert H Hammond3 and Bruce M Clemens1; 1Materials Science and Engineering, Stanford University, Stanford, California; 2Superconductivity Technology Center, Los Alamos National Laboratory, Los Alamos, New Mexico; 3Geballe Laboratory for Advanced Materials, Stanford University, Stanford, California.

Ion beam assisted deposition (IBAD) is used to biaxially texture magnesium oxide (MgO), which is useful as a template for the heteroepitaxial growth of high temperature superconductors and various thin film devices. It is uncertain as to the exact mechanism by which this biaxial texture is developed. Using a specially built quartz crystal microbalance (QCM) as a substrate in conjunction with reflected high-energy electron (RHEED) acting on the same surface, we have probed the initial stages of nucleation in IBAD MgO films in-situ. We have correlated corresponding RHEED images with real-time mass accumlation QCM data during the film growth and will present a model that describes the nucleation of biaxial texturing. The influence of different nucleation layers and the ion-to-atom arrival ratio on the nucleation of these films will be discussed.


11:30 AM *RR2.3
Using Ion Beams, Off-Normal Deposition, Preferred Nucleation and Anisotropic Growth to Control Grain Alignment in Polycrystalline Films. David Srolovitz, Yeshiva University, New York, New York.

In this presentation, I will review several very different mechanisms for controlling the crystallographic texture of polycrystalline thin films, including ion beams, off-normal deposition, preferred nucleation, and anisotropic film growth. While ion beam and off-normal deposition can be applied to a wide variety of materials, the tightness of the texture is limited by external factors, such as beam collimation. On the other hand, preferred nucleation and anisotropic growth can give sharper textures, but are limited in the types of materials to which they can be applied. In this talk, I focus on the theoretical limits and computer simulation of thin film grain alignment.


 

SESSION RR3: IBAD Materials and Applications
Chairs: Randy Groves and Vladimir Matias
Tuesday Afternoon, December 2, 2008
Room 111 (Hynes)


1:30 PM *RR3.1
Generating MgO single- and bi-crystal Templates on Hard and Soft Substrates using Ion Beam Assisted Texturing Process. Judy Wu, Rongtao Lu and Ronald Vallejo; Physics, University of Kansas, Lawrence, Kansas.

Ion beam assisted texturing process (IBAD) has provided a promising approach for development of epitaxial thin film devices on various low-cost nontextured substrates. The interface between the IBAD template and the substrate surface has been found to play the key role in texture quality of the template. In this work, we have investigated texture evolution of IBAD MgO templates on several technological important substrates including cereflex (hard) and polyimide (soft). The former may be an alternative of low AC loss substrates for high-Tc superconductor tapes but has extremely rough surface incompatible to IBAD MgO process. By developing a surface smoothening process, high-quality bi-axially textured MgO templates have been achieved on Ceraflex. On the amorphous polyimide films, preferential sputtering of the ion beam prevents texturing of IBAD MgO. With thin buffer layer on top of the polyimide surface, the preferential sputtering of polyimide surface can be minimized and highly textured MgO template with in-plane full-width-at-half-maximum of 9-10 degres and out-of-plane full-width-at-half-maximum~3.0 degree have been obtained. This method may provide a practical route for fabricating suspended epitaxial devices on polymer sacrificial layers as demonstrated. In addition, a two-step process was developed to generate textured MgO bicrystal templates on glass and Si substrates. After the first-step IBAD process, a mask was generated on the MgO template and a selected area was removed before a second MgO template was laid at a selected in-plane angle. The flexibility of this technique makes it possible to fabricate various two dimensional novel bicrystal devices of microscopic scales.


2:00 PM RR3.2
Ion-Beam Assited Deposition of Textured Transition-Metal Nitride Films. Ruben Huhne, Martin Kidszun, Konrad Gueth, Ludwig Schultz and Bernhard Holzapfel; Institute for Metallic Materials, IFW Dresden, Dresden, Germany.

It was shown within the last decade that highly textured MgO films can be prepared on amorphous or nanocrystalline seed layers using ion beam assisted deposition (IBAD). The ion beam influences the nucleation in this material leading to strong cube texture within the first 10 nanometres. More recently it was found that also other materials with a rocksalt structure, as for example TiN, can be textured in a similar way. Therefore, a reactive IBAD process was applied for the preparation of different transition metal nitride layers 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 conducting buffer layer architectures for YBCO coated conductors based on the IBAD approach. Furthermore, this approach was used to prepare highly textured superconducting transition metal nitride thin films as NbN, ZrN or HfN. Detailed measurement of the structural and superconducting properties of such layers will be presented.


2:15 PM RR3.3
IBAD Nano-texturing in Halite and Fluorite Structure Compounds. Vladimir Matias, MPA-STC, Los Alamos National Laboratory, Los Alamos, New Mexico.

We examine ion beam assisted deposition (IBAD) texturing at early film growth in a variety of compounds. We have found that many different halite-structure compounds share the ion beam texturing ability at nucleation, analogous to MgO. This includes numerous oxides and nitrides. We discuss trends in applicability of IBAD texturing to the various compounds. Fluorite-structure compounds also exhibit the possibility of fast IBAD texturing such as that for MgO, but in different crystalline orientation. We will discuss similarities and differences between the halites and flourites.


2:30 PM *RR3.4
Formation of Biaxial Crystalline Texture by Oblique Ion Bombardment. Paul Berdahl, Environmental Energy Technologies Division, Lawrence Berkeley National Laboratory, Berkeley, California.

The historical background for Ion TEXturing (ITEX) will be briefly reviewed, including IBAD (ion beam assisted deposition) and IBIEC (ion beam induced epitaxial crystallization). Also of interest is the orientation of metal films with high-energy ions and the formation of crystallites in SiO2 with low-energy neutral atom bombardment. I will also speculate about future ITEX processes, especially texturing of amorphous Ge, Si and C. The basic concept of ITEX is to obliquely bombard an amorphous material, to produce oriented crystallization at the surface. As a concrete example, ion texturing of yttria-stabilized zirconia (YSZ) can rapidly produce an out-of-plane 211 crystalline texture when oxygen-deficient amorphous YSZ is bombarded obliquely with Ar ions. The in-plane texture is 111 parallel, and 110 transverse, to the azimuth of the ion beam. Rapid two-dimensional Ostwald ripening accompanies production of the texture; crystallite diameter d exceeds 100 nm in 5 min. Theoretical arguments suggest that d is proportional to the time t as t3/7 and the crystallite orientation angle distribution widths are proportional to t-2/7. When the temperature is subsequently raised to 300 oC, the ion-induced surface texture grows down into the bulk of the film by epitaxial oxidation.


3:15 PM *RR3.5
Aligned-Crystalline Si Films on Non-Single-Crystalline Substrates. Alp T Findikoglu, Los Alamos National Lab, Los Alamos, New Mexico.

We have recently developed an ion-beam assisted deposition (IBAD) nano-texturing technique that presents a unique alternative to conventional methods to prepare high-quality Si films monolithically on inexpensive non-single-crystalline substrates, such as glass plates and flexible metal sheets. IBAD nano-texturing provides highly crystalline, 3-to-5 nm thick seed layers of MgO or TiN on the amorphous/polycrystalline surface of such substrates, enabling hetero-epitaxial growth of subsequent buffer layers and aligned-crystalline Si (ACSi) films. Optimized ACSi films show in-plane and out-of-plane grain mosaic spreads of only 1° to 2°. Due to good alignment and connectivity of the grains, these films also show high carrier mobilities, long carrier lifetimes, and long diffusion lengths. For example, we measured a hole mobility of 90 cm2/V.s at a B doping concentration of 4x1016 cm-3 for a 0.4-μm-thick ACSi film on a buffered metal substrate. Also, we measured an effective electron lifetime of >1 μs and effective diffusion length of >10 μm in a similarly doped 3-to-6-μm-thick p-layer of an ACSi-based diode on buffered glass. Our microstructural and electrical measurements demonstrate that improving the alignment of sub-micron-sized grains in ACSi films is an effective alternative to increasing grain size (for example, by laser annealing) in order to approach single-crystal-like electrical and optical performance. As such, ACSi films are promising for a wide range of applications, including electronics and photovoltaics.


3:45 PM *RR3.6
Active Plasmonic Electro-optic Switching Heterostructures on Biaxially Textures MgO Films. Harry Atwater, Applied Physics, California Institute of Technology, Pasadena, California.

Shrinking photonic device sizes has motivated increased attention to light-matter interactions, such as optical transmission through subwavelength apertures in metal films, propagation of surface plasmon-polaritons (SPPs), and metamaterials. Research in the plasmonics field has up to now has been primarily focused on designing and modeling of passive devices. The next step will be to create active elements, such as modulators, to act as the building blocks of communication networks. Modulators and interferometers based on SPP propagation are a good fit for this new regime chip-based of active elements at the subwavelength scale. SPPs are highly confined electromagnetic waves that propagate along a metal-dielectric interface. Light can be coupled into, and out of, these modes by scattering from abrupt structural features such as grooves or slits. It has been shown that these waves interact with light transmitted through slits to create an interference pattern in the overall transmission intensity. Here we investigate the possibility of dynamically changing the interference pattern by changing the index of the “dielectric” layer in the structure. Barium titanate (BTO) is a well known tetragonal ferroelectric material that exhibits a large electrooptic coefficient, r = 100 pm/V, and large birefringent effect, Delta n = 0.05. Thin films of BTO have been studied and utilized as electrooptic modulators for some time [Ref]. We have replaced the dielectric layer in a static, metal-dielectric interferometer based on propagating SPPs scattered from two parallel slits with an optically active layer of BTO. By utilizing an electrooptic thin film, we can change the index of refraction at the SPP propagating interface and thereby modulate the transmitted intensity. A simple model based on the total transmitted intensity being the result of interference between the incident field and the SPP field can be used to show that small changes in the index of the dielectric with lead to large changes in the intensity profile. To affect a change in the BTO optical index an electric field must be applied across the material. We have deposited strontium ruthenate, a well known transparent conductive oxide, to act both as the bottom electrode and as an epitaxial buffer layer between the MgO substrate and the BTO film. We will report the details of electrooptic switching and also the possible application of similar active devices at visible frequencies for display.


 

SESSION RR4: Poster Session: Artificially Induced Grain Alignement in Thin Films
Chairs: Alp Findikoglu and Vyacheslav Solovyov
Tuesday Evening, December 2, 2008
8:00 PM
Exhibition Hall D (Hynes)


RR4.1
Development of Conductive Buffer Architectures Based on IBAD-TiN. Ruben Huhne1, Konrad Gueth1, Rainer Kaltofen1, Thomas D Thersleff1, E. J Rowley2, Vladimir Matias2, Ludwig Schultz1 and Bernhard Holzapfel1; 1IFW Dresden, Dresden, Germany; 2Los Alamos National Laboratory, Los Alamos, New Mexico.

Ion Beam Assisted Deposition (IBAD) offers the possibility to prepare thin textured films on amorphous or non-textured substrates. It was shown within the last decade that cube textured MgO and TiN layers with a thickness of less than 10 nm can be produced on amorphous or nanocrystalline seed layers using this technique. In particular, the results corresponding to the in-plane textured growth of TiN are promising for the development of a conducting buffer layer architecture for YBCO coated conductors based on the IBAD approach. Accordingly, cube textured IBAD-TiN layers have been deposited reactively using pulsed laser deposition on polished Hastelloy tapes. An amorphous conducting seed layer was tested successfully for the IBAD-process leading to highly textured TiN films. Different metallic buffer layers such as Au, Pt or Ir were grown epitaxially on top of the TiN layer showing texture values similar to the IBAD layer. Smooth layers were obtained on the different substrates using a double layer of Au/Pt or Au/Ir. Finally, biaxially textured YBCO layers were achieved using doped SrTiO3 as a conductive oxide cap layer.


RR4.2
Fabrication of Biaxially Oriented Si Thin Films on Glass Substrates. Kosuke Nagata, Toshiya Doi, Kentaro Matsunaga and Yoshinori Hakuraku; Faculty of Engineering, Kagoshima University, Kagoshima, Japan.

In order to make the display more compact, reliable and further reduction in the cost, system on glass (SOG) integrated with functional devices on the display, such as controller, and memory, has been proposed for display technology development. The requirements for fabricating thin film transistors used for SOG are addressed. This paper focuses on the technology preparing biaxially oriented Si thin films on glass. We irradiated Ar+ ion beam during pulsed laser deposition(PLD) for obtaining biaxially oriented Y2O3 stabilized ZrO2(YSZ) layer on glass, then CeO2 layer was deposited by PLD on the YSZ buffered glass for reducing the lattice mismatch to Si. Finally, Si film was epitaxially grown by using electron beam evaporation on the CeO2/YSZ buffered glass. Electron backscattering diffraction (EBSD) results show that the biaxially oriented Si thin film was successfully obtained on the glass substrate.


RR4.3
Scaling of IBAD-MgO Texture Evolution under Different Growth Conditions. Vladimir Matias, Jens Haenisch and Alp Findikoglu; MPA-STC, Los Alamos National Laboratory, Los Alamos, New Mexico.

We examine crystalline-texture evolution during ion-beam assisted deposition (IBAD) of MgO thin films. We have demonstrated that in-plane crystalline texture evolution in IBAD-MgO scales with deposition rate. At high ion currents an in-plane texture full-width half maximum (FWHM) of 10° can be achieved in less than 1 second, and 6° in 2.2 seconds. For varying ion-to-molecule deposition ratios we show that the texture evolution scales best with the amount of material ion etched during deposition. To perform these experiments we developed a unique experimental methodology based on linear combinatorics. This technique allows us to fabricate film-thickness wedges that maximize data output and allow us to easily obtain texture evolution plots. MgO texture further improves with thickness of a homoepitaxial layer deposited on top. 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°. We discuss our results in the context of possible scenarios for the IBAD texturing mechanism. This work is supported by the Department of Energy Office of Electricity Delivery & Energy Reliability.


RR4.4
Low-Temperature Selective Growth of Hetero-epitaxial α-Al2O3 Thin Films on Atomically Stepped Substrates by Electron-Beam Assisted PLD Process. Makoto Hosaka1, Yasuyuki Akita1, Yuki Sugimoto1, Yushi Kato1, Yusaburou Ono1, Koji Koyama2 and Mamoru Yoshimoto1; 1Department of Innovative and Engineered Materials, Tokyo Institute of Technology, Kanagawa, Japan; 2Crystal Growth Laboratory, Namiki Precision Jewel Co., Ltd., Tokyo, Japan.

Aluminum oxide (Al2O3) has thermally and chemically stable property and is widely used as insulating ceramics materials in the electronic devices. Recently, it has attracted much attention as insulating layers of Tunnel Magneto-Resistance (TMR) devices, Metal-Oxide Semiconductor Field-Effect Transistor (MOSFET) and so on. For electronic applications, low-temperature fabrication techniques of epitaxial films are strongly desired because of development of the smooth surfaces and sharp interfaces. Previously we reported room-temperature homo-epitaxial growth of α-Al2O3 films using the electron-beam assisted process [1]. This method allows us to fabricate the epitaxial α-Al2O3 films having very smooth surface. In this work we could attain selective growth of hetero-epitaxial α-Al2O3 thin films on the NiO buffer layer at 300 oC by the electron-beam assisted pulsed laser deposition (PLD) process. By our originally developed metal oxide-reduction-epitaxy method [2], we could also fabricate epitaxial Al2O3/Ni films and further magneto-tunnel junctions. The fabricated films were characterized by reflection high energy electron diffraction (RHEED), X-ray diffraction (XRD), and atomic force microscope (AFM). NiO buffer layer was deposited on the atomically stepped sapphire (0001) substrates which have atomic steps of 0.2 nm in height and ultra smooth terraces of 50-100 nm in width [3]. Epitaxial growth of the NiO buffer layer was confirmed by RHEED and XRD measurements. We then fabricated α-Al2O3 films on the NiO buffer layer at 300 oC. During deposition, the substrate was partially irradiated with electron-beam of RHEED. The α-Al2O3 films were found to grow epitaxially only in the electron-beam irradiated region during deposition, while amorphous α-Al2O3 films grew in the non-irradiated region. Thus, we can control artificially the crystallinity of α-Al2O3 films and also the surface morphology in a nanoscale by applying the atomically stepped substrates. Further investigations on this electron-beam assisted process such as multi-beam irradiation may lead to novel fabrication techniques of artificially grain aligned films and development of various electronic devices. [1] A. Sasaki et al. Jpn. J. Appl. Phys. Vol. 41 (2002) 6534-6535. [2] A. Matsuda et al. Mater. Res. Soc. Symp. Proc. Vol.962 (2007) 0962-P09-04. [3] M. Yoshimoto et al. Appl. Phys. Lett. Vol. 67 (1995) 2615-2617


RR4.5
Artificially Controlled Epitaxial Growth of SrTiO3 Films on Silicon Substrates by Fe Doping. Hyun-Suk Kim1, Lei Bi1, Han-Jong Paik2, Gerald F Dionne3,1 and Caroline A Ross1; 1Material Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts; 2Materials Science and Engineering, Korea Advanced Institute of Technology, Daejeon, South Korea; 3Lincoln Laboratory, Massachusetts Institute of Technology, Lexington, Massachusetts.

The epitaxial growth of SrTiO3 thin film on silicon has attracted considerable attention in recent years. The SrTiO3/Si system not only provides an ideal model structure for the study of growth dynamics of perovskite-type oxides on silicon, but also a useful substrate for subsequent heteroepitaxy of various functional oxides including ferromagnetic and high-TC superconductor thin films on Si substrates. In addition, most perovskite phases such as SrTiO3 and BaTiO3 exhibit large anisotropy in physical properties depending on crystallographic orientation. In order to take advantage of these anisotropies to suit practical applications, control over the crystal orientation during film growth is essential. In this study, Fe-doped SrTiO3 (STF) films were deposited on (100) Si substrate by pulsed laser deposition using a double buffer layer of CeO2/YSZ. We report on the double epitaxial growth of STF films in which (100)-oriented grains are heteroepitaxially embedded in a (110) matrix. Both the (100) and (110) grains are heteroepitaxial with the substrate, with significant strain of opposite signs. It is shown that the size and volume fractions of both (100) and (110) epitaxial grains in films can be controlled as a function of Fe content. The origin and growth mechanism of coexisting (100) and (110) epitaxial grains will be discussed. Also, magnetic properties of STF films, including magnetic anisotropy, will be compared to understand their strain state. These results may provide a general method for steering the physical properties of SrTiO3-based functional films by controlling the orientation of epitaxial crystal.


RR4.6
Intensity-modulated Excimer Laser Annealing to Obtain (001) Surface-oriented Poly-Si Films on Glass : Molecular Dynamics Study. Norie Matsubara, Tomohiko Ogata, Takanori Mitani, Shinji Munetoh and Teruaki Motooka; Materials and Engineering, Kyushu University, Fukuoka, Japan.

We have investigated the dependence of melting and crystal-growth rates on the crystal orientation at solid/liquid silicon (Si) interfaces by using Molecular-dynamics (MD) simulations. There was no appreciable difference in the melting rates, but the growth rates substantially depend on the crystal-orientation at the solid/liquid interface. The growth rate at the (001) interface was found to be more than twice of that at the (111) interface. We have also performed MD simulations of an intensity-modulated excimer laser annealing (IMELA) of Si thin films, and the results suggest that (001) surface-oriented Si without {111} stacking faults can be obtained by repetitions of melting and solidification of amorphous Si on glass by IMELA.


RR4.7
Crystallization Processes of Amorphous Si During Excimer Laser Annealing in Complete-melting and Near-complete-Melting Conditions: A Molecular Dynamics Study. Tomohiko Ogata, Takanori Mitani, Shinji Munetoh and Teruaki Motooka; Material science and Engineering, Kyushu University, Fukuoka, Japan.

We investigated crystallization processes of amorphous Si (a-Si) during the excimer laser annealing in the complete-melting and near-complete-melting conditions by molecular dynamics simulations. The initial a-Si block was prepared by quenching liquid Si (l-Si) in a MD cell with a size of 50×50×150Å3 composed of 18666 atoms. KrF excimer laser (wavelength: 248nm) annealing of a-Si was performed by using a Gaussian-shape laser pulse with FWHM of 25ns. The supplied laser energy was calculated by taking account of reflection and absorption in the a-Si and l-Si layers. The refractive indices of a-Si and l-Si were set at n+ik=1.0+3.0i and n+ik=1.8+3.0i, respectively. Simulated results were generally in good agreement with the experimental date and the near-complete-melting and complete-melting conditions were obtained for the laser fluences 160mJ/cm2 and 180mJ/cm2, respectively. It was found that larger grains were obtained in the near-complete-melting condition. Our MD simulations suggest that nucleation occurs first in a-Si and subsequent crystallization proceeds toward l-Si occur in the near-complete-melting case, while both nucleation and crystal growth occur in quenched a-Si in the complete-melting case.


RR4.8
Abstract Withdrawn


RR4.9
Epitaxial Growth of LaFeO3 Films on SrTiO3 (001) Substrates with Controllable Crystallographic Orientations. Lei Bi1, Hyun-Suk Kim1, G. F Dionne1,2 and C. A Ross1; 1DMSE, MIT, Cambridge, Massachusetts; 2Lincoln Laboratory, Cambridge, Massachusetts.

LaFeO3 is a distorted perovskite structure antiferromagnet with high Neel temperature, and may be a good candidate for spin valves and other exchange-bias applications in magnetic memory and sensing. The crystallographic orientation of a LaFeO3 epitaxial film strongly influence its antiferromagnetic domain structure, and consequently the exchange bias effect on an adjacent ferromagnetic layer. Although both (001) and (110) LaFeO3 show a good lattice match to a SrTiO3 (001) substrate, only the (110) orientation has been previously reported in epitaxial LaFeO3 films on SrTiO3 (001) substrates. In this study, we report epitaxial growth of LaFeO3 films on SrTiO3 (001) substrates with controllable crystallographic orientation. Films were grown by pulsed laser deposition, and both one dimensional and two dimensional x-ray diffraction were carried out to characterize the epitaxial orientation of the films. It was found that films grown at high substrate temperature and high oxygen pressure show (110)-oriented grains only, while films grown at low substrate temperature and low oxygen pressure show (001)-oriented grains only. LaFeO3 films grown at low substrate temperature and high oxygen partial pressure show both (001) and (110) epitaxial orientations. The (111) pole figure of these films shows two sets of {111} poles, which originate from (001) and (110)-oriented grains. These two sets of {111} poles appear at the same in-plane φ positions with four fold symmetry, indicating that the (100) planes of the (001)-oriented grains are either parallel or perpendicular to the (001) planes of the (110)-oriented grains. Atomic force microscopy measurements were carried out on films with one or both epitaxial orientations, and the latter shows higher surface roughness (>10 nm) than the former (<5 nm). TEM dark field measurements were applied to analyze the grain structures in these films. The exchange bias of these films were also evaluated by measuring their exchange coupling with polycrystalline Co top layers. The growth mechanism of LaFeO3 films and its influence on the magnetic domain structure will be discussed. These results may provide a general method to control the crystallographic and magnetic structures of LaFeO3 films.


RR4.10
Fabrication of GdBCO Coated Conductor using Co-evaporation on LaMnO3/IBAD-MgO Buffer Layer. HongSoo Ha1, Hokyum Kim2, Jusaeng Yang2, Seongwook Jeong2, Rockkil Ko1, Hosup Kim1, Kyujeong Song1, Dongwoo Ha1, Sangsoo Oh1, Chan Park3, Sangim Yoo3, Dojun Youm4 and Seonghyun Moon2; 1Superconductor Research group, Korea Electrotechnology Research Institute, Changwon, Gyeongnam, South Korea; 2R&D laboratory, SuNAM Co., Anyang, Gyeongkido, South Korea; 3School of Materials Science and Engineering, Seoul national university, Seoul, South Korea; 4Dept. of Physics, KAIST, Daejeon, South Korea.

GdBCO coated conductor have been fabricated using reactive co-evaporation. The IBAD-MgO substrate with the architecture of LaMnO3(LMO)/IBAD-MgO/Hastelloy was used for coated conductor. The batch type co-deposition system was specially designed and was named EDDC (evaporation using drum in dual chamber) that is possible to deposit superconducting layer with optimum composition ratio of materials at temperature over 700 degree celcious and several mTorr of oxygen. In this study, optimal oxygen partial pressure (pO2) and deposition temperature were investigated for GdBCO deposition to increase the critical current density of GdBCO CCs. Surface morphology and texture of GdBCO coated conductors were analyzed by the SEM and XRD, respectively. Magnetic field property of GdBCO coated conductor was examined by using 6T magnet for the magnet applications. This research was supported by a grant from Center for Applied Superconductivity Technology of the 21st Century Frontier R&D Program founded by the Ministry of Education, Science and Technology, Republic of Korea.


RR4.11
Reactivity Dependent Selective Deposition of Nano-β-SiC on Diamond Facets and Its Effect in Controlling the Diamond Grain Growth. Srikanth Vadali1, Jiang Xin1, Thorsten Staedler1, Yan Ling Zhao2 and Rui Qin Zhang3; 1Institute of Materials Engineering, University of Siegen, Siegen, Germany; 2Institute of Material Science and Engineering, Ocean University of China, Qingdao, China; 3Centre of Super-Diamond and Advanced Films (COSDAF) & Department of Physics and Materials Science, City University of Hong Kong, Hong Kong SAR, China.

Selective deposition of nano-β-SiC phase on non-{100} diamond faces has been observed in a microwave chemical vapor deposition (MWCVD) process due to the presence of tetramethylsilane (Si(CH3)4,TMS). The process allows only growth of oriented diamond starting crystals with their [001] vertical to the film surface and interrupts the growth of other grains resulting in the growth of smooth diamond rounded faceted structures. It is also clearly observed that the incorporation of other nanocrystalline phases (both diamond and carbide) is growth sector dependent, leading to the significant appearance of these in {111} growth sectors as compared to {100} sectors. It is thus plausible that TMS presence affects the growth of {100} and {111} diamond faces in different ways. TMS appears to have a catalytic effect on the formation of {100} surfaces. There seems to be a threshold TMS concentration required to obtain large and smooth (001) rounded surfaces. To understand the experimentally obtained phenomenon, supportive theoretical study based on frontier orbital theory has been carried out. In these calculations, on HF/6-31G** level, chemical interactions between the gas mixtures (H2/CH4/Si(CH3)4) in contact with the exposed diamond facets have been understood. The outlines of frontier molecular orbital (FMO) from the diamond model exhibited denser isosurface on the four {111} faces than that on the (001) face which shows that {111} facets are more reactive with SiH3 when compared to {100} facets, forming SiC phases on the {111} facet and leaving the {100} facet clean and with diamond growth only. This proves the reason why β-SiC prefers to be deposited easily on {111} diamond but not on (001). The mechanical and tribological properties of the composite films containing diamond (001) facets will also be discussed. The findings provide us with a strong method to control the diamond growth and to obtain textured diamond films with small film thicknesses, which in turn may help in optimizing the technical performance of diamond films.


RR4.12
Flux Pinning of HTS Coated Conductor with Multilayers of REBa2Cu3O7-δ’s (RE=Nd, Sm, and Gd). Sung-Hwan Bae1, Rock-Kil Ko2,3, Sang-Soo Oh3, Myung-jin Jung1, Sejin Yoon1, Kyoung Pil Ko1, Sang Im Yoo1, Young-Cheol Kim2 and Chan Park3; 1School of materials science and engineering, Seoul national university, Seoul, South Korea; 2Pusan National University, Pusan, South Korea; 3Korea Electrotechnology Research Institute, Changwon, Kyungnam, South Korea.

Enhancement of flux pinning is needed to use high temperature superconducting coated conductors in devices which put the conductor under magnetic fields. The flux pinning centers can help retain high current carrying capability of coated conductors in the presence of magnetic field. Various kinds of defects in films can work as flux pinning centers. Multilayer structure in superconducting film of coated conductor (“multilayer coated conductor”) can have defects in interfaces which can act as pinning centers. The enhancement of flux pinning in “multilayer coated conductors” have been reported, and different multilayers of coated conductor are being investigated to further improve pinning properties. In this study, to investigate the pinning properties of coated conductor whose superconducting film consists of multilayers of NdBCO, SmBCO, and GdBCO, “multilayer coated conductor” was prepared by pulsed laser depositing three supercondutors in pre-determined sequence on single crystalline SrTiO3 substrates. The numbers of layers and the thicknesses of each layer were varied to study the effect of different multilayer structures on the pinning properties. The in-field critical current measured by physical property measurement system (PPMS) and the results of TEM studies which were carried out to investigate the defects mostly on the interfaces, will be presented. The effects of multilayers which consist of many repeated layers of three superconductors on the pinning properties of coated conductor will be discussed. This research was supported by a grant from Center for Applied Superconductivity Technology of the 21st Century Frontier R&D Program funded by the Ministry of Science and Technology, Republic of Korea.


RR4.13
Effect of Carbon on the Equilibrium shape of Ni Crystal. Ju-Seop Hong1, Wook Jo3, Nong-Moon Hwang2 and Doh-Yeon Kim2; 1Materials Science and Engineering, Seoul National University, Seoul, South Korea; 2Materials Science and Engineering, Seoul National University, Seoul, South Korea; 3Technische Universität Darmstadt, Darmstadt, Germany.

Thermodynamically, the equilibrium shape of a certain crystal is determined by the surface or interfacial energy. When the crystal has anisotropic interfacial energy, the crystal exhibits polyhedral shape composed with the planes of lowest interfacial energy. For the case when the interface energy is isotropic, it is well known that equilibrium crystal shape (ECS) becomes spherical. Indeed, the ECS itself is an interesting research subject because it has many implications in materials processing. Not only the single crystal growth but also the microstructural evolutions of polycrystalline material are observed to critically depend on the interface characteristics i.e. ECS. In this investigation, the equilibrium shape of a Ni crystal is determined and the shape change due to carbon impurity has been checked. For the purpose, two sets of specimens were prepared in a way that one contains carbon and the other is carbon-free. The specimens were prepared by annealing the 3000Å-thick Ni thin film deposited by DC magnetron sputter. Then they were annealed at 1200 degrees (0.8 Tm) for 100 hours. To minimize the effect of any possible unknown impurities, all the specimens were sealed in a quartz tube under ten to the minus fourth atmospheric pressure. The results showed that the ECS of pure Ni polyhedral but changed to spherical by carbon impurity. Therefore, it is confirmed that the surface energy anisotropy of pure Ni is decreased by carbon. The experimental results will be discussed in conjunction with the grain growth behavior of pure and carburized Ni.


RR4.14
2D and 3D Nanoscale Texture Analysis in Freestanding CVD Diamond Films. Dierk Raabe and Tao Liu; Max-Planck-Institut fuer Eisenforschung, Duesseldorf, Germany.

Three groups of freestanding chemical vapor deposition (CVD) diamond films with variations in substrate temperature, methane concentration, and film thickness are analyzed using high resolution 2D EBSD and tomographic 3D EBSD (EBSD: electron back scatter diffraction). We observed primarily {001}, {110}, and {111} fiber textures. Also, corresponding twinning and multiple twinning components were found. As interfaces we observed high angle, low angle, primary twin, and secondary twin boundaries. Growth and twinning are discussed in terms of sp4-hybridization of the bond in CH4 which served as deposition medium.


RR4.15
Polar Orientation of ZnO Films Grown by Pulsed Laser Deposition. Yutaka Adachi1, Naoki Ohashi1, Takeshi Ohgaki1, Isao Sakaguchi1, Hajime Haneda1, Tsuyoshi Ohnishi2 and Mikk Lippmaa2; 1National Institute for Materials Science, Tsukuba, Ibaraki, Japan; 2The University of Tokyo, Kashiwa, Chiba, Japan.

Zinc oxide (ZnO) is an attractive material for applications to optoelectronic devices because of its direct wide band gap energy (Eg~3.3 eV) and large exciton binding energy (~60 meV) at room temperature. Since ZnO crystallizes in wurtzite structure, which possesses no inversion symmetry, the crystal exhibits crystallographic polarity along the c axis: c(+) (Zn) polar and c(-) (O) polar. Many properties of ZnO depend on its polarity, for example, surface electronic structure, chemical stability of the surface, interfacial properties and impurity incorporation. Therefore, it is important for designing devices to examine and control the polarity of ZnO films. In this study, we have investigated the polarity of nominaly undoped and Al-doped ZnO films and found that Al doping into ZnO affects the polar orientation of the films. ZnO films were grown at 700°C on (0001) and (11-20) sapphire substrates by pulsed laser deposition (PLD) with a pulsed laser of the fourth harmonic generation (FHG) of neodymium-doped yttrium gallium garnet (Nd:YAG, 266 nm, 5 ns, 5 Hz). Nominally undoped and 1 mol% Al-doped ZnO ceramics were used as targets. The polarity of the films was determined by coaxial impact-collision ion scattering spectroscopy (CAICISS). All the films obtained were c-axis-oriented ZnO films. The spectral shape of CAICISS obtained from the undoped ZnO film and that from the c(-)-face of a ZnO single crystal were similar to one another, whereas the Al-doped ZnO films showed a similar spectral profiles to the c(+)-face of the ZnO single crystal. This behavior was observed regardless of the substrate orientation. This indicates that the polarity of the ZnO films was determined based on whether the film was doped or undoped. Electron microscope observations revealed that polarity change occurred without the formation of any interfacial phase between ZnO and sapphire substrates. In a prior study on PLD growth of ZnO on (0001) sapphire [1], the polarity of the films was closely correlated with in-plane orientation. The ZnO films with c(+)-face showed an in-plane orientation as ZnO[11-20] // sapphire [11-20], whereas those with c(-)-face showed the orientation as ZnO[11-20] // sapphire [10-10]. However, polarity change found in this study was simply due to Al-doping and polarity change occurred without formation of in-plane rotation domains. This suggests that the mechanism for polarity change in the prior study was totally different from that found in this study. The mechanism for polarity inversion in this study will be discussed at the conference site. [1] I. Okubo, A. Ohtomo, T. Ohnishi, Y. Mastumoto, H. Koinuma and M. Kawasaki, Surf. Sci. Lett. 443, 1043 (1999).


RR4.16
Oriented Carbon Nanotube Changes of the Crystal Growth in Isotactic Polypropylene Films. Georgi Georgiev1,2, Yaniel Cabrera2, Zarnab Iftikhar1, Michael Mattera1, Mark Cronin1, Andrew Buckley1, Christopher Rocheleau1, Lei Yu2, Bret Stenger2, Lauren Wielgus2, Brendan Andrade2 and Peggy Cebe2; 1Natural Sicences, Assumption College, Worcester, Massachusetts; 2Physics and Astronomy, Tufts University, Medford, Massachusetts.

Physical properties of thermoplastic semi-crystalline polymers are influenced by their morphology. Using carbon nanotubes as agents to introduce new crystalline structure leads to classes of materials with novel characteristics. Polymer nanocomposites (PNCs) are the most recent development in the field of polymer science and technology. Geared toward creating novel polymer based materials, PNCs are the largest commercial application for nanotubes. Isotactic Polypropylene (iPP) is one of the best model systems because it forms smectic liquid crystal phase, and monoclinic (alpha), hexagonal (beta), and triclinic (gamma) crystallographic phases under a variety of crystallization conditions, such as nonisothermal and isothermal melt crystallization, shear, stress, fiber extrusion etc. The spherulitic polymer crystal growth was changed by inducing new fibrillar crystals on the surface of carbon nanotubes. Upon isothermal melt crystallization at 135C, CNTs lead to monoclinic crystal growth perpendicularly to the long axis of the nanotubes, explained by the multiple nucleation centers formed at the interface of the carbon nanotube and the polymer chains. Using Microscopic Transmission Ellipsometry (MTE), the sign of the alpha crystallographic phase was determined as positive. With Differential Scanning Calorimetry (DSC), a decrease in the Avrami exponent was measured with increase of concentration of nanotubes. We are using zone drawing of films of iPP/CNT PNCs to align the CNTs in the drawing direction, which allows us to control the orientation of the crystals and thus the morphological structure of the material. Also, we are using spin casting and shearing to induce CNT orientation in the polymer matrix. To complement the MTE and DSC studies, we use dielectric spectroscopy measurements and small and wide angle X-ray scattering. Research supported by: the National Science Foundation, Polymers Program of the Division of Material Research, grant (DMR-0602473) and NASA grant (NAG8-1167).


 

SESSION RR5: IBAD Long Length Application
Chair: John Durrell
Wednesday Morning, December 3, 2008
Room 111 (Hynes)


8:00 AM *RR5.1
IBAD-MgO Architecture at SRL for Long Length IBAD/ PLD Coated Conductors. Yutaka Yamada, Seiki Miyata, Masateru Yoshizumi, Hiroyuki Fukushima, Akira Ibi, Teruo Izumi, Yuh Shiohara, Takeharu Kato and Tsukasa Hirayama; International Superconductivity Technology Center, Superconductivity Research Laboratory, Tokyo, Japan.

At SRL, a simplified 4 layered buffer architechture consisting of Gd2 Zr2 O7 (GZO) / IBAD-MgO/ LaMnO3 (LMO)/ CeO2 was proposed for high speed and low cost production processing. This unique structure has two different layers from the conventional 5 layered IBAD-MgO:1) a new barrier and nucleation GZO layer and 2) PLD-CeO2 layer showing self-epitaxy effect. The GZO layer was found to work both as the Ni diffusion barriea and nucleation layer for texturing MgO, and thus cost-effective to decrease the number of the layers and the processes. The third layer of PLD-CeO_2 showing the self-epitaxial growth effect resulted in the in-plane texturing (Δφ) of about 3 to 4 degrees from the 15 degrees of the in-plane texturing degree of LMO layer. These layers, IBAD-MgO and sputter LOM layers were fabricated in a reel to reel method with the production speed of 20 to 80m/hr. Subsequently, 41m PLD- GdBa2Cu3O7-X (GdBCO) coated conductor were prepared and high Ic values above 500 to 600 A/cm-width were successfully obtained. Furthermore, a new IBAD-MgO deposition method was developed, using DC- reactive sputtering which is expected to be inexpensive and easy to scale up, compared to the conventional ion beam sputtering. This system brought about a high production rate of 150 m/h in spite of the small deposition area (6x20cm^2 ). The GdBCO on this buffered substrate showed a high Ic value of 286 A/cm-width at 77 K and s.f.


8:30 AM *RR5.2
In-Plane Texturing of Buffer Layers by Alternating Beam Assisted Deposition: Large Area and Small Area Applications. Alexander Usoskin and Lutz Kirchhoff; HTS Coated Conductors, European High Temperature Superconductors GmbH & Co. KG, Alzenau, Germany.

In the well-known ion beam assisted deposition (IBAD) method, the growing film is exposed to inclined ion etching in order to achieve a preferable in-plane orientation of the crystalline structure. Recently, we suggested to expose the film periodically to deposition pulses and to etching pulses. As a long sequence of alternations of these two pulses is needed, we called this method “alternating beam assisted deposition” (ABAD). In real application, the substrates exposed to molecular/atomic flow provided by a sputter source, acquire a few nanometer thick layer of yttria-stabilized zirconia (YSZ). In the next step, this layer undergoes an ion etching with an Ar ion beam coming from the source with particle energy of from 200 to 300 eV. Simultaneously with ion-beam exposition, an additional electron beam provides neutralizing of the electrical change in the substrate plane. The ion beam guided under 55° incidence angle provides a selective etching YSZ layer leading, finally, after several tens of deposition-etching cycles, to sufficiently high in-plane texture (with FWHM=8°-9°) in the YSZ layer. We found that such deposition technique allows to achieve better quality of in-plane texture compared either to technique of “in-situ” etching performed during IBAD process. Basically, the effect of texture enhancement occurs due to decrease of substrate temperature because of reduced density of dissipated energy of two beams: this energy (or power) is distributed within two zones instead single one in IBAD. Furthermore, we found that partial superimposing of these zones may be beneficial regarding saving of space in processing area. Low scattering of in-plane texture parameters, within only ±1 % within substrate surface of 250mm x 200mm, was achieved by this novel method. We employed ABAD technique for manufacturing of both short (up to 1m long) and long (up to 100m) tapes. In later case, the tape was continuously moved through two zones mentioned above. Due to a helical translation system, the long tapes crossed a predetermined number of times the deposition and the etching zones. With these means, the homogeneity of the bi-axially textured YSZ buffer layer can be considerably improved. Recently, we employed ABAD in processing of bi-axially textured buffer layers on cylindrical surfaces. As a result the in-plane textures with the FWHM of 10° were achieved in YSZ layers grown on curved surfaces with radii down to 6 mm.


9:00 AM *RR5.3
Optimization of the Buffer Layer on the Biaxially Textured IBAD-MgO Template. Sang-Im Yoo1, Kyoung-Pil Ko1, Geo-Myung Shin1, Jung-Woo Lee1, Hong-Soo Ha2, Sang-Soo Oh2 and Seung-Hyun Moon3; 1Materials Science and Engineering, Seoul National University, Seoul, South Korea; 2Superconducting Material Research Group, Korea Electrotechnology Research Institute, Changwon, South Korea; 3Superconductor, Nano & Advanced Materials Corporation, Anyang, Gyonggi, South Korea.

We have recently succeeded in producing a highly-textured long-length IBAD MgO template (in-plane texture < 7o, a piece length > 300m) on electro-polished hastelloy tapes using a continuous multi-turn reel-to-reel process. On top of the homo-epi MgO of the IBAD MgO template, we tried to find the most appropriate buffer layer for coated conductors by investigating various perovskite oxides, including LaMnO3, LaGaO3, BaZrO3, and BaCeO3, and their effects on the superconducting properties of coated conductors. The PLD method was used to deposit the buffer layers. In this talk, we first present the analysis results of microstructure, surface roughness, and in-plane texture for each buffer layer. Next, characteristic features of optimally processed buffer layers are displayed for a comparison. Finally, we report the effect of these buffer layers on the critical currents of REBa2Cu3O7-δ coated conductors produced by several methods such as PLD and MOD. Present study shows that the effectiveness of a buffer layer on the IBAD MgO template depends on not only its characteristic in-plane texture and surface roughness but also the fabrication process of coated conductor. This research was supported by a grant from Center for Applied Superconductivity Technology of the 21st Century Frontier R&D Program funded by the Ministry of Science and Technology, Republic of Korea


9:30 AM RR5.4
High Yield Reactive IBAD MgO Process to Produce Long-length, High Quality, Biaxially-Textured Templates for Second-generation HTS Wire at SuperPower. Xuming Xiong, Karol Zdun, Balvinder Gogia, Andrei Rar, Kenneth Lenseth and Venkat Selvamanickam; SuperPower, Inc, Schenectady, New York.

High yield is the key to evaluate whether a process is really useful or not for commercial production. Processing of the IBAD MgO template for second generation HTS wire at SuperPower has been further improved in both process speed and biaxial texture with ~ 100% process yield. In order to increase IBAD MgO process speed, we implemented reactive ion beam sputtering deposition of IBAD MgO to achieve a higher deposition rate. The process speed was increased from 195 m/h to 360m/h of 4 mm wide tape equivalent with same or better biaxial texture. But it was found that reactive IBAD MgO process is a very sensitive process. Biaxial texture of IBAD MgO templates made with a reactive process was found to degrade very fast which made long length production of IBAD MgO template difficult. We investigated the reasons and eventually developed a new process procedure which enables us to produce sharp and uniform biaxal texture over a long length IBAD MgO template. Not only have we achieved high yield in long process runs, but also variability from run to run is well controlled. Now we are routinely producing IBAD MgO template tape of ~ 1.4km with uniform in-plane texture ~ 6 degrees (texture measured with ~ 35nm home-epi MgO and ~ 40nm LaMnO3). Both the average texture and texture deviation over 1,400 m lengths within one run and texture deviation from run to run are better than before. With an almost doubled process speed for IBAD MgO, the bottleneck in the IBAD buffer stack became the alumina process with a speed of 195 m/h for a 4 mm wide tape equivalent. In order to eliminate the bottleneck, we developed a magnetron-sputtering process to deposit alumina buffer and yttria buffer instead of the previous slow ion beam sputtering process. This achievement enabled us to increase alumina/yttria process speeds up to 750m/h for 4 mm wide tape in our Pilot Buffer system. The magnetron-sputtered alumina/yttria yielded the same IBAD MgO texture as ion beam sputtered alumina/yttria. This work was partially supported by Title III and the U.S. Department of Energy.


 

SESSION RR6: Texturing by Sputtering and Other Techniques
Chair: Judy Wu
Wednesday Morning, December 3, 2008
Room 111 (Hynes)


10:15 AM *RR6.1
Modeling the Growth of Biaxially Aligned Thin Films Deposited by Reactive Magnetron Sputtering. Stijn Mahieu and Diederik Depla; Solid State Sciences, Ghent University, Ghent, Belgium.

Biaxially aligned thin films have not only a preferential crystallographic out-of-plane orientation, but also have an alignment along a certain reference direction parallel to the substrate plane. These special structured films have been obtained by reactive magnetron sputter deposition on both amorphous glass and randomly textured polycrystalline substrates tilted with respect to the incoming material flux. The quality of the in-plane alignment can be evaluated from X-ray diffraction and electron back-scattering diffraction pole figures and is usually expressed as the full width at half maximum (FWHM) of the diffraction pole. The used deposition method allowed to deposit biaxially aligned TiN, MgO, Cr, ITO, InN, or YSZ with an in-plane alignment down to 14° FWHM. To model the growth of these biaxially aligned films, first the development of microstructure and crystallographic out-of-plane orientation will be discussed. These results are summarized in an extended structure zone model [1]. Based on experimental results, a mechanism for the in-plane alignment is proposed showing that the here observed in-plane alignment can only be obtained when an overgrowth mechanism drives the microstructural evolution of the thin film. The influence of several deposition parameters (target-substrate distance, target-substrate angle, deposition pressure, and substrate bias) on the degree of in-plane alignment is discussed. The influence of these parameters can be traced down to the influence of two main properties, i.e. the angular spread of the incoming material flux and the adatom mobility on the growing surface. A binary collision Monte Carlo code (SIMTRA) has been developed to model the material flux towards the substrate during sputtering [2]. Hence, the angular spread of the incoming material flux could be simulated by SIMTRA. Finally, a method to quantify the energy flux towards the substrate, and thus to have a measure for the adatom mobility, has been developed. [1] S.Mahieu, P. Ghekiere, D. Depla, R. De Gryse, Thin Solid Films 515 (2006) 1229-1249 [2] Simulation of Metal Transport (SIMTRA) free download: www.draft.ugent.be


10:45 AM RR6.2
Fiber Textures of Titanium Nitride and Hafnium Nitride Thin Films Deposited by Off-Normal Incidence Reactive Magnetron Sputtering. Derya Deniz and James M E Harper; Department of Physics, UNH, Durham, New Hampshire.

We studied the development of crystallographic texture in titanium nitride (TiN) and hafnium nitride (HfN) films deposited by off-normal incidence reactive magnetron sputtering at room temperature. Texture measurements were performed by x-ray pole figure analysis of the (111) and (200) diffraction peaks. For a deposition angle of 40° from substrate normal, we obtained TiN biaxial textures for a range of deposition conditions using radio frequency (RF) sputtering. Typically, we find that the <111> orientation is close to the substrate normal and the <100> orientation is close to the direction of the deposition source, showing substantial in-plane alignment. We also introduced a 150 eV ion beam at 55° with respect to substrate normal during RF sputtering of TiN. Ion beam enhancement caused TiN to align its out-of-plane texture along <100> orientation. In this case, (200) planes are slightly tilted with respect to substrate normal away from the ion beam source and (111) planes are tilted 50° towards the ion beam source. For comparison, we found that HfN deposited at 40° without ion bombardment has a strong <100> orientation parallel to the substrate normal. These results are consistent with momentum transfer among adatoms and ions followed by an increase in surface diffusion of the adatoms on (200) surfaces. The type of fiber texture results from a competition among texture mechanisms related to surface mobilities of adatoms, geometrical and directional effects.


11:00 AM RR6.3
Abnormal Grain Growth Behavior in Nanostructured Al Thin Films on SiO2/Si Substrates. Flavia P Luce1, Paulo F P Fichtner2, Luis F Schelp3 and Fernando Claudio Zawislak1; 1Departamento de Fisica, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS, Brazil; 2Escola de Engenharia, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS, Brazil; 3Departamento de Fisica, Universidade Federal de Santa Maria, Porto Alegre, RS, Brazil.

We report on the formation of nanocrystalline Al thin films (200 nm thick) via magnetron sputtering technique using a step-wise deposition concept where columnar growth is inhibited, giving place to the development of a nanocrystalline mosaic grain arrangement with characteristic diameters of about 30 nm and small size dispersion. The thermal evolution of the grain size distributions is investigated by transmission electron microscopy (TEM) in samples annealed in high vacuum for 1800s. For the temperature range 300≤T≤460 °C the system presents a 3-D regular growth behavior up to sizes about 50 nm. For T=475 °C a rather sharp transition from normal to abnormal grain growth occurs within a temperature interval of 15 °C. The grains extend to the film thickness and present mean lateral dimensions of about 1000 nm. The observed phenomenon is discussed in terms of a synergetic grain boundary mobility effect caused by the characteristics of the initial nanogranular grain boundary morphology. This leads to predictability and stability criterions for the normal to abnormal growth transition, thus stimulating distinct application possibilities.


11:15 AM RR6.4
Large Area Single Crystal Foils Grown by Epitaxial Electrodeposition. Eric Chason, Adam Standley, Meifang Li and Jae Wook Shin; Div of Engineering, Brown U, Providence, Rhode Island.

We describe an inexpensive method for creating large-area, free-standing single crystal foils from a template material, enabling the template to be used again. The method uses a combination of electrodeposition (to deposit epitaxial layers) and electrochemical etching (to remove sacrificial layers and separate the final layer from the template). Analysis of Ni(001) foils by electron backscattering (EBSP) and X-ray diffraction show that high quality foils can be produced with grain misorientations of less than 0.1 deg for both the in-plane and out-of-plane orientations. We also describe how the method can be scaled into a continuous process for creating long ribbons or continuous sheets. Because the films have a single orientation and no grain boundaries, they have potential applications as substrates for superconducting tapes, single-crystal solar cells or other applications where crystalline alignment is required.


11:30 AM *RR6.5
Artificial Grain Alignment of Organic Crystalline Thin Films. Toshihiro Shimada, Chemistry, Univ. Tokyo, Tokyo, Japan.

It is important to obtain single crystalline organic thin films for electronics and optics applications. Due to the mismatching in the crystal symmetry, it is difficult to align the crystalline grains of organic molecular films even on single crystalline surfaces. We have developed several techniques for the perfect grain alignment in organic epitaxial growth. Some of the following techniques might be specific to organic materials but they will provide hints for other materials. The first technique is the use of the nanoscale-textured surfaces prepared by step bunching of vicinally-cut surfaces [1,2]. The height of the steps are critically important: it must be greater than the height of one molecular layer. The mechanism of the grain alignment cannot be explained only by thermodynamic considerations, and kinetic effects revealed by molecular beam experiments [3] must be involved. The second technique is the application of external electric field [4]. We found that there are threshold field strength for the grain alignment. The third one is the optical excitation of the molecules which can be applied to the polar semiconducting molecules [5]. References [1] Appl. Phys. Lett. 68, 2502-2504 (1996) [2] Mater. Res. Soc. Conf. Proc. 965, S06-19 (2007) [3] Appl. Phys. Lett. 89,141912 (2006) [4] Surf. Sci. 564, L263 (2004) [5] Jpn. J. Appl. Phys. 44, L1469 (2005)


 

SESSION RR7: Inclined Substrate Deposition and Vicinal Substrates
Chair: Paul Berdahl
Wednesday Afternoon, December 3, 2008
Room 111 (Hynes)


1:30 PM *RR7.1
Inclined Substrate Deposition of Biaxially Textured Magnesium Oxide Films. Beihai Ma and U. (Balu) Balachandran; Energy Systems Division, Argonne National Laboratory, Argonne, Illinois.

Inclined substrate deposition (ISD) offers the potential for rapid production of high-quality biaxially textured template layers on non-textured substrates. Biaxially textured magnesium oxide (MgO) films were grown on metal substrates by ISD at a high deposition rate, 2-10 nm.s-1. The MgO was evaporated using an electron-beam evaporator. Scanning electron microscopy of the ISD MgO films showed columnar grain structures with a roof-tile-shaped surface. Analysis by X-ray diffraction pole figure revealed that the ISD MgO film is biaxially aligned with the c-axis tilted from its substrate normal. This tilt angle depends on the substrate inclination angle used during the deposition. Tilt angles of ≈32° and ≈25° were measured on ISD MgO films deposited at 55° and 35° inclination angles, respectively. A full width at half maximum of ≈10° was determined from a phi-scan for the ISD MgO films. Surface roughness and biaxial alignment were improved by homo-epitaxial growth of an additional layer of MgO film (≈0.5-μm-thick) at ≈700°C. Textured hetero-epitaxial buffer films can be subsequently grown on the MgO template by pulsed layer deposition. Details of the MgO film texturing mechanism will be discussed. *This work was supported by the U.S. Department of Energy under Contract DE-AC02-06CH11357.


2:00 PM RR7.2
Vicinality in Coated Conductors. John Hay Durrell and Noel Rutter; Materials Science and Metallurgy, University of Cambridge, Cambridge, United Kingdom.

The use of ion-beam routes to artificially generate grain alignment in coated conductor buffer layers has an important influence on the electromagnetic characteristics of the superconducting layer. For the IBAD process the c-axis of the superconducting layer is globally oriented perpendicular to the film surface whereas for the ISD process there is an overall preferential tilt of the c-axis away from the substrate normal. If this tilt is perpendicular to the current direction then the macroscopic current direction is still along the a-b planes and is not greatly reduced. However, such effectively vicinal films have been shown in model systems to exhibit strikingly different behaviour to c-axis orientated films. Moreover, in a practical conductor current percolation is an important mechanism by which the effect of local variations in critical current are ameliorated and this, at first sight, appears to be inhibited in such systems. We present critical current versus magnetic field angle data taken both in model systems, where the YBCO layer is grown on a vicinal strontium titanate substrate, and in ISD tapes. With the aid of a full characterisation of the field-angular dependence of the critical current, presented in the form of a pole figure, we analyse how the distinct critical current anisotropy in vicinal materials affects the overall behaviour of the conductor. We note that with careful regard to the details of applications the reduced symmetry in such conductors can give rise to enhanced performance.


2:15 PM RR7.3
Substrate-induced Tailoring of Physical Properties of Complex Oxide Thin Films. Hanns-Ulrich Habermeier, MPI-FKF, Stuttgart, Germany.

It is well known that (100)-oriented single crystal cubic substrates such as SrTiO3 with a vicinal cut along the [010]- direction are characterized by a regular step-and-terrace structure with a well defined tarrace width. In this contribution we demonstrate that such substrates offer an unique possibility to tailor the defect structure of complex oxide thin films and can cause enhanced flux-line pinning in YBCO-LCMO heterostructures, planar magnetic anisotropy in manganite thin films and offer the possibility to construct new types of devices based on the thermoelectric properties of NaxCoO2 thin films. The technological and physical mechanisms of defect formation will be addressed in detai,


2:30 PM RR7.4
Introducing Artificial YBa2Cu3O7-δ Thin Film Grain Boundaries with Controlled Geometry by Surface Modification of MgO Substrates. Henrik Pettersson1, David Gustafsson2, Karin Cedergren2, Floriana Lombardi2 and Eva Olsson2; 1Applied Physics, Chalmers University of Technology, Göteborg, Sweden; 2Microtechnology and Nanoscience, Chalmers University of Technology, Göteborg, Sweden.

Grain boundaries in high-temperature superconducting YBa2Cu3O7-δ (YBCO) thin films can act as weak links and thus be used as Josephson junctions in devices. The properties of the junctions strongly depend on the atomic structure of the junction where both misorientation between the two adjacent YBCO grains and also the exact geometry of the boundary plane are important. There is a need to control these two structural aspects by controlling the nucleation event and orientation of the YBCO on a local scale by patterning the substrate surface. A YBCO grain boundary can be introduced at an interface between two different substrate surface morphologies. It is also important to know the evolution of the thin film and grain boundary in order to control the boundary plane geometry. In this work artificial grain boundaries (AGB) of (103)/(001) YBCO films produced by pulsed laser deposition (PLD) have been investigated. The YBCO AGBs were deposited on (110) MgO substrates with a vicinal cut. The YBCO film grew with (001) orientation and a 45° in-plane rotation on the (110) MgO substrate. A patterned SrTiO3 (STO) template layer was used to locally introduce (103) YBCO growth. Further information about the thin film evolution was obtained by comparing ultra YBCO thin films (100 pulses) to full thickness (80 nm) films.


2:45 PM RR7.5
Influence of the Ceria Buffer Catalytic Activity on the Texture of YBCO Layers Manufactured by the Metal-Organic Deposition. Vyacheslav Solovyov, Brookhaen National Laboratory, Upton, New York.

A critical element of the second generation (2G) high-temperature superconducting wire is highly oriented Y1Ba2Cu3O7 (YBCO) layer. The YBCO layer is grown on a long length (several km) metal tapes substrate coated with an oxide buffer, which serves as an epitaxial substrate for YBCO. The buffered tape is quite different from a traditional single crystal substrate in many aspects, such as roughness, crystallographic alignment etc. One important and often overlooked variable is the catalytic activity which can be is defined as an ability of a substrate to generate nuclei of the epitaxial phase. We discuss effect of variation of the catalytic activity of industrials cerium oxide (CeO2) buffers on texture quality of epitaxial YBCO layers grown by the metal-organic deposition process. The central assumption of this work is that efficient YBCO nucleation requires high density of well-defined (001) substrate terraces, which are the low-energy nucleation sites. The terraces have to be large enough to accommodate the critical YBCO nuclei. Since size of the (001) terrace cannot exceed the lateral grain size, the substrate catalytic activity should be strongly affected by the cerium oxide grain size. To determine the lateral grain size, several types of buffers are analyzed by high-resolution X-ray diffraction and atomic force microscopy. The reciprocal space mapping of CeO2 peaks with various degree of inclination with respect to the film normal was used to separate of anisotropic broadening effects from tilt and twist of the CeO2 grains. The method is used for reconstruction of the grain shape and extraction of the lateral grain size. The lateral grain size is then correlated with AFM images to obtain influence of the grain size on the (001) CeO2 terrace width. We demonstrate that substrates with small lateral grain size (below 10 nm) provide very few nucleation sites, typically less than several microns apart. YBCO films growth on such substrates have low critical current density due to coarse grain morphology of YBCO layer. Site specific transmission electron microscopy is used to investigate the structure variation within the YBCO grain. The low critical current of coarse-grain layers is related to secondary phase accumulation build-up when the YBCO grain size exceeds 10 microns in diameter. It is concluded that to synthesize high-quality small-grained (<10 microns) YBCO layer one needs relatively coarse-grained (>10 nm) oxide substrate. This work has been performed under Contract No. DE-AC02-98CHI-886 with the U. S. Department of Energy.

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