bluuebunny/crossref_metadata_2025 huggingface dataset:
The Preparation of Bi-Pb-Sr-Ca-Cu-O Superconducting Powder for Thick Film Pastes
Authors: Hagberg J. , Uusimäki A. , Levoska J. , Leppävuori S , Rautioaho R
Published: March 2011

The oxalate route was used to prepare (Bi-Pb) -Sr-Ca-Cu-O powder with the nominal composition Bi1.75Pb0.4Sr1.3Ca2.1Cu3.2Oy. This powder was decomposed/annealed at different temperatures between 434 and 795°C. They were investigated by thermogravimetric analysis, X-ray diffraction and transmission electron microscopy. Particle size distribution and surface area were also determined. The specific surface area decreased from a value of 16.5 m2/g for powder decomposed at 434 °C to 1.0 m2/g for powder decomposed at 795 °C. The measured mean particle size reached a minimum of 0.52 juri for powder decomposed at 589 °C.
Preparation of High-Purity T12CanBa2Cun+1O6+2n (n=1,2) Powders from Stoichiometric Reactant Mixtures
Authors: Wu Nae-Lih , Yao Yeong Der
Published: March 2011

New powder synthesis Methods have been developed for preparing the single-phase T12CaBa2Cu2O8 (the 2122 coapound) and T12CaBa2Cu3O10 (the 2223 coapound) powders froa stoichioaetric reactant mixtures. The 2122 coapound was prepared froa a stoichioaetric Mixture of T12O3, CuO, and CaBa2CuO4, while the 2223 coapound was prepared froa the same aixture but with additional CaO and CuO to Batch the correct (T1:Ca:Ba:Cu=2:2:2:3) stoichioaetry. The single-phase 2122 saaples with Tc above 110 K were obtained by using one-step calcination at 830°C, while the 2223 saaples with Tc ranging between 115 and 120 K were obtained by employing a first calcination at 830°C for 5 hrs and a second calcination at 870°C. Powder aelting, which is strongly associated with the conventional aethods, was significantly suppressed in the new aethods.
Effects of Processing Parameters on the Excimer Laser Deposition of Yba2Cu3O7-δ Thin Films
Authors: Muenchausen R. E. , Wu X. D. , Dye R. C. , Hubbard K. M. , Estler R. C. , Flamme C. , Brainard R. , Foltyn S. , Tesmer J. , Maley M. , Martin J. , Nogar N. S.
Published: March 2011

Systematic studies of the effects of pulsed laser deposition processing parameters on plume dynamics and resultant film properties have been performed. Plume angular distributions, cosm(θ), were observed to be variable between 1 > m > 15 depending on laser energy density and spot size. Under optimized conditions, epitaxial, superconducting thin films could be grown in‐situ on a variety of single‐crystal substrates. High quality, 2000 Å  ss thick films were obtained at deposition rates approaching 150 Å/sec.
In Situ Growth of Epitaxial Superconducting Yba2Cu3O7-X Films on Insulating, Semiconducting and Ferroelectric K(Ta,Nb)O3 by Pulsed Laser Ablation
Authors: McCAMY J. W. , Norton David P. , Lowndes Douglas H. , Boatner L. A. , Christen D. K. , Feenstra R. , Sonder E.
Published: March 2011

K(Ta,Nb)O3 (KTN) is an interesting substrate for use in studies of epitaxial superconducting film‐substrate interactions because of a moderate lattice parameter mismatch with YBa2Cu3O7‐x and great versatility in electrical properties. KTN's properties are easily modified by doping to form an n‐type semiconductor and/or a ferroelectric with variable ferroelectric Tp. As an initial step in exploring such studies we have carried out what are believed to be the first epitaxial growth experiments of YBa2Cu3O7‐x films on insulating, semiconducting and ferroelectric KTN single crystals by pulsed laser ablation. We find that c‐axis‐normal epitaxial films can be consistently grown with TSc(R = 0) > 90K , △TSC ~1.5K, and Jc > IMA/cm2 on semiconducting and/or insulating KTaO3. However, growth on KNDO3 is problematic because of stresses generated by cooling the substrate through first order structural transitions, at even moderate cooling rates.
Growth and Properties of Epitaxial YBa2Cu3O7 thin Films on{1102}Al2O3
Authors: Fork D. K. , Geballe T. H. , Char K. , Laderman S. S. , Taber R. , Bridges F. , Ponce F. , Boyce J. B. , Connell G. A. N.
Published: March 2011

Epitaxial YBa2Cu3O7 (YBCO) films were grown on r‐plane A12O3 {1102} by laser ablation. X‐ray diffraction shows that films are epitaxial with the c‐axis perpendicular to the substrate and the a or b axes parallel to (2201), although the full width at half maximum of the rocking curve is larger compared to those of epitaxial films on SrTiO3. The critical temperatures (zero resistance) are between 85 K and 88 K with transition widths between 0.5 K and 3 K. The 300 K resistivity of 250 μΩextrapolates to zero at zero temperature and the critical current is as high as 5 x 106 A/cm2 at 4.2 K according to magnetization hysteresis measurements. Surface resistance data shows that 2000 Å thick epitaxial films on {1102} have about 1 mΩ at 13 GHz at 4.2 K.
In Situ Preparation of Y‐Ba‐Cu‐O Thin Films on Silicon Single Crystals
Authors: Habermeier Hanns—Ulrich , Wagner Gunter , Mertens Günter
Published: March 2011

Superconducting Y—Ba—Cu—O thin films with critical temperatures exceeding 80 K are deposited on silicon single crystal substrates using the pulsed laser deposition technique. Deposition from a sintered Y1 Ba2Cu3O7‐ target in oxygen ambient of 0.1 — 5 mbar onto substrates kept at 700°C to 820°C results in crystalline films in which the target composition of the metallic constituents is preserved. No post deposition treatments are required to obtain high values for the zero resistance. X— ray analysis as well as Raman spectroscopy reveal that specimens prepared at optimum conditions are single phase c—axis oriented. In contrast to films prepared on LaAlO3 or SrTiO3 the surface morphology shows a granular structure. The films prepared by this technique are quite stable against chemicals used in conventional lithographic patterning, however, a strong correlation between film quality before patterning and some degradation after patterning is observed.
In‐Situ Fabrication of YBa2Cu3O7‐x Superconducting Thin Films Directly on Silicon Substrates with Tc0 > 77K
Authors: Lee C. B. , Singh R. K. , Sharan S. , Singh A. K. , Tiwari P. , Narayan J.
Published: March 2011

We report in‐situ fabrication of c‐axis textured YBa2Cu3O7‐x superconducting thin films with Tco > 77K on unbuffered silicon substrates by the biased pulsed laser evaporation (PLE) technique in the temperature range of 550‐650°C. At substrate temperatures below 550°C, no c‐axis texturing of the superconducting film was observed. The YBa2Cu3O7‐x superconducting films were fabricated by ablating a bulk YBa2Cu3O7 target by a XeCl excimer laser (λ = 308 nm, τ = 45 × 10‐9 sec) in a chamber maintained at an oxygen pressure of 0.2 torr . The thickness of the films was varied from 0.3 to 0.5 nm depending on the number of laser pulses. Extensive diffusion was observed in thin films deposited at substrate temperatures above 550°C. However, microstructurally, with increase in the substrate temperature the films exhibited larger grain size and greater degree of c‐axis texturing (measured by the ratio of the (005) and (110) X‐ray diffraction peaks). This was found to give rise to better superconducting properties with Tco exceeding 77 K for YBa2Cu3O7‐x films deposited on Si substrates at 650°C.
Direct Observation by Transmission Electron Microscopy of the Early Stages of Growth of Superconducting Thin Films
Authors: Norton M. Grant , Tietz Lisa A. , Summerfelt Scott R. , Carter C. Barry
Published: March 2011

The fabrication of high quality thin films often depends on the early stages of the growth process during which epitaxy is established. The substrate surface structure generally plays a critical role at this stage. Many observations of the high‐Tc superconductor film‐substrate interface structure and chemistry have been made by transmission electron microscopy (TEM) of cross‐section samples. Ion‐milling induced damage, however, can be severe in these specimens. In the present study, the early stages of the growth of high Tc superconducting thin films of YBa2Cu3O7δ have been studied by TEM using a technique which requires no post‐deposition specimen preparation.
Crystal Chemistry and Sub-Solidus Phase Relations in (La,Re)2CuO4 Systems
Authors: Bringley Joseph F. , Trail Steven S. , McElfresh Michael , Scott Bruce A.
Published: March 2011

La2‐xRExCuO4 (RE = Nd‐Y) solid solution systems have been investigated to determine the factors stabilizing the T (La2CuO4), T’ (Nd2CuO4) and hybrid T*‐type structures. A simple ionic model with a perovskite‐like tolerance factor is found to accurately define the existence field of each. Metastable T* phases are observed for the larger RE cations Nd, Gd, Eu. The structure is quite stable for RE = Dy, Tb, but does not occur at all for the smallest rare earths. Oxygen activity plays a role in T’ and T* phase formation.
Epitaxial Growth and Superconducting Properties of Yba2Cu3O7 Thin Films and Yba2Cu3O7/Dy(Pr)Yba2Cu3O7 Superlattices
Authors: Triscone J.-M. , Karkut M.G. , Brunner O. , Antognazza L. , Kent A.D. , Fischer ø.
Published: March 2011

We have prepared in situ REBa2Cu3O7 (REBCO) (RE= Y, Pr, Dy) thin films and YBC0/Dy(Pr)BC0 superlattices by single target dc planar magnetron sputtering. YBCO/DyBCO superlattices have been realized with modulation wavelength as short as 24Å, i.e., a unit cell of YBCO alternates with a unit cell of DyBCO, on average. The superconducting properties of such superlattices are indistinguishable from those of single layers. Tco's (zero resistance) are between 85 and 89K, and the residual resistivity ratios are between 2.5 and 3. In contrast to these results, when YBCO is layered with PrBCO, which is insulating, a dramatic change in the superconducting properties is observed. We have been able to artificially vary the coupling between single 12Å unit cell of YBCO by interposing insulating planes of PrBCO. As the YBCO layer separation increases, T is reduced and the transition broadens showing evidence of 2‐D superconducting fluctuations.
Effects of Oxygen Stoichiometry on The Magnetic Ordering of La2Ni1-YCuY04+δ
Authors: Zhao J. , Suresh Babu V. , Seehra Mohindar S. , Hepp Aloysius F. , Gaier James R. , Richman Robert M.
Published: March 2011

Annealing and quenching experiments in a thermogravimetric analysis apparatus are used to vary the oxygen content in La2Ni1‐yCuy04+δ, followed by magnetic susceptibility and x‐ray diffraction experiments. These studies show that for certain δ, transition to antiferromagnetism occurs with TN < 20 K. The effect of Cu doping (y = 0.01 and 0.05) on TN is negligible.
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

High 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

Thin 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

Thin 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

The 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

Elementary 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

We 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

Partial melting followed by recrystallization at lower temperatures during high temperature treatment of superconducting Ba2YCu3O7-δ 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-δ. Short firing duration prevents segregation of liquid and permits recrystallization of the correct phase at around 920°C.
Atomic Resolution Electron Microscopy of Bismuth Cuprates
Authors: Ramesh R. , Bagley B.G. , Tarascon J.M. , Hetherington C.J.D. , Thomas G. , Green S.M. , Luo H.L.
Published: March 2011

Since the discovery of superconductivity in certain classes of cuprates, there has been much research activity aimed at understanding the structure, microstructure, electrical and other physical properties of these materials. In this paper, we present a summary of the current status of on-going research on structural and microstructural characterization of the Bi cuprates and cationically substituted derivatives of these superconducting compounds. High resolution structural imaging together with conventional and analytical electron microscopy is used to examine the structure[l]. The overall aim of these studies is to characterize the structural and microstructural evolution and ultimately to determine the effect on the superconducting properties.
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

Cross-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

The 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

Kosterlitz‐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

The 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

The 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

We 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

Considerations 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

The 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

We 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

N-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

Mechanisms 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

By 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

Rigid-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

Electron 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

Blends 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

To 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

The 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

Exciton-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

The 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.
Polymer Molecules at Interfaces: Studies by Small-Angle Neutron Scattering
Authors: Forsman W.C. , Latshaw B.E. , Wu D.T.
Published: March 2011

The behavior of polymer molecules at interfaces is an essential aspect of a wide variety of physical-chemical phenomena. For example, polymer molecules in the fiber-polymer interface play an important role in determining the mechanical properties of composites, and polymer molecules at the liquid-solid interface are critical in the stabilization of colloidal dispersions. In some cases polymer molecules are physically adsorbed at the interface and in other cases they are chemically bonded to the surface at one or more positions along the chain. To simplify the terminology, however, both cases will be referred to as polymer adsorption. The chains in the second case are said to be grafted to the surface. It is an example of this second case that we are concerned with in this paper, and in particular with polymer grafted to a finely divided substrate dispersed in a liquid.
The Effect of Masked Isocyanates on the Mechanical Properties of My720/dds Epoxy Resin
Authors: Rungsimuntakul N. , Lonikar S.V. , Fornes R. E. , Gilbert R.D.
Published: March 2011

The mechanical properties of epoxy resins and epoxy resin/graphite fiber composites are adversely affected by moisture absorption. Incorporation of masked isocyanates that unmask to release isocyanates in situ at the cure temperatures (150-177ºC) reduce the equilibrium absorption up to ∼70%. Dynamic mechanical analyses and stress-strain properties of epoxy resins containing masked isocyanates were examined to determine their effect on mechanical properties. The ultimate Tg of the epoxy is reduced by incorporation of masked isocyanate, but the actual Tg is comparable to the “as cured” Tg of the epoxy. The dynamic moduli up to the Tg are relatively unaffected. Ina number of cases, the initial modulus, elongation at break and peak stress are equal or better than the unmodified resins.
A Study of Short Metal Fiber Reinforced Composite Materials
Authors: Chung W. C.
Published: March 2011

Over the years, the conventional involvement of short fiber reinforced composites in electrical applications has been as electrical insulation. Contrary to this approach, with the increasing need of better electromagnetic interference (EMI), radio—frequencyinterference (RFI) shielding and control of electrostatic charge distribution (ESD) for computer, defense, space exploration and some high—tech structural components, itis expected that the development of conductive polymeric composite materials will grow strongly and significantly.

An experimental investigation is designed to systematically evaluate the mechanical properties and electrical properties of metal fiber reinforced composites subjected to various loading conditions. In this study, chopped Inconel 601 (nickel base) metal fiber witha fixed fiber aspect ratio (length/diameter ratio) is used to reinforce commercially available thermoset polyester resin. Mechanical testing of custom made samples, failure analyses using visual inspection, light microscopy and SEM are conducted to understand the fracture behaviors and possible failure causes in such composites. The feasibility of using metal fiber polymeric composites in structural/electrical applicationsis discussed in this paper.
Structural Studies of Semiflexible Fluorocarbon Chains Containing an Aromatic Core
Authors: Schulte A. , Hallmark V. M. , Twieg R. , Song K. , Rabolt J. F.
Published: March 2011

The molecular structure of a series of perfluoroalkane oligomers having two F(CF2)n chains attached to a phenyl group in the para position has beenstudied by Fourier Transform and conventional Raman spectroscopy at ambient and low temperatures. From comparison with model compounds bands attributable to both the substituted phenyl ring and the perfluoroalkane chains could be assigned. In particular, the low frequency region was investigated as a function of temperature and pressure in order to assess the impact of the rigid aromatic core on the bandshapes and frequencies.
The Effect of Low Power Ammonia and Nitrogen Plasmas on Carbon Fibre Surfaces
Authors: Jones C. , Sammann E.
Published: March 2011

The effect of low power nitrogen and ammonia plasmas on carbon fibre surfaces has been studied using X-ray photoelectron spectroscopy(XPS) and scanning electron microscopy (SEM). A comparison is made between two polyacrylonitrile based fibres and a pitch based fibre. Grazing angle techniques have been exploited to probe only the first 12-15A of the fibre surface. Plasma treatments were carried out in an insitu plasma treatment cell which was attached to a PHI 5400 X-ray photoelectron spectrometer enabling the immediate effects of the plasma to be studied before the treated surface was exposed to air.
Synthesis and Characterization of a Thermotropic Polyalkanoate of 4,4'- Dihydroxy-α,α'-Dimethylbenzalazine
Authors: Friutwala H. , Cimecioglu A. L. , Weiss R. A.
Published: March 2011

Several research projects in our laboratory have used an LCP based on 4,4'-dihydroxy,a-a' dimethylbenzalazine, that was first synthesized by Roviello and Sirigu 1.2 Copolymers with the following qeneral structure,

have been used in self-reinforcing polymer blends3 and are currently being used in small angle neutron scattering studies of the molecular conformation of an LCP in a nematic field. In this latter study, it is imperative that the polymer be well characterized, especially with respect to molar mass and thermal stability. This paper describes the effect of molar mass and thermal history on the thermal stability and transitions of this particular LCP.
Origin and Elimination of Scattering Losses in Fluoride Glasses and Fiber
Authors: Sanghera J. S. , Aggarwal I. , Harbisp B. , Busse L. , Pureza P. , Hart P. , Sachon M. G. , Sills L. , Miklos R.
Published: March 2011

The sources of scattering losses in fluorozirconate glasses and fibers are reviewed. Results are presented which show that the predominant mechanism responsible for the presence of fluoride crystals is heterogeneous nucleation. The nature and origin of the different nuclei are discussed and possible ways to eliminate them from the glasses assessed. It is proposed that extreme care be employed in the processing of the glasses with particular emphasis on the preform fabrication step as this is critical to the design of ultra-low loss fibers.
Fabrication of ALF3-Based Glass Fibers
Authors: Shahriari Mahmoud R. , Iqbal Tariq , Foy Paul R. , Saggese Steve J. , Sigel G. H.
Published: March 2011

Several glass systems based on AIF3 have been synthesized and fabricated into preforms by controlled melting and rotational casting. High optical quality preforms have been drawn into fibers using a specially modified drawing facility. The drawing tower is enclosed with a vertical glove box in which the levels of both moisture and oxygen are kept below 1 ppm during the drawing. The AIF3 -based fibers have shown dramatically superior chemical durability relative to the ZrF4 -based glass fibers. Selected optical, mechanical and thermal properties of these fibers will be presented. AIF3 -based glass fibers offer interesting opportunities for short range applications in the 2–4 micron region of the infrared such as sensing, remote spectroscopy and laser power delivery.
Property-Composition Relationship of Chalcogenide Glasses Containing Germanium
Authors: Yi Jay J. L. , Strutt Peter R.
Published: March 2011

In-depth studies of property-composition relationship in chalcogenide glasses have revealed some interesting structural features. For example, specific discoveries in the Ge-Se-Sb and similar systems were of (i) meta-stable phase separation for glasses with a high Se or S content ( >70 at.% ), and (ii) abnormal behavior of some structure-sensitive properties ( e.g. optical band-gap energy ) for glasses with Se or S in the range of 60–70 at.%. In carefully studying the Ge-Se system, the liquidus curve ( reported by H. Ipser et al, 1982 ).was reexamined; this was found to have an S-shape at the phase-separation region. Another interesting finding was the dependence of the band-gap energy on composition in (1−x)GeSe2 xSb2Se3 glasses; this was not a linear relation but a curve with a maximum band-gap energy at 9 at.% Sb.
Sol-Gel Processing for Fiber Optic Applications
Authors: Thomas Ian M.
Published: March 2011

The sol-gel process is a versatile process for the preparation of many types of glass and ceramics. This includes optical fibers. In this paper, the general principles of sol-gel processing are described first. This is followed by details of the specific methods that can be used for the fabrication of optical fibers. Finally, some conclusions are drawn as to the commercial potential of the various methods.
Mechanical Strength of Low-Dimension Class Fibers
Authors: Cerqua K. A. , Behrman E. C. , Lacourse W. C.
Published: March 2011

Chalcogenide glasses present a unique opportunity for the study of the effect of dimensionality of the properties of amorphous systems. Presented here are preliminary results of experiments on fibers of these materials. Strength in these fibers is related both to dimensionality, which is a continuously variable function of composition and to drawing conditions, which produce ordering. A simple theoretical model for the ordering effect is proposed and discussed.
The Growth and Characterization of Tungsten Bronze SrxBa1−xNb2O6 Single Crystal Fibers
Authors: Yamamoto Joyce K. , Bhalla A. S.
Published: March 2011

The growth of SrxBal−xNb2O6 solid solution single crystal fibers has been achieved using a modified float zone technique. The technique is described and the results of several property measurements are presented.
Infrared Spectroscopy of Protons in KTiOPO4
Authors: Crawford M. K. , Morris P. A. , Roelofs M. , Gashurov G.
Published: March 2011

We report infrared (IR) measurements of protons (H+), present as OH−, in KTiOPO4 grown by various techniques. The IR spectra are sensitive to the growth technique used. In high temperature hydrothermally grown crystals we observe IR bands which have strongly temperature dependent linewidths. The Arrhenius-type activation energies for these linewidths are small (6–15 meV). The IR bands are polarized and this information can aid in making OH− site assignments.
Diffusion of Hydrogen Through Hermetic Carbon Films on Silica Fibers
Authors: Lemaire P. J. , Walker K. L. , Kranz K. S. , Huff R. G. , DiMarcello F. V.
Published: March 2011

Recent work has made it possible to deposit hermetic carbon coatings on optical fibers during the drawing process. These coatings are used to protect the silica portion of the fiber from undesirable loss increases and strength reductions caused by H2 and H2O, respectively. The hermetic properties of the carbon films have been evaluated using accelerated test conditions where the coated fibers are exposed to H2 at elevated temperatures and hydrogen pressures. In-situ spectral loss monitoring has made it possible to measure changes in the characteristic optical loss features associated with either molecular H2or with species such as OH which form when hydrogen reacts with defects in the silica. By using long lengths of fiber it is thus possible to optically measure the extremely small amounts of hydrogen that penetrate the carbon films during accelerated tests. At temperatures in the range of 100 to 145°C the diffusion of H2 is readily modeled using classical diffusion theories for a composite cylinder, allowing calculation of the diffusion coefficient and the solubility for H2 in the carbon. At higher temperatures the diffusing H2 is partially depleted by reaction with defects in the glass. For these conditions the inward diffusion of the H2 and its reaction at defect sites tend to balance each other, giving rise to a constant, but extremely low, concentration of H2 in the fiber.
EPR Characterization of Carbon Coated Fiber
Authors: Inniss Daryl
Published: March 2011

An amorphous carbon coating has been developed to improve the resistance of silica optical fibers to static fatigue and hydrogen permeation. The carbon coated optical fibers are characterized by electron paramagnetic resonance spectroscopy. A Lorentzian lineshape is observed, centered at the g value of 2.002. Intensity measurements as a function of temperature suggest that localized spin centers contribute to the spin resonance. It is shown that atmospheric control of the carbonaceous environment results in the removal of these EPR active sites.