bluuebunny/crossref_metadata_2025 huggingface dataset:
Some Physical Properties of Suspendable Superconducting 123-Ag Composites
Authors: Huang C. Y. , Tai H. H. , Yao Y. D. , Li T. J. , Wu M. K.
Published: March 2011

We have measured the M-H hysteresis loops of n YBa2Cu3Oy: Ag (n = 3,5, and 7), and 3RBa2Cu3Oy:Ag (R = rare earth) as a function of temperature. We have found that the residual magnetization and, hence, pinning, is strong and is independent of n and R, but dependent on the metallurgy. The giant creep rates have been measured and are greater than those of pure 123 samples. Scanning electron microscopy and polarized light microscopy have shown that the presence of silver gives rise to the growth of large grains (~1 mm) in the 123-Ag samples. The field dependence of the critical current density is not strong at high field. We have also measured the resistance in field up to 200 kOe. The resistance remains zero even at 80 K and 200 kOe. The field dependence of the superconducting transition is discussed in terms of phase slippage.
The Dependence of Tc on Structural and Electronic Parameters for Ceramic High-Tc Superconductors
Authors: Giessen B.C. , Markiewtcz R.S.
Published: March 2011

Based on the description of high-Tc cuprate superconductors as intercalation compounds and the van Hove singularity (vHs) concept for these phases, [with its consequences concerning their density of states (dos)] we give a model that explains T2 semi-quantitatively as a function of both hole concentration and stage number and, in a simplified variation, yields a functional dependence of T2 on the CuO2 layer fraction of the unit cell that shows a maximum, as observed.
High Resolution Laser Diagnostics for Direct Gap Semiconductor Materials
Authors: Salathe R.P. , Gilgen H.H.
Published: March 2011

The laser-induced luminescence of direct gap semiconductors can be measured with high spatial (1 μm) and temporal (< 1 ns) resolution. A profiling technique is described for in-situ measurements during laser processing. It allows the evaluation of temperature, carrier density and band gap energy within the focal zone. The technique has been applied to (Al,Ga)As heterostructure material subjected to highly focused cw-Kr-ion laser radiation. The measurements reveal low temperature rises (<200 deg.C) at high excitation densities (>1kw/cm2) and an inhomogeneous distribution of optically excited carriers for concentrations above 2.1017 cm−3.
Laser Photolytic Deposition of Thin Films
Authors: Boyer P. K. , Moore C. A. , Solanki R. , Ritchie W. K. , Roche G. A. , Collins George J.
Published: March 2011

An excimer laser is used to photochemically deposit thin films of silicon dioxide, silicon nitride, aluminum oxide, and zinc oxide at low temperatures (100–350deg;C). Deposition rates in excess of 3000 Å/min and conformal coverage over vertical walled steps were demonstrated. The films exhibit low defect density and high breakdown voltage and have been characterized using IR spectrophotometry, AES, and C-V analysis. Device compatibility has been studied by using photodeposited films as interlayer dielectrics, diffusion masks, and passivation layers in production CMOS devices.

Additionally, we have deposited metallic films of Al, Mo, W, and Cr over large (>5 cm2) areas using UV photodissociation of trimethylaluminum and the refractory metal hexacarbonyls. Both shiny metallic films as well as black particulate films were obtained depending on the deposition geometry. The black films are shown to grow in columnar grains. The depositions were made at room temperature over pyrex and quartz plates as well as silicon wafers. We have examined the resistivity, adhesion, stress and step coverage of these films. The films exhibited resistivities at most ∼20 times that of the bulk materials and tensile stress no higher than 7 × 109 dynes/cm2
Characteristics of Laser Implantation Doping
Authors: Ibbs K G , Lloyd M L
Published: March 2011

UV laser photochemical dissociation and laser enchanced thermal dissociation have been used to generate free metal dopant species from a variety of organometallic molecules near a semiconductor substrate surface. Simultaneous laser annealing via a localised melt phase allows diffusion driven implantation of the metal atoms and subsequent electrical activation in the regrowing material. High levels of dopant concentration and activation are readily achieved in this way.

Results will be presented on doping of silicon by boron using an ArF laser. These will include data on junction depths, number density and carrier density as a function of depth and interpretation of the data in terms of calculated temperature profiles.

The possibility of tailoring junction characteristics by control of laser and gas flow parameters will be considered with preliminary experimental data.
Photoelectrochemical Deposition of Metal Patterns on Semiconductors
Authors: Rose Timothy L. , Micheels Ronald H. , Longendorfer David H. , David Rauh R.
Published: March 2011

Microscopic metal patterns may be produced on p-type semiconductors using a maskless photoelectrochemical procedure in which electroplating is induced by minority carriers in illuminated portions of a semiconductor electrode. Resolution exceeding l0μ has been achieved for deposits of Au on p-GaAs and Cu on p-Si. “Electroless” imaging and negative photoelectrochemical imaging are also discussed.
Analysis of Laser-Enhanced Adsorption/Desorption Processes on Semiconductor Surfaces via Electronic Surface State Excitation
Authors: Murphy William C. , Beri A. C. , George Thomas F. , Lin Jui-Teng
Published: March 2011

Electronic surface states in semiconductors often lie between the valence and conduction bands and give rise to charge densities confined to the surface region. Laser radiation of frequency less than the energy gap can excite electrons from delocalized valence band states to these localized surface states leading to large changes in the charge distribution at the surface. Selective enhancement of adsorption/desorption processes involving ionic or polar adspecies can result from such a charge redistribution. Using a onedimensional model for silicon, the cross-section for the laser-induced electronic transition to surface states is shown to be large. The interaction energy of an adspecies with the surface changes significantly with direct excitation of surface states in a semiconductor. For a one-dimensional metal, however, direct transitions between bulk and surface states are not allowed, but phonon-mediated transitions coupled with laser radiation lead to substantial charge transfer as for semiconductors.
Rheology of Blends of a Rodlike Polymer (PBO) and its Flexible Chain Analog
Authors: Sullivan V. J. , Berry G. C.
Published: March 2011

Rheological properties of isotropic solutions of rodlike poly(p-phenylene benzbisoxazole), PBO, flexible chain poly(2,5-benzoxazole), ABPBO, and their miscible blends in solution are described. Measurements include steady state properties (the viscosity and recoverable compliance as functions of shear rate), transient properties (the recoverable compliance), and dynamic mechanical properties (the loss and storage compliances as functions of frequency). The relaxation spectrum of the blends is broader than that for the rodlike chain, and tends to occur at longer times, reflecting a viscosity enhancement that occurs with the blends. The measured zero shear viscosities for rod and blend solutions are compared with predictions based on the model of Doi and Edwards.
The Ordered Bicontinuous Double Diamond Structure in Binary Blends of Diblock Copolymer and Homopolymer.
Authors: Winey Karen I. , Thomas Edwin L.
Published: March 2011

We report the observation of the ordered bicontinuous double diamond (OBDD) structure in binary blends of poly(styrene-isoprene) diblock copolymer and homopolystyrene. The overall polystyrene volume fraction range is 64 - 67 PSvol% for the OBDD structure in binary blends of a lamellar diblock (SI 27/22) and a homopolymer (14.0 hPS). This composition range is approximately within the polystyrene volume fraction range established for pure diblock copolymers in the strong segregation regime having the OBDD structure. Ordered lamellae are observed at approximately 65 PSvol% when the homopolystyrene molecular weight is greater than the molecular weight of the polystyrene block of the copolymer. This observation is discussed in terms of the decreased degree of mixing between the homopolymer and the corresponding block and the resultant effect on the interfacial curvature.
Morphological Consequences of Catalytic Hydrogenation of Polymers in the Bulk
Authors: Gilliom Laura R. , Schaefer Dale W. , Mark James E.
Published: March 2011

When suitable catalysts are molecularly dispersed in polymers, the polymers can be modified without added solvent. This paper describes studies on the morphology of samples of trans-l,4-polybutadiene and syn-1,2-polybutadiene which have been partially deuterated in the bulk. The development of a peak in the SANS data for the 1,2-polybutadiene suggests the formation of small domains upon deuteration. Possible explanations for this observation, including chemical and physical heterogeneity, are evaluated. Results of SAXS and thermal measurements are also considered.
Synthetic Control of Molecular Structure in Organic Aerogels
Authors: Pekala Richard W.
Published: March 2011

Organic aerogels have been formed from the aqueous, sol-gel polymerization of resorcinol with formaldehyde. These materials are transparent and have continuous porosity with cell/pore sizes of less than 1000 Å. Their microstructure is composed of interconnected colloidal-like particles with diameters of 30-200 Å. The particle size, cell size, surface area, and density of the aerogels are predominantly controlled by the catalyst concentration used in gel preparation.
Interfacial Segregation Effects in Mixtures of Homopolymers with Copolymers.
Authors: Wakharkar Vijay S. , Russell Thomas P. , Deline Vaughn R.
Published: March 2011

Secondary Ion Mass Spectroscopy (SIMS) has been used to study the surface and interfacial segregation of diblock copolymers in mixtures of the copolymer in the homopolymer. Symmetric, diblock copolymers of polystyrene (PS) and poly(methyl methacrylate) (PMMA), in either the PS or the PMMA homopolymers were investigated. In mixtures of the copolymer with the PS homopolymer, systematic surface enrichment of the copolymer as well as segregation of the copolymer to the polymer/Si interface or in the case of bilayered filmsto the polymer/polymer interface occurs with annealing treatments. These segregation effects persist over a large range of homopolymer molecular weights with changes in the kinetics of the segregation process being predominant.
Mechanically Induced Silica-Siloxane Mixtures. Structure of the Adsorbed Layer and Properties of the Network Structure
Authors: Cohen—addad J.P.
Published: March 2011

Properties specific to silica—siloxane mixtures are analysed and discussed. The effect of polymer adsorption is interpreted from the Gaussian statistics of chains: the amount of adsorbed polymer Qr is proportional to the square root of the chain molecular weight. The kinetics of adsorption is described as a process of surface saturation. It is discussed as a function of the silica concentration. The effect of swelling of the mixtures is interpreted within the statistical framework proposed by Flory for ordinary gels.
Deformation Behavior of Polymer Gels in Electric Field
Authors: Kurauchi Toshio , Shiga Tohru , Hirose Yoshiharu , Okada Akane
Published: March 2011

The deformation of poly(acrylic acid)—co—(acrylamide) gels and poly(vinyl alcohol)—poly(acrylic acid) gels under an electric field was investigated. Bending of these ionic gels was induced by an electic field. Using this deformation, we constructed a prototype of a robot hand having soft fingers, and an artificial fish able to swim.
Nylon 6–Clay Hybrid
Authors: Okada Akane , Kawasumi Masaya , Usuki Arimitsu , Kojima Yoshitsugu , Kurauchi Toshio , Kamigaito Osami
Published: March 2011

ζ-Caprolactam was polymerized in the interlayer spacing of montmorillonite, a clay mineral, yielding a nylon 6-clay hybrid (NCH) 1).

X-ray and TEM measurements revealed that each template of the silicate, which is 10 Å thick, was dispersed in the nylon 6 matrix and that the repeat unit increased from 12 Å in unintercalated material to 21 Å in the intercalated material.

Thus NCH, is a “polymer based molecular composite” or “nanometer composite”. NCH, when injection-molded, shows excellent properties as compared to nylon 6 in terms of tensile strength, tensile modulus and heat resistance. Heat distortion temperature increased from 65 °c for nylon 6 to 152 °c for NCH, containing 4 wt% (1.6 vol%) of clay mineral.
Reinforcement of Elastomers by The In-Situ Generation of Filler Particles
Authors: Mark James E. , Schaefer Dale W.
Published: March 2011

The goal of primary interest in these investigations was the development of novel methods for filling elastomeric networks. The techniques developed employ thein-situgeneration of reinforcing fillers such as silica or a glassy polymer such as polystyrene either after, during, or before network formation. The reaction involves decomposition of organometallic compounds, using a variety of catalysts and precipitation conditions, or freeradical polymerization of a suitable monomer. The effectiveness of the technique is gauged by stress-strain measurements carried out on these elastomeric composites to yield values of the maximum extensibility, ultimate strength, and energy of rupture. Also of interest are calorimetric studies of the networks, to determine their crystallizability. Information on the filler particles themselves is obtained from density determinations, electron microscopy, and scattering measurements.
Structure of Microphase-Separated Silica/Siloxane Molecular Composites
Authors: Schaefer Dale W. , Mark James E. , Mccarthy David , Jian Li , Sun C. -C. , Farago Bela
Published: March 2011

The structure of several classes of silica/siloxane molecular composites is investigated using small-angle x-ray and neutron scattering. These filled elastomers can be prepared through different synthethic protocols leading to a range of fillers including particulates with both rough and smooth surfaces, particulates with dispersed interfaces, and polymeric networks. We also find examples of bicontinuous filler phases that we attribute to phase separation via spinodal decomposition. In-situ kinetic studies of particulate fillers show that the precipitate does not develop by conventional nucleation-and-growth. We see no evidence of growth by ripening whereby large particles grow by consumption of small particles. Rather, there appears to be a limiting size set by the elastomer network itself. Phase separation develops by continuous nucleation of particles and subsequent growth to the limiting size. We also briefly report studies of polymer-toughened glasses. In this case, we find no obvious correlation between organic content and structure.
Nmr Imaging of Silica-Silicone Composites
Authors: Garrido Leoncio , Ackerman Jerome L. , Mark James E.
Published: March 2011

Polydimethylsiloxane (PDMS) model networks reinforced by in situ precipitated SiO2, and polymer-modified silica glasses were obtained following the usual sol-gel methods. The conditions were chosen to increase the probability of observing inhomogeneities: (i) bulky samples, and (ii) limited reaction times. These composites were characterized by measuring bulk spin-lattice (T1) and spin-spin (T2) relaxation times and using 1H NMR two-dimensional Fourier transform (2DFT) spin echo imaging techniques. The T1 and T2 maps show clear and significant variations of NMR signal intensity throughout the sample due to nonuniform hydrolysis of the tetraethylorthosilicate (TEOS) in the specimens.
Luminescence Measurement of Fused Silica in the Presence of Excimer Laser Radiation
Authors: Kuzuu Nobu , Komatsu Yohshikazu , Murahara Masataka
Published: March 2011

Exicimer laser induced luminsecence characteristics of type III fused silica was investigated. The luminescence characteristics in the ultraviolet wavelength region are strongly depending on the intensity of red luminescence at 650 nm. A sample without red luminescence shows a strong emission band at 280 nm. We found that the 280 nm band is corresponds to a absorption band at 225 nm. To clearfy the nature of the 280 nm band, we studied the difference of luminescence of samples which had been kept on heating under various atmosphares, i.e., N2, O2, He, H2, and air. By these results we suspect that the 280 nm band is related to hydrogen atom which are weakly bounded to the glass network.
Synthesis and Characterisation of Heavy Metal Fluoride Glasses and Fibres
Authors: France Paul W , Carter S F , Moore M W , Williams J R
Published: March 2011

The fabrication of optical fibres based on fluoride glasses has required the development of novel preparation techniques. Some of these techniques are based on methods used to prepare multicomponent oxide glass fibres although some have been developed specially for fluoride glasses. This paper will review such processes as glove-box melting, reactive atmosphere processing, and rapid quenching; show how these have been used to prepare fluoride glass fibres with losses down to 2.6 dB/km at 2.6 μm; and discuss remaining problems with the glass.
Proton Effects in KTiOPO4
Authors: Morris P. A. , Crawford M. K. , Roelofs M. G. , Bierlein J. D. , Gallagher P. K. , Gashurov G. , Loiacono G. M.
Published: March 2011

Evidence supporting the temperature dependent defect mechanism of nonstoichiometry on the potassium and oxygen sublattices in KTP is presented. The primary compensating defects for the formation of vacant potassium sites in typical flux grown KTP are vacant oxygen sites. Protons (OH-) are the principal defect compensating for the formation of vacant potassium sites in high temperature hydrothermal KTP. A model of the ionic conductivity in high temperature hydrothermal KTP is proposed in which specific protons participate in cooperative motion over a limited distance with the potassium vacancies migrating along the “channels” in the structure in the Z-direction. The higher activation energy measured for ionic conductivity in flux grown KTP (0.5 eV) relative to high temperature hydrothermal (0.3 eV) is suggested to be due to the energy required to dissociate from a defect complex, such as a (VO - VK). The correlation of ionic conductivity to damage susceptibility appears to be due to the levels of compensating defects for vacant potassium sites in KTP, which are related to the concentrations of Ti3+ formed in the crystals. Further study is ongoing to understand the specific mechanisms involved in the ionic conductivity and damage in KTP grown by the flux and hydrothermal techniques.
Materials and Processing Requirements for Efficient Fiber Optic Nonlinear Devices
Authors: Stolen R. H.
Published: March 2011

Materials and structures for efficient nonlinear devices are discussed in terms of Raman amplification, nonlinear switching, and self-organized gratings.
Fluid Dynamic Instabilities in Drawn Fibers
Authors: Thompson Charles , Mulpur Arun
Published: March 2011

The nonlinear stability analysis of viscoelastic fibers is presented. The molten fiber is modeled as a Maxwellian viscoelastic fluid and the zeroth order equations governing its behavior given. Linear stability analysis is performed to determine the influence of winder speed and impedance as well as viscosity and elasticity. The results of numerical solution of the nonlinear equations are given.
Deposition of Hermetic Carbon Coatings on Silica Fibers
Authors: Huff R. G. , DiMarcello F. V. , Hart A. C. , Walker K. L.
Published: March 2011

Carbon coated optical fibers have recently been shown to have excellent resistance to both static fatigue and hydrogen induced losses. The deposition technique used to form the carbon coating strongly affects the coating's ability to resist these degradation mechanisms. The system developed by AT&T utilizes an atmospheric CVD chamber in which a hydrocarbon has is pyrolyzed on the fiber surface. The heat retained in the fiber from the fiber forming process is used to drive the reaction, and high draw speeds are typically used to attain the ˜900°C temperature required to deposit the hermetic form of the carbon coating. Deposition rates of ˜1μm/sec are required to produce the ˜500 Å coating.
Superconducting and Normal State Properties of Organic Metals β- (Bedt-Ttf)2X
Authors: Tokumoto M. , Kinoshita N. , Murata K. , Bando H. , Anzai H.
Published: March 2011

Recent progress on the superconducting and normal state properties characteristic to the organic metals β-(BEDT-TTF)2X are presented. Out of a systematic study on the β-(BEDT-TTF)2X salts, including β-(BEDT-TTF)2trihalide mixed crystals, with the superconducting transition temperature (Tc) varying from 8 K to below 1 K, empirical rules for various factors governing the Tc in this class of organic metals have been extracted. In addition to the low- and high-Tc states, with Tc=l K and 8 K, respectively, a new superconducting state with Tc=2 K was found in α-(BEDT-TTF)2I3. A particular attention is paid for the correlation between Tc and resistivity. In addition, a correlation between Tc and the anisotropy of coherence length is also considered.
Thin Film Formations of Charge Transfer Complexes with Metallic Properties by Vacuum Deposition Method
Authors: Yudasaka M. , Hironaga K. , Yamochi H. , Nakanishi K. , Saito G.
Published: March 2011

Thin films of a charge transfer complex, hepta-(tetrathiafulvalene) pentaiodide ( TTF7I5, TTF:I0-71 ), were prepared by double source evaporation of TTF and iodine. Crystalline films of TTF:I0-7i were obtained when substrate temperatures were kept between 0°C and 25°C. Orientation alignment of the crystalline films were affected by supply rate of iodine. By controlling the substrate temprature and the supply rate of iodine, highly oriented crystalline films were grown on mica substrates. It showed strong dichroism and anisotropic electrical propert ies.
Synthesis, Crystal Structure and Spectroscopic Studies of New Charge Transfer Compounds Obtained by Reaction of TTF and the Polyoxoanion [Mo6O19]2−
Authors: Bellitto C. , Attanasio D. , Bonamico M. , Fares V. , Imperatori P. , Patrizio S.
Published: March 2011

Two different tetrathiafulvalene radical cation salts of the [M06O19]2−polyoxoanion have been isolated and characterized. Compound 1 corresponds to the chemical formula (TTF)3[Mo6019]. The crystal structure shows a ID stack of the donor TTF molecule, and each stack fits into channels formed by the anions. Within the stack a chain of trimers is identified, the inter-trimeric distance being 3.51 Å. The I.R., electronic and XPS spectra suggest the compound to be a mixed-valence salt. The electrical conductivity at room temperature is σ = 10−4Ω−1cm−1Compound 2 corresponds to the chemical+formula (TTF)2[M06019] . The compound consists of isolated (TTF+•)2dimers, interspersed with the polyoxoanions. In agreement with this crystal structure the compound is a diamagnetic insulator.
Synthesis of Bulk High Spin Density Charge Transfer Complexes for Organic Magnets
Authors: Chiang Long Y. , Upasani Ravindra B. , Goshorn D. P. , Tindall P.
Published: March 2011

We describe a synthetic approach to the preparation of high spin density organic solid as a probe to organic ferromagnetism utilizing an external doping process to achieve a molecular sequence of alternate donors and acceptors in different spin states for, in principle, the ground state ferrimagnets. In contrast to the irreversibility of electron oxidations of many triaminobenzene derivatives, we found that, by substituting three hindered diisopropylamino groups on benzene, stable monocationic TDIAB radicals can be obtained. In the case of HDMAB its cationic radicals can be stabilized in a strong acid medium. The observed bulk spin densities of 0.18 — 0.23 spins 1/2 per donor molecule in TDIAB-PF6 and HDMAB-PF6 solids are significant comparing to the diamagnetic properties normally obtained in solids of simple cationic salts of planar organic donor molecules. The results imply that a small degree of molecular spin separation due to the steric effect can readily increase sharply the paramagnetic spin density of solids. We also found that the introduction of arsenic pentafluoride into molecular crystals disintegrates the long range order of crystal without rearranging the molecular stacking sequence in HMT complexes. Arsenic pentafluoride serves as not only the oxidant, but also the physical molecular separator. That results in a molecular spin separation of triplet dicationic HMT spins from each other at high doping level. This concept of molecular spin separation explains the observation of static magnetic data with an observed high spin density of many doped HMT charge transfer complexes. Without the molecular spin separation, the segregated-stack complexes, such as HMT-(AsF5.5)3.4 and HMT-DDQ-(AsF5.5)4.1, should instead give a low net bulk spin density with no triplet resonance after the intermolecular spin exchanges resemble to those observed in the case of HMT+2(CIO4)2 crystals.
Bridged Macrocyclic Transition Metal Complexes, a New Type of Semiconducting Materials
Authors: Hanack Michael , Hirsch A. , Lange A. , Rein M. , Renz G. , Vermehren P.
Published: March 2011

Bridged quasi onedimensional macrocyclic transition metal complexes [MacM(L)]nusing phthalocyanine (Pc), tetrabenzoporphyrine (TBP), 1,2 -and 2,3-naphthalocyanines (1,2-; 2,3-Nc) as macrocycles (Mac) with M = e.g. Fe, Ru, Co and L = e.g. pyrazine (pyz), 1,4-diisocyanobenzene (dib), tetrazine (tz) exhibit interesting electrical properties. Regardless of the size of the bridging ligand after either chemical or electrochemical doping stable semiconducting compounds [MacM(L)Xy]n(X = e.g. I, BF4-, CIO4-…) are formed. For the first time the complete characterization of a soluble oligomer [MacM(L)]n(Mac = R4PC, M = Ru, L = dib) by1H-NMR spectroscopy is reported. Some of these shish kebab complexes e.g. [PcM(tz)]n, (M = Fe, Ru) or [MacMCN]n; (Mac = Pc, TBP; M = Co, Fe) exhibit good semiconducting properties without additional external doping. Whether or not these compounds are intrinsic semiconductors will be discussed. The synthesis of oligomeric bridged mixed valence compounds [PcM3+LPсM2+L]n(M = e.g. Fe) is another target of our work. We report here about first attempts to synthesize these oligomers.
Angular Dependence of the Magnetoresistance in (TMTSF)2C1O4
Authors: Naughton M.J. , Chung O.H. , Chiang L.Y. , Hannahs S.T. , Brooks J.S.
Published: March 2011

We discuss recent low temperature results on the magnetoresistance of (TMTSF)2C104 in the low field metallic and the moderate field FISDW phases. From constant field rotations in a plane perpendicular to the highest conducting a-axis, we observe oscillatory resistance behavior along certain orientations at al. fields measured. While at odds with usual considerations of resistance anisotropy due to the crystal structure, this feature may be consistent with the recent predictions of Lebed and Bak[1,2], wherein the oscillatory electron trajectories along the b* and c* directions become commensurate near particular “magic” orientations in the magnetic field. We compare our preliminary data with the Lebed-Bak model, finding some qualitative agreement.
Charge Transfer Complex of Hexakis (Alkylthio) Benzene with Tetrafluorotetracyanoquinodimethane (tEDTB)2 TCNQF4
Authors: Chasseau D. , Alleaume M. , Bravic G. , Lapouyade R. , Morand J. P. , Amiell J. , Delhaes P.
Published: March 2011

In order to evaluate the potentiality of organic donor molecules for molecular organic ferromagnets, with in principle C3 molecular symmetry, as in the hexakis (alkylthio) benzene, we have prepared single crystals of the charge transfer complex of tris [ethylene dithio] benzene (tEDTB) with TCNQF4, which have been subsequently oxidized with bromine and arsenic pentafluoride gas. The stoichiometry of this complex is 2:1 and it crystallizes in the triclinic system, space group P1 with the following cell parameters: a=11.515, b=11.044, c=10.460 A, α=111.50°, β=122.50°, γ=93.82°. The crystal structure consists of columns of alternating donor dyads and acceptors monads (DDADDA). The degree of charge transfer is estimated to be 0.2-0.3 from the methods based on bond lengths. While (tEDTB)2- TCNQF4 does not give a significant ESR spectrum, after treatment with the bromine or AsF5 gas, a single intense line, centered around the free electron g value, appears without any evidence of either a ground or an excited triplet state.
The Polyanilines: a Novel Class of Conducting Polymers
Authors: Macdiarmid Alan G. , Epstein Arthur J.
Published: March 2011

The synthesis of polyaniline in its fully oxidized, fully reduced and selected average intermediate oxidation states is described together with the synthesis of a self-protonic acid doped polyaniline. The processing of polyaniline films and fibers by thermal stretching to give conductivities up to ∼100 S/cm is reported. Both doped and undoped polyaniline fibers have tensile strengths approaching those of commercial polymers.
The 0.9 eV Absorption Band of Polyaniline: A Morphologically Sensitive Electronic Absorption
Authors: Zhang D. , Hwang J.-H. , Yang S. C.
Published: March 2011

The optical absorption spectra of polyaniline in the visible and UV spectral regions have been characterized before. The electrically conductive form has a band gap absorption at 3.8 eV and polaron absorptions at 2.9 and 1.5 eV [1,2] . An additional electronic absorption band at 0.9 eV was found to be also related to the existence of polaron. The assignment of this transition has yet to be made. Epstein and co-workers [31 have found a photo-induced absorption band at 0.9 eV by photo-exciting emeraldine base (insulator) with 2.0 eV light. It is not known yet whether these two 0.9 eV transitions belong to the same set of electronic energy levels of polaron, or they belong to two different electronic systems but are coincidentally have the same transition energy.
Infrared Reflection-Absorption Study of the Aniline Electropolymerization on Stainless Steel
Authors: Gaillard F. , Bouyssoux G. , Kumar S.N.
Published: March 2011

Polyaniline (PANI) films were grown on 304 L steel and studied by FTIR spectrometry. The spectra of the films formed carry evidence for quinonic/aromatic alternating structure involving head-to-tail coupling. The coupling is quite independent of the thickness of the polymeric layer. The quinonic/aromatic ratio can be varied when the film is subjected to further dedoping treatments (electrochemical reduction or KOH immersion).
Generation of Stable Radical Cations (Polarons) and Dications (Bipolarons) on Model Thiophene Oligomers
Authors: Fichou Denis , Horowitz Gilles
Published: March 2011

Oxidative doping of individual thiophene oligomers nT (n = 3 to 6) with FeC13 in dilute CH2Cl2 solution generates the corresponding radical cations (polarons) nT+.. as evidenced by in-situ visible/near infrared absorption and electron spin resonance spectroscopies. The nT+. species in solution progressively precipitate as conducting (0′300K = 10−1−10−2 S/cm) and strongly paraaagnetic radical cation salts (g = 2.003, ΔHPP ∼ 4–8 G). The conductivity of the 6T+. salt is weakly temperature dependent, with an activation energy of 32 meV above 100 K and a tendency to level Dff at lower temperatures. In the case of the sexithienyl radical 6T+., further doping results in the quantitative conversion into the dication 6T++ (bipolaron).
Photoluminescence and Odmr Studies of Pristine and Photodegraded Poly (3-Hexylthiophene) Films and Solutions
Authors: Swanson L. S. , Shinar J. , Lichty L. R. , Yoshino K.
Published: March 2011

The photoluminescence (PL) and optically detected magnetic resonance (ODMR) spectra of poly(3-hexylthiophene) in solutions of CCl4, toluene, and CH2Cl2, and films cast from these solutions, are described and discussed. In solution, the PL yield is 7%, and increases with increasing temperature. In oxygen-free, protected films cast from these solutions, the room-temperature yield is ∼0.7%, the spectra is red shifted by ∼0.5eV, and strong peaks at 1.52, 1.69, and 1.86eV appear. In films and CH2Cl2 solutions, the ODMR is resolvable into narrow and broad components, and its intensity ΔL/L is ∼5 × l0−5 at room temperature. A strong photoinduced oxidation process quenches the PL upon exposure to O2 but not water, at a rate possibly limited by O2 diffusion.
Determination of Correlation Parameters in π-Conjugated Polymers
Authors: Gammel J. Tinka , Campbell D.K. , Loh E.Y. , Mazumdar S. , Dixit S.N.
Published: March 2011

Using exact finite-size diagonalizations of extended Peierls-Hubbard Hamiltonians for systems of up to 15 sites, we study the excited state spectra of models for the finite oligomer analogs of trans– and cis– polyacetylene. We use a novel “phase randomization” technique and a variety of other methods to extract maximal information from these small systems. For several electron-phonon couplings in the expected range, we discuss the extent to which we are able to find consistent values of the Hubbard on-site (U) and nearest-neighbor (V) correlation parameters such that the band gap, the 2 1Ag state, optical phonon frequency, and the optical absorptions for charged and neutral solitons and dimers occur in the experimentally expected ranges. Our results suggest that these correlation parameters are in the intermediate coupling regime (U ⋍ 2.5t0), beyond the range of perturbation theory.
Reversible Photoproduction of Stable Charged Defects in Trans-Polyacetylene
Authors: Hoener Carolyn
Published: March 2011

Photoproduction and photodepletion of stable charged defects in trans-polyacetylene were observed, at low temperatures, by monitoring the IR signature of these defects: absorptions at 1368, 1289, 640 cm−1 (1053, 600 cm−1 for (CD)x). These absorptions could be observed at long times (two to several hundred minutes) after photolysis, only when the sample was protected from photolysis by the probe beam, by blocking v > 2,300 cm−1.

The location of these absorptions and the temperature dependence of their intensities were similar to those of previously observed photoinduced defects reported to have much shorter lifetimes (τ - ms). The stable defects reported here can be produced at much lower photolysis energies (v > 5,000 cm−1) than transient-photoinduced defects (v > 9,000 cm−1). A mechanism for the photoproduction of stable defects, involving a two-photon process catalyzed by existing neutral defects, is proposed to explain this low onset.

The slow decay of these defects observed when the sample is kept in the dark is attributed to photoinduced depletion by blackbody irradiation. This process was slow enough to allow the wavelength dependence of photodepletion (observed at 2,800 < v < 8,000 cm−1) to be studied. The photodepletion was fastest near 4,500 cm−1, suggesting that the defects possess an electronic absorption (with a peak near 4,500 cm−1) similar to that observed directly for the transient-photoinduced defects.
Band-To-Band Transitions in Poly (Phenyl Methyl Silane)
Authors: Kepler R. G. , Zeigler J.M.
Published: March 2011

We have measured the quantum efficiency for carrier generation as a function of photon energy and the electroabsorption spectrum in poly (phenyl methyl silane). The experimental data are consistent with a band gap of about 4.6 eV. A strong absorption peak which is observed at 3.7 eV is shown to be an exciton band.
Nonlinear Optical Polymers: Challenges and Opportunities in Photonics
Authors: Garito A. F. , Wu J. W. , Lipscomb G. F. , Lytel R.
Published: March 2011

In polymer structures, highly correlated virtual excitations of the π-electrons are responsible for the exceptionally large nonresonant nonlinear optical responses observed. Extremely large resonant nonlinear optical responses are also achievable in certain π-electron systems, which can be treated as optical Bloch systems. In addition to their obvious scientific importance, these large optical nonlinearities potentially make possible the implementation of powerful, new nonlinear optical devices and systems. After a description of nonlinear optical processes in polymers, two examples are presented. First, saturable absorption and optical bistability in ultrathin organic polymer films are described, illustrative of resonant third order processes. Saturable absorption studies of glassy polymer films consisting of quasi two-dimensional conjugated disc-like structures of silicon naphthalocyanine demonstrate that on-resonance the system behaves as an optical Bloch system with a linear absorptivity coefficient α0 of 1 × 105 cm−1 and an intensity dependent refractive index n2 of 1 × 104 cm2/kW in the wavelength range of standard laser diodes. A resonant nonlinear optical response of π-electron excitations provides the nonlinear interaction essential to the onset of bistability. Electronic absorptive optical bistability is observed on a nanosecond time scale in a nonlinear Fabry-Perot interferometer employing the saturably absorbing naphthalocyanine film as the nonlinear optical medium. As a second example, the nonresonant second order process of linear electrooptic effects in poled polymer films, is discussed. For such a second order nonlinear optical process, the broken global centrosymmetry is achieved by electric field poling of a thin polymer film. With high electrooptic coefficients of 10–50 pm/V and low dielectric constants of 3–4, poled polymers have potentially great advantages over inorganic crystals as electrooptic materials. As one device illustration, the application of poled polymers in electrooptic waveguide operations is presented.
Quadratic Nonlinear Optical Properties of Diva Crystal
Authors: Wada T. , Grossman C. H. , Yamada S. , Yamada A. , Garito A. F. , Sasabe H.
Published: March 2011

New organic nonlinear optical crystal : dicyanovinyl anisole (DIVA) has been grown from vapor by low pressure sublimation and from saturated solution by solvent evaporation. Crystallographic structure and quadratic nonlinear optical properties were investigated. Molecular orientation in DIVA crystal with space group P21, is favorable for the highest possible value of bulk phase-matchable coefficient. Both type I and type II phase matched second harmonic generation (PMSHG) were observed from naturally grown faces of single crystals. Efficient PMSHG was achieved at a fundamental wavelength of 812 and 1064 nm. The efficient type I PMSHG coefficient was determined as deff = 4.9 × 10−8 esu = 40 × (d11 of α-quartz) at a wave.LH length of 1064 nm. Blue light generation was demonstrated by both PMSHG and sum-frequency mixing of the 812 nm laser with 1064 nm.
Organic Polymer Semiconductor Superlattices
Authors: Jenekhe Samson A. , Chen Wen-Chang
Published: March 2011

We describe the synthesis and study of the first organic polymer semiconductor superlattices designed as periodic block conjugated copolymers, (−AxBy−)m. The observed variation of electronic spectra and wavelength of the lowest energy absorption maxima with block length y are interpreted in terms of quantum confinement size effects predicted for semiconductor superlattices. The periodic block conjugated copolymers were synthesized by a two-step strategy that ensure strict control of sequence, block length and periodicity. It is suggested that organic semiconductor superlattices provide a rational and systematic approach to the molecular engineering of electronic, optical, nonlinear optical, and electro–optical properties in polymeric materials and hold promise for molecular electronics and molecular photonics.
Synthesis and Characterization of Third Order Nonlinear Optical Materials
Authors: Yu L. P. , Chen M. , Dalton L. R. , Cao X. F. , Jiang J. P. , Hellwarth R. W.
Published: March 2011

New polymers incorporating a variety of electroactive moeities with defined π-electron conjugation lengths have been synthesized and characterized by degenerate four wave mixing (DFWM) techniques. The χ(3)/α values for these materials varied from 10−12 to 10−13 esu cm. This work has identified several promising structures with nonlinear optical activity including organometallic and purely organic materials. The preparation of composite materials has also permitted the measurement of χ(3)/α as a function of the electroactive unit concentration.
Enhanced Third Order Optical Nonlinear Response in Polythiophene Films—Polaron Contributions
Authors: Yang Lina , Dorsinville R. , Zamboni R. , Taliani C. , Tubino R. , Alfano R. R.
Published: March 2011

The enhancement of the third order nonlinear susceptibility χ(3)) of an homologous series of polycondensed thiophene based polymers was observed about photoinduced polaronic bands by a novel “pump-probe” degenerate four wave mixing echnique. Enhancement of the degenerate four wave mixing signal for more than an order of magnitude was achieved with response time of less than 25 ps. The intrachain polarons contribution is proposed as the possible mechanism responsible for the observed enhancement.
Nonlinear Optical Studies of Mixed π-Conjugated Polymer Multilayers by Second Harmonic Generation
Authors: Koezuka H. , Kurata T. , Tsumura A. , Fuchigami H.
Published: March 2011

The structures of the mixed LB monolayers, composed of two different kinds of π-conjugated system, poly(3-hexylthiophene) (PHT) and pentacosa-10, 12-diynoic acid (DA), have been investigated mainly by a second harmonic generation (SHG) Maker fringe method. The mixed LB films partly contain a double-layered structure consisting of PHT and DA. The second harmonic radiation has been produced from slightly twisted PHT in the double layer. Both UV-polymerization of DA and successive heat-treatments enhanced the SHG intensities. The enhancement of the SHG intensities has been elucidated by the enlargement of the PHT twisting and the interaction between PHT and a newly formed π-conjugated system.
Preparation and Properties of Organic Superconductor κ-(Bedt-TTF)2 [Cu(NCS)2] and Its Related Materials
Authors: Saito Gunzi
Published: March 2011

κ-(BEDT-TTF)2 [Cu(NCS)2] has a two-dimensional (2D) layered structure. The compound is metallic with the room temperature conductivity of 10–40 S/cm within the 2D plane but showed a semiconductive-like anomaly between 270 and 90K. The superconducting transition was observed at Tc=10.4K and Tc increased by 10% on the sample of deuterated BEDT-TTF (Tc=11.4K). The upper critical field, Hc2, was more than 20 Tesla below 2K within the 2D plane which is more than the expected value from the simple BCS theory. The transport critical current density was estimated as 100 A/cm2 (5.1K, 0 Tesla, l//b, H//c) which is an order of magnitude smaller than that obtained from the magnetization curve hysteresis. 1H-NMR showed a big enhancement of the relaxation rate well below Tc. The tunneling spectra showed anisotropic gap and the magnetic field penetration depth measurements strongly suggest that this system is a gapless superconductor. (BEDT-TTF)2[KHg(SCN)4] is an organic metal and showed both Shubnikov-de Haas effect and angle-dependent quantum oscillation indicating that this system has a warped 2D Fermi surface.
The Microstructures of the Biomineralized Bivalvia Shells
Authors: Huang L.J. , Li H.D.
Published: March 2011

The paper presents the detailed study of the structural features of the biomineralized bivalvia shells. The Cristaria plicata(Leach), Anodonta woodianal(Lea) and Lamprotula Leai(Gray) are selected as the prototype in the present study. Scanning electron microscope (SEM), X-ray diffraction, laser Raman spectroscope and electron spectroscopy for chemical analysis (ESCA) are employed to study the structures of the shells. It is found that three different layers of the shells possess distinct morphologies and structures with a clear boundary between every two layers. The prismatic layer can be further divided into two sub–layers. The preferential growth orientation of the biominerahzed phases were different from the natural ones. The Raman spectra present the detailed vibrational states of these biomineralized phases, while ESCA reveals that the chemical environments of the atoms in pearl layer are less varied than those in the other two layers.
Hierarchical Structure of the Intervertebral Disc
Authors: Cassidy J. J. , Hiltner A. , Baer E.
Published: March 2011

The intervertebral disc is a complex hierarchical structure composed of the annulus fibrosus and nucleus pulposus which are anchored to the vertebral bodies by cartilaginous endplates. The hierarchical structure of the collagenous components of the intervertebral disc is characterized using optical microscope techniques. In the lamellae of the annulus, collagen fibers exhibit a planar crimped morphology similar to that seen in other collagenous tissues. A model of the intervertebral disc has been developed that incorporates the structure of the collagen fibers on the macro- and microscopic scales.

Mechanical testing in load-deflection, stress relaxation, and creep modes reveals the response at each level of organization to compression. These mechanical data are analyzed with models that reflect the hierarchical composite structure.
Mechanical Properties of Bacterial Fibres
Authors: Thwaites John J , Mendelson Neil H.
Published: March 2011

Bacterial thread is the name given to a fibrillar fiber produced from cell-separation-suppressed mutants of Bacillus subtilis. which grow in long cellular filaments and produce in cultures aggregates that resemble randomly-laid textile webs. Threads are produced by steady withdrawal at the end of a sterile toothpick - for all the world like Carothers, 50 years ago! Individual filaments are drawn radially into the forming thread and adhere strongly to each other with axial alignment. Uniform threads up to 1 meter in length and 180 μm in diameter can be produced. Such threads contain about 50,000 filaments and upwards of 1010cells Tests on thread show that peptidoglycan, which is the load-bearing polymer of the bacterial cell wall, behaves mechanically like other visco-elastic polymers. When dry its behavior is glassy, with high modulus; when wet, it is relatively weak and of low initital modulus. Relaxation data indicate a very wide spectrum of relaxation times. All the mechanical properties depend strongly on the RH of the test environment; they are also influenced by the ionic environment at the time threads are drawn. Available evidence indicates that peptidoglycan is not crystaline. Nonetheless there is some degree of orientation in the bacterial cell wall. This is shown by the effect of enzyme attack on mechanical properties and by the twisted growth pattern of bacteria.
Enzymatic Synthesis of Chiral Lactones and Polyesters
Authors: Gutman Arie L.
Published: March 2011

Lipases in organic solvents catalyse lactonisation or polymerisation of ω-hydroxyesters. Under these conditions the enzymes exhibit both enantioselectivity and prochiral selectivity. This approach was used to develop the synthesis of chiral γ-lactones and polyesters.
Biological Production of Uniform Polypeptides for Optical Applications
Authors: Lawton Carl W. , Klei Herbert E. , Strausbaugh Linda D. , Crane Robert
Published: March 2011

Recent advances in recombinant DNA technology have created the potential for engineering of protein molecules to specific uses beyond those normally considered for biomaterials. This research project has demonstrated the feasibility of producing polypeptides useful for narrow band filters and nonlinear optical applications.

Synthetic genes, ranging in size from 36 to 576 base pairs, have been constructed from oligonucleotides using a restriction doubling technique. The synthetic genes have been inserted into a Protein A fusion expression system. Fused polypeptides from induced cells have been purified by affinity chromatography (IGG), and analyzed by polyacrylamide gel electrophoresis.