bluuebunny/crossref_metadata_2025 huggingface dataset:
In‐Situ Patterning and Critical Current Density Measurements in Laser Deposited High‐Tc Superconducting Thin Films
Authors: Singh R. K. , Lee C. B. , Tiwari P. , Narayan J.
Published: March 2011

We have performed transport critical current density, Jc, measurements on epitaxial superconducting thin films which were in‐situ patterned during the laser deposition process. Shadow masks of various dimensions were placed close to the substrate to generate different patterns. Epitaxial films of YBa2Cu3O7 on (100) SrTiO3, (100) YSZ, and (100) LaA1O3 substrates were fabricated at low processing temperatures (500‐650°Q by the biased laser deposition technique in an oxygen ambient of 200 mtorr. Excellent quality superconducting thin films were formed on patterned areas. The critical temperature of the films was found to be in the range of 88 to 90 K, and the best critical current density values (at 77K, and zero magnetic field) greater than 6.5 x106 Amps/cm2 were obtained for silver doped YBa2Cu3O7 films on (100)LaAlO3 substrates.
Macroscopic Persistent Currents in Laser Ablated YBa2Cu3O7-X Films
Authors: Stritzker B. , Leiderer P. , Feile R. , KrÜGer U. , Zander W.
Published: March 2011

Thin films of YBa2Cu3O7-x have been produced in situ by laser ablation. As the condensation of the superconducting film is done onto hot substrates (600 - 780°C) at high oxygen pressures (~ 1 mbar), this techniques does not require any special postannealing step. Thus the total process time amounts to less than 10 min. Films were found to be polycrystalline with the c-axis preferentially oriented normal to the substrate plane on single crystalline (001) SrTiO3 and (random) ZrO2, as measured by ion channeling (Xmin = 5.5 % on SrTiO3), x-ray scattering and TEM. Complete superconducting transitions above 90 K with transition widths of about 1 K have been observed even on YSZ substrates. Critical current densities, jc (77 K), of more than 2 x 106 A/cm2 could be obtained on SrTiO3-substrates. The high quality of the thin films over large areas was demonstrated by the measurement of persistent superconducting current densities at 77 K in the order of 105 A/cm2 in a 1.5 mm broad ring of 9 mm diameter. No dissipation of this persistent current could be observed during one hour. Measurements of the same film after 8 months in normal air showed a 40 % decrease of jc and a stronger decrease of jc with an externed magnetic field, suggesting that in the meantime the macroscopic ring current density is dominated by intergranular weak links.
Magnetic Flux Pinning in YBa2Cu3O7 Films
Authors: Kerchner H. R. , Feenstra R. , Thomson J. O. , Thompson J. R. , Christen D. K. , Sekula S. T. , Boatner L. A.
Published: March 2011

The magnetic hysteresis was studied for YBa2Cu3O7 films of different epitaxial orientations on single-crystal SrTiO3 and KTaO3 substrates. Deposition by coevaporation of Y, BaF2, and Cu was followed by annealing in flowing, wet oxygen at 800-850°C. The critical current density Jc deduced from magnetic hysteresis loops was compared with four-terminal transport-current results. Thermally activated magnetic flux flow was manifest in the audio-frequency data. Jc fits a scaling law similar to one used for describing Nb3Sn and other A15 materials.
Critical Current Enhancement in Single-Crystal Ba2Ycu3O7
Authors: van Dover R. B. , Gyorgy E. M. , Schneemeyer L. F. , White A. E. , Glarum S. , Felder R. J. , Waszczak J. V.
Published: March 2011

The critical current density, Jc, of single crystals of Ba2YCu3O7 is comparable to that of melt-textured-growth materials as well as to the intragrain Jc of bulk polycrystalline Ba2YCu3O7. Typical values at 77 K and 9 kOe are near 5x 103 A/cm2, and are presumably limited by weak pinning. We have obtained a significant enhancement of this pinning-limited Jc by three techniques: 1) a short reannealing procedure, 2) fast neutron irradiation, and 3) proton irradiation. Interestingly, the combination of the first technique followed by either irradiation is not as effective as the iradiation alone. That is, the best candidates for irradiation are not necessarily those with the highest initial Jc.
Significantly Enhanced Flux-Pinning in Y-Ba-Cu-O by Simple Processing
Authors: Jin S. , Tiefel T. H. , Nakahara S. , Graebner J. E. , O'Bryan H. M. , Fastnacht R. A. , Kammlott G. W.
Published: March 2011

Significantly improved flux-pinning has been achieved in bulk YBa2Cu3O7-δ superconductor (‘123’ compound) containing fine-scale defects (<~50 A thick). The measured Jc(magn.) of ~l05 A/cm2 at 77K, H = 0.9T is about ten times higher than the typical values for bulk Y-Ba-Cu-O. The improved structure was produced by rapid decomposition at 920°C of the YBa2Cu4O8 (‘124’) precursor.
Hysteretic Dependence of Critical Current on Applied Magnetic Field and Magnetic Irreversmujty Line Crossings in Polycrystalline YBa2Cu3C7
Authors: Askew Thomas R. , Flippen Richard B.
Published: March 2011

The transport critical current density Jc has been measured in high quality poly-crystalline YBa2Cu3C7 as a function of temperature and for various sweeps of sub-Tesla applied magnetic fields. Large increases over the virgin response were observed in Jc at fields of a few hundred gauss and are attributed to trapped flux in the samples. The amount of trapped flux was measured and correlated to the change at Jc at various temperatures. The position of the magnetic irreversibility line was measured by field induced absorption shift in AC susceptibility. The various data are discussed in the context of the weak link conduction model.
Harmonic Generation in the Alternating Magnetic Response of High-Temperature Superconductors
Authors: Shaulov A. , Bhargava R. , Dorman D.
Published: March 2011

We report a novel ac technique for characterizing the magnetic behavior of high-temperature superconductors. This technique is based on monitoring the spectrum of the magnetic response of these materials to small sinusoidal fields. A nonlinear magnetic behavior is indicated by the appearance of harmonic components in the spectrum. Measurements of these harmonics as a function of bias field, temperature and frequency provide valuable information about the processes of flux penetration, flux pinning and motion in these materials.
Ac Susceptibility Studies of the High Tc Superconductors: Dissipative Effects in La2.xSrxCuO4-Y and YBa2Cu3O7-Y Systems
Authors: Ling Xinsheng , Filipkowski M. E. , Heller E. K. , Budnick J. I.
Published: March 2011

We have studied the variation of dissipative effects with doping in the high Tc superconductors La2-xSrxCuO4-y and YBa2Cu3O7-y by studying the lossy component of ac susceptibility as a function of temperature. We find relatively strong excess losses at low temperature in both systems, which indicate stronger flux creep at grain boundaries, in lower level doped ceramic samples produced by a similar process. This effect is more significant in the La2-xSrxCuO4-y (214) system than in the YBa2Cu3O7-y(123) system. We suggest that the microscopic mechanisms of weakening of the order parameter in the grain boundaries may be different in the two systems. In the 214 system, as the charge carrier density in the CuO2 planes is reduced, the spatial fluctuation of the order parameter in the CuO2 planes is enhanced. In the 123 system, the initial removal of O from the sample, which weakens the coupling between planes and increases the spatial fluctuation of the order parameter between CuO2 planes. The grain boundaries are degraded in both systems. The degradation in the 214 samples is more significant than in the 123 samples.
The Effects of Oxygen and Strontium Vacancies on the Superconductivity of Single Crystals of Bi2sr2‐Xcuo6‐Y
Authors: Sales B. C. , Sonder Edward , Chakoumakos B. C.
Published: March 2011

Single crystals of Bi2Sr2‐xCuO6‐y were grown from CuO‐rich melts. The Sr content in the crystals was varied from x=0.1 to x=0.5 by varying the starting composition of the melt and the oxygen content was adjusted using an appropriate heat treatment of the crystals in a thermogravimetric system. With decreasing Sr content the superconducting transition temperature,Tc, of the crystals decreased rapidly from 10 K to below 4.2 K and the resistivity in the a‐b plane changed from metallic (linear in T from 30 to 300 K) to semiconducting. Reducing the oxygen content in the crystals had a similar effect on the resistivity. Only crystals with close to the maximum oxygen content (y=0) were superconducting, and removal of oxygen from previously superconducting crystals resulted in a rapid decrease of Tc , and the eventual loss of superconductivity (Tc < 4.2 K). Although crystals of Bi2Sr2‐xCuO6‐y could be made sequentially superconducting‐semiconducting‐superconducting by the addition‐removal‐addition of oxygen, the process was not totally reversible. After only one such cyclic heat treatment x‐ray diffraction indicated that for some compositions such cycling resulted in the appearance of CuO and an another layered structure that has been identified previously and is slightly deficient in CuO. The new layered structure is semiconducting and has a layer‐stacking repeat distance that is 1 å smaller than the superconducting “221” phase.
Studies of Tie Electronic Structure By XPS f HTSC and Related Compounds
Authors: Myhrai S. , Bocquet A.E. , Dobsoni J.F. , Goodman P. , Healy P.C. , Stewart A.M. , Thompson J.G. , Vhite T.J.
Published: March 2011

Measurements by photoemission spectroscopy have shown that the chemical environments of alkaline earth cations in HTSC compounds are different from the environments of these ions in the prototype perovskite structures. A recently discovered HTSC compound (Pb2Sr2Ca0.5Y0.5Cu3O8) exhibits the exceptional feature of having a typical HTSC signature for Sr, while Ca shows a perovskite-like signature. The crystal-chemical features of the relevant compounds have been correlated with these observations. These correlations may be indicative of inter-layer electronic interactions.
Measurement of Grain Boundary Parameters by Laser-Spot Photoconductivity
Authors: Poon E. , Evans H.L. , Hwang W. , Osgood R.M. , Yang E.S.
Published: March 2011

An experimental technique has been developed to study the electrical properties of semiconductor grain boundaries (GBs) by a focused laser beam. The laser beam is trained on a GB while the photoconductivity of the sample is measured. Both the steady-state and transient signals are recorded as functions of temperature. From these data, we obtain well-defined GB parameters, including the barrier height, interface charge density, trap energy and thermal capture cross-section. This technique allows us to examine localized regions of individual GBs in a semiconductor with multiple grains.
UV Laser-Initiated Formation of Si3N4
Authors: Deutsch T. F. , Silversmith D. J. , Mountain R. W.
Published: March 2011

Si3N4 films have been deposited on Si by using 193 nm ArF excimer laser radiation to initiate the reaction of SiH4 and NH3 at substrate temperatures between 200–600°C. Stoichiometric films having physical and optical properties comparable to those produced using low-pressure chemical vapor deposition (LPCVD) have been produced. The dielectric properties of the films are at present inferior to those of LPCVD material.
Evidence for Laser Induced Surface Silanol Formation
Authors: Muller D. F. , Rothschild M. , Rhodes C. K.
Published: March 2011

Evidence for the selective formation of surface silanol induced by ultraviolet irradiation in the intensity range between 3 × 107 W/cm2 and 108 W/cm2 is presented. Enhanced metallic deposition (Ti) on appropriately prepared samples is also reported.
Spectroscopy and Photoreactions of Organometallic Molecules on Surfaces
Authors: Chen C. J. , Osgood R. M.
Published: March 2011

A study of the UV photochemistry of organometallic molecules in the vapor and adsorbed phases is discussed. The gas-phase spectra is interpreted on the basis of molecular orbital theory and experimental data. The absorption spectra of the surface adlayers are determined by computer subtraction of the gas-phase spectra and an intepretation is provided. The influence of metalsubstrate microstructure on UV photochemical reactions of metal alkyls is briefly discussed.
The Spectroscopy and Photolysis of Metallo-Organic Precursors to III–V Compounds
Authors: Aylett Martin R , Haigh John
Published: March 2011

This paper describes the deposition by light-stimulated breakdown of gallium and indium on borosilicate glass, gallium arsenide and indium phosphide substrates, from precursors whose ultraviolet (uv) spectra have recently been reported. Some preliminary work on the deposition of indium phosphide is also reported, using an indium-phosphorus complex whose uv spectrum is also given.
Production of Microstructures by Laser Pyrolysis
Authors: Bä;uerle Dieter
Published: March 2011

Laser pyrolysis at short wavelengths is a powerful tool for micron-sized one-step local deposition of insulating, semiconducting and metallic materials from the gas phase. Various structures, e.g. stripes on different substrates, and rods of various lengths and diameters, have been produced. The morphology of the deposited material, the deposition rate, and the dimensions (typically 1-300 μm) of the structures were investigated quantitatively as functions of laser irradiance local temperature, laser focus diameter, scanning velocity, and gas pressure.
Laser Stimulated Growth of Epitaxial Gaas
Authors: Roth Walter , Kräutle Herbert , Krings Annemarie , Beneking Heinz
Published: March 2011

Stimulated growth of single crystalline GaAs has been obtained by irradiation of (100) oriented GaAs substrates inside an MOCVD reactor with a pulsed Nd-YAG laser.

Process temperatures have been varied between 540°C and 360°C. In the non-irradiated areas, below 480°C substrate temperature the growth rate decreases rapidly, whereas in the irradiated part of the substrate epitaxial layers could be grown in the whole temperature range investigated. Below 450°C, the growth is reaction limited.
Laser Induced Chemical Vapor Deposition of Hydrogenated Amorphous Silicon
Authors: Bilenchi Renzo , Gianinoni Iva , Musci Mirella , Murri Roberto
Published: March 2011

Some results on hydrogenated amorphous silicon growth by CO2 laser photodissociation of silane are reported. A 100 W CW CO2 laser was used as the excitation source. A horizontal configuration was adopted, where the laser beam is sent parallel to the substrate surface inside a flux reactor, and its energy is used to excite and dissociate the silane molecules flowing near the solid surface. The laser has no direct heating effect on the substrate, which is independently heated by an oven.

The photoproduced radicals by interacting with the surface grow a film at a rate strongly depending on silane pressure, substrate temperature and laser intensity. This experimental configuration allows depositions on large areas, owing to the large number of reactant molecules involved in the photochemical process. Moreover, material can be produced with a continuously variable hydrogen content, since the substrate temperature required for obtaining depositions can be as low as room temperature and adjusted independently of the other process parameters.

The film properties are similar to those of the glow discharge deposited material. The film amorphousness and the hydrogen presence either in monohydride and dihydride groups are evidenced by x-ray patterns and ir spectra. Results on the electrical and optical properties are also reported.
Direct Writing Using Laser Chemical Vapor Deposition
Authors: Allen S. D. , Trigubo A. B. , Jan R. Y.
Published: March 2011

Metal, dielectric and semiconductor films have been deposited by laser chemical vapor deposition (LCVD) using both pulsed and cw laser sources on a variety of substrates. For LCVD on substrates such as quartz, the deposition was monitored optically in both transmission and reflection using a collinear visible laser and the depositing CO2 laser. Deposition initiation and rate were correlated with irradiation conditions, the laser generated surface temperature, and the changing optical properties of the filmpsubstrate during deposition. Single crystallites of W greater than 100 pm tall were deposited using a Kr laser on Si substrates.
Using Optical Fibers in Laser Processing
Authors: Laude L.D. , Baufay L. , Pigeolet A.
Published: March 2011

Phase transformation occuring upon CW laser irradiating through optical fiber polymetallic, multilayered films deposited on insulating substrates is shown to provide a simple and versatile way to optically micro-print predetermined patterns. The technique allows both further reduction to the Rayleigh limit and simultaneous multiplication of the patterns.
Laser-Initiated Ga-Deposition on Quartz Substrates
Authors: Rytz-Froidevaux Y. , Salathe R.P. , Gilgen H.H.
Published: March 2011

The deposition of Ga on quartz substrates by photodissociation of trimethylgallium has been investigated. Light from a frequency doubled Ar-ion laser beam (257.2 nm) was focused onto quartz substrates. The Ar-ion laser was operated under cw or mode-locking conditions. The deposition rate has been investigated as a function of averaged UV power densities in the range of 1.8 – 1750 w/cm2 and is shown to depend critically on the laser operating mode. For cw operation, the maximum growth rate within the focal zone is limited to 17 Å/s whereas under mode-locking conditions, no saturation is observed and the growth rate increases linearly with the laser power up to 70 Å/s at 1.75 kW/cm2.
High Resolution Etching of Gaas and Cds Crystals
Authors: Podlesnik D. V. , Gilgen H.H. , Osgood R.M. , Sanchez A. , Daneu V.
Published: March 2011

Submicrometer gratings have been etched in GaAs and CdS crystals which have been immersed in an oxidizing etch and illuminated with interferring laser beams. A resolution of 170 nm was obtained. At high laser intensity and with prolonged etching time the surface properties of the material are degraded. The use of in-situ optical measurements of grating parameters allows ready optimization of the grating fabrication process.
Laser-Controlled Etching Of Chromium-Doped and N-Doped <100> Gaas
Authors: Tisone Gary C. , Wayne Johnson A.
Published: March 2011

The photochemical etching of chromium-doped and n-doped <100> GaAs in HNO3 and KOH is examined in the wavelength region of 334 to 514 nm from an argon-ion laser. The etching process is found to be not thermally controlled. The etch rates of chromium-doped GaAs agree with a diffusion-controlled model of the photochemically produced holes. For both types of GaAs, HNO3 is found to produce morphologically superior results.
Raman Scattering as a Temperature Frobe for Laser Heating of Si
Authors: Kirillov Dimitry , Merz James L.
Published: March 2011

The frequency of the phonon line in the Raman scattering spectrum recorded during CW laser-beam heating of Si was used as a characteristic of the lattice temperature inside the laser spot. It is shown that Raman scattering is a good temperature probe up to the laser power approaching optical damage of Si.
Synthesis and Properties of Copolymers of Diphenylsiloxane with Other Organosiloxanes
Authors: Ibemesi J. , Gvozdic N. , Kuemin M. , Tarshiani Y. , Meier D. J.
Published: March 2011

We describe the synthesis, characterization and properties of various types of siloxane polymers containing diphenylsiloxane (P) as a component. The polymer types include di-and tri-block copolymers with dimethylsiloxane (M) as the second component, and random and statistical copolymers with dimethylsiloxane or methylphenylsiloxane (P/M) as the second component. Such copolymers combine siloxane units whose polymers have very different properties. The polydiphenylsiloxane chain is rigid and inflexible, and the polymer is a highly crystalline solid with a liquid crystalline or condis crystalline state and a very high melting (clearing) temperature. In contrast, the polydimethylsiloxane or polymethylphenylsiloxane chains are very flexible and the polymers have very low glass transition temperatures.

Polymers of controlled molecular composition, size and architecture were prepared by anionic polymerization of the ‘cyclic trimers’, using lithium-based initiators.

The physical properties of the copolymers vary dramatically with composition and architecture. Two types of ‘random’ copolymers can be prepared. In one type, siloxane units of a given type are randomly placed in the chain in groups of three, i.e., the minimum sequence length of a given siloxane type is three siloxane units. In the other type of random copolymer, individual siloxane units are randomly distributed so that the minimum sequence length is a single siloxane unit. The properties of the two types are quite different, showing that subtle changes in sequence distribution can have major effects on physical properties. At molar ratios near 1/1 and with molecular weights of ∼105, the first type of ‘random’ copolymer is an elastic solid with appreciable mechanical properties, whereas the latter type is a sticky gum.

Diblock copolymer (P-M) with dimethylsiloxane as the major component are paste-like, whereas the triblock (P-M-P) and star-block copolymers of the same composition are tough elastomers. The block copolymers are molecular composites, in which the polydiphenylsiloxane component separates into crystalline microphases with very uniform fibrillar or lamellar morphologies, and with widths or thicknesses comparable to the length of the polydiphenylsiloxane block, i.e, typically of the order of 100 Å.
Pbzt/Polyamide Thermoplastic Micro-Composites - An Outgrowth of Molecular Composites Development
Authors: Uy William C. , Perusich E. R.
Published: March 2011

Molecular composites are dispersions of rigid-rod polymer molecules in a matrix of flexible coil polymers, formed by the coagulation of a solution containing these components. Where there is aggregation of the rigid-rod molecules, such composites are called micro-composites (MC's). These composites offer the potential for better economics and improvements in composite processing, and possibly performance, over conventional ‘string and glue’ composites. This paper describes work performed under contract to the U. S. Air Force to develop PBZT/thermoplastic molecular composites into a viable technology.

A commercially viable MC spinning and heat-treatment process has been defined based on a novel mixed solvent/quaternary solution technology developed by Du Pont. Advantages of this process include better economics, superior processing performance, and improved MC fiber tensile properties versus prior art. PBZT/polyamide MC fibers with strength/modulus of 332 ksi/29 Msi have been produced using this process. Adhesion equivalent to that obtained in conventional composites has been demonstrated. Uni-axial properties achieved to date compare favorably with conventional ‘string and glue’ PBZT/epoxy composites although compressive and shear strengths may be limiting factors in MC applications.
Equilibrium and Non-Equilibrium Phases and Phase Diagrams in Blends of Polymer Liquid Crystals with Enoineerino Polymers
Authors: Brostow Witold , Dziemianowicz Theodore S. , Hess Michael , Kosfeld Robert
Published: March 2011

This work represents a continuation of earlier studies of blends of polymer liquid crystals (PLC) with ordinary engineering polymers (EP). We now focus on connections between mechanical and other properties and phase structures and phase diagrams. Pure PLC are already two-phase systems; in each case addition of an EP complicates the situation further. In particular, we are concerned with phases which we call quasi-liquids, at temperatures between the glass transition and the melting point. Quasi-liquids do not have the mobility usually associated with liquids - because of the presence of other constituents and also because of orientational effects produced by the mesogenic groups. In phase diagrams of PLC-containing systems one should also take into account non-equlibrium phases. We are trying to show how such diagrams make possible Intelligent processing and a better control of properties of the PLC + EP materials.
Structure and Properties of Blends of Polycarbonate and Poly(Ethylene-Terephthalate-Co-p-Hydroxybenzoate): Phase Diagram and Mechanical Behavior
Authors: Kosfeld Robert , Schubert Frank , Hess Michael , Brostow Witold
Published: March 2011

The investigation of the thermal behavior of polymer blends leads to phase diagrams which involve Important information about the system. From these diagrams, equilibrium as well as non-equilibrium phases can be deduced and ranges of miscibility or partial miscibility of the polymers become obvious. Hence the diagrams are of a great value for processing of advanced polymer blends, especially If a polyphasic polymers such as a polymer liquid crystal is one of the constituents of the system.
“Dynamics of Phase Segrewation in Poly-P-Phenylene Terephtualamide and Amorphous Nylon Molfcular Composites”
Authors: Kyu Thein , Yang Jan Chang , Chen Tsuey Ing
Published: March 2011

Time-resolved light scattering has been employed to elucidate the dynamics of phase segregation of poly-p-phenylene terephthalamide (PPTA)/ amorphous nylon (AN) molecular composites. Miscible PPTA/AN blends can be prepared from sulfuric acid solution by rapidly coagulating the solution in distilled water. The composites, however, undergo phase segregation upon thermal treatment and exhibit a miscibility window reminiscent of a lower critical solution temperature (LCST). Several temperature-jump experiments were undertaken from ambient to a two-phase temperature region of 240, 250 and 260°C. Time-evolution of scattering profiles are analyzed in accordance with non-linear and dynamical scaling theories.
Dielectric Studies Of Polyester/Polycarbonate Blends
Authors: O'Reilly James K. , Sedita Joseph S.
Published: March 2011

Dielectric and enthalpic relaxation times have been measured as a function of composition and temperature. A fractional exponential (W–W) distribution of relaxation times fits both the dielectric and enthalpic relaxation times with different values which are a function of composition. Free volume parameters calculated using the WLF equation are not simple functions of the composition. Concentration fluctuations are considered to be important in these phenomena.
Small Angle X-Ray Scattering on Poly(Ethylene-Methacrylic Acid) Lead and Lead Sulfide Ionomers
Authors: Chu Benjami , Wu Dan O. , Mahler Walter
Published: March 2011

The morphology of ionomers, e.g., poly(ethylene-methacrylic acid) (EMA) lead salts (EMA/Pb) and lead sulfide compounds (EMA/PbS), has been studied by using the techniques of small angle x-ray scattering (SAXS), anomalous SAXS (ASAXS), wide angle x-ray scattering (WAXS), and differential scanning calorimetry (DSC). EMA/Pb containing less than 5 wt% of lead exhibited two characteristic SAXS peaks which corresponded to the lamellar structure of the partially crystalline polymer matrix and the ionic structure of the lead aggregates that were present in the amorphous regions. The lead aggregates were not distributed uniformly and increased in packing density with increasing lead content. Both DSC and WAXS showed that the crystalline phase was present for all EMA/Pb samples and that the crystallinity decreased slightly with increasing lead content. ASAXS near the L3 absorption edge of lead permitted the extraction of the scattered intensity of lead ions from the SAXS patterns of the superimposed crystalline and ionic structures. Correlation function analysis revealed that the ionic aggregates of the EMA/Pb containing 5 wt% of lead could be described by a liquid-like model with a short range order of 2-4 nm. EMA/PbS samples were made by a reaction of EMA/Pb ionomers with hydrogen sulfide. Instead of an ionic peak as shown by EMA/Pb samples, the SAXS patterns of EMA/PbS showed a broad diffraction peak located at the same q value as the lamellar peak of the EMA in acid form. The (lamellar) peak could be attributed to the interference between the PbS crystallites in the neighboring lamellae.
Studies on the Excess Free Energy and The Early Spinodal Decomposition of the Blend d-PS/Peavrmley Asntda tteh Eof Isotopic Blend d-PS/PS with Small Angle Neutron Scattering
Authors: Schwahn D. , Springer T. , Hahn K. , Streib J.
Published: March 2011

The article deals with the phase diagram and spinodal decomposition of two polymers blends, namely d—PS/PVME and d(deutero)—PS/PS, investigated by small angle neutron scattering (SANS). The result of the static experiments is the excess free energy and the phase diagram. This is used as a basis for studies of non—equilibrium phenomena as spinodal decomposition. In polymer blends the Cahn—Hilliard—Cook theory of the early state of spinodal decomposition can be tested easily, because the blends have rather low relaxation rates; and they are meanfield systems [2,6] which makes interpretation simple, except in a very narrow temperature region near the critical point [6]. The kinetics in the isotopic blend d—PS/PS are so slow that the early states of spinodal decomposition can be studied within minutes. The presented SANS results have been performed at the KWS I small angle instrument at the FRJ—2 reactor in the KFA Jülich.
Synthetic Procedures for Preparing Cross-Linkable Acrylic Comb-Like Copolymers Via Macromonomers
Authors: Chen Gang-Fung , Jones Frank N.
Published: March 2011

A versatile procedure was developed for synthesis of acrylic comb-like copolymers in three steps: (1) Hydroxyl terminated oligomers were synthesized from methyl methacrylate, butyl acrylate and glycidyl acrylate by free-radical initiated addition polymerization using a functional chain transfer agent, 2-mercaptoethanol, and very low initiator levels. (2) The oligomers were converted to macromonomers by reaction with isocyanatoethyl methacrylate. (3) The macromonomers were polymerized by free-radical initiation. Conditions during the first stage must be carefully selected to minimize formation of difunctional material which could cause gelation in the third stage. A variety of structures can be made such as comb-like copolymers with homopolymer tines or comb-like homopolymers with copolymer tines. Functional groups can be introduced by copolymerizing glycidyl acrylate into the macromonomer. Assignment of comb-like structures is not rigorously proven but is strongly supported by the synthetic route and by DSC, FT-IR and chromatographic data.
Synthesis and Characterization of Segmented Copolymers of a Methylated Polyamide and a Thermotropic Liquid Crystalline Polyester
Authors: Pawlikowski Gregory T. , Weiss R. A. , Huang S. J.
Published: March 2011

A block copolymer consisting of liquid crystalline polyester segments and methylated polyamide segments has been synthesized. Solution polycondensation of acid chloride end-capped poly(terephthaloyl phenylhydroquinone) (LCP portion) with an amine terminated poly(N,N'-dimethylethylene sebacamide) was utilized to prepare the block copolymer. Characterization by differential scanning calorimetry, infrared spectroscopy, thermogravimetric analysis, optical microscopy and elemental analysis has been performed to verify the existence of the block copolymer that may have potential as a molecular composite material or self-reinforcing thermoplastic.
Aggregation Structure and Electro—Optical Properties of (Liquid Crystalline Polymer)/(Low Molecular Weight Liquid Crystal) Composite System
Authors: Kajiyama Tisato , Kikuchi Hirotsugu , Miyamoto Akira , Moritomi Satoru , Hwang Jenn—Chiu
Published: March 2011

A series of thin films composed of liquid crystalline polymer (LCP) and low molecular weight liquid crystal (LMWLC) was prepared by a solventcasting method or by a bar—coating method. LCPs were of mesogenic side chain type with strong or weak polar terminalgroups in the side chain portion. A mixture of smectic LCP (LCP with side chain of strong polar end) and nematic LMWLC formed a smectic phase in a LCP weight fraction range above 50 %. Also, a mixture of nematic LCP (LCP with side chain of weak polar end) and nematic LMWLC with strong polar group induced a new smectic phase in a LCP molar fraction range of 20–80 %. Reversible and bistable electro-optical effects based on light scattering were recognized for a smectic phase of a binary composite composed of LCP and LMWLC. A light scattering state caused by many fragmented smectic lamellae appeared in the case of application of an a.c. electric field below a threshold frequency (∼l Hz). Furthermore, application of a 100 Vp—p a.c. field of 1 kHz made the transmission light intensity increased to 94 % within a few seconds. The optical heterogeneity in asmectic layer composed of the side chain group of LCP was caused by the difference of twoforces based on both dielectric anisotropy of the side chain and electrohydrodynamic motion of the main chain. Since application of a low frequency electric field causes an ioniccurrent throughout the mixture film, it is reasonable to consider that an induced turbulent flow of main chains by an ionic current collapsed a fairly well organized large smectic layer into many small fragments, resulting in an increase in light scattering. The response speed of LCP upon application of an electric field increased remarkably by mixingLMWLC. In the case of a smectic mesophase, turbid and transparent states remained unchanged as it was, even though after removing an electric field.1

Such abistable and reversiblelight switching driven by two different frequencies of electric field could be newly realized by both characteristics of turbulent effect of a wellorganized large smectic layer of LCP and rapid response of LMWLC. We believe that the LCP/LMWLC mixture system is promissing as a novel type of “light valve” exhibiting memory effect (bistable light switching).
The Catalytic Synthesis of Inorganic Polymers for High Temperature Applications and as Ceramic Precursors
Authors: Rahn Jeffrey A. , Laine Richard M. , Zhang Zhi-Fan
Published: March 2011

Absract

Polysilsesquioxanes,-[RSi(O)1.5 ]x-, exhibit many properties that are potentially quite useful for industrial applications. These properties include high temperature stability (−600°C in O2); good adhesion and, liquid crystal-like behavior for some derivatives. Moreover, [MeSi(O)l.5]x, polymethylsilsesquioxane has been used successfully as a precursor for the fabrication of carbon fiber/“black glass” (SiO2/SiC/C) composites and “black glass” fibers.

Current methods of preparation depend on hydrolysis of RSiCl3 or RSi(OR)3. Unfortunately, this approach leads to several products that are difficult to purify because polysilsesquioxanes exhibit a great propensity for forming gels. We describe here a simple catalytic approach to the synthesis of polymethylsilsesquioxane copolymers of the type -[MeRSiO].3[MeSi(O)1.5].7- where R - H, OMe, OEt, OnPr and OnBu. The R - H copolymer is produced by catalytic redistribution of -[MeHSiO]xoligomers using dimethyltitanocene, Cp2TiMe2 as the catalyst precursor.

Following catalytic redistribution, the resulting copolymer, -[MeHSiO].3[MeSi(O)1.5].7−, is reacted in situ with alcohols to produce -[Me(R'O)SiO].3[MeSi(0)1.5].7− (where R' - Me, Et, nPr and nBu) which serve as masked forms of the polymethylsilsesquioxane. These new copolymers have been characterized by 1H, 13C and 29Si NMR TGA and DTA. The NMR studies allow us to assign structures for the copolymer.

These new copolymers exhibit improved tractability. Their high temperature properties are all quite similar; although, the MeO-, EtO- and especially the nPrO- derivatives give much higher ceramic yields than expected.
Conducting Molecular Multilayers: Intercalation of Conjugated Polymers in Layered Media
Authors: Mehrotra V. , Giannelis E.P.
Published: March 2011

Polyaniline has been synthesized in the galleries of fluorohectorite, a two-dimensional mica-type layered silicate. Intercalation of aniline in the intracrystalline region of Cu-exchanged fluorohectorite results in oxidative polymerization to polyaniline (emeraldine base form) as demonstrated by electronic, infrared and Raman spectroscopy and x-ray diffraction data. The intercalated insulating form of polyaniline becomes conducting on exposure to HCl. In-plane electrical conductivity data measured in the temperature range 274 to 573 K show a complex thermally activated behavior with room temperature conductivity 0.05 Ohm−1cm−1. The polyaniline/layered silicate hybrids represent a new class of nanocomposites consisting of synthetic conductors with molecular dimensions contained in a quasi twodimensional environment of a crystalline host.
Materials Effects on the Radiation Sensitivity of Single Mode Optical Fibers
Authors: Friebele E. J. , Askins C. G. , Gingerich M. E. , Shaw C. M. , Schmidt W. H.
Published: March 2011

Statistically significant correlations have been established between certain fabrication parameters of matched clad single mode fiber waveguides and the induced attenuation and recovery kinetics following exposure to an ionizing radiation dose.
Process Analysis in the Preparation of Fluorozirconate Glasses
Authors: Braglia M. , Cocito G. , Ferraris M. , Grego G. , Parisi G. , Chiappetta R.
Published: March 2011

Different preparation processes for fluorozirconate glasses (ZBLAN) have been investigated by infrared spectroscopy (IR) and x-ray diffraction (XRD). Glasses have been prepared with different NH4 F.HF amount (20–10–5–0% weight) or with NF30 as fluorinating agent. The presence of NF3 in the fluorination step of the preparation is useful to improve the glass quality in terms of oxide and hydroxil content: electron spin resonance (ESR) on these glasses (γ-irradiated, 20 Mrad) does not detect any signal.
Tellurium Halide Glass Fiber for Transmission in the 8–12 μm Region
Authors: Zhang X. H. , Fonteneau G. , Ma H. L. , Lucas J.
Published: March 2011

Glasses in the Te-Br-Se and Te-I-Se systems show potential low losses in the 8–12 μm region. They are very stable against crystallization and against moisture. The lowest losses of a fiber at 10.6 μm, measured using a CO2 laser, is about 3 dB/m. The essential diffusion centers in these fibers have been proved to be bubbles. A power delivery experiment was made using a fiber having an attenuation of 5 dB/m. The power density of about 40 kw/cm2 can be injected into the fiber without damaging this fiber.
Structural Stability of Tellurium Halide Glasses
Authors: Yi Jay J. L. , Strutt Peter R.
Published: March 2011

In quantitative studies of the structural stability of Te-Cl and Te-Br glasses, specific attention has been devoted to determining the kinetics of their overall crystallization process and the glass composition range in which chemical decomposition occurs at elevated temperatures. The calorimetric studies reveal that the tendency of crystallization or thermal decomposition of these glasses is related to phase-diagram characteristics. It seems that the structure of these glasses is not an idealized random arrangement as described by the classic model. Underlaying causes for this deviation from a perfect random arrangement to one involving a degree of ordering ( structural group ) is discussed.
Potential Application of Bi(Pb)-Ca-Sr-Cu-O Glasses for Preparation of Integrated Optical Fibers
Authors: Zheng Haixing , Mackenzie J. D.
Published: March 2011

The infrared transmission, and possible high nonlinear optical susceptibility of Bi(Pb)-Ca- Sr-Cu-O glasses as well as their being the precursors for high temperature superconductors make them potential materials for integrated optical fibers. In this work, the glass formation and the fabrication of glass fibers have been investigated. The properties of the glasses have been studied. The infrared cutoff of the glasses is above 7 μm, and a high refractive index (˜ 2.9) and a high density (˜ 6 g/cm3) indicate the possible high nonlinear optical susceptibility. After being heat treated at high temperatures, the glasses become superconductors which show the response to the optical radiation due to the bolometric effect. Fabrication of an integrated optical fiber system incorporating the transmitting medium, optical modulator and detectors is possible.
Growth of Optical Quality Sapphire Single Crystal Fibers
Authors: Jundt Dieter H. , Fejer Martin. M. , Byer Robert. L.
Published: March 2011

Void-free sapphire single crystal fibers with diameters of 110 μm and 60 μm and lengths of over 2 m have been grown by the laser-heated pedestal growth method. The growth dynamics of the floating zone was studied and shows the features expected from a simple theoretical model. Optical losses have a minimum of 0.5 dB/m in the near infrared at 1064 nm. An absorption band centered at 400 nm results in losses of up to 20 dB/m in the visible. The fibers have potential applications in high temperature thermometry and in delivery systems for laser surgery. Absorption losses of 0.88 dB/m with a damage threshold higher than 1.2 kJ/cm2 at 2936 nm made tissue ablation feasible with fibers several meters in length.
Extended X-Ray Absorption Fine Structure study of Potassium Niobate
Authors: Kim K. H. , Elam W. T. , Skelton E. F.
Published: March 2011

Extended x-ray absorption fine structure (EXAFS) of potassium niobate (KnbO3 ) was measured at the K edge of Nb, at various temperatures to include all phases of the material. The first shell data were analyzed to determine the distances between the niobium atom and its oxygen neighbors. The single shell amplitude almost vanishes around k-7.5 A−1 at all temperatures, suggesting two distances with a separation of about 0.21 A. Nonlinear fitting was used to determine the structure more carefully and the data at all temperatures can be fit reasonably well with two Nb-O ditances. This is in disagreement with the displacive model which implies only one Nb-O distance in the cubic phase. This result suggests that the niobium atom is displaced along the (111) direction relative to the oxygen atom in all phases. Thus, the transitions are not displacive, but have a strong order-disorder character.
Scattering from Gas-Phase Synthesized Particles
Authors: Hurd Alan J.
Published: March 2011

Rational design and optimization for the next generation of fiber optics requires fundamental knowledge of the processes at each step of production [1], not the least of which is the formation and deposition of the glass precursor particles. Currently, gas-phase synthesis dominates the industry, owing, in part, to the high purity possible for gaseous reagents. However, the production engineer has relatively little control over the microstructure of the boule from which the fiber is drawn because many complex mechanisms take part in the growth and thermophoretic deposition of the precursors. Although it is desirable, for example, to obtain a porous boule in order to facilitate the removal of deleterious hydroxyls, connected porosity is by no means guaranteed. The successful attainment of high porosity depends on a number of variables such as the size distribution [2], internal structure, shape distribution, viscosity, and surface tension of the particles at the instant of deposition.
Application-Specific Optical Fibres Manufactured from Multicomponent Glasses.
Authors: Taylor E. R. , Taylor D. J. , Li L. , Tachibana M. , Townsend J. E. , Wang J. , Wells P. J. , Reekie L. , Morkel P. R. , Payne D. N.
Published: March 2011

Special fibres have been fabricated to demonstrate the potential of using multicomponent glass materials for sensors, devices and fibre lasers. High nonlinearity and large Verdet constants are confirmed for lead-silicate glass fibres. Nonlinear effects such as second harmonic generation (SHG), third harmonic generation (THG), electro-optic (EO) Kerr effect and optical switching are observed for F7 core glass fibres. Compound glasses are investigated as host glasses for fibre lasers and amplifiers. An all glass cladding pumped Nd-doped fibre laser from compound glassses is characterized.
Glasses for Er3+ -Doped Fiber Lasers and Optical Amplifiers
Authors: Miniscalco W. J. , Andrews L. J. , Zemon S. , Hall B. T. , Wei T. , Folweiler R. C.
Published: March 2011

Er3+-doped silica fibers have demonstrated excellent performance as active optical devices at 1.5 μm. In an effort to identify promising new hosts, we have measureed absorption and emission cross sections for a variety of Er3+-doped glass. Compositions have been identified which have advantages over silica, particularly for pumping with AIGaAs diode lasers at 800 nm.
An Investigation of Optical Fiber Coating Performance in Embedded Sensing Applications
Authors: Haaksma Rebecca A. , Cehelnik Marilyn J. , Kerkhoff M. Jonell
Published: March 2011

The use of composite materials for aerospace applications has created an increased need for developing nondestructive methods for assessment of composite performance. Embedded optical fiber sensor technology provides the potential for monitoring parameters of interest during processing and testing of composite materials as well as the opportunity for tracking properties over the lifetime of composite parts in service. The successful development of this technology depends on designing optical fiber sensor systems suitable for embedding in composite structures.

This paper focuses on the role played by optical fiber coatings in the design of embedded sensor systems. The performance of different optical fiber coatings under typical composite processing conditions will be discussed. Photomicrographs of test specimens containing embedded sensors will be presented which show delamination occurring at the coating/optical fiber interface in preference to the coating/epoxy resin interface. Coating performance criteria will be outlined for use in the selection of fiber optic sensors for composite applications.
Fabrication of Oxide Glass Coated Fluoride Glass Optical Fibers for Durability and Strength Improvement
Authors: Ohishi Yasutake , Fujiura Kazuo , Takahashi Shiro
Published: March 2011

The crystallization of fluoride glass being in contact with oxide glass is investigated using thermal analyses to perform oxide glass coating for durability and strength improvement. The chemical reaction does not occur in the fiber drawing temperature range and begin at the melting temperature of fluoride glasses. The crystallization of fluoride glass is suppressed by contact with oxide glass. Smooth contact between fluoride and oxide glasses is confirmed.
Specific Heat Measurements on κ-(Bedt-Ttf)2Cu(Ncs)2
Authors: Goodrich R. G. , Xu Jing-Chun
Published: March 2011

We have measured the specific heat of κ-(BEDT-TTF)2Cu(NCS)2 from 4 to 14 K. The superconducting transition at 9.4 K is observed in zero applied magnetic field and in a field of 0.3 T. Both the magnitude of the change in Cp at Tc and the temperature dependence of Cp below Tc indicate a strong coupling superconductor. If the lattice specific heat is assumed to contain contributions due to the eighteen vibrational degrees of freedom, the phonon contribution to the specific heat in our temperature range can be represented by a Debye integral expression with a Debye temperature of 95 K. A model of collective modes suggesting the origin of the eighteen degrees of freedom is presented.
A New Synthetic Metal Precursor: Dimethyltetrathiotetracene and Related Compounds
Authors: Maruo Toshio , Singh Megh , Jones Thomas M. , Rath Nigam P , Min Dong
Published: March 2011

The successful synthesis of dimethyltetrathiotetracene (DMTTT) has been achieved in our laboratory and an account of the details of the synthesis has been reported. Reported herein are studies of the physical properties of DMTTT and some of its chemistry. Both 1:1 and 2:1 DMTTTX charge transfer salts have been prepared and are in the process of being characterized in our laboratory. Comparisons of physical properties and the results of studies such as single crystal x-ray diffraction, solid state ESR spectra, cyclic voltammetry and electrical conductivity are reported. To date, these comparisons reveal considerable similarity between the properties of any given DMTTT charge transfer salt and its corresponding tetrathiotetracene (TTT) charge transfer salt.