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Sample records for bicrystals

  1. Shot noise in YBCO bicrystal Josephson junctions

    DEFF Research Database (Denmark)

    Constantinian, K.Y.; Ovsyannikov, G.A.; Borisenko, I.V.;

    2003-01-01

    We measured spectral noise density in YBCO symmetric bicrystal Josephson junctions on sapphire substrates at bias voltages up to 100 mV and T 4.2 K. Normal state resistance of the Josephson junctions, R-N = 20-90 Omega and ICRN up to 2.2 mV have been observed in the experimental samples. Noise...

  2. Recrystallization at grain boundaries in deformed copper bicrystals

    NARCIS (Netherlands)

    Heller, H.W.F.; Verbraak, C.A.; Kolster, B.H.

    1984-01-01

    The role of specific grain boundaries in the nucleation of recrystallization textures is demonstrated by experiments on copper bicrystals. It is deduced that the major part of the recrystallized grains that have nucleated at the grain boundary can be traced back to having nucleated in {100} <001>, {

  3. TEM and SEM (EBIC) investigations of silicon bicrystals

    Science.gov (United States)

    Gleichmann, R.; Ast, D. G.

    1983-01-01

    The electrical and structural properties of low and medium angle tilt grain boundaries in silicon bicrystals were studied in order to obtain insight into the mechanisms determining the recombination activity. The electrical behavior of these grain boundaries was studied with the EBIC technique. Schottky barriers rather than p-n junctions were used to avoid annealing induced changes of the structure and impurity content of the as-grown crystals. Transmission electron spectroscopy reveals that the 20 deg boundary is straight, homogeneous, and free of extrinsic dislocations. It is concluded that, in the samples studied, the electrical effect of grain boundaries appears to be independent of the boundary misorientation. The dominant influence appears to be impurity segregation effects to the boundary. Cleaner bicrystals are required to study intrinsic differences in the electrical activity of the two boundaries.

  4. STRESS DISTRIBUTION NEAR GRAIN BOUNDARY IN ANISOTROPIC BICRYSTALS AND TRICRYSTALS

    Institute of Scientific and Technical Information of China (English)

    万建松; 岳珠峰

    2004-01-01

    The rate dependent crystallographic finite element program was implemented in ABAQUS as a UMAT for the analysis of the stress distributions near grain boundary in anisotropic bicrystals and tricrystals, taking the different crystallographic orientations into consideration. The numerical results of bicrystals model with the different crystallographic orientations shows that there is a high stress gradient near the grain boundaries. The characteristics of stress structures are dependent on the crystallographic orientations of the two grains. The existing of triple junctions in the tricrystals may result in the stress concentrations, or may not, depending on the crystallographic orientations of the three grains. The conclusion shows that grain boundary with different crystallographic orientations can have different deformation, damage, and failure behaviors. So it is only on the detail study of the stress distribution can the metal fracture be understood deeply.

  5. A TEM and DLTS study of a near. Sigma. 25 CdTe bicrystal

    Energy Technology Data Exchange (ETDEWEB)

    Wang, N.; Haasen, P. (Inst. fuer Metallphysik, Univ. Goettingen (Germany))

    1991-11-16

    Cadmium precipitates are observed at the grain boundary (GB) of a CdTe bicrystal by means of transmission electron microscopy (TEM). In a simple model based on the theory of electron hopping, electrons can be excited by thermal activation and flow from boundary states to precipitates in the boundary. This model gives, in particular, a simple explanation for the emission properties of the precipitates, as determined by deep-level-transient spectroscopy (DLTS) on the bicrystal. (orig.).

  6. Influence of Grain Boundary on Fatigue Behavior of Ni-base Bicrystals

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    The influence of the grain boundary on the fatigue behavior was studied by two three-point-bending (TPB) specimens.One TPB specimen was named Bicrystal 1, whose pre-crack was along the grain boundary and the applied loadparalleled to pre-crack direction, while the other TPB specimen was named Bicrystal 2, whose the pre-crack wasperpendicular to the grain boundary and the applied load paralleled also to the pre-crack. It was found that the rateof the fatigue crack growth of Bicrystal 1 was about a tenfold higher than that of Bicrystal 2. The fatigue behaviorof Bicrystal 2 specimens was dependent on the distance between the crack tip and grain boundary. The crack growthrate was highest when the crack tip was at a critical distance to the grain boundary, while the rate was the lowestwhen the crack tip reached grain boundary. After the crack was over the grain boundary, the crack growth rateincreased. The crystallographic finite element method was applied to analyze the stress and strain structure aheadof the crack, in order to reveal the above characteristics of the fatigue behavior. It is the grain boundary-inducedredistribution of stresses near the crack tip that induces the difference of fatigue behavior.

  7. Low voltage excess noise and shot noise in YBCO bicrystal junctions

    DEFF Research Database (Denmark)

    Constantinian, K.Y.; Ovsyannikov, G.A.; Borisenko, I.V.;

    2002-01-01

    The spectral density of background noise emitted by symmetric bicrystal YBaCuO Josephson junctions on sapphire substrates have been measured by a low noise cooled HEMT amplifier for bias voltages up to V approximate to 50 mV. At relatively low voltages V <4 mV a noticeable noise rise has been reg...

  8. Experimental study of noise and Josephson oscillation linewidths in bicrystal YBCO junctions

    DEFF Research Database (Denmark)

    Constatinian, K.Y.; Ovsyannikov, G.A.; Borisenko, I.V.;

    2001-01-01

    The intensities of the noise in a bicrystal high-T-c (HTS) Josephson junction have been precision-measured at 1-2 GHz frequency band at bias voltages up to 50 mV at T = 4.2 K. At large bias voltages, V > 30 mV, the dependence of current noise density was found exactly coinciding with the Schottky...

  9. Preparation and photocatalytic activity of bicrystal phase TiO2 nanotubes containing TiO2-B and anatase

    Science.gov (United States)

    Huang, Chuanxi; Zhu, Kerong; Qi, Mengyao; Zhuang, Yonglong; Cheng, Chao

    2012-06-01

    Bicrystal phase TiO2 nanotubes (NTS) containing monoclinic TiO2-B and anatase were prepared by the hydrothermal reaction of anatase nanoparticles with NaOH aqueous solution and a heat treatment. Their structure was characterized by XRD, TEM and Raman spectra. The results showed that the bicrystal phase TiO2 NTS were formed after calcining H2Ti4O9·H2O NTS at 573 K. The bicrystal phase TiO2 NTS exhibit significantly higher photocatalytic activity than the single phase anatase NTS and Dessuga P-25 nanoparticles in the degradation of Methyl Orange aqueous solution under ultraviolet light irradiation, which is attributed to the large surface and interface areas of the bicrystal phase TiO2 NTS.

  10. Fabrication of ZnO Bi-crystals with twist boundaries using Co doped ZnO single crystals

    CERN Document Server

    Ohashi, N; Ohgaki, T; Tsurumi, T; Fukunaga, O; Haneda, H; Tanaka, J

    1999-01-01

    Zn O single crystals doped with Co were grown by using a flux method and their electrical properties were investigated by Hall effect. Then, these crystals were polished with diamond paste and bonded to form bi-crystal by hot pressing under a pressure of 10 MPa at 1000 .deg. C. The bi-crystals showed nonlinear I-V curves, and the curvature of I-V relation agreed with that for Co-doped polycrystalline ZnO.

  11. Systematic study of grain boundary atomistic structures and related properties in cubic zirconia bicrystals

    Energy Technology Data Exchange (ETDEWEB)

    Shibata, N.; Ikuhara, Y. [Inst. of Engineering Innovation, Univ. of Tokyo, Tokyo (Japan); Oba, F. [Dept. of Materials Science and Engineering, Graduate School of Engineering, Kyoto Univ., Kyoto (Japan); Yamamoto, T. [Dept. of Advanced Materials Science, Graduate School of Frontier Science, Univ. of Tokyo, Kashiwa, Chiba (Japan)

    2005-02-01

    Systematic grain boundary study of cubic zirconia has been conducted by using bicrystals. It is clearly demonstrated that grain boundary atomistic structures dramatically change according to the misorientations and plane orientations of the boundaries, resulting in a dramatic change of excess energies and solute segregation behaviors. Combining with theoretical calculations, it is found that grain boundaries possess unique coordination-deficient cation sites at the cores, and their densities have a clear correlation with these properties in high-angle grain boundaries. This result indicates that grain boundary properties in ceramics are possibly determined by the accumulation of coordination-deficient sites. Thus, systematic grain boundary study using bicrystal offers fundamental understandings of the relationship between atomistic structures and properties in ceramic grain boundaries. (orig.)

  12. Grain Boundary Relaxation in Bi-Crystals: Mechanical Spectroscopy and Molecular Dynamics Simulations

    Directory of Open Access Journals (Sweden)

    Maier A.-K.

    2015-04-01

    Full Text Available Different Au-Ag-Cu samples have been studied by mechanical spectroscopy. Both polycrystals and bi-crystals show a relaxation peak at 800 K, accompanied by an elastic modulus change. Since this peak is absent in single crystals it is related to the presence of grain boundaries. Molecular dynamics simulations reveal two microscopic mechanisms, when a shear stress is applied onto a Σ5 grain boundary: at 700 K, the boundary migrates perpendicularly to the boundary plane under an external stress. At 1000 K, only sliding at the boundary is observed. These two mechanisms acting in different temperature intervals are used to model the mechanic response of a polycrystal under an applied stress. The models yield expressions for the relaxation strength Δ and for the relaxation time τ as a function of the grain size. A comparison with the mechanical spectroscopy measurements of polycrystals and the bi-crystals show that the grain boundary sliding model reproduces correctly the characteristics of the grain boundary peak.

  13. Domain walls in Fe(001) bicrystals-thickness dependence and field-induced transitions

    Energy Technology Data Exchange (ETDEWEB)

    Hanson, M. [Department of Applied physics, Chalmers University of Technology, SE-412 96 Goeteborg (Sweden)]. E-mail: maj.hanson@fy.chalmers.se; Brucas, R. [Department of Applied physics, Chalmers University of Technology, SE-412 96 Goeteborg (Sweden)

    2007-03-15

    Magnetic domain walls (DW's) formed at the grain boundary (GB) of epitaxial bicrystal Fe(001) films, thickness t=50 and 70nm, were studied by magnetic force microscopy. The 'as-grown' samples displayed DW's with different magnetic contrast profiles yielding a single peak for t=50nm and a double peak with a change of sign at the centre of the wall for t=70nm. For t=50nm the wall is characterised as an asymmetric Bloch wall. The double peak of the 70nm thick film transformed into a single peak characteristic for a charged wall, when a field of 30mT was applied along the GB. At remanence this domain wall relaxed to a regular Bloch wall divided into segments of alternating signs.

  14. The 0 and pi contact array model of bicrystal junctions and interferometers

    DEFF Research Database (Denmark)

    Kornev, Victor K.; Soloviev, Igor I.; Klenov, Nikolai V.;

    2003-01-01

    simulation of the lumped Josephson junction circuits, e.g., PSCAN, WinS. The based on the model results for critical current dependence on applied magnetic field are compared with experimental data for the bicrictal junctions fabricated by dc sputtering at high pressure. Impact of no sinusoidal Josephson......The array model of the faceted bicrystal Josephson junctions has been developed more comprehensively. The facet size and the facet critical current dependence on. magnetic field are taken in to consideration. The model can be successfully used with high-performance software meant for numerical...... current-phase relation on the dc interferometer critical current as a function of magnetic field is analyzed as well....

  15. Study of magnetoresistance and conductance of bicrystal grain boundary in La0.67Ba0.33MnO3 thin film

    Indian Academy of Sciences (India)

    Neeraj Khare; A K Gupta; U P Moharil; A K Raychaudhuri; S P Pai; R Pinto

    2002-05-01

    La0.67Ba0.33MnO3 (LBMO) thin film is deposited on a $36.7°C SrTiO3 bicrystal substrate using laser ablation technique. A microbridge is created across bicrystal grain boundary and its characteristics are compared with a microbridge on the LBMO film having no grain boundary. Presence of grain boundary exhibits substantial magnetoresistance ratio (MRR) in the low field and low temperature region. Bicrystal grain boundary contribution in MRR disappears at temperature > 175 K. At low temperature, - characteristic of the microbridge across bicrystal grain boundary is nonlinear. Analysis of temperature dependence of dynamic conductance–voltage characteristics of the bicrystal grain boundary indicates that at low temperatures ( < 175$ K) carrier transport across the grain boundary in LBMO film is dominated by inelastic tunneling via pairs of manganese atoms and tunneling through disordered oxides. At higher temperatures ( > 175 K), magnetic scattering process is dominating. Decrease of bicrystal grain boundary contribution in magnetoresistance with the increase in temperature is due to enhanced spin-flip scattering process.

  16. Tl2Ba2CaCu2Ox Bicrystal Junction DC-SQUID Magnetometers Operating in Unshielded Environment

    Institute of Scientific and Technical Information of China (English)

    HAN Bing; CHEN Geng-Hua; CHEN Geng-Hua; ZHAO Shi-Ping; YANG Qian-Sheng; YAN Sha-Lin; LU Rong-Tao

    2000-01-01

    We fabricated direct-current superconducting quantum interference device magnetometers with single layer epitaxial Tl2Ba2CaCu2Ox films on 36.8°SrTiO3 bicrystal substrates. The white flux noise and the field-flux transformation coeficient of the devices are 1.5×10-5 φ0(/Hz) and 40 nT/φ0, respectively. The magnetometers can work in unshielded environment.

  17. Influence of twist angle on crack propagation of nanoscale bicrystal nickel film based on molecular dynamics simulation

    Science.gov (United States)

    Zhang, Yanqiu; Jiang, Shuyong; Zhu, Xiaoming; Zhao, Yanan

    2017-03-01

    Tensile deformation of nanoscale bicrystal nickel film with twist grain boundary, which includes various twist angles, is investigated via molecular dynamics simulation to obtain the influence of twist angle on crack propagation. The twist angle has a significant influence on crack propagation. At the tensile strain of 0.667, as for the twist angles of 0°, 3.54° and 7.05°, the bicrystal nickel films are subjected to complete fracture, while as for the twist angles of 16.1° and 33.96°, no complete fracture occurs in the bicrystal nickel films. When the twist angles are 16.1° and 33.96°, the dislocations emitted from the crack tip are almost unable to go across the grain boundary and enter into the other grain along the slip planes {111}. There should appear a critical twist angle above which the crack propagation is suppressed at the grain boundary. The higher energy in the grain boundary with larger twist angle contributes to facilitating the movement of the glissile dislocation along the grain boundary rather than across the grain boundary, which leads to the propagation of the crack along the grain boundary.

  18. Atomic and electronic structure of Lomer dislocations at CdTe bicrystal interface.

    Science.gov (United States)

    Sun, Ce; Paulauskas, Tadas; Sen, Fatih G; Lian, Guoda; Wang, Jinguo; Buurma, Christopher; Chan, Maria K Y; Klie, Robert F; Kim, Moon J

    2016-06-03

    Extended defects are of considerable importance in determining the electronic properties of semiconductors, especially in photovoltaics (PVs), due to their effects on electron-hole recombination. We employ model systems to study the effects of dislocations in CdTe by constructing grain boundaries using wafer bonding. Atomic-resolution scanning transmission electron microscopy (STEM) of a [1-10]/(110) 4.8° tilt grain boundary reveals that the interface is composed of three distinct types of Lomer dislocations. Geometrical phase analysis is used to map strain fields, while STEM and density functional theory (DFT) modeling determine the atomic structure at the interface. The electronic structure of the dislocation cores calculated using DFT shows significant mid-gap states and different charge-channeling tendencies. Cl-doping is shown to reduce the midgap states, while maintaining the charge separation effects. This report offers novel avenues for exploring grain boundary effects in CdTe-based solar cells by fabricating controlled bicrystal interfaces and systematic atomic-scale analysis.

  19. Grain boundary structure and solute segregation in titanium-doped sapphire bicrystals

    Energy Technology Data Exchange (ETDEWEB)

    Taylor, Seth T.

    2002-05-17

    Solute segregation to ceramic grain boundaries governs material processing and microstructure evolution, and can strongly influence material properties critical to engineering performance. Understanding the evolution and implications of grain boundary chemistry is a vital component in the greater effort to engineer ceramics with controlled microstructures. This study examines solute segregation to engineered grain boundaries in titanium-doped sapphire (Al2O3) bicrystals, and explores relationships between grain boundary structure and chemistry at the nanometer scale using spectroscopic and imaging techniques in the transmission electron microscope (TEM). Results demonstrate dramatic changes in solute segregation stemming from small fluctuations in grain boundary plane and structure. Titanium and silicon solute species exhibit strong tendencies to segregate to non-basal and basal grain boundary planes, respectively. Evidence suggests that grain boundary faceting occurs in low-angle twis t boundaries to accommodate nonequilibrium solute segregation related to slow specimen cooling rates, while faceting of tilt grain boundaries often occurs to expose special planes of the coincidence site lattice (CSL). Moreover, quantitative analysis of grain boundary chemistry indicates preferential segregation of charged defects to grain boundary dislocations. These results offer direct proof that static dislocations in ionic materials can assume a net charge, and emphasize the importance of interactions between charged point, line, and planar defects in ionic materials. Efforts to understand grain boundary chemistry in terms of space charge theory, elastic misfit and nonequilibrium segregation are discussed for the Al2O3 system.

  20. Effect of twin boundary on nanoimprint process of bicrystal Al thin film studied by molecular dynamics simulation

    Institute of Scientific and Technical Information of China (English)

    谢月红; 徐建刚; 宋海洋; 张云光

    2015-01-01

    The effects of twin boundary (TB) on the mechanical properties of two types of bicrystal Al thin films during the nanoimprint process are investigated by using molecular dynamics simulations. The results indicate that for the TB direction parallel to the imprinting direction, the yield stress reaches the maximum for the initial dislocation nucleation when the mould directly imprints to the TB, and the yield stress first decreases with the increase of the marker interval and then increases. However, for the TB direction perpendicular to the imprinting direction, the effect of the TB location to the imprinting forces is very small, and the yield stress is greater than that with the TB direction parallel to the imprinting direction. The results also demonstrate that the direction of the slip dislocations and the deformation of the thin film caused by spring-back are different due to various positions and directions of the TB.

  1. Combined measurement of surface, grain boundary and lattice diffusion coefficients on olivine bi-crystals

    Science.gov (United States)

    Marquardt, Katharina; Dohmen, Ralf; Wagner, Johannes

    2014-05-01

    Diffusion along interface and grain boundaries provides an efficient pathway and may control chemical transport in rocks as well as their mechanical strength. Besides the significant relevance of these diffusion processes for various geologic processes, experimental data are still very limited (e.g., Dohmen & Milke, 2010). Most of these data were measured using polycrystalline materials and the formalism of LeClaire (1951) to fit integrated concentration depth profiles. To correctly apply this formalism, certain boundary conditions of the diffusion problem need to be fulfilled, e.g., surface diffusion is ignored, and furthermore the lattice diffusion coefficient has to be known from other studies or is an additional fitting parameter, which produces some ambiguity in the derived grain boundary diffusion coefficients. We developed an experimental setup where we can measure the lattice and grain boundary diffusion coefficients simultaneously but independent and demonstrate the relevance of surface diffusion for typical grain boundary diffusion experiments. We performed Mg2SiO4 bicrystal diffusion experiments, where a single grain boundary is covered by a thin-film of pure Ni2SiO4 acting as diffusant source, produced by pulsed laser deposition. The investigated grain boundary is a 60° (011)/[100]. This specific grain boundary configuration was modeled using molecular dynamics for comparison with the experimental observations in the transmission electron microscope (TEM). Both, experiment and model are in good agreement regarding the misorientation, whereas there are still some disagreements regarding the strain fields along the grain boundary that are of outmost importance for the strengths of the material. The subsequent diffusion experiments were carried out in the temperature range between 800° and 1450° C. The inter diffusion profiles were measured using the TEMs energy dispersive x-ray spectrometer standardized using the Cliff-Lorimer equation and EMPA

  2. Millimeter wave inducing subharmonic steps in the Tl2Ba2CaCu2O8 thin film bicrystal Josephson junction

    Science.gov (United States)

    Liu, X.; Hu, L.; Xie, W.; Wang, P.; Ma, L. J.; Zhao, X. J.; He, M.; Zhang, X.; Ji, L.

    2015-04-01

    The bicrystal Josephson junction (BJJ) was fabricated by patterning microbridge into Tl2Ba2CaCu2O8 (Tl-2212) thin film grown epitaxially on the bicrystal SrTiO3 (STO) substrate. The millimeter wave responses of BJJ were researched by experiment and numerical simulation. Shapiro steps and subharmonic steps were both observed in the current-voltage (I-V) curve at the liquid nitrogen temperature. In the resistive-capacitive-inductive shunted junction (RCLSJ) model, both of the Shapiro steps and subharmonic steps were reproduced with varying capacitances and inductances. The result of simulation has a good agreement with the experiment. The relative large capacitance and inductance correspond to distinct subharmonic steps.

  3. Critical current density behaviors across a grain boundary inclined to current with different angles in YBa2Cu3O7-δ bicrystal junctions

    Science.gov (United States)

    Tao, Hua; Wei-Wei, Xu; Zheng-Ming, Ji; Da-Yuan, Guo; Qing-Yun, Wang; Xiang-Rong, Ma; Rui-Yu, Liang

    2016-06-01

    The critical current density behaviors across a bicrystal grain boundary (GB) inclined to the current direction with different angles in YBa2Cu3O7-δ bicrystal junctions in magnetic fields are investigated. There are two main reasons for the difference in critical current density in junctions at different GB inclined angles in the same magnetic field: (i) the GB plane area determines the current carrying cross section; (ii) the vortex motion dynamics at the GB affects the critical current value when the vortex starts to move along the GB by Lorentz force. Furthermore, the vortex motion in a bicrystal GB is studied by investigating transverse (Hall) and longitudinal current-voltage characteristics (I-V xx and I-V xy ). It is found that the I-V xx curve diverges from linearity at a high driving current, while the I-V xy curve keeps nearly linear, which indicates the vortices inside the GB break out of the GB by Lorentz force. Project supported by the National Natural Science Foundation of China (Grant Nos. 61501222, 61371036, and 61571219) and the School Scientific Research Fund of Nanjing Institute of Technology, China (Grant Nos. YKJ201418).

  4. Electromagnetic characterization of YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} thin films with calcium doping for bi-crystal grain boundary conductivity enhancement

    Energy Technology Data Exchange (ETDEWEB)

    Kleismit, Richard A; Kozlowski, Gregory [Physics Department, Wright State University, Dayton, OH 45435 (United States); Campbell, Angela L; Haugan, Timothy J; Biggers, Rand R; Maartense, Iman; Barnes, Paul L; Peterson, Timothy L [Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright-Patterson AFB, OH 45433 (United States); Hopkins, Simon C [Department of Materials Science and Metallurgy, University of Cambridge, Pembroke Street, Cambridge CB2 3QZ (United Kingdom)], E-mail: gregory.kozlowski@wright.edu, E-mail: gk286@cam.ac.uk

    2008-03-01

    The objective of this study was to examine the transport properties of two YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} thin films with (Y{sub 0.9}Ca{sub 0.1}){sub 2}BaCuO{sub 5} additions deposited on vicinal SrTiO{sub 3} 6{sup 0} bi-crystal substrates and to investigate the possible correlations between spatial calcium distribution and local electromagnetic properties across bi-crystal grain boundaries using evanescent microwave microscopy (EMM) and atomic force microscopy (AFM). The samples under consideration differed in transport critical current measurements by a factor of two although they were deposited on the same type of bi-crystal substrate. A near-field evanescent microwave microscope based on a coaxial transmission line resonator with an end-wall aperture was used to measure changes in conductivity local to the bi-crystal boundary of YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} thin films below (79.2 K) and above (room temperature) the superconducting transition temperature. Atomic concentration measurements by electron microprobe analysis were performed in the same regions, and a clear correlation between calcium distribution and conductivity at 79.2 K (as represented by the change in quality factor) was found. Surface potential imaging (SPI) and quality factor scans in the area of the bi-crystal grain boundaries were performed at room temperature using AFM and EMM, respectively, to evaluate local electromagnetic properties in the normal state and investigate their correlation with superconducting properties.

  5. DISLOCATIONS MOBILITY UNDER THE IMAGE FORCE EFFECT IN BICRYSTALS OF CFC MATERIALS: CU-X, X = PB, AL, AU, AG AND NI

    Directory of Open Access Journals (Sweden)

    A OUCHTATI

    2015-06-01

    Full Text Available The image force undergone by a matrix dislocations close and parallel to an interphase boundary is studied in Cu-X bicrystals (with X = Pb, Al, Au, Ag, Ni for disorientations ranging between 0° and 90°.  Dislocations have a Burgers vector  = a/2 [110]. The elastic energy of dislocation-boundary interaction is calculated within the framework of anisotropic linear elasticity. The elastic energy is related to the difference of the two metals shear moduli. It is about a few hundred pico Joule per meter. The image force can be repulsive or attractive according to the sign and the intensity of shear moduli difference. The isoenergy maps have various symmetries according to the disorientation.

  6. YBa2Cu3O7-δ long Josephson junctions on bicrystal Zr1-xYxO2 substrates fabricated by preliminary topology masks

    Science.gov (United States)

    Masterov, D. V.; Parafin, A. E.; Revin, L. S.; Chiginev, A. V.; Skorokhodov, E. V.; Yunin, P. A.; Pankratov, A. L.

    2017-02-01

    YBa2Cu3O{}7-δ (YBCO) films were fabricated by magnetron sputtering with modification of the substrate surface by preliminary topology masks. Formation features of Josephson junctions on bicrystal Zr1-xYxO2 (YSZ) substrates have been considered. The structural and electrical properties of such junctions were investigated. As a result, the presented technology allows us to fabricate YBCO structures on YSZ substrates with a buffer cerium dioxide (CeO2) layer where YBCO film sputtering is the final stage of structure formation. In particular, long Josephson junctions with good characteristics have been fabricated by this technology and measured, allowing us to achieve critical currents of 80 mA for 150 um junctions.

  7. Millimeter wave inducing subharmonic steps in the Tl{sub 2}Ba{sub 2}CaCu{sub 2}O{sub 8} thin film bicrystal Josephson junction

    Energy Technology Data Exchange (ETDEWEB)

    Liu, X.; Hu, L.; Xie, W. [College of Electronic Information and Optical Engineering, Nankai University, Tianjin 300071 (China); Wang, P. [Beijing Institute of Radio Measurement, Beijing 100854 (China); Ma, L.J.; Zhao, X.J.; He, M. [College of Electronic Information and Optical Engineering, Nankai University, Tianjin 300071 (China); Zhang, X., E-mail: nkzhangxu@nankai.edu.cn [College of Electronic Information and Optical Engineering, Nankai University, Tianjin 300071 (China); Ji, L. [College of Electronic Information and Optical Engineering, Nankai University, Tianjin 300071 (China)

    2015-04-15

    Highlights: • We observed the subharmonic steps based on Tl{sub 2}Ba{sub 2}CaCu{sub 2}O{sub 8} (Tl-2212) film which epitaxial grown on bicrystal SrTiO{sub 3} (STO) substrate. • The simulation of the RCLSJ model matched up well with the experimental results. • The dI/dV–V curves highlight the subharmonic steps. - Abstract: The bicrystal Josephson junction (BJJ) was fabricated by patterning microbridge into Tl{sub 2}Ba{sub 2}CaCu{sub 2}O{sub 8} (Tl-2212) thin film grown epitaxially on the bicrystal SrTiO{sub 3} (STO) substrate. The millimeter wave responses of BJJ were researched by experiment and numerical simulation. Shapiro steps and subharmonic steps were both observed in the current–voltage (I–V) curve at the liquid nitrogen temperature. In the resistive–capacitive–inductive shunted junction (RCLSJ) model, both of the Shapiro steps and subharmonic steps were reproduced with varying capacitances and inductances. The result of simulation has a good agreement with the experiment. The relative large capacitance and inductance correspond to distinct subharmonic steps.

  8. How grain boundaries affect the efficiency of poly-CdTe solar-cells: A fundamental atomic-scale study of grain boundary dislocation cores using CdTe bi-crystal thin films.

    Energy Technology Data Exchange (ETDEWEB)

    Klie, Robert [Univ. of Illinois, Chicago, IL (United States)

    2016-10-25

    It is now widely accepted that grain boundaries in poly-crystalline CdTe thin film devices have a detrimental effect on the minority carrier lifetimes, the open circuit voltage and therefore the overall solar-cell performance. The goal of this project was to develop a fundamental understanding of the role of grain boundaries in CdTe on the carrier life-time, open-circuit voltage, Voc, and the diffusion of impurities. To achieve this goal, i) CdTe bi-crystals were fabricated with various misorientation angels, ii) the atomic- and electronic structures of the grain boundaries were characterized using scanning transmission electron microscopy (STEM), and iii) first-principles density functional theory modeling was performed on the structures determined by STEM to predict the grain boundary potential. The transport properties and minority carrier lifetimes of the bi-crystal grain boundaries were measured using a variety of approaches, including TRPL, and provided feedback to the characterization and modeling effort about the effectiveness of the proposed models.

  9. Electric characterization of grain boundaries in ionic conductors by impedance spectroscopy measurements in a bicrystal; Caracterizacion electrica de fronteras de grano en conductores ionicos mediante medidas de espectroscopia de impedancias en un bicristal

    Energy Technology Data Exchange (ETDEWEB)

    Frechero, M. A.; Rocci Riner Schmidt, M.; Diaz-Guillen, M.; Doaz-Guillen, M. R.; Dura, O.; Rivera-Calzada, A.; Santamaria, J.; Leon, C.

    2012-07-01

    Here we show impedance spectroscopy measurements on a bicrystal of the ionically conducting Yttria stabilized zirconia (YSZ). By using micrometer sized electrodes it is possible to measure ionic transport perpendicular to a single grain boundary, and characterize its electrical properties. We are thus able to obtain the microscopic parameters that determine the charge distribution at the grain boundary and the ionic transport through it, as the potential energy barrier {delta}{phi} = 0.35{+-}0.01 V at 275 degree centigrade, and the space charge layer thickness {lambda} = 5{+-}1 A. These values are significantly different from those previously obtained in polycrystalline ceramic samples of the same material, and show much better agreement with the values predicted by the Mott-Schottky model for the charge distribution and ionic transport through the grain boundary. (Author) 31 refs.

  10. High-temperature superconducting YBCO dc SQUID gradiometers fabricated on STO bicrystal substrates

    Energy Technology Data Exchange (ETDEWEB)

    Carr, C.; Eulenburg, A.; Romans, E.J.; Pegrum, C.M.; Donaldson, G.B. [Department of Physics and Applied Physics, University of Strathclyde, Glasgow (United Kingdom)

    1998-11-01

    HTS dc gradiometers have been fabricated with slots and flux dams in their SQUID washers. Using a single layer of YBCO, the gradient sensitivity is limited by the sensing magnetometer in the centre of the structure. The spatial response of such devices has been measured experimentally indicating that single layer devices, in terms of gradient sensitivity, have characteristics that deviate slightly from idealized first order gradiometers. The flux noise of these devices is discussed with particular emphasis on their unshielded low frequency noise properties. We also discuss the effect of different cooldown procedures on the flux noise. (author)

  11. Observation of distinct, temperature dependent flux noise near bicrystal grain boundaries in YBa2Cu3O7-x films

    DEFF Research Database (Denmark)

    Bukh, K. R.; Jacobsen, Claus Schelde; Hansen, Jørn Bindslev;

    2000-01-01

    The characteristics of the magnetic flux noise in high temperature superconducting thin-films of yttrium-barium-copper-oxide (YBa2Cu3O7) in the vicinity of artificial grain boundaries have been studied by means of a low critical temperature superconducting quantum interference device (SQUID...

  12. Incipient plasticity during nanoindentation at grain boundaries in body-centered cubic metals

    NARCIS (Netherlands)

    Soer, WA; Aifantis, KE; De Hosson, JTM

    2005-01-01

    The mechanical response to nanoinclentation near grain boundaries has been investigated in an Fe-14%Si bicrystal with a general grain boundary and two Mo bicrystals with symmetric tilt boundaries, In particular, the indentations performed on the Fe-14%Si show that as the grain boundary is approached

  13. The roles of slip geometry and hardening behavior in intergranular toughness

    Energy Technology Data Exchange (ETDEWEB)

    Laird, C.; Bassani, J.

    1992-09-01

    Research is reported in the following areas: cyclic response of polycrystalline Cu, bicrystal experiments and boundary theory, interfacial discontinuities, shear localization in single crystals, coarse slip bands, and macroscopic shear bands.

  14. Characteristics of Off-Chip Millimeter-Wave Radiation from Serial Josephson Junction Arrays

    Institute of Scientific and Technical Information of China (English)

    WANG Zheng; FAN Bin; ZHAO Xin-Jie; YUE Hong-Wei; HE Ming; JI Lu; YAN Shao-Lin; FANG Lan; Klushin A. M.

    2011-01-01

    @@ We investigate the self-emissions from serial high-temperature superconductor bicrystal Josephson junction ar- rays embedded in a quasi-optical resonator.A bicrystal substrate is used as a dielectric resonator antenna, which increases the coupling strength between the junction array and the electromagnetic (EM) wave.Both three-dimension (3D) electromagnetic simulations and experiments are performed.Strong ofT-chip radiations axe measured from the junction array at 78 GHz and 78 K.The proposed method and the experimental results are important for millimeter wave applications in junction arrays.

  15. Harmonic frequency mixing using high Tc superconductor Josephson junction mounted on pulse tube cryocooler

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    A frequency mixing system including microwave coupling and intermediate frequency (IF) measurement arrangements is esigned. In lieu of liquid nitrogen, a pulse tube cryocooler is used to cool the whole system. With YBa2Cu3O7/Yttrium stabilized irconia (YBCO/YSZ) bicrystal Josephson junction as the mixing element, 36th harmonic frequency mixing at the 8 mm waveband is obtained.

  16. HTS dc SQUID based rf amplifier: development concept

    DEFF Research Database (Denmark)

    Prokopenko, G.V.; Shitov, S.V.; Borisenko, I.V.;

    2002-01-01

    We present a concept of a rf amplifier based on a directly coupled dc SQUID with bicrystal junctions, which have high saturation power and can be used with SIS mixers or possibly for satellite and cellular phone communications. A novel input resonant circuit is proposed using single layer of HTS...

  17. Fraunhofer regime of operation for superconducting quantum interference filters

    DEFF Research Database (Denmark)

    Shadrin, A.V.; Constantinian, K.Y.; Ovsyannikov, G.A.;

    2008-01-01

    Series arrays of superconducting quantum interference devices (SQUIDs) with incommensurate loop areas, so-called superconducting quantum interference filters (SQIFs), are investigated in the kilohertz and the gigahertz frequency range. In SQIFs made of high-T-c bicrystal junctions the flux-to-vol...

  18. Comparison of effective noise temperatures in YBa2BCu3O7-δ junctions

    DEFF Research Database (Denmark)

    Fischer, Gerd Michael; Mygind, Jesper; Pedersen, Niels Falsig

    1997-01-01

    The dc voltage response to 70 GHz radiation was measured for YBCO bicrystal junctions, step edge junctions and ramp edge junctions at temperatures from 4 K to 90 K. Employing the RSJ-model and assuming thermal noise, the Josephson radiation is about equal to the voltage difference of the voltage ...

  19. Magnetic properties of bi-, tri- and multicrystals of 3D topological insulator Bi{sub 1−x}–Sb{sub x}(0.06⩽x⩽0.2)

    Energy Technology Data Exchange (ETDEWEB)

    Muntyanu, F.M. [Institute of Electronic Engineering and Industrial Technologies, Academy of Sciences of Moldova, Chisinau 2028 (Moldova, Republic of); International Laboratory of High Magnetic Fields and Low Temperatures, Wroclaw 53421 (Poland); Gilewski, A., E-mail: andrzej.gilewski@ml.pan.wroc.pl [International Laboratory of High Magnetic Fields and Low Temperatures, Wroclaw 53421 (Poland); Nenkov, K. [International Laboratory of High Magnetic Fields and Low Temperatures, Wroclaw 53421 (Poland); Leibniz-Institut fur Festkorper und Werkstofforschung, Dresden 01171 (Germany); Rogacki, K. [International Laboratory of High Magnetic Fields and Low Temperatures, Wroclaw 53421 (Poland); Institute of Low Temperatures and Structural Research, Polish Academy of Sciences, Wroclaw 50950 (Poland); Zaleski, A.J. [Institute of Low Temperatures and Structural Research, Polish Academy of Sciences, Wroclaw 50950 (Poland); Fuks, G. [International Laboratory of High Magnetic Fields and Low Temperatures, Wroclaw 53421 (Poland); Leibniz-Institut fur Festkorper und Werkstofforschung, Dresden 01171 (Germany); Chistol, V. [Technical University of Moldova, Chisinau 2004 (Moldova, Republic of)

    2014-03-01

    The magnetic properties of bi-, tri- and multicrystals of 3D topological insulator Bi{sub 1−x}Sb{sub x}(0.06bicrystals are identified. It has been found that due to the different stress structure the transition temperature T{sub c} for one superconducting phase changes considerably, from 8.3 to 36 K, while for another superconducting phase, T{sub c} remains within the range 3.7–4.6 K. In tricrystals and bicrystals with high contents of structural disorder and topological defects, ferromagnetic hysteresis loops and magnetic field expulsion have been observed simultaneously.

  20. Hierarchically-Driven Approach for Quantifying Fatigue Crack Initiation and Short Crack Growth Behavior in Aerospace Materials

    Science.gov (United States)

    2016-08-31

    density functional theory (DFT) [11,12] as implemented in the Vienna Ab-initio Simulation Package (VASP) [13] while the same quantities DISTRIBUTION A...performed on a rectangular cell having x, y, and z-axes oriented along the 1210 , 1010 , and 0001 directions, respectively. The length along the...Massively Parallel Simulator (LAMMPS) [42]. Here, the analysis cell consisted of a standard bicrystal cell with a single grain boundary that divides the

  1. Shock-induced spall in copper: the effects of anisotropy, temperature, loading pulse and defect

    Energy Technology Data Exchange (ETDEWEB)

    Luo, Shengnian [Los Alamos National Laboratory; Germann, Timothy C [Los Alamos National Laboratory; An, Qi [Los Alamos National Laboratory; Han, Li - Bo [USTC

    2009-07-28

    Shock-induced spall in Cu is investigated with molecular dynamics simulations. We examine spallation in initially perfect crystals and defective solids with grain boundaries (columnar bicrystals), stacking faults or vacancies, as well as the effect of temperature and loading pulses. Spall in single crystal Cu is anisotropic, and defects and high temperature may reduce the spall strength. Taylor-wave (triangular shock-release wave) loading is explored in comparison with square wave shock loading.

  2. Multiscale Modeling for the Analysis for Grain-Scale Fracture Within Aluminum Microstructures

    Science.gov (United States)

    Glaessgen, Edward H.; Phillips, Dawn R.; Yamakov, Vesselin; Saether, Erik

    2005-01-01

    Multiscale modeling methods for the analysis of metallic microstructures are discussed. Both molecular dynamics and the finite element method are used to analyze crack propagation and stress distribution in a nanoscale aluminum bicrystal model subjected to hydrostatic loading. Quantitative similarity is observed between the results from the two very different analysis methods. A bilinear traction-displacement relationship that may be embedded into cohesive zone finite elements is extracted from the nanoscale molecular dynamics results.

  3. High-temperature single-layer SQUID gradiometers with long baseline and parasitic effective area compensation

    Energy Technology Data Exchange (ETDEWEB)

    Pegrum, C.M.; Eulenburg, A.; Romans, E.J.; Carr, C.; Millar, A.J.; Donaldson, G.B. [Department of Physics and Applied Physics, University of Strathclyde, Glasgow G4 0NG (United Kingdom)

    1999-11-01

    First-order HTS SQUID gradiometers were fabricated on 30x10 mm{sup 2} bicrystal substrates. These devices have a baseline of 13 mm, intrinsic balance levels of {approx}1/700 and a typical gradient sensitivity at 1 kHz of 79 fT cm{sup -1}Hz{sup -1/2}. A two-SQUID coupling scheme is discussed that further enhances the device's ability to reject uniform fields. (author)

  4. Mathematical analysis and STEM observations of arrangement of structural units in 〈001〉 symmetrical tilt grain boundaries.

    Science.gov (United States)

    Inoue, Kazutoshi; Saito, Mitsuhiro; Chen, Chunlin; Kotani, Motoko; Ikuhara, Yuichi

    2016-12-01

    A collaborative work between mathematics and atom-resolved scanning transmission electron microscopy (STEM) has been conducted. The grain boundary in a bicrystal of a simple rock-salt oxide can show a complicated arrangement of structural units, which can be well predicted by an algorithm utilizing the Farey sequence. The estimated arrangements had a nice agreement with those observed by STEM in atomic-scale up to several tens of nanometers.

  5. Non-uniform Stress Field and Stress Concentration Induced by Grain Boundary and Triple Junction of Tricrystal

    Institute of Scientific and Technical Information of China (English)

    Jiansong WAN; Zhufeng YUE

    2003-01-01

    The stress characteristics in the anisotropic bicrystal and tricrystal specimens were analyzed using the anisotropic elastic model, orthotropic Hill's model and rate-dependent crystallographic model. The finite element analysis results show that non-uniform stresses are induced by the grain boundary. For bicrystal specimens in different crystallographic orientations, there exist stress concentrations and high stress gradients nearby the boundaries. The activation and slipping of the slip systems are dependent on the crystallographic orientations of the grains and also on the relative crystallographic orientations of the two adjoining grains. For the tricrystal specimens, there is not always any stress concentrations in the triple junction, and the concentration degree depends on the relative crystallographic orientations of the three grains. Different from the bicrystal specimens, there may be or no stress concentration in the vicinity of grain boundaries for the tricrystal specimens, which depends on the relative crystallographic orientations of the three grains. The stress concentration near to the grain boundaries and triple junction can be high enough for the local plastic deformation, damage and voiding or cracking even when the whole specimen is still under the elastic state.It can be further concluded that homogeneous assumption for polycrystalline materials is not suitable to study the detailed meso- or micro-mechanisms for damaging and fracturing.

  6. Transport properties of variable-angle YBa2Cu3O7 - δ step-edge junctions in the a-b plane

    Science.gov (United States)

    Mitchell, E. E.; Macfarlane, J. C.; Foley, C. P.

    2011-05-01

    The superconductor-barrier-superconductor interface in a range of YBa2Cu3O7 - δ (YBCO) step-edge Josephson junctions was engineered to lie at angles θ other than normal to the a-b axes of the YBCO crystal. This systematic study enabled the effect of the d-wave anisotropy to be probed over the range θ = 0° ([100] direction) to θ = 45° ([110] direction) in a way not possible with junction technologies such as bicrystals. Anomalous temperature dependence of the critical current and a peak in the differential conductance at low voltage were reminiscent of features attributed elsewhere to zero-energy states in a range of [001]-tilt bicrystal and ramp-edge junctions. Moreover, IcRN products decreased with increasing θ, and conductance minima or gap-related structures were measured for large θ. The data reported here for variable-angle junctions are compared with results from studies of other grain boundary junctions (such as bicrystal and biepitaxial junctions) and provide support for theories developed by Shirai et al (2003 J. Phys. Soc. Japan 72 2299-307) in particular.

  7. Optimum high temperature strength of two-dimensional nanocomposites

    Energy Technology Data Exchange (ETDEWEB)

    Monclús, M. A.; Molina-Aldareguía, J. M., E-mail: jon.molina@imdea.org [IMDEA Materials Institute, C/Eric Kandel 2, 28906 Getafe, Madrid (Spain); Zheng, S. J.; Mayeur, J. R.; Beyerlein, I. J.; Mara, N. A. [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Polcar, T. [Czech Technical University in Prague, Technická 2, Prague 6 (Czech Republic); Llorca, J. [IMDEA Materials Institute, C/Eric Kandel 2, 28906 Getafe, Madrid (Spain); Department of Materials Science, Polytechnic University of Madrid, E. T. S. de Ingenieros de Caminos, 28040 Madrid (Spain)

    2013-11-01

    High-temperature nanoindentation was used to reveal nano-layer size effects on the hardness of two-dimensional metallic nanocomposites. We report the existence of a critical layer thickness at which strength achieves optimal thermal stability. Transmission electron microscopy and theoretical bicrystal calculations show that this optimum arises due to a transition from thermally activated glide within the layers to dislocation transmission across the layers. We demonstrate experimentally that the atomic-scale properties of the interfaces profoundly affect this critical transition. The strong implications are that interfaces can be tuned to achieve an optimum in high temperature strength in layered nanocomposite structures.

  8. Strain gradient effects in surface roughening

    DEFF Research Database (Denmark)

    Borg, Ulrik; Fleck, N.A.

    2007-01-01

    A thin aluminium sheet comprising of large polycrystals is pulled in uniaxial tension and the resulting surface profile is measured in a scanning electron microscope. The surface profile near the grain boundaries reveals a local deformation pattern of width of a few micrometres and is strong...... evidence for strain gradient effects. Numerical analyses of a bicrystal undergoing in-plane tensile deformation are also studied using a strain gradient crystal plasticity theory and also by using a strain gradient plasticity theory for an isotropic solid. Both theories include an internal material length...

  9. Optimum high temperature strength of two-dimensional nanocomposites

    Directory of Open Access Journals (Sweden)

    M. A. Monclús

    2013-11-01

    Full Text Available High-temperature nanoindentation was used to reveal nano-layer size effects on the hardness of two-dimensional metallic nanocomposites. We report the existence of a critical layer thickness at which strength achieves optimal thermal stability. Transmission electron microscopy and theoretical bicrystal calculations show that this optimum arises due to a transition from thermally activated glide within the layers to dislocation transmission across the layers. We demonstrate experimentally that the atomic-scale properties of the interfaces profoundly affect this critical transition. The strong implications are that interfaces can be tuned to achieve an optimum in high temperature strength in layered nanocomposite structures.

  10. Influence of Grain Boundary on Melting

    Institute of Scientific and Technical Information of China (English)

    王暾; 周富信; 刘曰武

    2001-01-01

    The temperature behaviour of an Al bicrystal with surfaces consisting of (110) and (111) crystals is simulated using molecular dynamics. The result shows that the (110) crystal losses its crystalline order at 820K, whereas the disorder does not propagate through the (111) crystal at this temperature. Instead, some disordered atoms are recrystallized into the (111) crystal and the initial grain boundary changes into a stable order-disorder interface. Thus, it was discovered that at a temperature near its melting point, the (111) crystal grew and obstructed the propagation of disorder. Such an obstruction is helpfulfor understanding melting.

  11. Interactions between displacement cascades and Σ3 tilt grain boundaries in Cu

    Science.gov (United States)

    Li, Bo; Long, Xiao-Jiang; Shen, Zhao-Wu; Luo, Sheng-Nian

    2016-12-01

    With large-scale molecular dynamics simulations, we investigate systematically the interaction of displacement cascades with a set of Σ3 tilt grain boundaries (GBs) in Cu bicrystals at low ambient temperatures, as regards irradiation-induced defect production/absorption and GB migration/faceting. Except for coherent twin boundary, GBs exhibit pronounced preferential absorption of interstitials, which depends on initial primary knock-on atom distance from GB plane and inclination angle. GB migration occurs when displacement cascades overlap with a GB plane, as induced by recrystallization of thermal spike, and concurrent asymmetric grain growth. Faceting occurs via expanding coherent twin boundaries for asymmetric GBs.

  12. Size effects in crystal plasticity

    DEFF Research Database (Denmark)

    Borg, Ulrik

    2007-01-01

    of plastic flow in a single crystal, grain boundary effects in a bicrystal, and grain size effects in a polycrystal are studied. Single crystals containing micro-scale voids have also been analyzed at different loading conditions with focus on the stress and deformation fields around the voids, on void......Numerical analyses of plasticity size effects have been carried out for different problems using a developed strain gradient crystal plasticiy theory. The theory employs higher order stresses as work conjugates to slip gradients and uses higher order boundary conditions. Problems on localization...

  13. Martensitic transformation of pure iron at a grain boundary: Atomistic evidence for a two-step Kurdjumov-Sachs-Pitsch pathway

    Science.gov (United States)

    Meiser, Jerome; Urbassek, Herbert M.

    2016-08-01

    Using classical molecular dynamics simulations and the Meyer-Entel interaction potential, we study the martensitic transformation pathway in a pure iron bi-crystal containing a symmetric tilt grain boundary. Upon cooling the system from the austenitic phase, the transformation starts with the nucleation of the martensitic phase near the grain boundary in a plate-like arrangement. The Kurdjumov-Sachs orientation relations are fulfilled at the plates. During further cooling, the plates expand and merge. In contrast to the orientation relation in the plate structure, the complete transformation proceeds via the Pitsch pathway.

  14. Direct observation of nanometer-scale amorphous layers and oxide crystallites at grain boundaries in polycrystalline Sr1−xKxFe2As2 superconductors

    KAUST Repository

    Wang, Lei

    2011-06-01

    We report here an atomic resolution study of the structure and composition of the grain boundaries in polycrystallineSr0.6K0.4Fe2As2superconductor. A large fraction of grain boundaries contain amorphous layers larger than the coherence length, while some others contain nanometer-scale crystallites sandwiched in between amorphous layers. We also find that there is significant oxygen enrichment at the grain boundaries. Such results explain the relatively low transport critical current density (Jc) of polycrystalline samples with respect to that of bicrystal films.

  15. Ag-catalyzed InAs nanowires grown on transferable graphite flakes

    DEFF Research Database (Denmark)

    Meyer-Holdt, Jakob; Kanne, Thomas; Sestoft, Joachim E.;

    2016-01-01

    Semiconducting nanowires grown by quasi-van-der-Waals epitaxy on graphite flakes are a new class of hybrid materials that hold promise for scalable nanostructured devices within opto-electronics. Here we report on high aspect ratio and stacking fault free Ag-seeded InAs nanowires grown......-needle manipulator. Besides the possibilities for fabricating novel nanostructure device designs, we show how this method is used to study the parasitic growth and bicrystal match between the graphite flake and the nanowires by transmission electron microscopy....

  16. Guidance to Design Grain Boundary Mobility Experiments with Molecular Dynamics and Phase-Field Modeling

    Energy Technology Data Exchange (ETDEWEB)

    Michael R Tonks; Yongfeng Zhang; S.B. Biner; Paul C Millett; Xianming Bai

    2013-02-01

    Quantitative phase-field modeling can play an important role in designing experiments to measure the grain boundary (GB) mobility. In this work, molecular dynamics (MD) simulation is employed to determine the GB mobility using Cu bicrystals. Two grain configurations are considered: a shrinking circular grain and a half loop grain. The results obtained from the half loop configuration approaches asymptotically to that obtained from the circular configuration with increasing half loop width. We then verify the phase- field model by directly comparing to the MD simulation results, obtaining excellent agreement. Next, this phase-field model is used to predict the behavior in a common experimental setup that utilizes a half loop grain configuration in a bicrystal to measure the GB mobility. With a 3D simulation, we identify the two critical times within the experiments to reach an accurate value of the GB mobility. We use a series of 2D simulations to investigate the impact of the notch angle on these two critical times and we identify an angle of 60? as an optimal value. We also show that if the notch does not have a sharp tip, it may immobilize the GB migration indefinitely.

  17. Deformation of nanocrystalline binary aluminum alloys with segregation of Mg, Co and Ti at grain boundaries

    Science.gov (United States)

    Zinovev, A. V.; Bapanina, M. G.; Babicheva, R. I.; Enikeev, N. A.; Dmitriev, S. V.; Zhou, K.

    2017-01-01

    The influence of the temperature and sort of alloying element on the deformation of the nanocrystalline (NC) binary Al alloys with segregation of 10.2 at % Ti, Co, or Mg over grain boundaries has been studied using the molecular dynamics. The deformation behavior of the materials has been studied in detail by the simulation of the shear deformation of various Al bicrystals with the grain-boundary segregation of impurity atoms, namely, Ti, Co, or Mg. The deformation of bicrystals with different grain orientation has been studied. It has been found that Co introduction into grain boundaries of NC Al has a strengthening effect due to the deceleration of the grain-boundary migration (GBM) and difficulty in the grain-boundary sliding (GBS). The Mg segregation at the boundaries greatly impedes the GBM, but stimulates the development of the GBS. In the NC alloy of Al-Ti, the GBM occurs actively, and the flow-stress values are close to the values characteristic of pure Al.

  18. Preparation of high-quality HTS rings for application in the magnetic bearing of cryotanks and pinning in grain boundaries

    Science.gov (United States)

    Bringmann, B.; Walter, H.; Jooss, Ch.; Leenders, A.; Freyhardt, H. C.

    2002-08-01

    Seeded melt growth of YBCO high-temperature superconductors is one of the most promising preparation techniques to obtain high-quality HTS tiles for application, e.g. in magnetic bearings. Semi-finished HTSL products of complex shapes have to be developed by different seeding and multi-seeding techniques. To obtain large hollow cylinders designed for application in the magnetic bearing of a cryotank a modified multi-seeded melt growth (MSMG) process was employed. This cryotank will be mounted for testing in a vehicle of a major German car manufacturer. The MSMG process introduces grain boundaries into the HTS tiles. For transport current investigations of [0 0 1]-tilt grain boundaries in melt textured YBCO a series of MSMG bicrystals have been prepared. They exhibit a dependence of the critical current density on misorientation angle which is much weaker than the one observed in thin-film bicrystals. The bulk samples have dimensions larger than the magnetic penetration depth along the grain boundary. Thus, flux pinning has to be taken into account. Different contributions to the longitudinal pinning force have to be considered: vortices at grain boundaries can be pinned by magnetic interaction with Abrikosov vortices in the banks, by defects in the grain boundary itself or by defects which are located next to the grain boundary.

  19. Ebic and Dlts measurements of Si-and polycrystalline silicon

    Energy Technology Data Exchange (ETDEWEB)

    Bary, A.; Hamet, J.F.; Ihlal, A.; Chermant, J.L.; Nouet, G.

    1988-10-01

    Influence of grain boundaries on the electronic properties of silicon has been studied by electron-beam induced current (EBIC), thermally stimulated capacitance (TSCAP) and deep-level transient spectroscopy (DLTS). Low-angle grain boundaries taken from as-grown polycrystalline wafers for solar cells have been analyzed by EBIC and their behaviors have been compared after the junction diffusion treatment. This treatment gives a decrease of the local diffusion length and recombination velocity of the minority carriers. TSCAP and DLTS methods have been applied to a coincidence orientation grain boundary ..sigma..13. These measurements have been made on a gold diffused bicrystal. These results are then compared with those of a bicrystal without gold diffusion. After annealing a narrow interface state continuum appears. On the contrary the gold diffusion prevents the formation of this continuum and only the donor level of gold is detected in the space charge region of the grain boundary (0 - 0.5 ..mu..m). This diffusion of phosphorus or gold can be interpreted as a grain boundary passivation.

  20. How predictable is plastic damage at the atomic scale?

    Science.gov (United States)

    Li, D.; Bucholz, E. W.; Peterson, G.; Reich, B. J.; Russ, J. C.; Brenner, D. W.

    2017-02-01

    The title of this letter implies two questions: To what degree is plastic damage inherently predictable at the atomic scale, and can this predictability be quantified? We answer these questions by combining image analysis with molecular dynamics (MD) simulation to quantify similarities between atomic structures of plastic damage in a database of strained copper bi-crystals. We show that a manifold of different outcomes can originate ostensibly from the same initial structure, but that with this approach complex plastic damage within this manifold can be statistically connected to the initial structure. Not only does this work introduce a powerful approach for analyzing MD simulations of a complex plastic damage but also provides a much needed and critical framework for analyzing and organizing atomic-scale microstructural databases.

  1. Structures of dissociated <1 1-bar 0 0> dislocations and {l_brace}1 1-bar 0 0{r_brace} stacking faults of alumina ({alpha}-Al{sub 2}O{sub 3})

    Energy Technology Data Exchange (ETDEWEB)

    Tochigi, E. [Institute of Engineering Innovation, University of Tokyo, 2-11-16, Yayoi, Bunkyo-ku, Tokyo 113-8656 (Japan); Shibata, N. [Institute of Engineering Innovation, University of Tokyo, 2-11-16, Yayoi, Bunkyo-ku, Tokyo 113-8656 (Japan)] [PRESTO, JST, 4-1-8, Honcho Kawaguchi, Saitama 332-0021 (Japan); Nakamura, A. [Department of Intelligent Materials Engineering, Osaka City University, 3-3-138, Sugimoto, Sumiyoshi-ku, Osaka 558-8585 (Japan); Mizoguchi, T. [Institute of Engineering Innovation, University of Tokyo, 2-11-16, Yayoi, Bunkyo-ku, Tokyo 113-8656 (Japan); Yamamoto, T. [Institute of Engineering Innovation, University of Tokyo, 2-11-16, Yayoi, Bunkyo-ku, Tokyo 113-8656 (Japan)] [Nanostructures Research Laboratory, Japan Fine Ceramics Center, 2-4-1, Mutsuno, Atsuta-ku, Nagoya, Aichi 456-8587 (Japan); Ikuhara, Y., E-mail: ikuhara@sigma.t.u-tokyo.ac.jp [Institute of Engineering Innovation, University of Tokyo, 2-11-16, Yayoi, Bunkyo-ku, Tokyo 113-8656 (Japan)] [Nanostructures Research Laboratory, Japan Fine Ceramics Center, 2-4-1, Mutsuno, Atsuta-ku, Nagoya, Aichi 456-8587 (Japan)] [WPI-AIMR Research Center, Tohoku University, 2-1-1, Katahira, Aoba-ku, Sendai, Miyagi 980-8577 (Japan)

    2010-01-15

    An alumina ({alpha}-Al{sub 2}O{sub 3}) bicrystal with a {l_brace}1 1-bar 0 0{r_brace}/<1 1 2-bar 0> 2{sup o} low-angle grain boundary was fabricated by diffusion bonding, and the grain boundary was observed by high-resolution transmission electron microscopy (HRTEM). It was found that 1/3<1 1-bar 0 0> partial-dislocation triplets were periodically arrayed along the boundary. The atomic structure within the {l_brace}1 1-bar 0 0{r_brace} stacking faults in between the partial-dislocation triplets was determined by HRTEM combined with first-principles calculations. We discuss the stacking fault structures and their excess energies in detail.

  2. Partial dislocation configurations in a low-angle boundary in {alpha}-Al{sub 2}O{sub 3}

    Energy Technology Data Exchange (ETDEWEB)

    Tochigi, E. [Department of Materials Science, University of Tokyo, 2-11-16 Yayoi, Bunkyo-ku, Tokyo 113-8656 (Japan); Shibata, N. [Institute of Engineering Innovation, University of Tokyo, 2-11-16 Yayoi, Bunkyo-ku, Tokyo 113-8656 (Japan); PRESTO, JST, 4-1-8, Honcho Kawaguchi, Saitama 332-0012 (Japan); Nakamura, A. [Department of Intelligent Materials Engineering, Osaka City University, 3-3-138 Sugimoto, Sumiyoshiku, Osaka 558-8585 (Japan); Yamamoto, T. [Institute of Engineering Innovation, University of Tokyo, 2-11-16 Yayoi, Bunkyo-ku, Tokyo 113-8656 (Japan); Ikuhara, Y. [Institute of Engineering Innovation, University of Tokyo, 2-11-16 Yayoi, Bunkyo-ku, Tokyo 113-8656 (Japan)], E-mail: ikuhara@sigma.t.u-tokyo.ac.jp

    2008-05-15

    The dislocation structures of a low-angle tilt grain boundary in alumina bicrystal were investigated by transmission electron microscopy. The grain boundary was found to consist of two regions: an area with pairs of partial dislocations and an area with groups of odd numbered partial dislocations (multiple-partial-structure). Eight kinds of multiple-partial-structures were found in the fabricated grain boundary. The Burgers vectors of each partial dislocation in the grain boundary can be distinguished by dark-field imaging, and thus the arrangement of partial dislocations in the multiple-partial-structures are determined. It is concluded that a slight twist component of the boundary is the origin of the characteristic multiple-partial-structures.

  3. Measurement and analysis of grain boundary grooving by volume diffusion

    Science.gov (United States)

    Hardy, S. C.; Mcfadden, G. B.; Coriell, S. R.; Voorhees, P. W.; Sekerka, R. F.

    1991-01-01

    Experimental measurements of isothermal grain boundary grooving by volume diffusion are carried out for Sn bicrystals in the Sn-Pb system near the eutectic temperature. The dimensions of the groove increase with a temporal exponent of 1/3, and measurement of the associated rate constant allows the determination of the product of the liquid diffusion coefficient D and the capillarity length Gamma associated with the interfacial free energy of the crystal-melt interface. The small-slope theory of Mullins is generalized to the entire range of dihedral angles by using a boundary integral formulation of the associated free boundary problem, and excellent agreement with experimental groove shapes is obtained. By using the diffusivity measured by Jordon and Hunt, the present measured values of Gamma are found to agree to within 5 percent with the values obtained from experiments by Gunduz and Hunt on grain boundary grooving in a temperature gradient.

  4. High-Tc planar SQUID gradiometer for eddy current non-destructive evaluation

    Institute of Scientific and Technical Information of China (English)

    Zhang Ming-Jian; Lang Pei-Lin; Peng Zhi-Hui; Chen Ying-Fei; Chen Ke; Zheng Dong-Ning

    2006-01-01

    This paper reports the fabrication and test of a high-Tc SQUID planar gradiometer which is patterned from YBCO thin film deposited on a SrTiOs bicrystal substrate. The measurement of noise spectrum at 77K shows that the white noise at 200 Hz is about 1×10-4Φ0/Hz. The minimal magnetic gradient is measured and the results suggest that the minimal magnetic gradient is 94 pT/m. The planar gradiometer is used in non-destructive evaluation (NDE) experiments to detect the artifacts in conducting aluminium plates by performing eddy current testing in an unshielded environment. The effect of the exciting coil dimension on the NDE results is investigated. By mapping out the induced field distribution, flaws about 10mm below the plate surface can be clearly identified.

  5. Diffusion-controlled intergranular penetration and embrittlement of copper by liquid bismuth between 300 and 600 Celsius degrees; Penetration intergranulaire fragilisante du cuivre par le bismuth liquide: identification de la cinetique et du mecanisme de type diffusionnel entre 300 et 600 deg

    Energy Technology Data Exchange (ETDEWEB)

    Laporte, V

    2005-02-15

    Hybrid reactors are a new concept for energy production and nuclear waste treatment. Among other requirements, structural materials have to withstand liquid metal embrittlement. This thesis aimed therefore to identify the controlling mechanism for the intergranular embrittlement of copper in contact with liquid bismuth. Scanning electron microscopy, Auger electron spectroscopy, X-ray photoelectron spectroscopy and Rutherford backscattering spectroscopy have been used to analyze fracture surfaces of both copper polycrystals and a copper bicrystal (symmetric tilt boundary 50 degrees <100>). These analyses reveal both parabolic intergranular penetration kinetics and a maximal intergranular bismuth concentration that is less than two monolayers equivalent. These two results allow us to identify grain boundary diffusion as the controlling mechanism for the intergranular penetration of copper by liquid bismuth between 300 and 600 Celsius degrees, showing the absence of perfect grain boundary wetting. (author)

  6. Enhancement of high-TC superconducting thin film devices by nanoscale polishing

    Science.gov (United States)

    Michalowski, P.; Shapoval, T.; Meier, D.; Katzer, C.; Schmidl, F.; Schultz, L.; Seidel, P.

    2012-11-01

    The effects of mechanical nanoscale polishing on the superconducting parameters of YBa2Cu3O7-δ (YBCO) thin films and bi-crystal grain boundary Josephson junctions have been investigated. We prepared samples with additional gold nanocrystallites in the YBCO film. As they are distributed throughout the whole YBCO film, they provide a low-resistance ohmic contact even if parts of the film are removed. Polishing was performed either before or after the patterning and did not change the properties of the grain boundary. However, nanopolishing reduces the film roughness in a significant way, which makes it an indispensable tool for the preparation of integrated superconducting circuits. We also succeeded in tuning the IC and RN of the Josephson junctions of direct current superconducting quantum interference devices (dc-SQUIDs) by systematically reducing the film thickness, which opens up new possibilities in the application of magnetic field sensors.

  7. Grain boundaries analysis in polycrystalline silicon by TEM

    Energy Technology Data Exchange (ETDEWEB)

    Komninou, F.; Karakostas, T.; Bleris, G.L.; Economou, N.A. (Aristoteles University, Thessaloniki (Greece))

    1982-01-01

    Polycrystalline Si interfaces were examined within the CSL's approach. The rotation relationship of every bicrystal has been analyzed with the technique of the instrumental system and the small angle description has been used for the CSL characterization. The most frequently occuring descriptions are CSL' ..sigma..=3 coherent and incoherent twins, the later being microscopically coherent. Cases of multiple boundaries were also examined and interelations were found between low or high angle boundaries for CSL's with ..sigma..>3. A special case of interest is a ..sigma..=39 CSL which is formed from a combination of ..sigma..=13b and ..sigma..=3 and is a triclinic CSL lacking 180/sup 0/ rotational operations. The results presented indicate that for polycrystalline Si the CSL model could be used in describing the interfaces occuring.

  8. Crystal Frameworks, Matrix-valued Functions and Rigidity Operators

    CERN Document Server

    Power, S C

    2011-01-01

    An introduction and survey is given of some recent work on the infinitesimal dynamics of \\textit{crystal frameworks}, that is, of translationally periodic discrete bond-node structures in $\\mathbb{R}^d$, for $ d=2,3,...$. We discuss the rigidity matrix, a fundamental object from finite bar-joint framework theory, rigidity operators, matrix-function representations and low energy phonons. These phonons in material crystals, such as quartz and zeolites, are known as rigid unit modes, or RUMs, and are associated with the relative motions of rigid units, such as ~SiO$_4$ tetrahedra in the tetrahedral polyhedral bond-node model for quartz. We also introduce semi-infinite crystal frameworks, bi-crystal frameworks and associated multi-variable Toeplitz operators.

  9. Terahertz frequency metrology based on high-T sub c Josephson junctions

    CERN Document Server

    Chen, J; Wang, H B; Nakajima, K; Yamashita, T; Wu, P H

    2002-01-01

    Using YBa sub 2 Cu sub 3 O sub 7 /MgO bicrystal Josephson junctions operating between 6-77 K, we have studied their responses to monochromatic electromagnetic radiation from 50 GHz to 4.25 THz. We have obtained direct detections for radiation at 70 K from 50 GHz to 760 GHz and at 40 K from 300 GHz to 3.1 THz. This indicates that fast detectors can be realized to cover the 10:1 frequency band at one operation temperature, and about 100:1 can be covered by operating only one junction at two different temperatures. Both the highest response frequency and the maximum value of the normalized response are shown to be proportional to the I sub C R sub N product of the junction, where I sub C and R sub N are the critical current and the normal resistance of the junction, respectively.

  10. Superconducting Josephson vortex flow transistors

    CERN Document Server

    Tavares, P A C

    2002-01-01

    The work reported in this thesis focuses on the development of high-temperature superconducting Josephson vortex-flow transistors (JVFTs). The JVFT is a particular type of superconducting transistor, i.e. an electromagnetic device capable of delivering gain while keeping the control and output circuits electrically isolated. Devices were fabricated from (100) YBa sub 2 Cu sub 3 O sub 7 sub - subdelta thin films grown by Pulsed Laser Deposition on 24 deg magnesium oxide and strontium titanate bicrystals. The design of the JVFTs was guided by numerical simulations and the devices were optimised for current gain. Improvements were made to the fabrication process in order to accurately pattern the small structures required. The devices exhibited current gains higher than 60 in liquid nitrogen. Gains measured at lower temperatures were significantly higher. As part of the work a data acquisition suite was developed for the characterisation of three-terminal devices and, in particular, of JVFTs.

  11. Evidence for nonlocal electrodynamics in planar Josephson junctions.

    Science.gov (United States)

    Boris, A A; Rydh, A; Golod, T; Motzkau, H; Klushin, A M; Krasnov, V M

    2013-09-13

    We study the temperature dependence of the critical current modulation I(c)(H) for two types of planar Josephson junctions: a low-Tc Nb/CuNi/Nb and a high-Tc YBa2Cu3O(7-δ) bicrystal grain-boundary junction. At low T both junctions exhibit a conventional behavior, described by the local sine-Gordon equation. However, at elevated T the behavior becomes qualitatively different: the I(c)(H) modulation field ΔH becomes almost T independent and neither ΔH nor the critical field for the penetration of Josephson vortices vanish at Tc. Such an unusual behavior is in good agreement with theoretical predictions for junctions with nonlocal electrodynamics. We extract absolute values of the London penetration depth λ from our data and show that a crossover from local to nonlocal electrodynamics occurs with increasing T when λ(T) becomes larger than the electrode thickness.

  12. Variable-charge method applied to study coupled grain boundary migration in the presence of oxygen

    Energy Technology Data Exchange (ETDEWEB)

    Elsener, A. [Paul Scherrer Institute, Villigen, PSI-Villigen CH-5232 (Switzerland); Politano, O. [Institut Carnot de Bourgogne, UMR 5209 CNRS-Universite de Bourgogne, 9 Avenue Alain Savary, 21078 Dijon Cedex (France); Derlet, P.M. [Paul Scherrer Institute, Villigen, PSI-Villigen CH-5232 (Switzerland); Van Swygenhoven, H. [Paul Scherrer Institute, Villigen, PSI-Villigen CH-5232 (Switzerland)], E-mail: helena.vs@psi.ch

    2009-04-15

    One of the important differences between simulation and experiments in grain boundary (GB)-dominated metallic structures is the lack of impurities such as oxygen in computational samples. A modified variable-charge method [Elsener A, Politano O, Derlet PM, Van Swygenhoven H. Modell Simul Mater Sci Eng 2008;16:025006] based on the Streitz and Mintmire approach [Streitz FH, Mintmire JW. Phys Rev B 1994;50:11996] is used to study coupled GB motion in an Al bicrystal with a [1 1 2] symmetrical tilt GB in the presence of substitutional O, and compared with the stick-slip process identified by Cahn and Mishin [Cahn JW, Mishin Y, Suzuki A. Acta Mater 2006;54:4953]. It is found that the critical shear stress for migration of the GB increases linearly with the number of O atoms. These observations are then rationalized in terms of the internal stress signature of the O atoms in the vicinity of the boundary.

  13. Geometry of polycrystals and microstructure

    Directory of Open Access Journals (Sweden)

    Ball John M.

    2015-01-01

    Full Text Available We investigate the geometry of polycrystals, showing that for polycrystals formed of convex grains the interior grains are polyhedral, while for polycrystals with general grain geometry the set of triple points is small. Then we investigate possible martensitic morphologies resulting from intergrain contact. For cubic-totetragonal transformations we show that homogeneous zero-energy microstructures matching a pure dilatation on a grain boundary necessarily involve more than four deformation gradients. We discuss the relevance of this result for observations of microstructures involving second and third-order laminates in various materials. Finally we consider the more specialized situation of bicrystals formed from materials having two martensitic energy wells (such as for orthorhombic to monoclinic transformations, but without any restrictions on the possible microstructure, showing how a generalization of the Hadamard jump condition can be applied at the intergrain boundary to show that a pure phase in either grain is impossible at minimum energy.

  14. Phase-field theory of grain growth in the presence of mobile second-phase particles

    Energy Technology Data Exchange (ETDEWEB)

    Vedantam, Srikanth, E-mail: srikanth@nus.edu.sg [Department of Mechanical Engineering, National University of Singapore, Singapore 117576 (Singapore); Mallick, Ashis [Department of Mechanical Engineering, National University of Singapore, Singapore 117576 (Singapore)

    2010-01-15

    We have developed a phase-field model for grain growth in the presence of mobile second-phase particles. In this model, each grain and particle is represented by a unique order parameter. The grain boundaries sweep the mobile particles during grain growth. The particle velocity is taken to be proportional to the driving force arising from the curvature of the phase boundary in the neighborhood of the particle. The proportionality factor is the constitutive parameter representing the mobility of the particle. We first study the model in a one-dimensional axisymmetric setting and compare the results with theoretical calculations. We then study the interaction of a bicrystal grain boundary with a dilute distribution of particles. Finally we show the effect of particles on polycrystalline grain growth.

  15. Thermally driven grain boundary migration and melting in Cu.

    Science.gov (United States)

    Li, Y H; Wang, L; Li, B; E, J C; Zhao, F P; Zhu, J; Luo, S N

    2015-02-07

    With molecular dynamics simulations, we systematically investigate melting of a set of Σ3〈110〉70.53° tilt grain boundaries (GB) in Cu bicrystals, including coherent twin boundaries (CTBs), 12 asymmetric tilt grain boundaries (ATGBs), and symmetric incoherent twin boundaries (SITBs), in the order of increasing length weight of SITB or GB energy. ATGBs decompose into CTBs and SITBs, which migrate and coalesce as a result of internal stress relaxation. GBs can be superheated or premelted, and GB melting temperature decreases exponentially with increasing SITB weight, owing to the systematics in GB microstructure. GB melting nucleates at disordered CTB-SITB junctions, and grows along SITBs and then into grain interiors, with the solid-liquid interfaces preferentially aligned with {111}.

  16. Twin Boundaries merely as Intrinsically Kinematic Barriers for Screw Dislocation Motion in FCC Metals

    Science.gov (United States)

    Zhang, Jiayong; Zhang, Hongwu; Ye, Hongfei; Zheng, Yonggang

    2016-03-01

    Metals with nanoscale twins have shown ultrahigh strength and excellent ductility, attributed to the role of twin boundaries (TBs) as strong barriers for the motion of lattice dislocations. Though observed in both experiments and simulations, the barrier effect of TBs is rarely studied quantitatively. Here, with atomistic simulations and continuum based anisotropic bicrystal models, we find that the long-range interaction force between coherent TBs and screw dislocations is negligible. Further simulations of the pileup behavior of screw dislocations in front of TBs suggest that screw dislocations can be blocked kinematically by TBs due to the change of slip plane, leading to the pileup of subsequent dislocations with the elastic repulsion actually from the pinned dislocation in front of the TB. Our results well explain the experimental observations that the variation of yield strength with twin thickness for ultrafine-grained copper follows the Hall-Petch relationship.

  17. YBa{sub 2}Cu{sub 3}O{sub 7} grain boundary junction dc SQUIDs for operation in high magnetic fields

    Energy Technology Data Exchange (ETDEWEB)

    Konovalenko, Konstantin; Nagel, Joachim; Turad, Markus; Bailer, Matthias; Gruenzweig, Matthias; Kleiner, Reinhold; Koelle, Dieter [Physikalisches Institut, Center for Collective Quantum Phenomena, Universitaet Tuebingen (Germany)

    2009-07-01

    We investigate the suitability of dc SQUIDs for operation in high magnetic fields at 4.2 K. For this purpose, we fabricated small (micron-sized) YBa{sub 2}Cu{sub 3}O{sub 7}(YBCO) grain boundary junction dc SQUIDs on SrTiO{sub 3} bicrystals with thin film Au shunt resistors. Fabrication was done by pulsed laser deposition of YBCO films, in-situ deposition of electron-beam evaporated Au films and Ar ion milling with photolithographically defined masks. For the fabricated SQUIDs we present results on electric transport properties, measured in a four-point arrangement, and on noise properties, measured with a Nb dc SQUID amplifier.

  18. Capturing recrystallization of metals with a multi-scale materials model

    Energy Technology Data Exchange (ETDEWEB)

    D. A. Hughes; D. J. Bammann; A. Godfrey; V. C. Prantil; E. A. Holm; M. A. Miodownik; D. C. Chrzan; M. T. Lusk

    2000-04-01

    The final report for a Laboratory Directed Research and Development project entitled, ``Capturing Recrystallization of Metals in a Multiscale Materials Model'' is presented. In this project, deformation and recrystallization processes have been followed experimentally and theoretically in order to incorporate essential mechanisms from the defect (dislocation) and grain size length scales. A nonlinear rotational gradient theory has been developed which enables the incorporation of microstructural parameters. The evolution of these parameters during deformation and recrystallization has been characterized qualitatively and quantitatively, applying various electron optic techniques ranging over several length scales. The theoretical and experimental framework developed is general. It has been exemplified by an application to recrystallization in single crystals and bicrystals of aluminum. The recrystallization process has been modeled using a 3-D model for the changes in key structural parameters during recrystallization.

  19. Influence of inductance induced noise in an YBa2Cu3O7 dc-SQUID at high operation temperatures

    DEFF Research Database (Denmark)

    Nilsson, P. Å.; Claeson, T.; Hansen, J. B.;

    1994-01-01

    The voltage modulation depth of a high T(c) dc-SQUID was measured at temperatures close to T(c) and compared to a model by Enpuku et al. where the flux noise from the SQUID inductance is taken into account. The device was an YBa2Cu3O7 dc-SQUID made on a bicrystal substrate of SrTiO3. The design...... was of the Ketchen square-washer type with an inductance of 67 pH. Measurements were made in a temperature interval from 75 to 87 K, where the voltage modulation depth changed from 4.5 to 1.4 muV in close agreement with the model....

  20. Ag-catalyzed InAs nanowires grown on transferable graphite flakes

    Science.gov (United States)

    Meyer-Holdt, Jakob; Kanne, Thomas; Sestoft, Joachim E.; Gejl, Aske; Zeng, Lunjie; Johnson, Erik; Olsson, Eva; Nygård, Jesper; Krogstrup, Peter

    2016-09-01

    Semiconducting nanowires grown by quasi-van-der-Waals epitaxy on graphite flakes are a new class of hybrid materials that hold promise for scalable nanostructured devices within opto-electronics. Here we report on high aspect ratio and stacking fault free Ag-seeded InAs nanowires grown on exfoliated graphite flakes by molecular beam epitaxy. Ag catalyzes the InAs nanowire growth selectively on the graphite flakes and not on the underlying InAs substrates. This allows for easy transfer of the flexible graphite flakes with as-grown nanowire ensembles to arbitrary substrates by a micro-needle manipulator. Besides the possibilities for fabricating novel nanostructure device designs, we show how this method is used to study the parasitic growth and bicrystal match between the graphite flake and the nanowires by transmission electron microscopy.

  1. Operation of a high-T C SQUID gradiometer with a two-stage MEMS-based Joule-Thomson micro-cooler

    Science.gov (United States)

    Kalabukhov, Alexey; de Hoon, Erik-Jan; Kuit, Kristiaan; Lerou, Pieter-Paul P. P. M.; Chukharkin, Maxim; Schneiderman, Justin F.; Sepehri, Sobhan; Sanz-Velasco, Anke; Jesorka, Aldo; Winkler, Dag

    2016-09-01

    Practical applications of high-T C superconducting quantum interference devices (SQUIDs) require cheap, simple in operation, and cryogen-free cooling. Mechanical cryo-coolers are generally not suitable for operation with SQUIDs due to their inherent magnetic and vibrational noise. In this work, we utilized a commercial Joule-Thomson microfluidic two-stage cooling system with base temperature of 75 K. We achieved successful operation of a bicrystal high-T C SQUID gradiometer in shielded magnetic environment. The micro-cooler head contains neither moving nor magnetic parts, and thus does not affect magnetic flux noise of the SQUID even at low frequencies. Our results demonstrate that such a microfluidic cooling system is a promising technology for cooling of high-T C SQUIDs in practical applications such as magnetic bioassays.

  2. Noise properties of high-quality step-edge YBCO Josephson junctions

    Energy Technology Data Exchange (ETDEWEB)

    Foley, C.P.; Lam, S.; Sloggett, J.; Savvides, N; Katsaros, A. [CSIRO, Lindfield, NSW (Australia). Division of Applied Physics; Hao, L.; Macfarlane, J.C.; Pegrum, C.M. [University of Strathclyde, Glasgow (United Kingdom). Department of Physics and Applied Physics; Kuznik, J. [Czech Academy of Science, Prague (Czech Republic).

    1996-12-31

    Full text: We report the results of noise and other measurements on YBCO step-edge Josephson junctions whose morphology closely approaches the ideal of a homogeneous tilt angle grain boundary. The junctions exhibit near-perfect resistively-shunted-junction (RSJ) current voltage characteristics and magnetic field dependence. Excess noise in the junctions was comparable to the best bicrystal types previously measured, the normalised amplitude of the critical current fluctuations, S{sub i}{sup 1/2}, being less than 1x10{sub -4} Hz{sub -}1{sub /2} at 1 Hz and 77 K. S{sub i}{sup 1/2} was found to be independent of temperature and also independent of magnetic field provided the zero-field critical current was used for normalisation

  3. Foundations for quantitative microstructural models to track evolution of the metallurgical state during high purity Nb cavity fabrication

    Energy Technology Data Exchange (ETDEWEB)

    Bieler, Thomas R [Michigan State University; Wright, Neil T [Michigan State University; Compton, Chris C [Facility for Rare Isotope Beams

    2014-03-15

    The goal of the Materials Science SRF Cavity Group of Michigan State University and the National Superconducting Cyclotron has been (and continues to be) to understand quantitatively the effects of process history on functional properties. These relationships were assessed via studies on Nb samples and cavity parts, which had various combinations of forming processes, welding, heat treatments, and surface preparation. A primary focus was on large-grain cavity building strategies. Effects of processing operations and exposure to hydrogen on the thermal conductivity has been identified in single and bi-crystal samples, showing that the thermal conductivity can be altered by a factor of 5 depending on process history. Characterization of single crystal tensile samples show a strong effect of crystal orientation on deformation resistance and shape changes. Large grain half cells were examined to characterize defect content and surface damage effects, which provided quantitative information about the depth damage layers from forming.

  4. A thermal-mechanical constitutive model for b-HMX single crystal and cohesive interface under dynamic high pressure loading

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    Due to the significant thermal-mechanical effects during hot spot formation in PBX explosives,a thermodynamic constitutive model has been constructed for HMX anisotropic single crystal subjected to dynamic impact loading. The crystal plasticity model based on dislocation dynamics theory was employed to describe the anisotropic plastic behavior along the preferential slip systems. A modified equation of state (EOS) was introduced into the constitutive equations through the decomposing stress tensor and the nonlinear elasticity for materials was taken into account. The one-dimensional strain impact simulations for HMX single crystal and quasi-bicrystal were performed respectively,in which the cohesive elements were inserted over the interface areas for the latter. The predicted particle velocities for the single crystal sample agreed well with the experimental results in the literature. Furthermore,the effects of crystal orientations,interface,misorientations on localized strain,stress and temperature distributions were predicted and discussed.

  5. Twin Boundaries merely as Intrinsically Kinematic Barriers for Screw Dislocation Motion in FCC Metals.

    Science.gov (United States)

    Zhang, Jiayong; Zhang, Hongwu; Ye, Hongfei; Zheng, Yonggang

    2016-03-10

    Metals with nanoscale twins have shown ultrahigh strength and excellent ductility, attributed to the role of twin boundaries (TBs) as strong barriers for the motion of lattice dislocations. Though observed in both experiments and simulations, the barrier effect of TBs is rarely studied quantitatively. Here, with atomistic simulations and continuum based anisotropic bicrystal models, we find that the long-range interaction force between coherent TBs and screw dislocations is negligible. Further simulations of the pileup behavior of screw dislocations in front of TBs suggest that screw dislocations can be blocked kinematically by TBs due to the change of slip plane, leading to the pileup of subsequent dislocations with the elastic repulsion actually from the pinned dislocation in front of the TB. Our results well explain the experimental observations that the variation of yield strength with twin thickness for ultrafine-grained copper follows the Hall-Petch relationship.

  6. Simulation of dc magnetic effects due to geometrically defined grain boundaries in type-II superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Bartolome, E. [Escola Universitaria Salesiana de Sarria, Passeig Sant Joan Bosco, 74, 08017 Barcelona (Spain)], E-mail: ebartolome@euss.es; Granados, X.; Bozzo, B. [Institut de Ciencia de Materials de Barcelona, CSIC, Campus UAB, 08193 Bellaterra (Spain); Navau, C. [Grup d' Electromagnetisme, Universitat Autonoma de Barcelona, 08193 Bellaterra (Spain); Puig, T.; Obradors, X. [Institut de Ciencia de Materials de Barcelona, CSIC, Campus UAB, 08193 Bellaterra (Spain)

    2008-03-30

    A Bean model-based program ('Trazacorrientes') has been used to simulate the current distribution in the saturated remanent state of type-II superconducting bicrystal-like squared samples. The grain boundary was modeled by a set of periodically spaced holes geometrically defining the current transparency. Current simulations performed as a function of the boundary transparency, width and geometry are analyzed. Current distributions agree qualitatively with previously reported imaging measurements, while quantitative results can be obtained with an accuracy of {approx}5% due to present computing resolution limits. Thanks to 'Trazacorrientes' easy way of implementing irregular defects, meandering grain boundaries formed by straight facets of different local transparency could be simulated. The advantages and disadvantages of the program for the simulation of type-II superconductors with defects, among which GB's, are discussed.

  7. Dislocation structures and electrical conduction properties of low angle tilt grain boundaries in LiNbO3

    Science.gov (United States)

    Furushima, Yuho; Nakamura, Atsutomo; Tochigi, Eita; Ikuhara, Yuichi; Toyoura, Kazuaki; Matsunaga, Katsuyuki

    2016-10-01

    Dislocations in crystalline materials constitute unique, atomic-scale, one-dimensional structure and have a potential to induce peculiar physical properties that are not found in the bulk. In this study, we fabricated LiNbO3 bicrystals with low angle tilt grain boundaries and investigated the relationship between the atomic structure of the boundary dislocations and their electrical conduction properties. Observations by using transmission electron microscopy revealed that dislocation structures at the (0001) low angle tilt grain boundaries depend on the tilt angle of the boundaries. Specifically, the characteristic dislocation structures with a large Burgers vector were formed in the boundary with the tilt angle of 2°. It is noteworthy that only the grain boundary of 2° exhibits distinct electrical conductivity after reduction treatment, although LiNbO3 is originally insulating. This unique electrical conductivity is suggested to be due to the characteristic dislocation structures with a large Burgers vector.

  8. Computational micromechanics

    Science.gov (United States)

    Ortiz, M.

    1996-09-01

    Selected issues in computational micromechanics are reviewed, with particular emphasis on multiple-scale problems and micromechanical models of material behavior. Examples considered include: the bridging of atomistic and continuum scales, with application to nanoindentation and the brittle-to-ductile transition; the development of dislocation-based constitutive relations for pure metallic crystals and intermetallic compounds, with applications to fracture of single crystals and bicrystals; the simulation of non-planar three-dimensional crack growth at the microscale, with application to mixed mode I III effective behavior and crack trapping and bridging in fiber-reinforced composites; and the direct micromechanical simulation of fragmentation of brittle solids and subsequent flow of the comminuted phase.

  9. Flip-chip-type high-Tc gradiometer for biomagnetic measurements in unshielded environment

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    A flip-chip-type gradiometer has been constructed with a 10 mm×5 mm planar DC-SQUID gradiometer fabricated on a SrTiO3 bicrystal substrate and a flux transformer made from a YBCO*/YBCO/CeO2/YSZ multilayer on a φ50.8 mm Si wafer. The coupling coefficient between the flux transformer and the planar gradiometer is 0.18. The transformer increases effectively the resolution of the gradiometer. A magnetic field gradient resolution of 73 fT·cm-1·Hz-1/2 in the white region and 596 fT·cm-1Hz-1/2 at 1 Hz has been obtained. High quality magnetocardiogram signals have been successfully measured by using this flip-chip-type gradiometer in an unshielded environment.

  10. Flip-chip-type high- T_c gradiometer for biomagnetic measurements in unshielded environment

    Institute of Scientific and Technical Information of China (English)

    田永君; 王天生; 陈珂; 漆汉宏; 陈烈; 郑东宁; Sven; LINZEN; Frank; SCHMIDL; Paul; SEIDEL

    2000-01-01

    A flip-chip-type gradiometer has been constructed with a 10 mm × 5 mm planar DC-SQUID gradiometer fabricated on a SrTiO3 bicrystal substrate and a flux transformer made from a YB-CO* /YBCO/CeO2/YSZ multilayer on a φ50.8 mm Si wafer. The coupling coefficient between the flux transformer and the planar gradiometer is 0.18. The transformer increases effectively the resolution of the gradiometer. A magnetic field gradient resolution of 73 fT·cm-1·Hz-1/2 in the white region and 596 fT·cm-1Hz-1/2 at 1 Hz has been obtained. High quality magnetocardiogram signals have been successfully measured by using this flip-chip-type gradiometer in an unshielded environment.

  11. Critical properties of the high-energy electron-beam-irradiated superconductor weak links

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Sung Hoon; Lee, Soon Gul [Korea University, Sejong (Korea, Republic of)

    2014-11-15

    We have studied the effects of high-energy electron-beam irradiation on the superconducting transition properties of an YBCO bicrystal junction, a focused ion-beam (FIB)-patterned YBCO nanobridge, a MgB{sub 2} intergrain nanobridge, and a BaKFeAs multigrain microbridge. We used one sample for each junction type and repeated the irradiation-and-measurement process at 6 accumulated-dose steps: 0, 3 x 10{sup 14}, 10{sup 15}, 3 x 10{sup 15}, 10{sup 16}, and 10{sup 17} e/cm{sup 2}. A uniform electron beam with a 1-MeV kinetic energy was irradiated indiscrimately over the samples. We measured the resistive transition temperature, the normal-state resistance, and the critical current. The irradiation effect was significant for all the samples except the BaKFeAs microbridge. The critical current data for the YBCO bicrystal junction and the MgB{sub 2} intergrain nanobridge had a maximum at 3 x 10{sup 15} e/cm{sup 2}, and the YBCO nanobridge showed a monotonic decrease. For all the samples, the normal state resistance increased monotonically with increasing dose by up to ∼20% at 10{sup 16} e/cm{sup 2}, and the change in T{sub c} was negligible. The results showed that the YBCO and MgB{sub 2} weak links were susceptive to irradiation, indicating the possibility of controlling the critical current of those junctions by using high-energy electron-beam irradiation.

  12. Grain boundary tunnel spectroscopy of the electron-doped cuprate superconductor La{sub 2-x}Ce{sub x}CuO{sub 4}; Korngrenzen-Tunnelspektroskopie am elektronendotierten Kupratsupraleiter La{sub 2-x}Ce{sub x}CuO{sub 4}

    Energy Technology Data Exchange (ETDEWEB)

    Wagenknecht, Michael

    2008-07-01

    The electron doped superconductor La{sub 2-x}Ce{sub x}CuO{sub 4} (LCCO) has been investigated by electric transport measurements at low temperatures T down to 5 K and high magnetic fields up to 16 T. For this purpose LCCO thin film tunnel junctions have been prepared on bicrystal substrates by molecular beam epitaxy and micro structuring. The samples were characterised by measuring the thin film resistivity and the tunnel conductance of quasi particles across the grain boundary. By these measurements an unconventional symmetry of the order parameter could be revealed for La{sub 2-x}Ce{sub x}CuO{sub 4}. Furthermore it was shown, that the tunnel conductance can be used as a probe for the upper critical field B{sub c2}(T). By using this method a value of B{sub c2}{proportional_to}24 T has been found for La{sub 2-x}Ce{sub x}CuO{sub 4}, a value roughly three times bigger than previously known. By this observation it was shown that the superconducting phase covers a larger region in the B-T-phase diagram. In addition it was concluded, that the pseudogap phase in La{sub 2-x}Ce{sub x}CuO{sub 4} is either not existent at all or covers only a small temperature region. Besides quasiparticle tunneling also the tunneling of Cooper pairs in small magnetic fields has been investigated. It was shown that the critical current across the grain boundary depends on the supplier of the bicrystal substrate. (orig.)

  13. Behaviour and damage of aged austenitic-ferritic steels: a micro-mechanical approach; Comportement et endommagement des aciers austeno-ferritiques vieillis: une approche micromecanique

    Energy Technology Data Exchange (ETDEWEB)

    Bugat, St

    2000-12-15

    The austenitic-ferritic steels are used in the PWR primary cooling system. At the running temperature (320 C), they are submitted to a slow aging, which leads to the embrittlement of the ferritic phase. This embrittlement leads to a decrease of the mechanical properties, in particular of the crack resistance of the austenitic-ferritic steels. The damage and rupture of the austenitic-ferritic steels have been approached at the ENSMP by the works of P. Joly (1992) and of L. Devilliers-Guerville (1998). These works have allowed to reveal a damage heterogeneity which induces a strong dispersion on the ductilities and the toughnesses as well as on the scale effects. Modeling including the damage growth kinetics measured experimentally, have allowed to verify these effects. Nevertheless, they do not consider the two-phase character of the material and do not include a physical model of the cleavage cracks growth which appear in the embrittled ferrite. In this study, is proposed a description of the material allowing to treat these aspects while authorizing the structure calculation. In a first part, the material is studied. The use of the ESBD allows to specify the complex morphology of these steels and crystal orientation relations between the two phases. Moreover, it is shown that the two phases keep the same crystal orientation in the zones, called bicrystals, whose size varies between 500 {mu}m and 1 mm. The study of the sliding lines, coupled to the ESBD, allows to specify too the deformation modes of the two phases. At last, tensile and tensile-compression tests at various deformation range are carried out to characterize the macroscopic mechanical behaviour of these materials. Then, a micro-mechanical modeling of the material behaviour is proposed. This one takes into account the three scales identified at the preceding chapter. The first scale, corresponding to the laths is described as a monocrystal whose behaviour includes both an isotropic and a kinematic

  14. Domain pinning near a single-grain boundary in tetragonal and rhombohedral lead zirconate titanate films

    Science.gov (United States)

    Marincel, D. M.; Zhang, H. R.; Britson, J.; Belianinov, A.; Jesse, S.; Kalinin, S. V.; Chen, L. Q.; Rainforth, W. M.; Reaney, I. M.; Randall, C. A.; Trolier-McKinstry, S.

    2015-04-01

    The interaction of grain boundaries with ferroelectric domain walls strongly influences the extrinsic contribution to piezoelectric activity in Pb Zr1 -x,TixO3 (PZT), ubiquitous in modern transducers and actuators. However, the fundamental understanding of these phenomena has been limited by complex mechanisms originating from the interplay of atomic-level domain wall pinning, collective domain wall dynamics, and emergent mesoscopic behavior. This contribution utilizes engineered grain boundaries created by depositing epitaxial PZT films with various Zr:Ti ratios onto 24° tilt SrTi O3 bicrystals. The nonlinear piezoelectric response and surface domain structure across the boundary are investigated using piezoresponse force microscopy while the cross-sectional domain structure is studied using transmission electron microscopy. The grain boundary reduces domain wall motion over a width of 800 ±70 nm for PZT 45:55 and 450 ±30 nm for PZT 52:48. Phase field modeling provides an understanding of the elastic and electric fields associated with the grain boundary and local domain configurations. This study demonstrates that complex mesoscopic behaviors can be explored to complement atomic-level pictures of the material system.

  15. DC SQUID RF magnetometer with 200 MHz bandwidth

    Science.gov (United States)

    Talanov, Vladimir; Lettsome, Nesco; Orozco, Antonio; Cawthorne, Alfred; Borzenets, Valery

    2012-02-01

    Because of periodic flux-to-voltage transfer function, Superconducting QUantum Interference Device (SQUID) magnetometers operate in a closed-loop regime [1], which linearizes the response, and increases the dynamic range and sensitivity. However, a transmission line delay between the SQUID and electronics fundamentally limits the closed-loop bandwidth at 20 MHz [1], although the intrinsic bandwidth of SQUIDs is in gigahertz range. We designed a DC SQUID based RF magnetometer capable of wideband sensing coherent magnetic fields up to 200 MHz. To overcome the closed-loop bandwidth limitation, we utilized a low-frequency flux-modulated closed-loop to simultaneously lock the quasi-static magnetic flux and provide AC bias for the RF flux. The SQUID RF voltage is processed by RF electronics based on a double lock-in technique. This yields a signal proportional to the amplitude and phase of the RF magnetic flux, with more than four decades of a linear response. For YBaCuO SQUID on bi-crystal SrTiO substrate at 77 K we achieved a flux noise density of 4 μφ0/Hz at 190 MHz, which is similar to that measured at kHz frequencies with conventional flux-locked loop. [1] D. Drung, et al., Supercond. Sci. Technol. 19, S235 (2006).

  16. Irreversible thermodynamics of creep in crystalline solids

    Science.gov (United States)

    Mishin, Y.; Warren, J. A.; Sekerka, R. F.; Boettinger, W. J.

    2013-11-01

    We develop an irreversible thermodynamics framework for the description of creep deformation in crystalline solids by mechanisms that involve vacancy diffusion and lattice site generation and annihilation. The material undergoing the creep deformation is treated as a nonhydrostatically stressed multicomponent solid medium with nonconserved lattice sites and inhomogeneities handled by employing gradient thermodynamics. Phase fields describe microstructure evolution, which gives rise to redistribution of vacancy sinks and sources in the material during the creep process. We derive a general expression for the entropy production rate and use it to identify of the relevant fluxes and driving forces and to formulate phenomenological relations among them taking into account symmetry properties of the material. As a simple application, we analyze a one-dimensional model of a bicrystal in which the grain boundary acts as a sink and source of vacancies. The kinetic equations of the model describe a creep deformation process accompanied by grain boundary migration and relative rigid translations of the grains. They also demonstrate the effect of grain boundary migration induced by a vacancy concentration gradient across the boundary.

  17. Effects of self-assembled gold nanoparticles on YBa2Cu3O7-δ thin films and devices

    Science.gov (United States)

    Michalowski, P.; Katzer, C.; Schmidl, F.; Seidel, P.

    2012-11-01

    In our work we prepared YBa2Cu3O7-δ (YBCO) thin films with self-assembled gold nanoparticles on SrTiO3 (STO) substrates. We carried out different experiments to determine the effects on the crystallographic properties of the YBCO matrix as well as of the gold nanoparticles. Furthermore, we investigated how the particles influence the superconducting parameters of the film, e.g. the critical temperature TC and the critical current density jC. To ascertain jC we employed magneto-optical Faraday microscopy. In addition, the YBCO film was deposited and structured on STO bi-crystal substrates, thus producing grain boundary Josephson junctions. We studied those junctions with respect to the normal state resistance RN, and the dependence of the critical current IC on the temperature T as well as on the magnetic flux Φ. Finally, we prepared direct current superconducting quantum interference device (dc-SQUID) gradiometers and embedded gold nanoparticles at well-defined areas such as only the antenna or the SQUID region. We measured the flux noise in a shielded environment using an ac-bias reversal technique and compared it with that of sensors without gold nanoparticles. Thus, we demonstrate a new preparation method and an innovative application of gold nanoparticles.

  18. Spatially resolved analytical electron microscopy at grain boundaries of {alpha}-Al{sub 2}O{sub 3}; Ortsaufgeloeste analytische Elektronenmikroskopie an Korngrenzen in {alpha}Al{sub 2}O{sub 3}

    Energy Technology Data Exchange (ETDEWEB)

    Nufer, S.

    2001-10-01

    Aluminum oxide, {alpha}-Al{sub 2}O{sub 3}, is a common structural ceramic material. The most technologically important properties are either determined or strongly influenced by the polycrystalline microstructure. For instance, the grain boundaries control the mechanical behavior (e.g. plasticity, creep, and fracture) or various transport phenomena (e.g. ion diffusion, segregation, and electrical resistivity). In order to understand the structure-properties relationships, it is therefore important to characterize the structure and chemistry of grain boundaries, both experimentally and theoretically. In this work the electronic structure of the basal and rhombohedral twin grain boundaries and the impurity excess at different tilt grain boundaries in bicrystals were investigated, using electron energy-loss spectroscopy (EELS) and energy dispersive X-ray spectroscopy (EDXS). The electronic structure of the rhombohedral twin grain boundary was determined by comparing spatially resolved EELS measurements of the O-K ionisation edge with the theoretical density of states (DOS), obtained from local density functional theory (LDFT) calculations. The interface excess of impurities was quantitatively analysed at grain boundaries with and without Y-doping. (orig.)

  19. Large grain CBMM Nb ingot slices: An ideal test bed for exploring the microstructure-electromagnetic property relationships relevant to SRF

    Energy Technology Data Exchange (ETDEWEB)

    Sung, Zu-Hawn, E-mail: ZSung@uss.com [The Applied Superconductivity Center, National High Magnetic Field Laboratory, Florida State University, Tallahassee FL 32310, US (United States); Now at US-Steel, Pittsburgh, US (United States); Lee, Peter J., E-mail: lee@asc.magnet.fsu.edu; Polyanskii, Anatolii, E-mail: polyanskii@asc.magnet.fsu.edu; Balachandran, Shreyas, E-mail: shreyasb@asc.magnet.fsu.edu; Chetri, Santosh, E-mail: sc13ad@my.fsu.edu [The Applied Superconductivity Center, National High Magnetic Field Laboratory, Florida State University, Tallahassee FL 32310, US (United States); Larbalestier, David C., E-mail: larbalestier@asc.magnet.fsu.edu [The Applied Superconductivity Center, National High Magnetic Field Laboratory, Florida State University, Tallahassee FL 32310, US (United States); FSU/FAMU College of Engineering (United States); Wang, Mingmin, E-mail: wangmi22@msu.edu; Compton, Christopher, E-mail: compton@nscl.msu.edu; Bieler, Thomas R., E-mail: bieler@egr.msu.edu [Michigan State University, US (United States)

    2015-12-04

    High purity (RRR > 200), large grain (> 5-10 cm) niobium ingot slices have been successfully used to fabricate radio frequency (RF) cavities for particle accelerators. They offer significantly reduced fabrication cost by eliminating processing steps and furthermore they provide the opportunity to study the influence of individual grain boundaries in SRF Nb. Here we summarize our measurements of grain boundary (GB) effects on the superconducting properties of large grain high purity niobium sheet manufactured by CBMM. We show by magneto-optical (MO) imaging that GBs allow premature flux penetration, but only when they are oriented close to the direction of the magnetic field. However, even low angle GBs produced by minor deformations commensurate with half-cell forming produce localized flux penetration. The transport properties of grain boundaries were investigated by direct transport across them and evidence for preferential vortex flow along the GBs of SRF Nb was observed for the first time. Using transmission electron microscopy (TEM) and micro crystallographic analysis with electron backscattered diffraction (EBSD), we were able to quantitatively characterize surface substructures that can lead to localized thermal breakdown of superconductivity. Important to these studies was the development of sample preparation techniques that made the cutout single, bi-crystal and tri-crystal Nb coupons as representative as possible of the surface properties of cavities manufactured by standard techniques.

  20. Structural and electrical properties of grain boundary Josephson junctions based on Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} thin films

    Energy Technology Data Exchange (ETDEWEB)

    Lopera, W.; Girata, D. [Antioquia Univ., Medellin (Colombia). Dept. of Fisica; Osorio, J.; Prieto, P. [Dept. de Fisica, Univ. del Valle, Cali (Colombia)

    2000-07-01

    An in situ deposition sputtering process at high pressure has been developed for preparing high quality superconducting Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} thin films on different substrates. Both microstructural and electrical properties were well characterized by TEM, AFM, RBS, X-ray diffraction, resistivity and magnetic susceptibility. The high reproducibility of the film quality facilitated a detailed study of Josephson effect in bicrystalline grain boundary junctions (GBJs). Thin films were deposited on (001) SrTiO{sub 3} bicrystals with misorientation angles of 24 and patterned by a photolithography process using Br-ethanol chemical etching. The width of the microbridges ranges from 10 to 50 {mu}m. The critical current densities across the grain boundary have been measured and compared to the critical current in the film. A modulation in the critical current was found under magnetic field and also Shapiro steps in the I-V curves under microwave irradiation have been observed indicating a Josephson behavior. Electrical properties are well described by the resistively shunted junction (RSJ) model. The I{sub c}R{sub n} product reaches values around 2.0 mV at 4.2 K. (orig.)

  1. Characterization of Josephson junctions for the elaboration of high-T{sub c} SQUIDS

    Energy Technology Data Exchange (ETDEWEB)

    Vivas, P.; Chacon, M.; Gomez, M.; Prieto, P. [Valle Univ., Cali (Colombia). Dept. de Fisica

    2000-07-01

    In this work we report the fabrication of superconductor loops, formed by an array of two Josephson junctions (JJ) in parallel. The JJ are based on YBa{sub 2}Cu{sub 3}O{sub 7-x} epitaxial thin films deposited on SrTiO{sub 3} bicrystal substrates with misorientation angles of 24 and 36.8 . The epitaxial, c-axis oriented YBa{sub 2}Cu{sub 3}O{sub 7-x} films were grown ''in situ'' by a high oxygen pressure DC sputtering technique. For the fabrication of the superconductor loop a photolithographic method and a non-aqueous chemical etching were used. The superconducting properties of the superconductor loops were analyzed by measuring the current-voltage characteristics. The magnetic field dependence of the critical current I{sub c}(B) and the I-V curves under microwave irradiation showed weak-link Josephson behavior. The dependence of I{sub c}(B) shows an interference pattern due to the phase differences across the both junctions. (orig.)

  2. High temperature superconducting thin films and quantum interference devices (SQUIDs) for gradiometers

    CERN Document Server

    Graf zu Eulenburg, A

    1999-01-01

    the best balance and gradient sensitivity at 1kHz were 3x10 sup - sup 3 and 222fT/(cm sq root Hz))) respectively. The measured spatial response to a current carrying wire was in good agreement with a theoretical model. A significant performance improvement was obtained with the development of a single layer gradiometer with 13mm baseline, fabricated on 30x10mm sup 2 bicrystals. For such a device, the gradient sensitivity at 1kHz was 50fT/(cm sq root Hz)) and the gradiometer was used successfully for unshielded magnetocardiography. A parasitic effective area compensation scheme was employed with two neighbouring SQUIDs coupled in an opposite sense to the same gradiometer loop. This improved the balance from the intrinsic value of 10 sup - sup 3 to 3x10 sup - sup 5. This thesis describes several aspects of the development of gradiometers using high temperature Superconducting Quantum Interference Devices (SQUID). The pulsed laser deposition of thin films of YBa sub 2 Cu sub 3 O sub 7 sub - subdelta (YBCO) on Sr...

  3. High critical current density YBCO films and fabrication of dc-SQUIDs

    CERN Document Server

    Kuriki, S; Kawaguchi, Y; Matsuda, M; Otowa, T

    2002-01-01

    In order to improve the sensitivity of SQUID magnetometers made of high-T sub c films, we have studied the conditions of pulsed-laser deposition of YBCO films. Among the different deposition parameters examined, extensive degassing of the vacuum chamber before and precise control of the substrate temperature during the film deposition were found effective for obtaining high critical temperature T sub c and high critical current density J sub c. It was also found that the residual-resistance ratio has a clear correlation with J sub c , indicating that it can be a good, and easy to measure, index of the film quality. Films having T sub c approx 89-90 K and J sub c >= 5x10 sup 6 A cm sup - sup 2 at 77 K were used to fabricate SQUIDs without a pickup loop. Grain-boundary junctions formed on bicrystal substrates with a 30 deg. misorientation angle exhibited I sub c R sub n values of more than 100 mu V at 77 K. The well-known scaling behaviour of the relation I sub c R sub n propor to (J sup G sup B sub c) sup 1 su...

  4. Resonant behavior of the barrier of YBa{sub 2}Cu{sub 3}O{sub 7} grain boundary Josephson junctions fabricated on bicrystalline substrates with different geometries

    Energy Technology Data Exchange (ETDEWEB)

    Navacerrada, M.A., E-mail: mdelosangeles.navacerrada@upm.es [Grupo de Acustica Arquitectonica, Escuela Tecnica Superior de Arquitectura, Universidad Politecnica de Madrid, Avenida Juan de Herrera 4, 28040 Madrid (Spain); Lucia, M.L.; Sanchez-Quesada, F. [Departamento Fisica Aplicada III (Electricidad y Electronica), Facultad de Cc. Fisicas, Universidad Complutense, Avenida Complutense s/n, 28040 Madrid (Spain)

    2012-12-14

    We have analyzed a resonant behavior in the dielectric constant associated to the barrier of YBa{sub 2}Cu{sub 3}O{sub 7} (YBCO) grain boundary Josephson junctions (GBJJs) fabricated on a wide variety of bicrystalline substrates: 12 Degree-Sign [0 0 1] tilt asymmetric, 24 Degree-Sign [0 0 1] tilt asymmetric, 24 Degree-Sign [0 0 1] tilt symmetric, 24 Degree-Sign [1 0 0] tilt asymmetric, 45 Degree-Sign [1 0 0] tilt asymmetric and 24 Degree-Sign [0 0 1] tilt symmetric +45 Degree-Sign [1 0 0] tilt asymmetric bicrystals. The resonance analysis allows us to estimate a more appropriate value of the relative dielectric constant, and so a more adequate value for the length L of the normal N region assuming a SNINS model for the barrier. In this work, the L dependence on the critical current density Jc has been investigated. This analysis makes possible a single representation for all the substrate geometries independently on around which axes the rotation is produced to generate the grain boundary. On the other hand, no clear evidences exist on the origin of the resonance. The resonance frequency is in the order of 10{sup 11} Hz, pointing to a phonon dynamic influence on the resonance mechanism. Besides, its position is affected by the oxygen content of the barrier: a shift at low frequencies is observed when the misorientation angle increases.

  5. Paving the way to nanoionics: atomic origin of barriers for ionic transport through interfaces

    Science.gov (United States)

    Frechero, M. A.; Rocci, M.; Sánchez-Santolino, G.; Kumar, Amit; Salafranca, J.; Schmidt, Rainer; Díaz-Guillén, M. R.; Durá, O. J.; Rivera-Calzada, A.; Mishra, R.; Jesse, Stephen; Pantelides, S. T.; Kalinin, Sergei V.; Varela, M.; Pennycook, S. J.; Santamaria, J.; Leon, C.

    2015-12-01

    The blocking of ion transport at interfaces strongly limits the performance of electrochemical nanodevices for energy applications. The barrier is believed to arise from space-charge regions generated by mobile ions by analogy to semiconductor junctions. Here we show that something different is at play by studying ion transport in a bicrystal of yttria (9% mol) stabilized zirconia (YSZ), an emblematic oxide ion conductor. Aberration-corrected scanning transmission electron microscopy (STEM) provides structure and composition at atomic resolution, with the sensitivity to directly reveal the oxygen ion profile. We find that Y segregates to the grain boundary at Zr sites, together with a depletion of oxygen that is confined to a small length scale of around 0.5 nm. Contrary to the main thesis of the space-charge model, there exists no evidence of a long-range O vacancy depletion layer. Combining ion transport measurements across a single grain boundary by nanoscale electrochemical strain microscopy (ESM), broadband dielectric spectroscopy measurements, and density functional calculations, we show that grain-boundary-induced electronic states act as acceptors, resulting in a negatively charged core. Besides the possible effect of the modified chemical bonding, this negative charge gives rise to an additional barrier for ion transport at the grain boundary.

  6. Solidification in a Supercomputer: From Crystal Nuclei to Dendrite Assemblages

    Science.gov (United States)

    Shibuta, Yasushi; Ohno, Munekazu; Takaki, Tomohiro

    2015-08-01

    Thanks to the recent progress in high-performance computational environments, the range of applications of computational metallurgy is expanding rapidly. In this paper, cutting-edge simulations of solidification from atomic to microstructural levels performed on a graphics processing unit (GPU) architecture are introduced with a brief introduction to advances in computational studies on solidification. In particular, million-atom molecular dynamics simulations captured the spontaneous evolution of anisotropy in a solid nucleus in an undercooled melt and homogeneous nucleation without any inducing factor, which is followed by grain growth. At the microstructural level, the quantitative phase-field model has been gaining importance as a powerful tool for predicting solidification microstructures. In this paper, the convergence behavior of simulation results obtained with this model is discussed, in detail. Such convergence ensures the reliability of results of phase-field simulations. Using the quantitative phase-field model, the competitive growth of dendrite assemblages during the directional solidification of a binary alloy bicrystal at the millimeter scale is examined by performing two- and three-dimensional large-scale simulations by multi-GPU computation on the supercomputer, TSUBAME2.5. This cutting-edge approach using a GPU supercomputer is opening a new phase in computational metallurgy.

  7. Operation of high- Tc SFQ devices at near liquid nitrogen temperature

    Science.gov (United States)

    Kim, Y. H.; Kang, J. H.; Lee, J. M.; Hahn, T. S.; Choi, S. S.; Park, S. J.

    1997-02-01

    As the operating temperature of the SFQ logic circuits gets higher by using high- Tc superconductors, the effect of noise on switching a Josephson junction to the voltage state becomes more important. In this paper, we report our work on high- Tc SFQ RS flip-flop which was made with YBCO thin film deposited on a SrTiO 3 bi-crystal. The circuit operated correctly at 71 K over the 200 computer-generated clock cycles without making errors, where a reset or a set operation was made over one clock cycle. Good agreement between the measured data and the calculation based on the thermal activation theory was obtained. The effective noise temperature used to fit the data was much higher than the physical temperature. This could be due to the instrument noise. Improvement in the measurement set-up might reduce the effective noise temperature. Also our measurement results indicate that the elevation of the operating temperature near the liquid nitrogen temperature may not affect the margin of the circuit.

  8. Miniaturization of Micro-Solder Bumps and Effect of IMC on Stress Distribution

    Science.gov (United States)

    Choudhury, Soud Farhan; Ladani, Leila

    2016-07-01

    As the joints become smaller in more advanced packages and devices, intermetallic (IMCs) volume ratio increases, which significantly impacts the overall mechanical behavior of joints. The existence of only a few grains of Sn (Tin) and IMC materials results in anisotropic elastic and plastic behavior which is not detectable using conventional finite element (FE) simulation with average properties for polycrystalline material. In this study, crystal plasticity finite element (CPFE) simulation is used to model the whole joint including copper, Sn solder and Cu6Sn5 IMC material. Experimental lap-shear test results for solder joints from the literature were used to validate the models. A comparative analysis between traditional FE, CPFE and experiments was conducted. The CPFE model was able to correlate the experiments more closely compared to traditional FE analysis because of its ability to capture micro-mechanical anisotropic behavior. Further analysis was conducted to evaluate the effect of IMC thickness on stress distribution in micro-bumps using a systematic numerical experiment with IMC thickness ranging from 0% to 80%. The analysis was conducted on micro-bumps with single crystal Sn and bicrystal Sn. The overall stress distribution and shear deformation changes as the IMC thickness increases. The model with higher IMC thickness shows a stiffer shear response, and provides a higher shear yield strength.

  9. The effect of strain on grains and grain boundaries in YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} coated conductors

    Energy Technology Data Exchange (ETDEWEB)

    Van der Laan, D C [Department of Physics, University of Colorado, Boulder, CO 80309 (United States); Haugan, T J; Barnes, P N [Air Force Research Laboratory, Wright-Patterson AFB, OH 45433 (United States); Abraimov, D; Kametani, F; Larbalestier, D C [National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL 32310 (United States); Rupich, M W, E-mail: danko@boulder.nist.go [American Superconductor Corporation, Westborough, MA 01598 (United States)

    2010-01-15

    The role of grains and grain boundaries in producing reversible strain effects on the transport current critical current density (J{sub c}) of YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} (YBCO) coated conductors that are produced with metal-organic deposition (MOD) was investigated. The strain ({epsilon}) dependence of J{sub c} for full-width coated conductors is compared with that for samples in which the current transport was limited to a few or single grain boundaries by cutting narrow tracks with a laser or focused ion beam, as well as with thin films deposited on bicrystalline SrTiO{sub 3} substrates by use of pulsed-laser deposition (PLD). Our results show that the dependences of J{sub c} on {epsilon} for the grains and for the grain boundaries from the two kinds of YBCO samples can be expressed by the same function, however with a greater effective tensile strain at the grain boundaries than in the grains. The really striking result is that the grain boundary strain is 5-10 times higher for grain boundaries of in situ PLD grown bicrystals as compared to the aperiodic, meandered, nonplanar grain boundaries that develop in ex situ grown MOD-YBCO in the coated conductor of this study.

  10. Dynamics of d-wave YBa{sub 2}Cu{sub 3}O{sub 7-x} dc SQUIDs

    Energy Technology Data Exchange (ETDEWEB)

    Bauch, T [Quantum Device Physics Laboratory, Department of Microtechnology and Nanoscience, MC2, Chalmers University of Technology, S-41296 Goeteborg (Sweden); Cedergren, K [Quantum Device Physics Laboratory, Department of Microtechnology and Nanoscience, MC2, Chalmers University of Technology, S-41296 Goeteborg (Sweden); Johansson, J [Quantum Device Physics Laboratory, Department of Microtechnology and Nanoscience, MC2, Chalmers University of Technology, S-41296 Goeteborg (Sweden); Rotoli, G [Dipartimento di Ingeneria Meccanica, Energetica e Gestionale, Universita of L' Aquila, Localita Moneluco, L' Aquila (Italy); Tafuri, F [Dipartimento Ingeneria dell' Informatione, INFM, Seconda Universita di Napoli, Aversa (Italy); Lombardi, F [Quantum Device Physics Laboratory, Department of Microtechnology and Nanoscience, MC2, Chalmers University of Technology, S-41296 Goeteborg (Sweden)

    2007-02-15

    The predominant d-wave pairing symmetry in high temperature superconductors leads to an unconventional current-phase relation in Josephson junctions. This circumstance may induce new effects in the dynamics of dc SQUIDs. In this contribution we report on the measurements of the dependence of the SQUID Josephson current on the external magnetic field taken at very low temperatures, down to 20 mK. Different grain boundaries have been fabricated by using the biepitaxial and the bicrystal technique. Some of the effects which are induced by a nonsinusoidal current-phase relation can be clearly identified in the dynamics of the SQUIDs. The experimental data are also compared with theoretical simulations taking into account the inductance of the loop. The data show that, in specific conditions, a non-negligible inductance of the loop can induce effects similar to an unconventional current-phase relation, with a pronounced second harmonic sin(2{psi}) term. This fact has to be taken into account when designing d-wave SQUIDs for quantum circuitry.

  11. Synthesis of Uniformly Distributed Single- and Double-sided Zinc Oxide (ZnO) Nanocombs

    Energy Technology Data Exchange (ETDEWEB)

    Petford-Long, Amanda K.; Liu, Yuzi; Altintas Yildirim, Ozlem

    2015-11-15

    Uniformly distributed single- and double-sided zinc oxide (ZnO) nanocomb structures have been prepared by a vapor-liquid-solid technique from a mixture of ZnO nanoparticles and graphene nanoplatelets. The ZnO seed nanoparticles were synthesized via a simple precipitation method. The structure of the ZnO nanocombs could easily be controlled by tuning the carrier-gas flow rate during growth. Higher flow rate resulted in the formation of uniformly-distributed single-sided comb structures with nanonail-shaped teeth, as a result of the self-catalysis effect of the catalytically active Zn-terminated polar (0001) surface. Lower gas flow rate was favorable for production of double-sided comb structures with the two sets of teeth at an angle of similar to 110 degrees to each other along the comb ribbon, which was attributed to the formation of a bicrystal nanocomb ribbon. The formation of such a double-sided structure with nanonail-shaped teeth has not previously been reported.

  12. Simulations of thermal conductance across tilt grain boundaries in graphene

    Institute of Scientific and Technical Information of China (English)

    Peng Wang; Bo Gong; Qiong Feng; Hong-Tao Wang

    2012-01-01

    Non-equilibrium molecular dynamics (MD) method was performed to simulate the thermal transportation process in graphene nanoribbons (GNRs).A convenient way was conceived to introduce tilt grain boundaries (GBs) into the graphene lattice by repetitive removing C atom rows along certain directions.Comprehensive MD simulations reveal that larger-angle GBs are effective thermal barriers and substantially reduce the average thermal conductivity of GNRs.The GB thermal conductivity is ~ 10 W.m-1·K-1 for a bicrystal GNR with a misorientation of 21.8°,which is ~97% less than that of a prefect GNR with the same size.The total thermal resistance has a monotonic dependence on the density of the 5-7 defects along the GBs.A theoretical model is proposed to capture this relation and resolve the contributions by both the reduction in the phonon mean free path and the defect-induced thermal resistance.

  13. Characterization of directly coupled YBa{sub 2}Cu{sub 3}O{sub 7-x} SQUID magnetometers

    Energy Technology Data Exchange (ETDEWEB)

    Guillaume, Alexander; Beister, Verena; Scholtyssek, Jan M.; Ludwig, Frank; Schilling, Meinhard [Institut fuer Elektrische Messtechnik und Grundlagen der Elektrotechnik, Technische Universitaet Braunschweig, Hans-Sommer-Str. 66, D-38106 Braunschweig, Germany. (Germany)

    2012-07-01

    Superconducting Quantum Interference Devices (SQUIDs) can be employed as highly sensitive magnetic field sensors in a variety of applications such as magnetoencephalography or magnetic nanoparticle detection. We fabricated SQUIDs from the high-T{sub c} superconductor YBa{sub 2}Cu{sub 3}O{sub 7-x} on symmetric SrTiO{sub 3}-bicrystal substrates by pulsed laser deposition and argon ion etching. The layout consists of two directly coupled magnetometers on one chip which are attached to a rectangular pickup loop. The measurements were carried out in a liquid nitrogen container using a variable temperature insert. The temperature at the magnetically shielded sample holder can be adjusted between 77 K and 100 K. Here, we present measurements of the I-V-curves under the influence of a magnetic field for different sample temperatures. Also, the influence of the temperature and the influence of the bias current on the V-{Phi}-curves were investigated. From these measurements, parameters of the SQUID were calculated and compared to the theoretical estimations. Additionally, noise spectra were recorded for different bias reversal frequencies by using a direct-coupled flux-locked loop electronics from Magnicon GmbH.

  14. Measurement of Localized Nonlinear Microwave Response of Superconductors

    Science.gov (United States)

    Lee, Sheng-Chiang; Palmer, Benjamin; Maiorov, B.

    2005-03-01

    We measure the local harmonic generation from superconducting thin films at microwave frequencies to investigate the intrinsic nonlinear Meissner effect near T/c in zero magnetic field. Both second and third harmonic generation are measured to identify time-reversal symmetry breaking (TRSB) and time-reversal symmetric (TRS) nonlinearities. The microscope can measure the local nonlinear response of a bicrystal grain boundary [Sheng-Chiang Lee and Steven M. Anlage, Physica C 408-410, 324 (2004); cond-mat/0408170]. We also performed a systematic doping-dependent study of the nonlinear response and find that the TRS characteristic nonlinearity current density scale follows the doping dependence of the de-pairing critical current density [cond-mat/0405595]. We extract a spontaneous TRSB characteristic current density scale that onsets at T/c, grows with decreasing temperature, and systematically decreases in magnitude (at fixed T/T/c) with under-doping. The origin of this current scale could be Josephson circulating currents or the spontaneous magnetization associated with a TRSB order parameter.

  15. LLE review, Volume 77. Quarterly report, October--December 1998

    Energy Technology Data Exchange (ETDEWEB)

    Regan, S.P. [ed.

    1998-12-31

    This volume of the LLE Review, covering the period October--December 1998, includes two articles addressing issues applicable to direct-drive ICF on the National Ignition Facility (NIF): laser-plasma interactions and laser-irradiation uniformity. Additional highlights of the research presented in this issue are: (1) P.B. Radha and S. Skupsky present a novel charged-particle diagnostic that performs simultaneous {rho}R measurements of the fuel, shell, and ablator regions of a compressed ICF target, consisting of an inner DT fuel region, a plastic (CH) shell, and an ablator (CD), by measuring the knock-on deuteron spectrum. (2) F. Dahmani, S. Burns, J. Lambropoulos, S. Papernov, and A. Schmid report results from stress-inhibited laser-driven crack propagation and stress-delayed damage-initiation experiments in fused silica at 351 nm. Research is underway presently to determine the ramifications of these findings for large-aperture systems, such as OMEGA. (3) V. Goncharov presents an analytic theory of the ablative Richtmyer-Meshkov instability, which shows that the main stabilizing mechanism of the ablation-front perturbations is the dynamic overpressure of the blowoff plasma with respect to the target material. The perturbation evolution during the shock transit time is studied to determine the initial conditions for the Rayleigh-Taylor phase of the instability and to analyze the level of laser imprint on ICF direct-drive targets. (4) J.M. Larkin, W.R. Donaldson, T.H. Foster, and R.S. Knox examine the triplet state of rose bengal, a dye used in photodynamic therapy, that is produced by 1,064-nm excitation of T{sub 1}. (5) R. Adam, M. Currie, R. Sobolewski, O. Harnack, and M. Darula report measurements of the picosecond photoresponse of a current-biased YBCO microbridge coupled to a bicrystal YBCO Josephson junction.

  16. Improvement in the properties of Ag-doped YBa{sub 2}Cu{sub 3}O{sub 7-x} grain boundary Josephson junctions

    Energy Technology Data Exchange (ETDEWEB)

    Bolanos, G.; Baca, E.; Osorio, J.; Prieto, P. [Valle Univ., Cali (Colombia). Dept. de Fisica

    2000-07-01

    Ag-doped YBa{sub 2}Cu{sub 3}O{sub 7-x} (YBCO) thin films using 5 to 20 wt% Ag-doped YBCO targets have been grown by a DC sputtering technique on SrTiO{sub 3} bicrystals. Critical currents of 4 to 5 x 10{sup 6} A/cm{sup 2} at 77 K were measured in YBCO films doped with 5 wt% Ag which has been found to be higher than the value of 1 x 10{sup 6} A/cm{sup 2} measured in undoped samples. The normal resistivity decreases by a doping of 5 wt% Ag and increases for higher Ag concentrations. The critical temperature, T{sub c}, of the Ag-YBCO films remained unchanged at 92 K as in the undoped YBCO samples. An I{sub c}R{sub n} product of 170 {mu}V at 77 K was found in grain boundary Josephson junctions (GBJJs) with 5 wt% Ag, compared with the value of 100 {mu}V measured in undoped samples at the same temperature. Current-voltage characteristics were measured in GBJJs, showing Shapiro steps under microwave radiation and Fraunhofer patterns with an external magnetic field. The improvement in the normal and superconducting properties of Ag-doped YBCO films has been interpreted using the De Genes model to establish that YBCO containing metallic Ag addition shows a superconductor-normal metal-superconductor (S-N-S) behavior, thereby the Ag-doping enhances the weak link behavior and is, therefore, appropriate for electronic applications. (orig.)

  17. Effect of natural homointerfaces on the magnetic properties of pseudomorphic La0.7Sr0.3MnO3 thin film: Phase separation vs split domain structure

    Science.gov (United States)

    Congiu, Francesco; Sanna, Carla; Maritato, Luigi; Orgiani, Pasquale; Geddo Lehmann, Alessandra

    2016-12-01

    We studied the effect of naturally formed homointerfaces on the magnetic and electric transport behavior of a heavily twinned, 40 nm thick, pseudomorphic epitaxial film of La0.7Sr0.3MnO3 deposited by molecular beam epitaxy on ferroelastic LaAlO3(001) substrate. As proved by high resolution X-ray diffraction analysis, the lamellar twin structure of the substrate is imprinted in La0.7Sr0.3MnO3. In spite of the pronounced thermomagnetic irreversibility in the DC low field magnetization, spin-glass-like character, possibly related to the structural complexity, was ruled out, on the base of AC susceptibility results. The magnetic characterization indicates anisotropic ferromagnetism, with a saturation magnetization Ms = 3.2 μB/Mn, slightly reduced with respect to the fully polarized value of 3.7 μB/Mn. The low field DC magnetization vs temperature is non bulklike, with a two step increase in the field cooled MFC(T) branch and a two peak structure in the zero field cooled MZFC(T) one. Correspondingly, two peaks are present in the resistivity vs temperature ρ(T) curve. With reference to the behavior of epitaxial manganites deposited on bicrystal substrates, results are discussed in terms of a two phase model, in which each couple of adjacent ferromagnetic twin cores, with bulklike TC = 370 K, is separated by a twin boundary with lower Curie point TC = 150 K, acting as barrier for spin polarized transport. The two phase scenario is compared with the alternative one based on a single ferromagnetic phase with the peculiar ferromagnetic domains structure inherent to twinned manganites films, reported to be split into interconnected and spatially separated regions with in-plane and out-of-plane magnetization, coinciding with twin cores and twin boundaries respectively.

  18. Resistively shunted YBa{sub 2}Cu{sub 3}O{sub 7} grain boundary junctions and low-noise SQUIDs patterned by a focused ion beam down to 80 nm linewidth

    Energy Technology Data Exchange (ETDEWEB)

    Nagel, J; Konovalenko, K B; Kemmler, M; Turad, M; Werner, R; Kleiner, R; Koelle, D [Physikalisches Institut-Experimentalphysik II and Center for Collective Quantum Phenomena, Universitaet Tuebingen, Auf der Morgenstelle 14, D-72076 Tuebingen (Germany); Kleisz, E; Menzel, S; Klingeler, R; Buechner, B, E-mail: koelle@uni-tuebingen.de [Leibniz-Institut fuer Festkoerper- und Werkstoffforschung (IFW) Dresden, D-01171 Dresden (Germany)

    2011-01-15

    YBa{sub 2}Cu{sub 3}O{sub 7} 24{sup 0} (30{sup 0}) bicrystal grain boundary junctions (GBJs), shunted with 60 nm (20 nm) thick Au, were fabricated by focused ion beam milling with widths 80 nm {<=} w {<=} 7.8 {mu}m. At 4.2 K we find critical current densities j{sub c} in the 10{sup 5} A cm{sup -2} range (without a clear dependence on w) and an increase in resistance times junction area {rho}{sub n} with an approximate scaling {rho}{sub n{proportional_to}}w{sup 1/2}. For the narrowest GBJs j{sub c{rho}n} = I{sub c}R{sub n{approx}}100 {mu}V (with critical current I{sub c} and junction resistance R{sub n}), which is promising for the realization of sensitive nanoSQUIDs for the detection of small spin systems. We demonstrate that our fabrication process allows the realization of sensitive nanoscale dc SQUIDs; for a SQUID with w{approx}100 nm wide GBJs we find an rms magnetic flux noise spectral density of S{sub {Phi}}{sup 1/2{approx}}4 {mu}{Phi}{sub 0} Hz{sup -1/2} in the white noise limit. We also derive an expression for the spin sensitivity S{sub {mu}}{sup 1/2}, which depends on S{sub {Phi}}{sup 1/2}, on the location and orientation of the magnetic moment of a magnetic particle to be detected by the SQUID, and on the SQUID geometry. For the unoptimized SQUIDs presented here, we estimate S{sub {mu}}{sup 1/2} = 390 {mu}{sub B} Hz{sup -1/2}, which could be further improved by at least an order of magnitude.

  19. High transition-temperature SQUID magnetometers and practical applications

    Energy Technology Data Exchange (ETDEWEB)

    Dantsker, E [Univ. of California, Berkeley, CA (United States). Dept. of Physics

    1997-05-01

    The design, fabrication and performance of SQUID magnetometers based on thin films of the high-transition temperature superconductor YBa{sub 2}Cu{sub 3}O{sub 7{minus}x} (YBCO) are described. Essential to the achieving high magnetic field resolution at low frequencies is the elimination of 1/f flux noise due to thermally activated hopping of flux vortices between pinning sites in the superconducting films. Through improvements in processing, 1/f noise in single layer YBCO thin films and YBCO-SrTiO{sub 3}-YBCO trilayers was systematically reduced to allow fabrication of sensitive SQUID magnetometers. Both single-layer directly coupled SQUID magnetometers and multilayer magnetometers were fabricated, based on the dc SQUID with bicrystal grain boundary Josephson junctions. Multilayer magnetometers had a lower magnetic field noise for a given physical size due to greater effective sensing areas. A magnetometer consisting of a SQUID inductively coupled to the multiturn input coil of a flux transformer in a flip-chip arrangement had a field noise of 27 fT Hz{sup {minus}1/2} at 1 Hz and 8.5 fT Hz{sup {minus}1/2} at 1 kHz. A multiloop multilayer SQUID magnetometer had a field noise of 37 fT Hz{sup {minus}1/2} at 1 Hz and 18 fT Hz{sup {minus}1/2} at 1 kHz. A three-axis SQUID magnetometer for geophysical applications was constructed and operated in the field in the presence of 60 Hz and radiofrequency noise. Clinical quality magnetocardiograms were measured using multilayer SQUID magnetometers in a magnetically shielded room.

  20. The influence of grain boundary structure on the penetration of gallium into aluminum grain boundaries

    Science.gov (United States)

    Hugo, Richard Charles

    1998-12-01

    Liquid Metal Embrittlement is a form of environmental embrittlement that dramatically reduces the fracture toughness of many metals and alloys. It occurs when surfaces of certain solid metals are wet by certain liquid metals. The Al-Ga system provides a remarkable example of intergranular attack. The Al-Ga equilibrium phase diagram reveals no intermetallic compounds and very limited mutual solubilities, which implies that interactions between Al and Ga should be minimal. Yet when liquid Ga wets the surface of an unstressed Al specimen, the Ga will penetrate the Al grain boundaries, replacing each boundary with a liquid layer. The driving force is generally considered to be the reduction in energy when a grain boundary is replaced by two Ga-Al interfaces. Once an Al sample has been penetrated by Ga, it fails at almost no load. In this dissertation, in-situ Transmission Electron Microscope (TEM) studies are presented that elucidate the physical nature of the Ga penetration front. Although many of the TEM specimens were bicrystals, all but one of the grain boundaries studied were "general" boundaries; that is, they were low symmetry boundaries with high-index rotation axes, and no low-index planes common to both grains. Since the atomic structure of these grain boundaries cannot be resolved experimentally, atomistic computer models were constructed to assist in interpreting TEM results. TEM observations indicated that the penetration front is a line defect, possessing a stress field that interacts with lattice dislocations. The penetration front was also observed to interact with structural variations within the grain boundary. Interactions with lattice dislocations were used to estimate the penetration front thickness. Penetration speeds were not found to be determined by grain boundary energy or grain boundary excess volume. Penetration speeds were, however, found to depend qualitatively on the presence of penetration barriers in the grain boundary.

  1. High transition-temperature SQUID magnetometers and practical applications

    Energy Technology Data Exchange (ETDEWEB)

    Dantsker, Eugene [Univ. of California, Berkeley, CA (United States). Dept. of Physics

    1997-05-01

    The design, fabrication and performance of SQUID magnetometers based on thin films of the high-transition temperature superconductor YBa2Cu3O7-x (YBCO) are described. Essential to the achieving high magnetic field resolution at low frequencies is the elimination of 1/f flux noise due to thermally activated hopping of flux vortices between pinning sites in the superconducting films. Through improvements in processing, 1/f noise in single layer YBCO thin films and YBCO-SrTiO3-YBCO trilayers was systematically reduced to allow fabrication of sensitive SQUID magnetometers. Both single-layer directly coupled SQUID magnetometers and multilayer magnetometers were fabricated, based on the dc SQUID with bicrystal grain boundary Josephson junctions. Multilayer magnetometers had a lower magnetic field noise for a given physical size due to greater effective sensing areas. A magnetometer consisting of a SQUID inductively coupled to the multiturn input coil of a flux transformer in a flip-chip arrangement had a field noise of 27 fT Hz-1/2 at 1 Hz and 8.5 fT Hz-1/2 at 1 kHz. A multiloop multilayer SQUID magnetometer had a field noise of 37 fT Hz-1/2 at 1 Hz and 18 fT Hz-1/2 at 1 kHz. A three-axis SQUID magnetometer for geophysical applications was constructed and operated in the field in the presence of 60 Hz and radiofrequency noise. Clinical quality magnetocardiograms were measured using multilayer SQUID magnetometers in a magnetically shielded room.

  2. Phase field simulations of plastic strain-induced phase transformations under high pressure and large shear

    Science.gov (United States)

    Javanbakht, Mahdi; Levitas, Valery I.

    2016-12-01

    Pressure and shear strain-induced phase transformations (PTs) in a nanograined bicrystal at the evolving dislocations pile-up have been studied utilizing a phase field approach (PFA). The complete system of PFA equations for coupled martensitic PT, dislocation evolution, and mechanics at large strains is presented and solved using the finite element method (FEM). The nucleation pressure for the high-pressure phase (HPP) under hydrostatic conditions near a single dislocation was determined to be 15.9 GPa. Under shear, a dislocation pile-up that appears in the left grain creates strong stress concentration near its tip and significantly increases the local thermodynamic driving force for PT, which causes nucleation of HPP even at zero pressure. At pressures of 1.59 and 5 GPa and shear, a major part of a grain transforms to HPP. When dislocations are considered in the transforming grain as well, they relax stresses and lead to a slightly smaller stationary HPP region than without dislocations. However, they strongly suppress nucleation of HPP and require larger shear. Unexpectedly, the stationary HPP morphology is governed by the simplest thermodynamic equilibrium conditions, which do not contain contributions from plasticity and surface energy. These equilibrium conditions are fulfilled either for the majority of points of phase interfaces or (approximately) in terms of stresses averaged over the HPP region or for the entire grain, despite the strong heterogeneity of stress fields. The major part of the driving force for PT in the stationary state is due to deviatoric stresses rather than pressure. While the least number of dislocations in a pile-up to nucleate HPP linearly decreases with increasing applied pressure, the least corresponding shear strain depends on pressure nonmonotonously. Surprisingly, the ratio of kinetic coefficients for PT and dislocations affect the stationary solution and the nanostructure. Consequently, there are multiple stationary solutions

  3. Low-frequency noise in high-{Tc} superconductor Josephson junctions, SQUIDs, and magnetometers

    Energy Technology Data Exchange (ETDEWEB)

    Miklich, A.H.

    1994-05-01

    Design and performance of high-T{sub c} dc superconducting quantum interference devices (SQUEDs), junctions that comprise them, and magnetometers made from them are described, with attention to sources of 1/f noise. Biepitaxial junctions are found to have large levels of critical current fluctuations which make them unsuitable for low-noise SQUIDS; this suggests a poorly connected interface at the grain boundary junction. SQUIDs from bicrystal junctions have levels of critical current noise controllable using bias current reversal techniques which leave the noise white down to frequencies of a few Hz. A SQUID with an energy resolution of 1.5{times}10{sup {minus}30} J Hz{sup {minus}1} at 1 Hz is reported. Magnetometers in which a (9 mm){sup 2} pickup loop is directly coupled to a SQUID body have achieved field resolutions of 93 fT Hz{sup {minus}1/2} down to frequencies below I Hz, improving to 39 fT Hz{sup {minus}1/2} at 1 Hz with the addition of a 50mm-diameter single-turn flux transformer. Poor coupling to pickup loop makes it difficult to satisfy competing goals of high field resolution and small detector size necessary for multichannel biomagnetic imaging. Improved coupling is demonstrated by the use of multiturn-input-coil flux transformers, and a resolution of 35 fT Hz{sup {minus}1/2} in the white noise region is reported with a (10 mm){sup 2} pickup loop. However, additional 1/f noise from processed multilayer structures in the transformer limits the resolution at 1 Hz to 114 fT Hz{sup {minus}1/2}. High-T{sub c} SQUIDs exhibit additional 1/f noise when cooled in a nonzero static magnetic field because of additional flux vortices trapped in the film, with the noise power at 1 Hz typically increasing by a factor of 10--20 in a field of 0.05mT (0.5 G). Finally, a SQUID-based voltmeter with a resolution of 9.2 pV.Hz{sup {minus}1/2} at 10 Hz (24 pV Hz{sup {minus}1/2} at 1 Hz) is described.

  4. Surface polishing of niobium for superconducting radio frequency (SRF) cavity applications

    Energy Technology Data Exchange (ETDEWEB)

    Zhao, Liang [College of William and Mary, Williamsburg, VA (United States)

    2014-08-01

    Niobium cavities are important components in modern particle accelerators based on superconducting radio frequency (SRF) technology. The interior of SRF cavities are cleaned and polished in order to produce high accelerating field and low power dissipation on the cavity wall. Current polishing methods, buffered chemical polishing (BCP) and electro-polishing (EP), have their advantages and limitations. We seek to improve current methods and explore laser polishing (LP) as a greener alternative of chemical methods. The topography and removal rate of BCP at different conditions (duration, temperature, sample orientation, flow rate) was studied with optical microscopy, scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD). Differential etching on different crystal orientations is the main contributor to fine grain niobium BCP topography, with gas evolution playing a secondary role. The surface of single crystal and bi-crystal niobium is smooth even after heavy BCP. The topography of fine grain niobium depends on total removal. The removal rate increases with temperature and surface acid flow rate within the rage of 0~20 °C, with chemical reaction being the possible dominate rate control mechanism. Surface flow helps to regulate temperature and avoid gas accumulation on the surface. The effect of surface flow rate on niobium EP was studied with optical microscopy, atomic force microscopy (AFM), and power spectral density (PSD) analysis. Within the range of 0~3.7 cm/s, no significant difference was found on the removal rate and the macro roughness. Possible improvement on the micro roughness with increased surface flow rate was observed. The effect of fluence and pulse accumulation on niobium topography during LP was studied with optical microscopy, SEM, AFM, and PSD analysis. Polishing on micro scale was achieved within fluence range of 0.57~0.90 J/cm2, with pulse accumulation adjusted accordingly. Larger area treatment was proved possible by

  5. Discovering the Role of Grain Boundary Complexions in Materials

    Energy Technology Data Exchange (ETDEWEB)

    Harmer, Martin P. [Lehigh Univ., Bethlehem, PA (United States)

    2015-03-19

    in a range of materials systems, and to characterize their structures, range of stability and selected physical properties. First, an Au-based bilayer interfacial phase was discovered at a bicrystal boundary in the Si-Au system. This bilayer transitioned abruptly to an intrinsic (“clean”) grain boundary phase, suggesting first-order phase behavior. This study represents the discovery of grain boundary complexions in a completely new system, i.e., a semiconductor-metal system, giving further support to the expectation that grain boundary complexions are a general phenomenon not limited to any particular class of materials. The TiO2-CuO system exhibited four grain boundary interfacial phases: a monolayer, disordered bilayer, disordered trilayer, and non-wetting nanoscale amorphous drop (which likely resulted from dewetting of a nanoscale IGF). SiO2 contamination was discovered in the TiO2-CuO samples, and we hypothesize that this impurity may have caused an “order-disorder” transition to occur. In other words, we expect that pure TiO2-CuO may have a higher tendency to exhibit ordered bilayer and trilayer complexions, which may also exhibit a well-defined order-disorder transition temperature. In this effort we have also identified unique complexion transitions in yttria and strontium titanate.

  6. Study of the annealing of defects introduced in silver by cold-working (1962); Etude sur le recuit des defauts introduits dans l'argent par ecrouissage (1962)

    Energy Technology Data Exchange (ETDEWEB)

    Regnier-Lebouteux, F. [Commissariat a l' Energie Atomique, Saclay (France). Centre d' Etudes Nucleaires

    1962-07-01

    The tempering and the recrystallisation of silver (99.99 per cent purity) following cold-working is studied by means of density ({delta}d / d {approx_equal} 5.10{sup -6}) and microhardness measurements, and of X-ray diagrams. The results depend in particular on the type and the conditions of the cold-working. For a rolling of 200 per cent carried out at temperatures under 80 deg. C, the recrystallisation occurs already at room temperature. By means of isothermal annealings it has been possible to measure the self-diffusion energy (1.90 eV). For a rolling of 200 per cent carried out at room temperature, there occurs already at 25 deg. C an increase in the density corresponding to an elimination of vacancies. For a bicrystal subjected to a 200 per cent rolling, the tempering is accompanied, from 65 to 90 deg. C, by a decrease in the density due probably to the evaporation of vacancy-impurity complexes formed during the cold-working, the impurity is very likely oxygen. At high temperature, after recrystallisation, a new and big decrease in the density let on a swelling of the silver due no doubt to slightly soluble oxygen. The density of the dislocations formed is evaluated for the different types of cold working. (author) [French] On etudie par des mesures de densite ({delta}d / d {approx_equal} 5.10{sup -6}) I de microdurete, et par des diagrammes de rayons X le revenu et la recristallisation de l'argent (purete 99,99 pour cent) apres ecrouissage. Les resultats dependent notablement du type et des conditions de l'ecrouissage. Pour un laminage de 200 pour cent effectue a temperature inferieure a 80 deg. C, on a observe la recristallisation des l'ambiante. Des recuits isothermes ont permis de mesurer l'energie d'autodiffusion (1,90 eV). Pour un laminage de 200 pour cent effectue a temperature ambiante, on constate des 25 deg. C une augmentation de densite correspondant a l'elimination de lacunes. Pour un bicristal lamine de 200 pour cent

  7. Realizing Controllable Quantum States

    Science.gov (United States)

    Takayanagi, Hideaki; Nitta, Junsaku

    -- 4. Mesoscopic superconductivity with unconventional superconductor or ferromagnet. Ultraefficient microrefrigerators realized with ferromagnet-superconductor junctions / F. Giazotto et al. Anomalous charge transport in triplet superconductor junctions by the synergy effect of the proximity effect and the mid gap Andreev resonant states / Y. Tanaka and S. Kashiwaya. Paramagnetic and glass states in superconductive YBa[symbol]Cu[symbol]O[symbol] ceramics of sub-micron scale grains / H. Deguchi et al. Quantum properties of single-domain triplet superconductors / A. M. Gulian and K. S. Wood. A numerical study of Josephson current in p wave superconducting junctions / Y. Asano et al. Tilted bi-crystal sapphire substrates improve properties of grain boundary YBa[symbol]Cu[symbol]O[symbol] junctions and extend their Josephson response to THZ frequencies / E. Stepantsov et al. Circuit theory analysis of AB-plane tunnel junctions of unconventional superconductor Bi[symbol]Sr[symbol]Ca[symbol]Cu[symbol]O[symbol] / I. Shigeta et al. Transport properties of normal metal/anisotropic superconductor junctions in the eutectic system Sr[symbol]RuO[symbol]Ru / M. Kawamura et al. Macroscopic quantum tunneling in d-wave superconductor Josephson / S. Kawabata et al. Quasiparticle states of high-T[symbol] oxides observed by a Zeeman magnetic field response / S. Kashiwaya et al. Experimentally realizable devices for controlling the motion of magnetic flux quanta in anisotropic superconductors: vortex lenses, vortex diodes and vortex pumps / S. Savel'ev and F. Nori. Stability of vortex-antivortex "molecules" in mesoscopic superconducting triangles / V. R. Misko et al. Superconducting network with magnetic decoration - Hofstadter butterfly in spatially modulated magnetic field / Y. Iye et al. Observation of paramagnetic supercurrent in mesoscopic superconducting rings and disks using multiple-small-tunnel-junction method / A. Kanda et al. Guidance of vortices in high

  8. PREFACE: Superconductivity in ultrathin films and nanoscale systems Superconductivity in ultrathin films and nanoscale systems

    Science.gov (United States)

    Bianconi, Antonio; Bose, Sangita; Garcia-Garcia, Antonio Miguel

    2012-12-01

    A, Gonzalez E M and Vicent J L 2012 Superconducting vortex dynamics on arrays with bicrystal-like structures: matching and rectifier effects Supercond. Sci. Technol. 25 124006 [7]Lehtinen J S and Arutyunov K Yu 2012 The quantum phase slip phenomenon in superconducting nanowires with a low-Ohmic environment Supercond. Sci. Technol. 25 124007

  9. Preface

    Science.gov (United States)

    Gorse, D.; Boutard, J.-L.

    2002-09-01

    propagation kinetics can now be followed at ESRF (Grenoble) using synchrotron radiation imaging techniques. It is now possible to follow the propagation, structure and chemistry of the embrittling phase in the crack, at microscopic and at nanometric scale. It is also possible, in principle, to take into account the role of defects in grain-boundaries (GB) on the penetration of the embrittling species and conversely to investigate the role of the defects produced by wetting on the GB microstructure. We do hope that these techniques open a new and attractive field of research to improve the understanding of LME. The HRTEM study carried out by A. Charai et al. enlightens the importance of crystallography on wetting. Two exemplary couples are thoroughly investigated: the Mo/Ni couple giving rise to an interfacial nanometer thick interface for one type of Mo bicrystal wetted by nickel and the Ni/Pb couple pointing out the role of the GB plane on wetting. Y. Brechet et al. investigated not only the microstructure effects on “LM" penetration into cracks (cracks kinetics and morphologies), but also the plasticity effects ahead of the crack tip, studying a variant of the mythic Al/Ga couple, say the 7010 Aluminum alloy in contact with Gallium, allowing for modifications of the precipitation state at the GBs by applying various heat treatments. Y. Brechet et al. conclude in favour of a step by step penetration process, quasi at atomic scale and give an estimate of crack propagation velocity, of the order of a few micrometers per second, in good agreement with experimental observations. The author stresses the importance of defects in the GBs (precipitates...) at different scales which can explain discrepancies between the experimental crack velocity and the one calculated using a continuum elastic model. The paper presented by W. Ludwig et al. concentrates on two synchrotron radiation imaging techniques (X-ray micro-radiography and micro-fluorescence) available at ESRF (Grenoble) in