bluuebunny/crossref_metadata_2025_split huggingface dataset:
Chemical Vapor Deposition Route to the Fabrication of thin Films of High Temperature Oxide Superconductors
Authors: Kaloyeros Alain E. , Brooks Kenneth C. , Feng Aiguo , Garhart Jonathan 
Published: March 2011

AbstractHigh quality Y‐Ba‐Cu‐O thin films were produced by metal‐organic chemical vapor deposition (MOCVD) using metal chelates of P‐diketonate ligands. The films were grown in a cold‐wall CVD reactor at a reactor pressure of 10 torr and substrate temperature in the range 450‐550°C. Characterization studies were performed using Rutherford Backscattering (RBS), Auger electron spectroscopy (AES), scanning electron microscopy (SEM), and energy‐dispersive x‐ray spectroscopy (EDXS). These studies showed that the films were uniform, continuous, adherent and highly pure—carbon and fluorine contents were below the detection limits of the techniques used. Four point resistivity measurements showed that the films had a sharp superconducting transition at 9OK and exhibited current densities of ‐3x105 A/cm2 (B=0, T=65K) . The Y‐Ba‐Cu‐0 films thus grown were subsequently compared to radio‐frequency (rf) sputtered Y‐Ba‐Cu‐O films. It was found that the MOCVD‐produced films were superior in terms of uniformity, adherence, and electrical properties.
Production of Y‐Ba‐Cu‐0 Superconducting Thin Films by an Aerosol Chemical Vapor Deposition Process
Authors: Driessen A. , Tang Q. , Hilderink L. , Popma Th.J.A. 
Published: March 2011

AbstractThin film production by aerosol deposition is a simple, non‐vacuum method, which under certain conditions of the process parameters, can be considered as a chemical vapor deposition (CVD) process. In this paper we describe the formation of superconducting thin films by aerosol deposition in the CVD regime by using metal‐organic precursors. The best results were obtained with the metal β‐diketonates of Y, Ba and Cu dissolved in butylacetate. This solution was nebulized and sprayed on a heated Si‐substrate with a Zr02‐buffer layer at a temperature of 450 C. After deposition a final heat treatment at a temperature of 800 C was applied. The resulting superconducting film has a Tc>2ero of 75 K.
Multilayer E-Beam Deposition and Annealing of Yba2Cu3O7-δ Thin Films on Lagao3 Substrates
Authors: DeVito Richard , Pazol Brian G. , Chaffin John H. , Belt Roger F. , Uhrin Robert 
Published: March 2011

AbstractThin films of YBa2Cu3O7‐δ have been deposited on samples of LaGaO3 substrates by multilayer E‐beam evaporation. Alternating layers of Cu, Y2O3, and BaF2 were deposited on polished (001) substrates. An annealing study was performed to thoroughly blend the layers and minimize substrate interdiffusion. Films were prepared by annealing in wet oxygen at temperatures between 800 °C and 1000 °C.
Four point resistance versus temperature curves were obtained to determine the superconducting transition temperature and transition width. Auger depth profiling was performed as a function of annealing cycle to determine the amount of blending of the layers and quantify any substrate diffusion..
Molecular Beam Epitaxy of Layered Bi-Sr-Ca-Cu-O Compounds
Authors: Schlomtt D.G. , Eckstein J.N. , Bozo Vic I. , Marshall A.F. , Sizemore J.T. , Chent Z.J. , Von Dessonneck K.E. , Harris J.S. , Bravmant J.C. 
Published: March 2011

AbstractThe in situ epitaxial growth of Bi‐Sr‐Ca‐Cu‐O films by molecular beam epitaxy (MBE) is reported. The suitability of ozone to the MBE growth of cuprate superconductors is discussed. Molecular beams of the constituents were periodically shuttered to grow various Bi2Sr2Can‐1CunOx phases, including 2201, 2212,2223,2245, and layered mixtures of these phases. Using these techniques a superconducting film with TConset near 100 K and Tc (ρ=0) of 81 K was achieved under entirely MBE conditions (Pchamber≤xl0‐4 Torr during growth and cooling). The films are smooth on an atomic scale. The results demonstrate the ability of shuttered MBE growth to selectively grow Bi2Sr2Can‐1CunOx phases.
Study on the Elementary Steps of the Epitaxial Growth of Bi-Sr-Ca-Cu-O on the Surface of Si and Mgo by Means of Rheed and Photoelectron Spectroscopies.
Authors: Hanada Takashi , Kawai Maki , Goda Tsutomu , Teratani Shousuke 
Published: March 2011

AbstractElementary steps of the oxide formation on a Si(001) substrate surface have been studied by means of RHEED, LEED, XPS and UPS. A Bi monolayer on Si (001 ) terminates with a surface dangling bond. Oxide formation on to this surface was studied one by one. Oxidation of Bi overlayered system with oxygen and N2O revealed that the surface Si was inactive to NoO exposure unless Sr was evaporated on. Bi overlayer was easily oxidized with O2 but not with N2O. Further oxidation of surface with Sr and Cu coevaporated system has also been studied.
The Use of Curium as a Rare Earth Substitute in High Tc‐Related Compounds
Authors: Soderholm L , Williams C.W. , Welp U. 
Published: March 2011

AbstractWe report the synthesis of Cm2CuO4. The lattice constants of this material, determined by x‐ray diffraction, show it to be a new member of the isostructural series R2CuO4 (R=Pr, Nd, Sm, Eu, and Gd). Analysis of magnetic measurements is consistent with a free‐ion effective moment for Cm3+, with no contribution to the susceptibility from Cu‐ions.
Recrystalljzation of Non-Vacuum Derived Ba2ycu3o7-δ Films
Authors: Ng Man Fai , Peterson Simone C. , Cima Michael J. 
Published: March 2011

AbstractPartial melting followed by recrystallization at lower temperatures during high temperature treatment of superconducting Ba2YCu3O7-&#X03b4; films is associated with texture development In these films, partial melting is induced by rapid thermal annealing at a temperature slightly above the peritectic melting temperature of Ba2YCu3O7-&#X03b4;. Short firing duration prevents segregation of liquid and permits recrystallization of the correct phase at around 920°C.
Characterization of Cross-Sections of Tibacacuo Thin Films on Ceramic Substrates by Analytical and High Resolution Electron Microscopy
Authors: Mayer J. , Lanham M. , James T.W. , Evans A.G. , RÜHle M. 
Published: March 2011

AbstractCross-sectioned TEM specimens of thin TIBaCaCuO superconducting films on MgO and LaAlO3 substrates have been obtained using special ceramic holders. The superconductor/substrate interface as well as grain boundaries and defects in the superconductor have been characterized by means of analytical and high-resolution electron microscopy. EDX analysis and lattice images confirm that interdiffusion and the formation of an amorphous layer takes place at the interface between the LaA1O3 substrate and the superconducting film, while no indication for such reactions has been found in the case of the MgO substrates. The presence of intergrowth and defects in the superconducting film have been demonstrated by high-resolution electron microscopy. The chemical nature of such defects has been determined by a quantitative evaluation of high-resolution micrographs.
Crystal Chemistry and Phase Equilibrium Studies of the Bao(baco3)‐r2o3‐cuo Systems. V. Melting Relations in ba2(y,nd,eu)cu3o6+x
Authors: Wong‐Ng Winnie , Cook Lawrence P. , Hill Michael D. , Paretzkin Boris , Fuller E.R. 
Published: March 2011

AbstractThe influence of the ionic size of the lanthanides R on melting relations of Ba2RCu3O6+x, where R=Y, Eu and Nd, was studied and compared with that of a high Tc superconductor mixed‐lanthanide phase Ba2(Y.75Eu.125Nd 125)Cu3O6+xThese materials have been characterized by a variety of methods including differential thermogravimetric analysis (DTA), scanning electron microscopy (SEM) with energy dispersive X‐ray spectroscopy (EDX) and X‐ray powder diffraction. Single phase samples of Ba2(Y.75Eu.125Nd.125)Cu3O6+x were annealed at 1004, 1040, 1052, 1060, 1078, 1107 and 1160°C and quenched into a helium gas container cooled by liquid nitrogen. The SEM micrographs of these samples showed the progressive chnages in features of the microstructures from sintering and grain growth through melting and then recrystallization from the melt. The addition of the SEM technique in conjunction with X‐ray diffraction has been helpful in the study of phase equilibria in this system.
Observation of Kosterlitz‐Thouless Transition and Conductivity Fluctuation in Superconducting Ybco Thin Films
Authors: Ying Q. Y. , Kwok H. S. 
Published: March 2011

AbstractKosterlitz‐Thouless properties of laser deposited high Tc superconducting thin films of YBa2Cu3O7‐x were examined. The exponent of the power law dependence of V on I showed a “universal jump” at Tc. ID like conductivity fluctuation was also found at temperatures slightly above the mean‐field transition temperature Tco, which may be the result of imperfections of the sample.
Thermally Activated Flux Flow in thin Films of y2ba4cu8016‐δ
Authors: Berghuis P. , Kes P.H. , Dam B. , Stollman G.M. , Bentum J. Van 
Published: March 2011

AbstractThe resistive transition of a preferentially oriented thin film of Y2Ba4Cu8O16‐δ has been measured in fields up to 20 T oriented parallel to the c‐axis. The data can be analysed in terms of thermally activated flux flow and flux pinning due to dislocation lines. The analysis yields the upper critical field Bc2 which shows an unusual upward curvature at low temperatures. Furthermore an estimate can be made of the correlation length Lc of the flux line lattice in the field direction. Lc is found to be very small, however, remaining larger than the Cu02 plane distance.
Magnetic Relaxation in Bi2Sr2Ca1Cu2O8+x Single Crystal
Authors: Agostinelli E. , Balestrino G. , Fiorani D. , Paroli P. , Tejada J. , Testa A.M. 
Published: March 2011

AbstractThe results of measurements of critical currents and magnetic relaxation on a Bi2 Sr2 Ca1 Cu2O8+x single crystal are reported. Activation energies for the flux motion have been determined from the temperature dependence of the critical current density and the time decay of the zero‐field‐cooled and the remanent magnetization. The effective activation energy increases with temperature, in agreement with the existence of a distribution of activation energies.
Dissipative Effects of Vortex Movements in YBa2Cu3O7 Measured by Magnetothermal Effects
Authors: Simon Ch. , Rosenman I. , Legrand L. , Collin G. 
Published: March 2011

AbstractWe have measured the temperature and the magnetization of singlecrystalline YBaCuO samples in a variable magnetic field under quasi adiabatic conditions. By varying the sweep rate of the field, the thermal link to the bath, the size of the sample, the critical temperature and the sample temperature, we have measured the time dependence of the vortex relaxation (the penetration of the critical state, flux jumps, and the instability regime). This magnetothermal instability controls the value of the effective critical current.
A Correlation Between the Optimum Levels of Hole Doping in the Sr‐ and Ba‐ Classes of Copper Oxide Superconductors
Authors: Parise John B. , McCarron DJ Eugene M. 
Published: March 2011

AbstractConsiderations of the in‐plane Cu‐0 bond distance in a variety of cuprate‐based superconducting systems indicate: (1) that an optimum level of hole doping exists in these systems, and (2) that this optimum value is roughly the same for Sr‐ and Ba‐classes of superconductors when one normalizes for structural effects due to the difference in ionic size. Structural adjustment at the optimum level of doping leads to variations in Tc between structure‐types.
Magnetization and Flux Behaviour of YBa2Cu3O7-y Superconducting Rings
Authors: Yokoyama Shoichi , Shimohata Kenji , Ushijima Toshie , Yamada Tadatoshi 
Published: March 2011

AbstractThe magnetization and flux creep in YBa2Cu3O7-y +xAg superconducting rings at 77K has been studied experimentally. Decay of the magnetization caused by the induced intergrain current was measured using the ring shaped specimen. The decay in proportion to logarithmic of the time was observed. The pinning potentials (Uo) of about 1.0eV at zero external field and 0. 3eV at 100G were estimated by Anderson and Kim model (1,2). In order to measure the intragrain flux creep, the rings were crushed into powder and pressed to disks without sintering. It was found that the dependence of Uo on external field for the ring was greater than that for the disk.
Tunnel Junctions on Chemically Etched YBa2Cu3O7 Thin Films
Authors: Phillips Julia M. , Valles J. M. , Cucolo A. M. , Dynes R. C. , Gurvitch M. , Garno J. P. , Marshall J. H. 
Published: March 2011

AbstractWe have prepared low leakage tunnel junctions on epitaxial YBa2Cu3O7 (YBCO) films grown on SrTiO3(001) by evaporating Pb counterelectrodes onto chemically etched YBCO surfaces. Structure in the voltage dependence of the tunneling conductance is reproducible and strongly resembles what has been obtained in similarly etched junctions on YBCO single crystals.
Light Induced Etching Of Gaas In A Zinc Atmosphere
Authors: Salathe R.P. , Baskhara Rao G. 
Published: March 2011

ABSTRACTN-type GaAs substrates have been exposed to zinc atmospheres at 600 – 800 deg.C and focused light from a Krion laser at 647.1 nm. Etch pits are generated at optical densities of 0.2 – 10 KW/cm2 and exposure times of 5 – 60 minutes. They are characterized by a smooth profile with typical diameters of 50 – 80μm and depths of 0.1 – 50 μ The etch depth depends strongly on the laser power and on the zinc and arsenic vapor concentrations. The onset of etching is characterized by an increase in surface reflectivity of up to 10 per cent which is probably due to the formation of a thin liquid metal film. The growth of this film is initiated by optically generated holes at the semiconductor surface. The film is not saturated and dissolves GaAs from the substrate. In addition to etching, thermal diffusion of zinc can be observed in samples subjected to long exposure times or high temperatures.
Wafer-Scale Laser Lithography: I. Pyrolytic Deposition Of Metal Microstructures
Authors: Herman Irving P. , Hyde Roderick A. , Mcwilliams Bruce M. , Weisberg Andrew H. , Wood. Lowell L. 
Published: March 2011

ABSTRACTMechanisms for laser-driven pyrolytic deposition of micron-scale metal structures on crystalline silicon have been studied. Models have been developed to predict temporal and spatial properties of laser-induced pyrolytic deposition processes. An argon ion laser-based apparatus has been used to deposit metal by pyrolytic decomposition of metal alkyl and carbonyl compounds, in order to evaluate the models. These results of these studies are discussed, along with their implications for the high-speed creation of micron-scale metal structures in ULSI systems.
Dynamic IR Studies of Microdomain Interphases of Isotope-Labeled Block Copolymers
Authors: Noda I. , Smith S. D. , Downey A. E. , Grothaus J. T. , Marcott C. 
Published: March 2011

ABSTRACTBy probing the localized segmental motion of isotope-labeled block copolymers, the physical nature of the interphase region between microphaseseparated domains of block polymers was examined. Dynamic infrared linear dichroism (DIRLD) spectroscopy, which measures the reorientations of submolecular structures induced by a small-amplitude oscillatory strain, was combined with specific isotope-labeling using deuterium-substituted monomers. The latter technique enabled us to differentiate the dynamic responses of well-defined parts of block segments, e.g., near the segment junction, chain end, or middle of the block. The degree of segmental interactions near the interphase region of styrene-isoprene diblock copolymers were studied as a function of the segment location and temperature. The reorientational motion of the polystyrene segment, especially near the block junction, was monitored around the glass transition temperature of the polyisoprene matrix. From this result, the degree of segmental mixing in the interphase region which leads to local plasticization of the polystyrene segment was determined.
Recent Advances in Morphology and Mechanical Properties of Rigid-Rod Molecular Composites
Authors: Krause Stephen J. , Hwang Wen-Fang 
Published: March 2011

ABSTRACTRigid-rod molecular composites are a new class of high performance structural polymers which have high specific strength and modulus and also high thermal and environmental resistance. The concept of using a rigid-rod, extended chain polymer to reinforce a ductile polymer matrix at the molecular level has been demonstrated with morphological and mechanical property studies for aromatic heterocyclic systems, but new materials systems and processing techniques will be required to produce thermoplastic or thermoset molecular composites. Improved characterization and modeling will also be required. In this regard, new results on modeling of mechanical properties of molecular composites are presented and compared with experimental results. The Halpin-Tsai equations from ‘shear-lag’ theory of short fiber composites predict properties reasonably well when using the theoretical modulus of rigid-rod molecules in aromatic heterocyclic systems, but newer matrix systems will require consideration of matrix stiffness, desired rod aspect ratio, and rod orientation distribution. Application of traditional and newer morphological characterization techniques are discussed. The newer techniques include: Raman light scattering, high resolution and low voltage SEM, parallel EELS in TEM, synchrotron radiation in X-ray scattering, and ultrasound for integrity studies. The properties of molecular composites and macroscopic composites are compared and it is found that excellent potential exists for use of molecular composites in structural applications including engineering plastics, composite matrix resins, and as direct substitutes for fiber reinforced composites.
Morphology and Formation of Fibrillar Structure in Pbo Fiber
Authors: Chau C.C. , Blackson J.H. , Klassen H.E. , Hwang W.-F. 
Published: March 2011

ABSTRACTElectron microscopy studies showed that the porous structure of PBO fiber may contain fractal geometries; i.e., the void spaces are self-similar with variations in magnification. At the fiber surface, a dense skin which consists of fibrils was observed. In the matrix, the fibril size is about 5 to 50 nm with the voids distributed randomly among the fibrils. The fractal dimension of voids in PBO fiber as determined by microscopy and image analysis was found to be 2.44. The fibrillated fiber showed a continuous fibril size distribution with no evidence of fibril size hierarchy. These observations suggest a nucleation and growth mechanism for the formation of the fibrillar structure in PBO fiber.
In Situ Composites Based on Thermotropic and Flexible Polymers
Authors: Crevecoeur Guido , Groeninckx Gabriel 
Published: March 2011

ABSTRACTBlends of a thermotropic liquid crystalline polymer (TLCP) and a thermoplastic matrix were compounded. Upon subsequent injection moulding and spinning, the TLCP was deformed into fine fibrils in the matrix, giving in-situ reinforcement. Especially after spinning, the composite fibres contain fibrils with very high aspect ratio, and exhibit mechanical properties in accordance with simple composite models for modulus and strength.
Characterization of Polyquinoline Blends Using Small Angle Scattering
Authors: Wu Wen-Li , Stille John K. , Tsang Joseph W. , Parker Alex J. 
Published: March 2011

ABSTRACTTo determine the compatibility between the rigid rod and the flexible chain polyquinolines, both small angle x-ray and neutron scattering measurements were conducted on blends containing deuterated flexible chains. The scattering intensities from both x-ray and neutron were reduced to their absolute scales in order to remove the scattering contribution from microvoids which tended to overshadow the signal of molecular origin. Quantitative information regarding the molecular dispersion in a 50/50 rigid rod and flexible chain blend was obtained. The result indicated that this material was partially segregated but not to the point of single component phases.
Factors Influencing Properties of San/Pmma Blends
Authors: Subramanian R. , Huang Y. S. , Roach J. F. , Niff O. R. 
Published: March 2011

ABSTRACTThe versatility of polymeric blends is reflected in the range of usable end properties that can be achieved through alterations in the composition and/or effective control of the morphologies of the mixtures. Solvent cast and melt mixed blends of SAN and PMMA have been studied to understand the Influence of PMMA tacticity and the acrylonitrile content of the SAN copolymer on their phase behavior. The results show a shifting of the cloud point curves and the miscibility windows for the blends of SAN with different stereo-regular PMMAs. This is interpreted as being due to specific interactions between the acrylonitrile and methacrylate groups. The ‘goodness’ of mixing in the melt mixed blends were determined by FTIR ATR spectroscopy. The effects of the processing conditions on the mixing characteristics and subsequent improvement in mechanical properties are discussed. The limits of mixing that can be achieved using standard mixing procedures and their role in affecting the end use properties such as the flexural strength will also be discussed.
Excimer and Exciton Fusion of Blends and Molecularly Doped Polymers--A New Morphological Tool.
Authors: Shi Zhong-You , Li Ching-Shan , Kopelman Raoul 
Published: March 2011

ABSTRACTExciton-exciton and exciton-excimer triplet fusion kinetics is monitored in medium molecular weight P1VN/PMMA solvent cast films with concentrations from 0.005 to 100% (weight), at temperatures of 77 to 300 K, via time resolved fluorescence and phosphorescence (10 ns to 10 sec). The heterogeneity exponent (h) is 0.5 for isolated P1VN chains, zero (classical) for pure P1VN and “fractal-like” throughout certain concentration regimes. However, h is not monotonic with blend concentration but rather oscillates between zero and 0.5. Correlation is made with morphology changes (phase separation, filamentation). As expected, the triplet exciton kinetics is dominated by short-range hops (about 5 A) and thus monitors the primary topology of the chains. At concentrations below 0.01%, the excitons are constrained to a truly one-dimensional topology. At higher concentrations there is a fractal-like topology. Similar studies were conducted on naphthalene-doped PMMA (1-20% weight). The lower concentration samples are neither segregated nor random solution phases.
Diblock Copolymers at Surfaces
Authors: Green Peter F. , Christensen Thomas M. , Russell Thomas P. , Anastasiadis Spiros H. 
Published: March 2011

ABSTRACTThe surface properties of symmetric microphase separated diblock copolymers of polystyrene (PS) and polymethylmethacrylate (PMMA) were investigated using X-ray photoelectron spectroscopy (XPS), the specular reflectivity of neutrons and secondary ion mass spectrometry (SIMS). PS, the lower surface energy component, exhibited a preferential affinity for the free surface. For copolymers that are far from the bulk microphase separation transition (MST), the surface consists of a layer of pure PS. When the system is close to the MST the surface is a mixture of PS and PMMA. The PS surface excess can be described bya N-1/2 dependence, where N is the number of segments that comprise the copolymer chain. It is shown that the surface undergoes an ordering transition at a temperature T2 that is above that of the bulk MST. The ordering of the bulk lamellar morphology is induced by an ordering at the surface. This is analogous to the ferromagnetic order observed in systems such as Gd at temperatures above the bulk Curie temperature. The results here are discussed in light of previous work on copolymer surfaces and in light of mean field theory.