bluuebunny/crossref_metadata_2025 huggingface dataset:
A Novel Approach for the Complete Removal of Threading Dislocations from Mismatched Heteroepitaxial Layers
Authors: Zhang X. G. , Rodriguez A. , Li P. , Jain F. C. , Ayers J. E.
Published: April 2011

The application of mismatched combinations of heteroepitaxial semiconductors has been quite limited due to the presence of high threading dislocation densities. In recent years, great progress has been made toward solving this problem using compliant substrates and lateral epitaxial overgrowth. We have proposed another approach which we call patterned heteroepitaxial processing (PHP), and which involves post-growth patterning and thermal annealing. In this paper we describe the successful application of the PHP technique to the ZnSe/GaAs (001) material system.

Epitaxial layers of ZnSe on GaAs (001) were grown to thicknesses of 2000 - 6000 Å by photoassisted metalorganic vapor phase epitaxy (MOVPE). Following growth, layers were patterned by photolithography and then annealed at elevated temperature under flowing hydrogen. Threading dislocation densities were determined using a bromine/methanol etch followed by microscopic evaluation of the resulting etch pit densities.

We found that as-grown layers contained more than 107 cm-2 threading dislocations. The complete removal of threading dislocations was accomplished by patterning to 70 μm by 70 μm square regions followed by thermal annealing for 30 minutes at temperatures greater than 500°C. Neither post-growth annealing alone nor post-growth patterning alone had a significant effect. By studying the annealing temperature dependence, we have determined that the dislocation removal by PHP is thermally activated. It appears that the maximum dimension for patterned regions in PHP is determined by the annealing temperature rather than an effective range for image forces.

These results show that PHP can be used to completely remove threading dislocations from lattice-relaxed heteroepitaxial layers. In principle this approach should be generally applicable to mismatched heteroepitaxial materials.
Effects of Y and Zr Dopants on Grain Boundary Structure in Creep Resistant Polycrystalline Alumina
Authors: Cargill G. S. , Wang C. M. , Rickman J. M. , Chan H. M. , Harmer M. P.
Published: April 2011

Dopants Y and Zr at 100 ppm levels in high purity, micron grain-size polycrystalline alumina are mainly segregated to the alumina grain boundaries and strongly reduce high temperature creep. Information about this segregation has come from high resolution STEM composition mapping experiments. Information about local structural surroundings of the dopant atoms has come from EXAFS experiments, and information about local bonding of the dopant atoms has come from XANES experiments. Structural models for dopant grain boundary segregation provide a context for these experimental results and for effects of dopant incorporation on grain boundary mediated transport. Recent experimental and theoretical results are discussed in this paper.
Atomic and Electronic Structure of Symmetric Tilt Boundaries in ZnO
Authors: Oba Fumiyasu , Nishitani Shigeto R. , Adachi Hirohiko , Tanaka Isao , Kohyama Masanori , Tanaka Shingo
Published: April 2011

We have investigated the atomic and electronic structure of symmetric tilt boundaries in ZnO by a first-principles plane-wave pseudopotential method. Equilibrium boundary geometries with distorted- and dangling-bonds are obtained. Localized electronic states form mainly at the lower valence band and the bottom of the upper valence band owing to the bond disorder. However, the electronic states near the band gap are not significantly affected; deep states are not generated in the band gap. The small effects of the bond disorder on the electronic structure can be attributed to the band structure characteristic of ZnO.
Atomic Scale Characterization of Oxygen Vacancy Segregation at SrTiO3 Grain Boundaries
Authors: Klie R.F. , Browning N. D.
Published: April 2011

We have examined the structure, composition and bonding at an un-doped 58° [001] tilt grain-boundary in SrTiO3 in order to investigate the control that the grain boundary exerts over the bulk properties. Room temperature and in-situ heating experiments show that there is a segregation of oxygen vacancies to the grain boundary that is increased at elevated temperatures and is independent of the cation arrangement. These measurements indicate that the widely observed electronic properties of grain boundaries may be due to an excess of mobile oxygen vacancies that cause a highly doped n-type region in the close proximity ( ≍ 1 unit cell) to the boundary. These results are shown to be consistent with both theoretical models and lower resolution chemical analysis.
Interfacial Structure of BaRuO3 Thin Films Grown On (111) SrTiO3
Authors: Tian W. , Lee M. K. , Eom C. B. , Pan X. Q.
Published: April 2011

BaRuO3 thin films were grown on (111) SrTiO3substrate by 90° off-axis rf-sputtering. Transmission electron microscopy studies revealed that the films consist of the metastable 4H hexagonal polymorph of BaRuO3 along with few defects. The films are c-axis oriented, single crystalline with the in-plane orientation relationship with respect to the SrTiO3substrate of [112 0] BaRuO3 // [110] SrTiO3. High-resolution transmission electron microscopy (HRTEM) studies of the film-substrate interface revealed the existence of a thin intermediate layer of the 9R hexagonal polymorph of BaRuO3 between the (111) SrTiO3 substrate and the 4H film. The formation mechanism for the intermediate layer is not fully understood though. Through the combination of HRTEM and quantitative image simulations, the atomic structure of the interface between the 9R intermediate layer and the underneath (111) SrTiO3 was constructed. Three initial growth modes were observed, each of them adopting the local continuity of the oxygen octahedral sublattice across the interface.
Atomic Force Microscopy Studies of Fracture Surfaces From Oxide / Polymer Interfaces
Authors: Jenkins Maura , Snodgrass Jeffrey , Chesterman Aaron , Dauskardt Reinhold H. , Bravman John C.
Published: April 2011

Atomic Force Microscopy (AFM) is used to characterize fracture surfaces in silicon oxide / silane adhesion promoter / BCB polymer systems. Fatigue striations were found on some samples, and these were correlated with the crack growth rate per fatigue cycle. X-ray Photoelectron Spectroscopy (XPS) was used to identify the species present on each surface, and it was found that striations only form when the fracture path is through the polymer.
The Interfacial Reaction Products and Mechanical Properties with Oxidized Layer Thickness of SiC Particle in 2014Al/SiC Composites
Authors: Kim Youngman , Jeong Jong-Hoon , Lee Jae-Chul
Published: April 2011

Metal matrix composites (MMC's) are known to have wide applications in parts of transportation devices such as automobiles and aircraft. Al matrix composites using SiC particles as reinforcements are especially spotlighted because of low cost, superior specific modulus, specific strength, wear resistance and high temperature stability. However, Al4C3 formed by the interfacial reaction between Al and SiC weakens the interfacial bonding strength. It is also known to be unstable in the water-soluble atmosphere.

In this study, the passive oxidation of SiC powder is used as protective layer against the reaction between the Al matrix and the SiC particle. We investigated the changes in interfacial product of the composites and mechanical properties such as interfacial bonding strength, and tensile strength in terms of the oxidized layer thickness of the reinforcement.
Segregation of Yttrium at Grain Boundaries in α-Al2O3
Authors: Nufer Stefan , Kurtz Wolfgang , Rühle Manfred
Published: April 2011

Quantitative X-ray analysis allows the investigation of yttrium-doped grain boundaries. In the present study well-defined bicrystal interfaces were characterized. The quantitative comparison of segregation at different bicrystals requires a correction of artifacts in the X-ray spectra due to mass absorption, fluorescence, and beam spread. Mean grain boundary excess values of 3 Y/nm2 and around 5 Y/nm2 were found at a ∑17 and ∑37 symmetrical grain boundary, respectively. Additionally, with the ∑17 bicrystal YAG precipitation and presence of silicon was found.
Ellipsometry as a Sensitive Technique to Probe film -Substrate Interfaces: Al2O3 on Si(100)
Authors: Singh M. P. , Raghavan G. , Tyagi A. K. , Shivashankar S. A.
Published: April 2011

An attempt has been made to study the film-substrate interface by using a sensitive, non- conventional tool. Because of the prospective use of gate oxide in MOSFET devices, we have chosen to study alumina films grown on silicon. Film-substrate interface of alumina grown by MOCVD on Si(100) was studied systematically using spectroscopic ellipsometry in the range 1.5-5.0 eV, supported by cross-sectional SEM, and SIMS. The (ε1,ε2) versus energy data obtained for films grown at 600°C, 700°C, and 750°C were modeled to fit a substrate/interface/film “sandwich”. The experimental results reveal (as may be expected) that the nature of the substrate -film interface depends strongly on the growth temperature. The simulated (ε1,ε2) patterns are in excellent agreement with observed ellipsometric data. The MOCVD precursors results the presence of carbon in the films. Theoretical simulation was able to account for the ellipsometry data by invoking the presence of “free” carbon in the alumina films.
Relationships between Film Chemistry, Structure, and Mechanical Properties in Titanium Oxide
Authors: Pang M. , Eakins D.E. , Norton M.G. , Bahr D.F.
Published: April 2011

Titanium oxides were grown anodically to selected final potentials on grade II polycrystalline titanium under different anodization rates. XPS and RBS results show that the oxide consists of primarily TiO2with a non-stoichiometric oxide/metal interface, with the slower growth rate associated with a thicker layer at the interface. Characterization using TEM reveals that the structure of the oxide evolves from a primarily amorphous phase to islands of crystallites in an amorphous matrix, to an entirely crystalline phase by increasing the polarization potential. Slower growth rates tend to remain crystalline at higher potentials. The mechanical strength of oxide films extracted from load-depth data by nanoindentation varies dramatically for oxide films grown by different rates at 9.4 V, and to a lesser extent at lower potentials. The variation of film strength is associated with both compositional and structural characteristics.
Influence of Pre-Gate Cleaning ON Si/SiO2 Interface and Electrical Performance of Cmos Gate Oxide
Authors: Duan X. , Kisslinger K. , Mayes L. , Ruby S. , Barrett J.
Published: April 2011

The Si/SiO2 interface is attracting new interest as gate dielectrics in MOS devices become ultra thin. In this paper, the impact of pre-gate cleaning on the morphology of the Si/SiO2 interface and the electrical performance of CMOS gate oxides has been systematically investigated. Using the High-Resolution Transmission Electron Microscopy (HRTEM) technique, we observed the Si/SiO2 interface at an atomic level. We have found a direct experimental relationship between the pre-gate cleaning scheme, Si/SiO2 interface morphology, and the electrical properties of CMOS gate oxides. When the ratio of H2O2:NH4OH ≥ 1.45, the roughness of the Si/SiO2 interface was dramatically improved, which, in turn, increased the Charge-to-Breakdown to an ideal value.
A Subnanoscale Study of Segregation at CdO/Ag(Au) Heterophase Interfaces
Authors: Sebastian Jason T. , Hellman Olof C. , Seidman David N.
Published: April 2011

Three-dimensional atom-probe (3DAP) microscopy permits the atom-by-atom reconstruction of a small volume (typically 10 nm × 10 nm × 100 nm) of a material with respect to both the positions and chemical identities of individual atoms. It is, therefore, ideally suited for the study of solute segregation at internal heterophase interfaces. We present recent results of a 3DAP microscopy study of solute segregation at ceramic/metal (C/M) heterophase interfaces prepared by internal oxidation. In particular, results on the CdO/Ag(Au) (where Au is the segregating species) system are presented. In the 3DAP atomicreconstructions, the interfaces of nanometer-size CdO ceramic particles are delineated as Cd isoconcentration surfaces. The distribution of the segregating species as a function of distance to the isoconcentration surfaces is determined with the proximity histogram (or proxigram) method. Two interfaces are investigated in detail. The first shows no appreciable Au segregation, while the second exhibits segregation with a Gibbsianinterfacial excess of 1.65 nm-2at 650°°C.
Understanding Metal Oxide Surfaces at the Atomic Scale: STM Investigations of Bulk-defect Dependent Surface Processes
Authors: Diebold Ulrike
Published: April 2011

Surface defects are important in oxide surface chemistry, because they change not only the surface geometric structure, but also affect the local electronic structure. Scanning Tunneling Microscopy (STM) images with atomic-scale resolution, in combination with area-averaging surface spectroscopies, is an ideal tool to study local surface defects and their relationship to surface reactivity. We report STM results onTiO2(110) surfaces which show the surprising influence of bulk defects on surface properties. Thereduced crystals used in this and other surface science studies contain Ti interstitials and oxygen vacancies. Re-oxidation at elevated temperatures results in the growth of additional TiO2 layers with Ti coming from the bulk of the crystal and O from the gas phase. This often result in partially incomplete surface structures with many undercoordinated atoms. The esorption behavior of elemental S, dosed at room temperature, depends on the reduction state of the sample. This is explained by a mechanism where desorption froma weaklybound precursor state competes with the availability of new adsorption sites in the form of oxygen vacancies which migrate from the bulk to the surface.
Growth and Characterization Studies of ABi2ta2o9 (A = Ba, Sr and Ca) Ferroelectric Thin Films
Authors: Das R. R. , Opérez W. , Rodríguez R. J. , Dobal P. S. , Katiyar R. S. , Krupanidhi S.B.
Published: April 2011

Thin films of ferroelectric ABi2Ta2O9 bismuth-layered structure, where A = Ba, Sr and Ca, were prepared by pulsed laser deposition technique on Pt/TiO2/SiO2/Si(100) substrates. The influence of substrate temperature between 500 to 750°C, and oxygen partial pressure 100-300 mTorr, on the structural and electrical properties of the films was investigated. The films deposited above 650°C substrate temperature showed complete Aurivillius layered structure. Films annealed at 750°C for 1h in oxygen atmosphere have exhibited better electrical properties. Atomic force microscopy study of surface topography shows that the films grown at lower temperature has smaller grains and higher surface roughness. This paper discusses the pronounced influence of A-site cation substitution on the structural and ferroelectric properties with the aid of Raman spectroscopy, X-ray diffraction and electrical properties. The degradation of ferroelectric properties with Ba and Ca substitution at A-sites is attributed to the higher structural distortion caused by changing tolerance factor. A systematic proportionate variation of coercive field is attributed to electronegativity difference of A-site cations.
Oxidation Resistance of TaSiN Diffusion Barriers for Stacked Capacitors
Authors: Letendu F. , Hugon M.C. , Agius B. , Vickridge I , Ayguavives F. , Kingon A.I.
Published: April 2011

Due to its resistance to oxidation, TaSiN is a promising candidate as an electrically conductive barrier layer for integration of high permittivity oxides in advanced memory devices. In this study we report on the properties and the resistance to oxidation of TaSiN thin films deposited by reactive magnetron sputtering and processed by rapid thermal annealing (RTA) in 18O2 at 650°C. In order to determine the composition, RBS (Rutherford Backscattering Spectroscopy) and NRA (Nuclear Reaction Analysis) techniques have been used. 18O depth profile concentrations were measured after RTA using the narrow (fwhm=100eV) resonance at 151 keV in the nuclear reaction 18O(p,α)15N.
Process Degradation of a Ferroelectric Capacitor
Authors: Otani Seigen , Tamura Tetsuro
Published: April 2011

Ferroelectrics used in a memory device such as (Pb,La)(Zr,Ti)O3 (PLZT) are vulnerable to reducing atmosphere and lose remanent polarization easily. In the semiconductor processes, hydrogen gas is generated both from deposition gas of interlayer dielectric and from reaction between metals and moisture in the dielectric. Improving the ferroelectrics resistance to reducing environments is required for the planarization and multi-layer interconnections in future devices. Loss of remanent polarization is related to the imprint properties of the capacitor and can be improved by controlling the deposition condition of sol-gel PLZT and annealing IrOx electrode in oxygen.
Property Improvement of PLZT Capacitor Using CaRuO3 Top Electrode
Authors: Funakubo Hiroshi , Higashi Noriyuki , Okuda Norikazu
Published: April 2011

SrRuO3 and CaRuO3 films prepared by MOCVD were compared not only in term of their own properties but for their characteristics as the top electrodes of (Pb, La)(Zr, Ti)O3[PLZT] capacitor, especially for H2 degradation. Resistivity of CaRuO3 and SrRuO3 films increased after heat treatment in H2-containing atmosphere, but was recovered by a heat treatment at 600 °C under O2 atmosphere. When SrRuO3 and CaRuO3 films deposited at 600 °C were used as top electrodes, the remanent polarization(Pr) value of SrRuO3/PLZT/Pt and CaRuO3/PLZT/Pt capacitors were almost the same as the values for capacitors with a Pt top electrode. After a heat treatment in a 3 % H2 atmosphere at 200 °C, followed by one in O2 atmosphere at 450 °C, Pr value was perfectly recovered for both of SrRuO3 and CaRuO3 films. The leakage current become the smallest when using 50 nm-thick CaRuO3 film as a top electrode. Moreover, no degradation was observed for fatigue test up to 1010 cycles when MOCVD-CaRuO3 films were used as top electrodes. These data show that MOCVD-CaRuO3 film with thin thickness is a useful top electrode for PLZT capacitor.
Role of the Electrode Morphology, Thickness and Orientation in the Ferroelectric Performance of Epitaxial Pb(Zr,Ti)O3Thin Films
Authors: Guerrero Cesar , Sánchez Florencio , Roldán José , Güell Frank , García-Cuenca María V.
Published: April 2011

A comparison of pulsed laser deposited PbZr0.53Ti0.47O3(PZT) thin film capacitors with SrRuO3(SRO) and LaNiO3(LNO) electrodes on (001) yttria-stabilized zirconia (YSZ) and lattice matched (001) LaAlO3substrates is presented. Both electrode materials allow for the formation of ferroelectric capacitors with large remnant polarization (20-30 μC/cm2) and negligible fatigue, although slight differences arise regarding the promotion of either the rhombohedral or tetragonal phases of PZT. Far more crucial seems to be the tendency of SrRuO3to develop a rougher surface at either small (<30 nm) or large thickness (>100 nm), and on YSZ substrates. In those cases a highly defective and possibly low dielectric interface forms between the electrode and the ferroelectric layer, resulting in greatly degraded ferroelectric performance. LaNiO3is free from these limitations except for the cracks forming at very large thickness (>300 nm), and therefore appears as a more versatile electrode material.
Low-Temperature Growth of C-Axis Oriented Y-Type Hexagonal Ferrite'S Films by Polymerized Complex Method
Authors: Fujii Tatsuo , Komatsu Koutarou , Nakanishi Makoto , Takada Jun
Published: April 2011

Well-crystallized Y-type hexagonal ferrite (Me2-Y, Me=Zn and Co) films with highly c-axis orientation were successfully prepared on Ag substrates by dip coating technique. The procedure consisted of preparation of homogeneous metal-organic solution by polymerized complex method, dip coating and subsequent heat-treatment. The films deposited on α-Al2O3 easily reacted with the substrate, while the films deposited on Ag formed hexagonal planar structures. The formation temperature of Me2-Y structures on Ag was 800 °C, which was much lower than that of Me2-Y bulk crystals. The Me2-Y films on Ag had a large in-plane magnetic anisotropy. The observed anisotropy field of the Zn2-Y film was about 13 kOe and that of Co2-Y was too large beyond our experimental limits.
Experimental and Theoretical Investigation into the Dielectric Behaviour of Ferroelectric Thin Film Superlattices
Authors: Gregg J. M. , O'Neill D. , Catalan G. , Bowman R. M.
Published: April 2011

Pulsed laser deposition has been used to fabricate thin-film capacitor structures in which the dielectric layer is composed of a superlattice of Ba0.8Sr0.2TiO3 and Ba0.2Sr0.8TiO3. The properties of the capacitors were investigated as a function of superlattice periodicity. The dielectric constant was significantly enhanced, and temperature migration of the peak in dielectric constant as a function of frequency was observed, at stacking periodicities of a few unit cells. However, such “relaxor-like’ features were found to be associated with high dielectric loss. Analysis of the imaginary permittivity as a function of frequency showed that fine-scale superlattices conform to Maxwell-Wagner behaviour, indicating that the observed features may be an artefact of increased carrier mobility. Modelling showed that both dielectric enhancement and frequency relaxation could readily be reproduced by Maxwell-Wagner formalism.
Anisotropic Fracture Behavior of Electroless deposited Ni-P Amorphous Alloy Thin Films
Authors: Takashima Kazuki , Ogura Akio , Ichikawa Yusuke , Higo Yakichi
Published: April 2011

Fracture tests have been carried out for an electroless deposited Ni-P amorphous alloy thin film with different crack growth directions. Cantilever beam type specimens with dimensions of 10 × 10 × 50 μm3 were prepared from a Ni-P amorphous thin film and notches with different directions, which are perpendicular and parallel to the deposition growth direction, were introduced by focused ion beam machining. Fatigue pre-cracks were introduced ahead of the notches. Fracture tests were performed using a mechanical testing machine for micro-sized specimens. Fracture behavior is different between the two types of specimens. As KIC values were not obtained because the criteria of plane strain were not satisfied for this size of the specimen, the provisional fracture toughness KQ values were determined. The KQ value of the specimen with crack propagation direction being perpendicular to the deposition growth direction was 4.2 MPam1/2, while that with crack propagation direction being parallel to the deposition growth direction was 7.3 MPam1/2. This result suggests that the electroless deposited Ni-P amorphous alloy thin film has anisotropic fracture properties.
Nanoindentation of Microspring Thin Films
Authors: Seto Mary W. , Dick Brian , Brett Michael J.
Published: April 2011

Porous thin films with helical microstructures were fabricated with the Glancing Angle Deposition technique. These films consisted of arrays of “microsprings” whose geometries could be engineered with nanometer scale control. Some of the mechanical properties of these helically structured films were studied with a nanoindentation technique. Several microscopic “springbed” films were tested over a range of forces using a spherical indenter tip. The geometries of the microsprings were varied, and a number of different materials were used to fabricate these films, which were typically a few micrometers thick. Slanted post arrays, resembling micro-cantilevers, were also subjected to nanoindentation tests. Results of initial experiments, theory, and simulations show that these microstructures behave in a manner analogous to macroscopic springs and cantilevers, and may offer some insight into how materials behave at the microscale.
Double Sided Porous Silicon on Patterned Substrates for Thermal Effect Microsystems
Authors: Périchon S. , Lysenko V. , Remaki B. , Barbier D.
Published: April 2011

Application of porous silicon in thermal microsystem structures often requires the formation of deep localized porous silicon layers. The most commonly used method to prepare the porous layers is the dc anodic etching of monocrystalline silicon in a hydrofluoric acid (HF) based electrolyte. However inhomogeneity of the nanocrystallite size along the layer depth due to the decrease of HF concentration within the pores as well as the poor uniformity of the porous layer thickness limit the elaboration of deep porous layers. Thus we propose an original pulsed anodisation technique, using a double tank etching cell that allows localized porous silicon layers formation throughout the whole wafer thickness.

Furthermore a selective double sided pulsed anodisation of silicon was performed on patterned silicon substrates. Porous silicon is formed in pre-determined parts of the wafer using composite polysilicon-silicon nitride masking layers. Technological solutions to get rid of porous layer thickness inhomogeneity due to non uniform current density distribution are discussed. Finally a toric porous silicon layer, crossing the whole silicon wafer, surrounding a 20 mm diameter monocrystalline silicon cylinder was successfully achieved ensuring a new approach of thermal insulation for thermal effect microsystems.
On the Role of the Underlying Microstructure on the Mechanical Properties of Microelectromechanical Systems (MEMS) Materials
Authors: Dirras G. F. , Coles G. , Wagner A. J. , Carlo S. , Newman C. , Hemker K. J. , Sharpe W. N.
Published: April 2011

The microstructure of Low Pressure Chemical Vapor Deposition (LPCVD) Polycrystalline silicon (Polysilicon) thin films was investigated by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), atomic force microscopy (AFM) and Auger electron spectroscopy (AES). SEM characterization of tensile tested samples showed a brittle like-rupture, along with grooves located at the surface sides of the sample. TEM investigations of as-deposited samples showed equiaxed or fully columnar grains bridging from the bottom to the top of the films. A microstructural coarsening was observed with annealing. In the as-deposited state, the films exhibited a {110} texture as showed by the XRD analysis. The films' top and bottom surfaces were observed to be smooth with a roughness (standard deviation) of about 11nm and 20 nm respectively. A chemical analysis of the thin films showed the presence of carbon and oxygen impurities on the surface and oxygen through the sample as observed in the depth profile. The hypothetical influence of these findings is subsequently discussed in relation to the measured mechanical properties.
Microfabrication of Crevice Corrosion Samples
Authors: Wang Xiaoyan , Kelly Robert G. , Lee Jason S. , Reed Michael L.
Published: April 2011

A major challenge in developing computer models for crevice corrosion lies in fabricating appropriate experimental crevice samples. The geometry and dimensions of these samples must be controlled to a high order of precision in order to be amenable for comparison to computational models. In this work we report an effort to construct crevice samples with rigorously defined dimensions by using microfabrication techniques developed for microelectromechanical systems (MEMS). These techniques include microfabrication with SU- 8, electroplating, and other standard semiconductor device fabrication techniques as well. The crevice substrates contain one-dimensional arrays of metal electrodes to be studied, which are isolated by walls of SU-8. The electrodes have individual electrical connections so that spatial information of the in-situ corrosion process can be obtained. The crevice formers with SU-8 posts were coupled to crevice substrates to maintain a uniform crevice gap. Further, crevice formers with regular rectangular subcrevices were fabricated to study the roles of subcrevices in crevice corrosion.
Low Temperature Si Direct Bonding by Plasma Activation
Authors: Cho Yonah , Cheung Nathan W.
Published: April 2011

Chemical and physical effects of plasma exposed Si wafer pairs were investigated on Si wafer bonding. Oxygen plasma treated Si wafer pairs bonded more strongly at room temperature compared to chemically cleaned, hydrophilic and hydrophobic Si. After 50 hours of annealing at 105°C, the surface energy of the bonded Si pair reached the surface energy of bulk Si (100). X- ray photoemission spectroscopy (XPS) measurements indicated that the exposure of both hydrophilic and hydrophobic Si to oxygen plasma increased a SiO2 like state in the surface layer to a depth of 1.5 nm. Atomic force microscopy (AFM) study showed that plasma irradiation at 300 watts up to 30 seconds did not change surface roughness below 0.5 nm. Exposure to He plasma or N2 did result in enhanced bonding after annealing at 165°C, however, over smaller areas.
Superconductivity and Magnetic Properties of High-Pressure Oxygen Synthesized Ru1−xSr2GdCu2+xO8-z Compounds
Authors: Klamut P.W. , Dabrowski B. , Maxwell M. , Mais J.
Published: April 2011

We report on the new superconducting materials with the formula Ru1−xSr2GdCu2+xO8-z that have been synthesized under high-pressure oxygen conditions. By changing the ratio between Ru and Cu in the compound we were able to increase the temperature of the superconducting transition up to 72 K for x=0.3 and 0.4. Reentrant dependencies of the magnetization found at low temperatures are qualitatively explained assuming a quasi two-dimensional character of the superconducting regions. The magnetic characteristics of these compounds are discussed and compared to the existing data on RuSr2GdCu2O8 magnetic superconductor (Tcon=45K, TN=132 K).
Development of High Critical Current YBCO Coated Conductors By Photo-Assisted MOCVD
Authors: Chen Yimin , Chen Xin , Tang Zhongjia , Chou PenChu , Zhang Xin , Ignatiev Alex
Published: April 2011

YBa2Cu3O7 (YBCO) films have been deposited by photo-assisted MOCVD at rates of greater than 0.3μm/min on both single crystal oxide substrates and atomically textured metallic substrates. The YBCO films of thickness from 0.5μm to 3μm deposited on LaAlO3 substrates are shown to be highly atomically ordered with Jc> 1 × 106 A/cm2. CeO2 buffer layers have also been developed by photo-assisted MOCVD for the integration of YBCO with metallic substrates. The CeO2 layers were found to be crack-free when grown on nickel even above 1 micron thickness, and exhibited crystal orientation and in-plane alignment similar to that of the atomically textured Ni substrates. YBCO films grown on the thick CeO2 buffer layers on nickel substrates have shown promising results with Jc∼6 × 105 A/cm2.
Development of LPE process for fabrication of coated conductors
Authors: Izumi Teruo , Hobara Natsuro , Izumi Toru , Hasegawa Katsuya , Kai Masahiko , Fuji Hiroshi , Honjo Tetsuji , Xin Yao , Krauns Christian , Kuznetsov Maxim , Nakamura Yuichi , Shiohara Yuh
Published: April 2011

Recent Progress of development for coated conductors by the LPE technique was reviewed. Double layered LPE films were applied to the growth on metal substrates. In both cases of MgO- and NiO- buffers, the constructions were succeeded to grow on Hastelloy and Ni tapes, respectively. In the case of the MgO-buffer, the problem, which is the melting back of the 1st LPE layer during dipping for the growth of the 2nd LPE layer, was found. The problem was solved by means of the selection of the materials for each LPE layer to introduce the difference in the growth temperature for the 1st and the 2nd layers. The lower growth temperature for the 1st LPE layer than that for 2nd one is effective to avoid the problem. On the other hand, the double layered LPE films on Ni tapes revealed Tc of 85K. Concerning the long tape processing, the high growth rate of 1≈ was confirmed even without rotation using the long tape apparatus.
Texture Analysis of Coated Conductors by Micro-Raman and Synchrotron x-ray Diffraction
Authors: Puig Teresa , Puig-Molina Anna , Mestres Narcís , Seijen Harm Van , Alsina Francesc , González Juan C. , Obradors Xavier , Graafsma Heinz , Usoskin Alexander , Freyhardt Herbert C.
Published: April 2011

Two novel complementary and non-destructive techniques for texture analysis of YBCO coated conductors are presented. Micro-Raman (μ-Raman) spectroscopy enables an easy analysis of the film homogeneity by determining the distribution of a- and c-oriented grains within the tape with a 1 μm spatial resolution and acquisition times of 5 min/spot. In addition, synchrotron x-ray diffraction analysis in transmission geometry and 2D detectors enables, with acquisition times of 100 ms, simultaneous observation of a- and c- crystallites and in-plane textures of substrates, buffers and superconducting layer. Thus, opening the field of this technique to in-situ analysis of epitaxial growth of coated conductors prepared by ex-situ processes. Results from these two techniques for stainless steel tapes buffered with IBAD-YSZ and coated with PLD-YBCO are analyzed.
Synthesis and Interface Structure of Sol Gel YBa2Cu3Ox Thin Films for Conductor Development
Authors: Shi Donglu , Xu Yongli , Wang S. X. , Wang L. M. , McClellan Shaun M.
Published: April 2011

In our previous work we have obtained YBCO thick films on silver alloy substrate via the peritectic solidification. To further develop grain-textured YBCO thin films for conductor development, in this study, we have used a sol gel approach to deposit YBCO thin films on two different substrates, namely, yttrium-stabilized zirconia (YSZ) and a silver alloy containing 10 % of palladium (Ag –10%Pd). We have found that the sol gel film on YSZ exhibits an epitaxial growth. This is confirmed by both x-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). XRD data also indicate that the YBCO film on Ag-10%Pd has a c-axis grain orientation. The details are reported on sol gel synthesis and XRD and HRTEM characterization of the YBCO thin films.
Magnetic Imaging of Superconducting Tapes to Determine Current Flow
Authors: Brown G.W. , Hawley M.E. , Foltyn S.R. , Mueller F.M.
Published: April 2011

We have developed a magnetic imaging system that uses magnetoresistive read heads from computer hard disk drives to map the transport-current-induced magnetic field at the surface of superconducting tapes at liquid nitrogen temperature. Transport current pathways are determined from the 2-dimensional magnetic field maps using established inversion schemes. We examined the current flow in pulsed-laser-deposited YBa2Cu3O7-σ films patterned on single crystal SrTiO3 substrates and on a textured yttria-stabilized-zirconia layer deposited on an Inconel ribbon by ion beam assisted deposition. The transport current densities in all cases were consistent with the Critical State Model. For the Inconel-based sample, the transport current density maps have allowed us to observe defects and determine the region that limits the current carrying capacity of the structure.
Tailoring Microstructures Under Strong Non-Equilibrium Conditions: A Feasible Path Towards High JC in Melt Textured YBa2Cu3O7
Authors: Sandiumenge Felip , Plain Jérôme , Puig Teresa , Obradors Xavier , Rabier Jacques , Martínez Maria J.
Published: April 2011

Melt textured YBa2Cu3O/Y2BaCuO5 were post processed by high oxygen pressure for different periods and temperatures. This process permits the control of the microstructure, in particular the growth and shape of the stacking faults and thereby the partial dislocation density. Analysis of the Jc(H,T) behavior allow to separate the contribution of Y2BaCuO5 interface from that of dislocations. It is shown that the in-plane partial dislocations act as point-like pinning centers increasing Jc up to 180% but this enhancement factor is counterbalanced by the effect of the stacking faults associated to the partial dislocations.
Modification of Structure and Properties of Superconducting YBaCuO Crystals by Combined Irradiations
Authors: Ibragimova Elvira M. , Kirk Marquis A.
Published: April 2011

Effects of electron irradiations in combination with 60Co gamma-quanta on magnetic properties of YBa2Cu3O7−x crystals have been studied to determine the contribution from oxygen defects to the pinning, and the condition of improving the critical parameter, Jc, of the crystals. Irradiation with 300 keV electrons followed by gamma-irradiation makes strong oxygen disorder, causing degradation of SC-transition and appearance of diamagnetic transition at 200 K, but no flux pinning in H>1 Tesla at 77 K. However, it is shown that oxygen defects do contribute substantially to the flux pinning at cation-anion defect clusters in CuO-planes created by moderate fluences of 1 MeV-electrons. A model is suggested for different oxygen and copper defects induced by the irradiations.
High Levitation Force and Trapped Field of Large Grain YBCO at 77K by Ga Doping
Authors: Zhou Yu X. , Lo Wai , Tang Tong B. , Salama Kamel
Published: April 2011

Levitation force and magnetic field trapping are the most important properties of YBCO large grain materials. They are dependent on the pinning force exerting on the magnetic flux lines by various crystal defects in YBCO. In this paper, Ga-doped bulk YBCO samples were fabricated by SmBCO seeded melt-growth process. The levitation force and trapped field were enhanced by the introduce of nanometer scale week superconducting regions which are formed by the Ga partially substituting for Cu on the Cu-O chain.
Magnetic properties of melt-textured DyBCO single domains
Authors: Vanderbemden Philippe , Ausloos Marcel , Cloots Rudi
Published: April 2011

This communication aims at reporting the superconducting properties of several bulk melt- processed DyBa2Cu3O7−x samples determined by using various measuring techniques. The original single domain material was first cut into 9 similar cubic samples which have been characterized by AC susceptibility, flux profiles and DC magnetization. The results indicate good quality melt- processed (RE)BCO materials with Tc ≈ 89 K. Next, the effect of post oxygen annealing treatments on these samples was studied. The influence of the non-uniformity of the oxygen content on the magnetic property anisotropy is discussed. Finally, additional magnetic measurements were carried out by using a couple of parallel pick-up coils wound on the same sample. From the results we conclude that geometric effects have to be taken into account in order to extract the critical current density from the magnetic properties.
Microtexture Mapping of Elecrtron Backscattered Diffraction in (Bi,Pb)2Sr2Ca2Cu3O10 Superconductor Tapes
Authors: Li Sean , Tan Thiam Teck
Published: April 2011

Grain boundaries is believed to act as weak-links limiting the critical current density (Jc) of bulk high-Tcsuperconductors. The weak-link problem can be greatly reduced by elimination or minimization of the large-angle grain boundaries. It has been reported that the Jc distribution in the transverse cross-section of (Bi,Pb)2Sr2Ca2Cu3O10+x (Bi2223) superconductor tapes follows a parabolic relationship, with the lowest currents occurring at the center of the tapes. The Jc distribution is proposed to be strongly dependent on the local crystallographic orientation distribution of the Bi2223 oxides. However, the local three dimensional crystallographic orientation distribution of Bi2223 crystals in (Bi,Pb)2Sr2Ca2Cu3O10+×superconductor tapes has not been experimentally determined yet. In this work, Electron Backscattered Diffraction technique was employed to map the crystallographic orientation of the crystals in Bi2223 superconductor tapes. From this, the misorientation of grain boundaries and also their distribution are obtained. Through crystallographic orientation mapping, the relationship of the crystallographic orientation distribution, the boundary misorientation distribution and the fabrication parameters may be understood. This can be used to optimize the fabrication processes thus increasing the critical current density in Bi2223 superconductor tapes.
Homogeneity area of Bi2Sr2CaCu2O8 - based solid solutions with substitution of alkaline earth elements by Nd and La
Authors: Veresov A.G. , Knotko A.V. , Korolyov D.V. , Garshev A.V. , Putlayev V.I.
Published: April 2011

Creation of precipitates in bulk matrix to act as pinning centres is a prospective way to improve critical current density in high temperature superconductors. It is possible to generate such precipitates via partial decomposition of the supersaturated solid solution derived from a superconducting phase. To control this process one should go by a knowledge of stability field for these solutions. The objective of present work was determination of the homogeneity area of Bi2Sr2Ca1−xRxCu2O8+d and Bi2Sr2−xCaRxCu2O8+d (R = Nd, La). Semi-quantitative XRD analysis was used to evaluate phase composition of specimens quenched from various temperatures. It was found that solubility limits of Nd and La in Bi-2212 for cases of alkaline earth element substitution by rare earth elements with smaller ionic radii (substitution Ca by Nd; Sr by Nd and La) were the same (values of x are about 0.8). These limits are determined by fraction of Cu+ ions in lattice site attributed to Cu2+. In case of substitution of Ca by La stability area of 2212 was found to be much narrower (values of x about 0.3) compared to other substitutions. One ca n deduce this fact from the difference of Ca2+ and La3+ ionic radii.
A Neutron Powder Diffraction Study of the Ferromagnetic Superconductor RuSr2(Gd1.3Ce0.7)Cu2O10-σ
Authors: Knee Christopher S. , Weller Mark T.
Published: April 2011

The temperature dependence of the crystal structure of the ferromagnetic superconductor RuSr2(160Gd1.3Ce0.7)Cu2O10-σ, which orders magnetically at TC ∼ 180 K and exhibits a Tc ∼ 30 K, has been investigated by time-of-flight neutron powder diffraction. In this system superconductivity is believed to occur in the CuO2 layers while the magnetic order is associated with the Ru moments. The tetragonal structure evolves from that of YBa2Cu3O7-σ by inserting a fluorite-type Gd1.3Ce0.7O2 layer instead of the Y ion and replacing the chain copper site with RuO6 octahedra. Rietveld analysis reveals that the basal oxygens of the RuO6 octahedra are displaced within the xy-plane to accommodate physically reasonable Ru-O in-plane bonds. These displacements are consistent with rotations of the octahedra by ∼ 15° around the c-axis. Data were collected at 40 K, 70 K, 100 K, 130 K, 150 K, 170 K 190 K and 230 K but no large structural response associated with the ferromagnetic transition is observed. A small level of oxygen deficiency within the (Gd/Ce)2O2−x, fluorite layer (x = 0.1) is detected leading to a refined stoichiometry of RuSr2(Gd1.3Ce0.7)Cu2O9.9.
Improvement in Fabrication of Hg-1223 Superconductor by Te-Doping
Authors: Yau K.K. , Lam C.C. , Shen L.J. , Li S.H.
Published: April 2011

The sealed quartz tube method is one of the usual methods used for sintering mercury-based copper oxide superconductors. By this method, precursor pellets are inserted into the quartz tube together with certain mass ratio to the reagent sample pellets for controlling the mercury vapour pressure. A certain amount of excess HgO is required to ensure the fabricated sample to have the desired composition. In our research, it was found that if a small amount of TeO2 is added and mixed with the pulverized precursor after first calcination, Hg-1223 superconductors can be fabricated without using the precursor pellet and no excess HgO is required. Thus, the fabrication process can be simplified. As mercury and its oxide are toxic, if no excess Hg is involved, it is safe and good for the laboratory-environment. In this research, some amounts of 0.10 and 0.18 wt% (weigh percentage) of TeO2 were added into the precursor, it is shown that the critical temperature of the fabricated samples is comparable to that of the undoped Hg-1223 samples. For 0.10 wt% of TeO2, the Tc of the as-synthesized sample is about 116.7 K whereas the annealed Te-doped Hg-1223 is about 134.2 K. For 0.18 wt% of TeO2, the Tc of the as- synthesized and annealed samples are 115.8 K and 134.6 K, respectively. The phase structure of samples fabricated in this research has been analyzed by the X-ray diffraction technique. It shows that the Hg-1223 phase is dominated.
Synthesis And Magnetic Properties Of Block Copolymer-CoFe2O4 Nanoclusters
Authors: Ahmed Sufi R. , Kofinas Peter
Published: April 2011

The overall goal of this research is to explore techniques for the development of novel binary magnetic oxide nanoclusters uniformly distributed within a polymer matrix. These CoFe2O4 nanoclusters were synthesized at room temperature, and are confined within the self-assembled nanoscale structure exhibited by block copolymers templates. The diblock copolymers were synthesized by ring opening metathesis polymerization of norbornene and norbornene trimethylsilane and the binary magnetic oxide was introduced through a nanoreaction scheme using wet chemical methods. Transmission electron micrographs of microtomed thin sections of these nanocomposites show that the metal oxide nanoclusters are ellipsoidal in shape and are uniformly distributed within the polymer matrix. A SQUID magnetometer was used to study the magnetic properties of the polymeric nanocomposites at applied fields up to 5 Tesla and at a temperature range between 300 °K and 5 °K. Mössbauer spectroscopy was used to study the structure of the nanoconfined metal oxide, and confirmed the synthesis of CoFe2O4 nanoclusters exhibiting an inverse spinel structure. This study provided a better understanding of the nucleation, growth and distribution of metal oxide nanoclusters within block copolymers and indicated ways to control the magnetic properties of polymeric based nanocomposite materials. The development of such binary metal oxide - block copolymer nanocomposites is targeting the functionalization of such nanostructures into magnetic device technologies.
Advanced Nanocomposite Polymer Films for Bimorphic Gas Sensors
Authors: Gerlach G. , Guenther M. , Suchaneck G. , Sahre K. , Eichhorn K.-J. , Deineka A. , Jastrabik L.
Published: April 2011

Thin films of aromatic polymers such as polyimide (PI) and polyethersulfone (PES) find an extensive use in aerospace and electronic applications, in particular, as sensitive to moisture and gas uptake layers for bimorphic sensors. In this work, a complex investigation of the film composition, microstructure and physical properties of ion beam modified polymer films was carried out to optimize the moisture uptake. To modify thin films of polyimide and polyethersulfone 50, 130 and 180 keV boron ions with irradiation doses between 1013 and 1016 B+/cm2 were implanted. It could be shown, that partly destruction of chemical bonding under ion bombardment leads to the creation of new amorphous and graphite-like structures, which increase the modified surface film conductivity by several orders of magnitude and enhances the sensitivity of these nanocomposite films to moisture uptake.