bluuebunny/crossref_metadata_2025 huggingface dataset:
Laser-Induced Fluorescence Diagnostics of CF4/O2/H2 Plasma Etching
Authors: Pang S. , Brueck S. R. J.
Published: March 2011

Laser-induced fluorescence experiments have been carried out during CF4/O2/H2 plasma etching of Si and SiO2. Measurements of relative CF2 radical concentrations as a function of rf power, frequency, pressure, and gas composition are reported. The results are correlated with etch rates of Si and SiO2. The balance between CF2 and F concentrations is shown to influence the etching process strongly.
Semiconductor Thin Films Grown by Laser Photolysis
Authors: Eden J.G. , Greene J.E. , Osmundsen J.F. , Lubben D. , Abele C.C. , Gorbatkin S. , Desai H.D.
Published: March 2011

Thin (< 1.2 μpm) Ge and Si films have been grown with rates up to 3.6 μm/hr by laser-induced chemical vapor deposition (LCVD) on a variety of substrates. Germanium films grown on amorphous SiO2 (quartz) by photodissociating GeH4 in He at 248 nm (KrF laser) exhibit grain sizes of 0.3 – 0.5 μm that increase only slightly up to the pryolytic threshold for GeH4 (280°C). On (100) NaCl, however, Ge films grown at a substrate temperature of 120°C are expitaxial. The activation energy for the LCVD growth of Ge films (from GeH4) on SiO2 is measured to be 85 ± 20 meV which suggests that germanium is arriving at the substrate in atomic form. The wavelength and intensity dependence of the initial film growth rate supports the conclusion that this process is photolytic and is initiated by the absorption of a single photon.
Pulsed UV Excimer Laser Doping of Semiconductors
Authors: Deutsch T. F.
Published: March 2011

UV excimer lasers have been used to dope semiconductors by a one–step process in which the laser serves both to release dopant atoms from a parent molecule and to melt the surface, allowing incorporation of dopant atoms by liquid state diffusion. The technique has been used to dope Si, GaAs, and InP. Shallow junctions formed by the technique have been fabricated into efficient Si and GaAs solar cells.
Formation of CdO and Cu2O Films by Laser Irradiation of the Corresponding Metallic Films in Air
Authors: Andrew Rod , Baufay Luc , Pigeolet Andre , Wautelet Michel
Published: March 2011

We describe the oxidation of 1000 Å thick metal films on glass substrates when exposed to a scanning laser beam. For Cd and Cu films optical spectroscopy shows an energy gap of 2.45 eV and 2 eV respectively, in agreement with published data for CdO and Cu2O. We measure the power threshold for complete oxidation in a single scan and deduce the maximum temperature, which is inconsistent with thermal oxidation data but corresponds to the m.p. of the metals. We point out the important contribution of the heat of formation to the temperature balance and demonstrate that in the case of Al this effect is sufficient to destroy any oxide formed.
Laser Fabrication of Microstructures: Effect of Geometrical Scaling on Chemical Reaction Rates
Authors: Ehrlich D. J. , Tsao J. Y.
Published: March 2011

Laser chemical processing for microfabrication makes use of chemical reactions and phase changes confined to micrometer-scale dimensions at vapor/solid and liquid/solid interfaces. When conditions are established for rapid interfacial reactions, processing speeds can become limited by diffusive transport. These diffusion-limited rates, however, increase by many orders of magnitude as the microreaction geometry is reduced to micrometer lengths using well-focused visible and UV beams. A calculation of the geometric scaling of such rates is summarized here. For realistic conditions, rate increases of up to four decades are predicted relative to corresponding reactions on semi-infinite plane surfaces.
UV Photodecomposition for Metal Deposition: Gas Vs. Surface Phase Processes
Authors: Wood Thomas H. , White J. C. , Thacker B. A.
Published: March 2011

Photodecomposition of organometallic gases has been shown to be potentially useful for high resolution direct metal deposition. However, a number of problems, particularly the low writing rates, must first be solved. An understanding of the deposition mechanism is essential to this task. In particular, the decomposition must be shown to occur either in the gas phase or in the adsorbed layer. This question can be resolved by the dependence of the writing rate on spot size. Measurements of the process show that once the deposition begins the bulk of the deposit occurs from decomposition in the gas phase.
Optical Microanalysis of Small Semiconductor Structures
Authors: Murphy D. V. , Brueck S. R. J.
Published: March 2011

Raman spectroscopy is a powerful tool for evaluating semiconductor crystal characteristics with a diffraction–limited spatial resolution of approximately 0.5 μm, comparable to device structure dimensions. Examples are presented of the use of Raman scattering to measure stress variations across Sion-insulator and Si-on-sapphire stripes with dimensions down to 2 μm and, to probe the spatial variation in the effectiveness of annealing of a Si layer deposited over metal device structures. Detailed measurements of the variation in the Raman spectra of thin crystalline Si films, with thicknesses down to 3.0 nm, are discussed. Measurements made on roughened Si surfaces are presented which show that surface morphology on a submicron spatial scale results in enhanced Raman intensities.
Light Scattering Studies of the State of Dispersion in Molecular Composites
Authors: Hsiao Benjamin S. , Stein Richard S. , Addad Silvie Cohen
Published: March 2011

Polymer solutions comprising stiff-chain polyester and flexible polysulfone were examined via light scattering techniques. Results were analyzed using the Stein-Wilson extension of the Debye-Bueche theory, in which the correlation lengths due to orientation fluctuations and mean-squared fluctuations of the molecular anisotropy were obtained. For a molecular dispersion, the correlation length is small and a function of concentration; as the anisotropy is attributed to the rod molecules. Aggregation of rods is associated with an increase in the magnitude and size of the density fluctuations, and a change in anisotropy fluctuations is dependent on the degree of orientation correlation of the rods in the aggregate. Blends prepared by solution casting were studied by a small-angle light scattering method. Results thus far demonstrate that aggregates are present in most of the rod/coil composites prepared.
The Synthesis, Structure and Property Behavior of Inorganic-Organic Hybrid Network Materials Prepared by The Sol Gel Process
Authors: Wilkes G.L. , Brennan A.B. , Huang Hao-Hsin , Rodrigues David , Wang Bing
Published: March 2011

The synthesis, structure/property behavior of inorganic-organic hybrid network materials prepared by the sol gel process have been chronologically reviewed with emphasis on those systems prepared in the authors laboratory. Specific features of reactions as well as the nature of reactants are included. The morphological features of these “ceramer” systems formed have many features in common even though the reactants may be quite different. The mechanical properties of the final materials in conjunction with SAXS have proven beneficial in establishing the basics of their morphological texture. Finally, it is demonstrated how microwave radiation in some cases, can serve as an efficient way in processing the ceramer systems.
Pbzt Microcomposites with Advanced Thermoplastic Matrices
Authors: Sanford W. Michael , Prilutski Gerard M.
Published: March 2011

Thermoplastic microcomposites offer the potential for better economics and improvements in composite processing, and possibly performance, over conventional ‘string-and-glue’ composites. The early development of molecular composite technology focused on polyamide matrix polymers; however, for many aerospace applications higher use temperatures and greater solvent resistance than that of conventional polyamide matrices will be required. This paper describes work performed under contract to the U.S. Air Force to develop PBZT (poly p-phenylene benzobisthiazole)/thermoplastic molecular composites with high performance matrix resins into a viable technology.

A scaleable process has been defined based on a novel technology developed by Du Pont. Advantages of this process include better economics, superior processing performance, and improved MC fiber tensile properties versus prior art. Using this process we have obtained rule-of-mixtures properties in our microcomposite fibers with matrix polymers offering use temperatures from 330 to 600°F. Consolidation of PBZT/PEKK fibrous preforms into uniaxial panels up to 1011 × 1511 has been demonstrated and material propperty evaluation and data base development are in progress. Uniaxial property levels achieved to date for all systems compare favorably with conventional ‘string-and-glue’ PBZT/epoxy composites although as with other organic fiber reinforcements, compressive and shear performance may be limiting factors in MC applications.
Small Angle Neutron Scattering Studies of Blends of Protonated Linear Polystyrene with Crosslinked Deuterated Polystyrene
Authors: Briber Robert M. , Bauer Barry J.
Published: March 2011

Small angle neutron scattering (SANS) has been used to study the scattering function and thermodynamics of blends of linear protonated polystyrene (PSH) and crosslinked deuterated polystyrene (PSD). Two series of samples were synthesized. In both cases the samples were made by dissolving the linear PSH in deuterated (d8) styrene monomer containing a small amount of divinyl benzene as a crosslinker which was then polymerized to form the PSD network around the linear PSH chains. The samples were all made at a concentration of 50/50 by weight PSD/PSH. A special effort was made to keep the samples single phase so that SANS could be used to study the thermodynamics of the system and compare with theory. This entailed working at relatively low crosslink densities (<1 mole % crosslink units). Series 1 is a set of samples with the same crosslink density varying the length of the linear chain. Series 2 is a set of samples containing the same length linear chain varying the crosslink density systematically. By extrapolating S(q) obtained from SANS to q=O the zero angle scattering, S(O), was obtained. S(O) is inversely proportional to the second derivative of the free energy with respect to composition, ∂2 (Δf/kT)/∂ø2. Assuming additivity of the free energies of mixing and elasticity, the portion of the zero angle scattering due to elasticity is calculated.
Interpenetrating Polymer Networks and Related Topological Isomers
Authors: Frisch Harry L.
Published: March 2011

We have studied the phase compatibility of simultaneous interpenetrating polymer networks poly (2,6–dimethyl–l,4–phenylene oxide) with a number of other polymer networks as a function of their solubility parameters. Even when the blends of the corresponding linear chain polymers are immiscible their interpenetrating polymer networks can be miscible in all proportions. We have also prepared the corresponding pseudo (or semi) interpenetrating polymer networks where one component is linear and in one system the polymeric catenanes. All these systems generally show microphase separation.
Mechanical Properties and Structure of Melamine Formaldehyde/Poly(Vinyl Alcohol) Molecular Composites
Authors: Gong Kecheng , Zhang Xinghua
Published: March 2011

The mechanical properties and structure of melamine formaldehyde (MF)/poly(vinyl alcohol) (PVA) composites were studied in this paper. When PVA content was less than a certain value(about 20 weight %), both flexible strength and impact resistance were improved obviously. While the impact resistance improvement remained the previous trend the flexible strength didn't increase so rapidly as before when the PVA content was more than 20%. The morphology and reactivity of the prepolymer powder and the morphology of the finished specimens were investigated by means of microscope, infrared spectrum and transmission electron microscope(TEM). The results indicated that molecular composite structure was formed in this two-component system. The well-distributed PVA in this system was beneficial to the formation of the molecular composite structure. That could explain the effects of PVA on the mechanical properties and showed that the molecular composite structure are favourable for making full use of the macromolecular potentiality.
Inorganic-Organic Composites by Sol-Gel Techniques
Authors: Schmidt Helmut
Published: March 2011

The sol-gel process opens the possibility of combining inorganic and organic units to new hybrid polymers. Organic units can be used for structural modification of the inorganic backbone, for creating new functions within an inorganic network and for building up organic polymeric chains. The materials show interesting perspectives with respect to structural (surface hardness, strength) and functional properties (e. g. diffusion, photocuring, incorporation of dyes, optical properties). A review over structural and functional properties of sol-gel derived inorganic-organic polymers (ORMOCERs = organically modified ceramics) is given.
On the Scale of Diffusion Lengths Observable by Neutron Reflection: Application to Polymers.
Authors: Karim A. , Mansour A. , Felcher G.P.
Published: March 2011

A systematic approach has been applied to neutron reflectivity data to study interdiffusion across an interface. It is shown that with this technique it is possible to probe interface broadening from ∼10Å to upward of 200 Å, the upper limit being already within the range of observation of other techniques such as Rutherford backscattering spectrometry (RBS), forward recoil spectrometry (FRES) and secondary ions massspectroscopy (SIMS). As example is analyzed the interdiffusion of a bilayered polymer system: a deuterated polystyrene (d-PS) layer on protonated polystyrene (h-PS).
Neutron Reflection Study of Surface Enrichment in an Isotopic Polymer Blend
Authors: Jones R.A.L. , Norton L.J. , Kramer E.J. , Composto R.J. , Steint R.S. , Russell T.P. , Felcher G.P. , Mansour A. , Karim A.
Published: March 2011

We have measured neutron reflectivities from the surface of films of deuterated polystyrene (d-PS) and protonated polystyrene (PS) blends before and after annealing, and used the results to determine the concentration versus depth profile of the films. After annealing, the surface is enriched in d-PS, with a surface excess proportional to the bulk concentration of d-PS, in agreement with previous measurements using forward recoil spectrometry[l]. The decay of the enhanced concentration into the bulk occurs over a length approximately equal to the bulk correlation length (∼200 A), in closeagreement with that predicted by current mean-field theoryometry[2]. However, the agreement between the experimental reflectivity curves and the fitted curves is not completely adequate. Figure 1, a plot of k4R against k, demonstrates thi point for a 15% d-PS sample. The dashed line is the best fit assuming the mean field profile. The inset shows the corresponding concentration profile and a trial profile, solidline, which fits the data much better. The small deviation between the theoretical and trial profiles may be due to the assumption of the theory that surface interactions leading to enrichment is short ranged.
Biaxial Extrusion of Polyimide Larc—tpi and Larc—tpi Blends
Authors: Haghighat R. Ross , Elandjian Lucy , Lusignea Richard H.
Published: March 2011

Biaxial films of polyimide LARC—TPI and LARC—TPI/liquid crystal polymer Xydar®were extruded directly from the melt for the first time via an innovative new extrusion technique. Three types of films, neat LARC—TPI, LARC—TPI/lO wt percent and 30 wt percent blends were processed as a part of this NASA funded program. This new process offers an alternative technique to costly post—processing stretching of both solution cast and sheet extruded films. The post—processing step is often required to enhance certain properties. Processability was greatly enhanced by incorporating Xydar. The coefficient of thermal expansion was reduced from 34 ppm/ºC for the neat LARC—TPI to 15 ppm/º C for the 10 wt percent Xydar blend and ultimately down to I to 3 ppm/º C for the 30 wt percent blend films in the direction of extrusion. The maximum improvementin stiffness was realized by incorporating 10 wt percent Xydar (2.8 GPa up to 4.9 GPa). Tensile strength, however, experienced a drop as a result of Xydar addition, probably caused by inefficient mixing of the two phases.
Polymer-Derived Si3N4/BN Composites
Authors: Schmidt Wayde R. , Hurley William J. , Sukumar Vijay , Doremus Robert H. , Interrante Leonard V.
Published: March 2011

Partially crystalline silicon nitride, with a specific surface area greater than 200 m2/g, is obtained by the pyrolysis of an organometallic, polymeric precursor under NH3 to 1000 °C. Additional heating to 1400 °C under N2 produces alpha-Si3N4. The addition of up to 15% h-BN was found to affect the coarsening characteristics of amorphous silicon nitride by promoting surface area reduction and suppressing crystallinity. By combining Si3N4 and BN molecular and polymeric precursors prior to ceramic conversion, or incorporating Si, N, and B into a single preceramic polymer, the relative proportion and crystallinity of the ceramic phases can be controlled in the resulting Si3N4/BN composites.
The Physical Properties of Microcellular Composite Foams
Authors: Nyitray Alice M. , Williams Joel M. , Onn David , Witek Adam
Published: March 2011

Recently we reported on a method of preparing microcellular composite foams. In this procedure an open-celled polystyrene foam is prepared by the polymerization of a high-internal-phase water-in-oil emulsion containing styrene, divinylbenzene, surfactant, free-radical initiator and water. After drying, the cells of the polystyrene foam are then filled with other materials such as aerogel or resoles. The physical properties of these materials e.g., surface area, density, thermal conductivity, and compressive strength will be presented.
Investigation of Differential Induced Attenuation of Orthogonal Axes in Polarization Maintaining Fibers
Authors: Gingerich M. E. , Hickey S. J. , Harrington C. C. , Marrone M. J. , Friebele E. J. , Looney L. D. , Onstott J. R.
Published: March 2011

Recent studies have indicated that the birefringent-inducing stress of polarization-maintaining (PM) fibers decreases the long term, permanent loss induced by ionizing radiation and that light polarized along the two orthogonal axes of PM fibers may be attenuated differently by exposure to irradiation sources. This paper reports the results of specific studies of this differential attenuation induced in a series of PM fibers by both steady state and transient irradiations. It has been found that the response to ionizing radiation depends on the materials properties of the fiber, i.e. the core and clad dopants and/or degree of stress, and that the magnitude of the differential attenuation is small relative to the total or one-axis incremental loss.
Photoluminescence Induced by 6.4 eV Photons in High Purity Silica
Authors: Tsai T. E. , Lin H. B.
Published: March 2011

photoluminescence in the visible range in high purity silica rods at room temperature was studied using 6.4 eV photons as the excitation source. Electron spin resonance (ESR) was used to monitor the induced paramagnetic centers. Broad luminescence bands at 2.7 eV, 2.2 eV and 1.9 eV were observed. The relative intensities of these bands were found to be intensity dependent. The fluence dependence of these bands were also studied. The results are discussed in relationship to the excitonic mechanism for defect generation in silica.
Effect of Compositional Variations and Processing on the Optical Scattering of Zblan Glass
Authors: Neeves A. E. , Reed W. A. , Chui-Sabourin M. , Bruce A. J.
Published: March 2011

The effects of compositional modifications, specifically oxide and p-block fluoride additions, and melt processing, via “on-situ oxidation”, have been investigated on bulk samples of ZBLAN glasses. Molecular light scattering in the Mie and Rayleigh regime has been measured as a function of scattering angle at wavelengths between 0.6 and 2.6 μm. From an analysis of the angular scattering of both vertically and horizontally polarized beams the Rayleigh ratios and dissymmetry factors are determined as a function of wavelength. The average size of the scattering sites can be estimated in the range of 0.02 and 2.0 μm. Relatively high oxide substituted ZBLAN glasses exhibit light scattering losses only moderately higher than the ZBLAN base glass, and do not show any evidence of gross phase separation or precipitation. InF3 containing samples also exhibit scattering comparable to the ZBLAN base glass. The scattering of ZBLAN at 2.6 μm is larger than the scattering predicted by extrapolating data taken at 0.647 μm using a λ−4 dependence. This added scattering may interpreted as due to either a wavelength independent contribution or a result of a difference in the wavelength dependence of the dispersion between the host and the scattering center.
Thermochemistry of the Amorphous System SiO2-GeO2: Comparision of Flame Hydrolysis Materials to High Temperature Fused Glasses
Authors: Maniar P. D. , Navrotsky A. , Draper C. W.
Published: March 2011

Energetics and structure of germania doped silica prepared from high temperature melts and by flame hydrolysis were investigated using transposed temperature drop and solution calorimetry. Heat contents (H973-H298) are similar for first and second drops for the flame hydrolysis preforms reflecting the effect of temperature of deposition (1073 K) in creating a relaxed structure which is not easily rearranged. Heats of solution, at 973 K in molten lead borate, of fused glasses along the SiO2-GeO2 binary show ideal heats of mixing between the endmembers. This'indicates that fused glasses behave in a simple manner, with ideal substitution of Ge for Si in the tetrahedral framework. Flame hydrolysis samples (preform and annealed glasses) also show ideal heats of mixing. This suggests that the flame hydrolysis materials are energetically very similar to their bulk-melted counterparts. This insensitivity of energetics to preparation conditions is consistent with our previous studies on silica prepared at various temperatures [1].
Design Parameters for Multimode Fluoride Fibers: Effects of Coating and Bending on Loss
Authors: Busse L. E. , Aggarwal I. D.
Published: March 2011

Numerical calculations of losses due to polymer coatings and macrobending have been made for step index multimode fluoride fibers. To avoid such losses, fiber core and cladding diameters and numerical aperture must be chosen carefully.
New Stable Iodide Glasses in the Cd-As-I and Cd-As-Ge-I Systems
Authors: Heo Jong , Sigel George H.
Published: March 2011

Iodide glasses presently being investigated suffer from their poor glass forming abilities, thermal instabilities and general lack of chemical durability. Glasses in the Cd-As-I and Cd-As-Ge-I systems are investigated in this study for the purpose of developing water-resistant, thermally stable iodide glasses and optical fibers. Differential scanning calorimetry(DSC) showed that glasses in these systems have glass transition temperature(Tg) values above 300°C. Devitrification of glasses during cooling and reheating can be suppressed by incorporating small amount of Ge atoms into ternary Cd-As-I glasses. They are transparent up to 14μm in the infrared region with excellent durability against liquid water at 90°C.
Crystallization Studies of Glassy Te-Se-Br Thin Films
Authors: Adam J. L. , Ortiz C. , Salem J. R. , Zhang X. H.
Published: March 2011

We have studied the effect of laser irradiation on Te-Se-Br thin films. The major effects were found to be dominated by changes in composition because of the complete loss of Br and variable loss of Se. These losses are measured by EIDS and are reasonable in view of the temperatures obtained from a heat flow calculation. The remaining Te-Se material can be made crystalline under specific conditions of laser pulse length and laser power (which determine the cooling rate). We have been able to establish that the crystallization starts with surface filamentary growth exhibiting fractal network formation. With higher laser energy it tends to coalesce to form three dimensional crystals.
Low-Loss GI Plastic Optical Fiber and Novel Optical Polymers
Authors: Koike Yasuhiro , Ohtsuka Yasuji
Published: March 2011

A low-loss GI plastic optical fiber in which the attenuation of transmission was about 130 dB/km at 650 nm wavelength was successfully obtained by a new interfacial-gel copolymerization technique. Novel optical functional polymer glasses, such as birefringence-free copolymers for any degree of orientation and optically active amorphous polymers which act as polarization modulators, were synthesized and characterized.
Silica-Based Single-Mode Waveguides and Their Applications to Integrated-Optic Devices
Authors: Takato Norio , Sugita Akio
Published: March 2011

Low-loss silica-based single-mode waveguides are fabricated on Si substrates by flame hydrolysis deposition and reactive ion etching. The waveguide loaded with a thin film heater operates as a phase shifter due to the refractive index dependence on temperature. The phase shifter can afford optical switching and/or tuning functions for silica-based integrated-optic devices. The waveguides have large stress-induced birefringence due to the difference in thermal expansion coefficients between SiO2 and Si. Waveguide birefringence control techniques are proposed for constructing various polarization insensitive and sensitive devices.
Continuous Casting of Particulate Silica Gels
Authors: Rabinovich E. M. , Jackson K. A. , Kopylov Nonna A.
Published: March 2011

A feasibility study of continuous casting of particulate silica sols has been conducted. The process consists in measured pumping of the sol and a gelling agent into a heated mold where the sol gels. The gel is continuously pushed out of the cylindrical mold by the pressure of the pumped sol. Gel rods of 2.5 cm diameter, up to 150 cm long, were prepared by this method. Temperature dependence of the gelation was studied, and activation energies of the process were determined.
Optical Absorption and Emission in Rare Earth Heavy Metal Fluoride Glasses
Authors: Pafchek R. , Aniano J. , Snitzer E. , Sigel G. H.
Published: March 2011

Trivalent thulium is a 4-level laser system which operates in the 1.47μm spectral region. A tunable amplifier at this wavelength is of great interest since it falls in one of the telecommunication windows. For lasing action to occur the relatively long lived 3F4 lower laser level must be quenched to eliminate the self-terminating behavior of thulium. Rosenblatt et al. co-doped Tm and Th into a ZBLAN host to quench the 3F4 lower laser level.[1] Co-doping with Ho offers the possibility of more efficient laser operation, but it must be established whether Ho can effectively quench the lower level of Tm. This preliminary study indicated appreciable energy transfer occurred from the 3F4 level of Tm to the 5I7 level of Ho which decreased the lower laser level lifetime by as much as two orders of magnitude. The subsequent decay of the Ho ions is an issue requiring further investigation.
Chemical Reactions at Glass/Liquid Interfaces
Authors: Ferris Kim F. , Sosa C. P. , Pederson L. R.
Published: March 2011

Electronic structure calculations were performed on model silicate complexes in the presence of a perturbing dielectric field. Solid state dielectric effects were represented by an electrostatic representation of surrounding molecular subunits, which were developed from quantum mechanical electron density distributions. Only minor changes in the molecular geometry of the surface silicate model were noted; however, significant intramolecular charge redistribution and intermolecular interaction energy changes occur in the presence of the perturbing field. Molecular probes of surface absorption show a differential stabilization of donor and acceptor interactions for hydrogen bonding species.
Pressure Dependence of the Structural and Electronic Properties of Organic Superconductors
Authors: Chasseau D. , Gaultier J. , Houbib H. , Rahal M. , Ducasse L. , Kurmoo M. , Day P.
Published: March 2011

The pressure dependence (≤12 × 102 MPa) of the cell parameters of (TMTSF)2 - C104 and κ - (BEDT-TTF)2 - Cu(NCS)2 has been measured at room temperature. The magnitudes of the principal compressibilities calculated and the bulk modulus (B) do not vary all over the experimental pressure range for (TMTSF)2 - C104, while ki decrease slightly for κ - (ET)2 - Cu(NCS)2 and its Dulk modulus strongly increases. The directions of the principal compressibilities strongly varywith pressure for the former salt; in the latter case, the projections of the directions of the smallest and of the largest principal compressibilities remain parallel and perpendicular to the long molecular axis respectively whereas the intermediate is along the monoclinic b axis.

The crystal structures have been refined at 4 × 102 ,6 × 102 and 9.5 × 102 MPa (R = 0.05) for (TMTSF)2 - C104 and at 7 × 102 MPa (R = 0.095) for κ - (ET)2 - Cu(NCS)2. The transfer integrals have been calculated for the two compounds. In (TMTSF)2 - C104, both normal and transverse overlaps strongly increase with pressure; the dimerization is reduced under pressure and the two largest transverse interactions become identical. In κ - (ET)2 - Cu(NCS)2, the intra-dimer interaction strongly increases whereas the variations of the inter-dimer interactions may be very different.
Tetranitroquinodimethane (Tnq)—Electron-Deficient Prototype for a New Series of Organic Solid State Materials
Authors: Vanderah David J. , Nielsen A. T. , Hollins R. A. , Baum Chris
Published: March 2011

Recently we have synthesized several new aryl compounds substituted with two or more trinitromethyl groups. Vacuum pyrolysis of one of these—±,±,±,±’,±’,±’-hexanitro-p-xylene (p-HNX)—gave the title compound via 1,6-elimination of N2O4. Structural assignment of TNQ is based on spectral evidence (UV, 1H NMR and mass spectrometry) and conversion to the known l,4-bis(bromodinitromethyl)benzene. Evidence for the formation of the TNQ radical anion has been obtained.
Electron Paramagnetic Resonance Studies of Donor-Acceptor Salts in Polymer Media
Authors: Fann Yang-Cheng , Jansen Susan Ann
Published: March 2011

Charge transfer complexes, their inherent electrical conductivity, magnetic properties and donor-acceptor redox relationships have been a focus of much research in the last several years. One direction has been in the design of memory devices and applications in molecular electronics.1,2 Our work has focused on analysis of such processes in a polymeric medium. Polycarbonate films of 7,7’,8,8’-Tetracyanoquinodimethane (TCNQ) and o-tolidine (o-T) complexes were studied by EPR spectroscopy from 100-300K. EPR spectra and magnetic susceptibility of the dispersed charge-transfer complexes are presented and compared with the pristine materials. These studies were carried out as a function of donor/acceptor stoichiometry and concentration within the polymer matrix. Saturation studies show significant differences as the composition varies. In addition the g-tensor and linewidth are strongly dependent on temperature and composition.
Low-Dimensional Critical Behaviors and Competition Between Order Parameters in the Organic Metal (Tmtsf)2ClO4
Authors: Pesty F. , Garoche P. , Heritier M.
Published: March 2011

In low-dimensional conductors, the instability of the metallic state can lead to the formation at low temperature of a spin density wave induced by the magnetic field (FISDW). The transition results from the complex interplay between the one dimensional instability of the electronic gas and the quantization of the magnetic field’s flux. This second-order phase-transition line has been investigated by measuring both specific heat and thermal conductivity along the c* direction. The mean-field jump and the gap value have been deduced respectively from the anomaly and the exponential decay of the electronic specific heat. The coupling strength λ has been evaluated, and the λ > 0.3 value indicates clearly a strong coupling behavior at high field. Below 8 teslas, the specific heat displays a double anomaly in relation with the competition between subphases. Above the second-order transition line, critical fluctuations are observed on both specific heat and lattice thermal conductivity. Along this line, one-dimensional fluctuations increase with increasing magnetic field. It is proposed that the very high field reentrance of the metal is to be related to enhancement of the 1D fluctuations.
Sound Propagation in Cdw and Sdw
Authors: Virosztek Attila , Maki Kazumi
Published: March 2011

We present a microscopic theory of the sound propagation in quasi one dimensional charge density wave (CDW), spin density wave (SDW) and field induced spin density wave (FISDW). First, we consider the ideal situation that the phase correlation length in the CDW or the SDW is infinite. In this limit due to the diffusion pole at iω = Dq2 in a variety of correlation functions the sound propagation depends on a) what is the ratio ω/Dq2 and b) if the CDW (or the SDW) is pinned or unpinned where D is the diffusion constant. Second, when the CDW (or the SDW) is unpinned, the phason starts to participate in the screening of the ionic potential. However, since the unpinned part is strongly inhomogeneous, the contribution of the phason term depends on the wave vector of q of the sound wave like (1 + (Lq)2)−1 where L is the Fukuyama-Lee-Rice coherence length. The present theory accounts for a variety of features observed in sound propagation in quasi-one dimensional CDW systems like NbSe3 and TaS3.
Optical Studies of Polyanilines: Effects of Alkyl Ring-Substitution and Solvent Environment
Authors: Ray Anjan , MacDiarmid Alan G. , Ginder John M. , Epstein Arthur J.
Published: March 2011

Methyl and ethyl ring-substituted polyaniline derivatives have been synthesized and characterized by UV-visible-near IR spectroscopy. Optical spectra of the base forms in DMF solution suggest that the torsion angle between adjacent rings is increased by steric hindrance due to the alkyl groups in the substituted polymers, leading to blue shifts in the ∼4 eV (“bandgap”) and ∼2 eV (“exciton”) absorptions and an accompanying decrease in the relative intensity of the “exciton” band.

The methyl ring-substituted derivative, poly(o-toluidine), is shown to exhibit solvatochromism. The “exciton” absorption shifts from 2.03 eV in pure NMP to 2.19 eV in CH2CI2, accompanied by a loss in intensity relative to the “exciton” absorption.The phenomenon is attributed to the presence of a more “rod-like” state in NMP as compared to a more “coil-like” state in CH2CI2.

The effects of alkyl substituents on acetic acid solution spectra of “emeraldine” salt will be discussed with respect to polaron band formation in these systems.
Polyaniline as a Reversibly Switchable Electrochromic Material
Authors: Shieh Woan-Ru , Yang Sze C. , Marzzacco Charles , Hwang Jyun-Huei
Published: March 2011

Polyaniline is an interesting electrochromic material because its color can be changed from clear to green, to blue, and to purple by electrochemical oxidation[1]. The structural transformations associated with these color changes are shown in Scheme I. One of the possible applications for polyaniline is to use it as the active material in electrochromic windows.
Ferromagnetic Intermolecular Interaction and Crystal Structure of α-Nitronyl Nitroxide
Authors: Awaga Kunio , Inabe Tamotsu , Maruyama Yusei
Published: March 2011

The temperature dependence of the magnetic susceptibilities for several ±-nitronyl nitroxides have been measured. It is found that the intermolecular magnetic coupling in these radical crystals changes from antiferromagnetic to ferromagnetic depending on the substituents at ±-position. X-Ray crystal analysis and MO calculation have been carried out on the ferromagnetic ±-nitronyl nitroxide, 2-(4-nitrophenyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazolyl-1-oxy 3-oxide, revealing a two-dimensional ferromagnetic network linked by the Nδ+...0δ− Coulomb attraction.
Synthesis, Structure, Infrared Spectra, and Iodine Doping of Unsubstituted Polyazines
Authors: Euler William B. , Gill Benjamin C.
Published: March 2011

Polyazines, -[N=CH-CH=N]x-, are environmentally stable conjugated polymers that can be doped with iodine into an electrically conductive state. These polymers are prepared by the condensation of glyoxal and glyoxal di-hydrazone with acid catalysis. IR spectra of the undoped polymers, independent of the synthetic conditions, exhibit a broad band centered around 3240 cm−1 indicative of the presence of OH groups in the polymer. Solid state NMR spectra show that the OH groups are covalently bound to the polymer chain so that the polymer chain has a number of defect and/or cross-linking sites present. The polymer can be doped with iodine into a poorly conducting state. Iodine doping introduces one new vibrational band into the IR spectra at 1490 cm−1, associated with a bipolaronic charge carrier.
Helical Conformations of Conducting Polymers
Authors: Kertesz Miklos , Cui Changxing
Published: March 2011

Helical conformations of polymers occur due to a variety of factors, some of which are electronic in origin. We briefly review the situations in which there is an electronic driving force towards a helix including a case that might be called a helical Peierls distortion. Energetics and geometries of helical conformations of polythiophene and polypyrrole are also analyzed.
Hall Effect and Magnetoresistance in Undoped Poly(3 Hexylthiophene)
Authors: Assadi Azar , Svensson Christer , Willander Magnus
Published: March 2011

We report studies of transport properties of thin films of undoped poly(3-hexylthiophene) (P3HT) fabricated by spinning a polymer solution onto oxidised silicon or glass. The film thicknesseswere on the order of 1000 Å. We studied magnetoresistance, the effect of magnetic field on field effect mobility and Hall effect.

Transverse magnetoresistance was measured on films on glass. A positive anomalous magnetoresistance with a saturation value of about 0.1 % was found. Transverse magnetoresistance was also studied by measuring the change of a field effect mobility with magnetic field. This measurement was performed using the field effect transistor structure. An initial mobility of 6.5 × 10−5 cm2/Vs was reduced by about 15 % in a transverse magnetic field.

We also carried out Hall effect measurements on films on glass using a Van der Pauw contact configuration. The measured Hall mobility was 2.17 × 10−5 cm2/Vs. Finally we measured the temperature dependence of the Hall mobility and found it follow the exp(T-l/4) law of variable range hopping.
Insulator-Metal Transition and Conduction Processes in Trans-Polyacetylene
Authors: Conwell Esther M. , Mizes Howard A , Jeyadev Surendar
Published: March 2011

We show by calculations for a chain of stage-1 (16.7%) potassium-doped (CH)x that the metallic state is obtained by adding to the Su-Schrieffer-Heeger Hamiltonian the Coulomb potential of the doping ions and solitons on other chains. Good agreement with the measured Pauli susceptibility is obtained. Adding interchain coupling is found to lead to essentially the same density of states.
Thermally Activated Charge Hopping Transport Studies in a Σ-Conjugated Polymer
Authors: Samuel L. , Sanda P. N. , Miller R. D. , Thompson D.
Published: March 2011

Time of flight (TOF) and thermally stimulated current (TSC) measurements were performed on poly(methylphenylsilane) (PMPS), poly(ethyl-p-methoxyphenylsilane) (PMeOPhEtS) and poly(ethylphenylsilane) (PEtPhS), to study the mechanism of interchain charge hopping transport. The value of the hole mobility at a given electric field and temperature varied with the substituent side groups. The activation energies, which were assigned to the hopping transport, ranged between 0.1-0.3eV and were dependent on the applied electric field. The nature of this dependence also varied with the substituent side groups. In the TSC spectra, a well defined current peak was observed in the temperature range between 100K-160K. The peak temperature was dependent both on the electric field and the heating rate. For a constant electric field and heating rate it was also dependent on the side groups, in a manner which was consistent with the results obtained by TOF. When the samples were exposed to high doses of UV radiation, a secondary peak at ∽180K was observed, which was attributed to surface defect sites produced by the UV exposure.
Synthesis, Thermal Behavior, and Second-Order Nonlinear Optical Properties of Conjugated, Acceptor/Donor Compounds
Authors: Wolfe James F. , Ermer Susan P. , Lovejoy Steven M. , Leung Doris S. , Aron Kenneth P. , Hansen Glenn A. , Bitler Steven P.
Published: March 2011

New noncentrosymmetric compounds having both electron-accepting and electron-donating substituents on a conjugated, aromatic heterocyclic structure were synthesized and their spectroscopic, thermal, and solubility properties were determined. D.C. electric field-induced second harmonic generation (EFISH) experiments were performed to provide values of the second-order nonlinear optical susceptibility/dipole moment product βμ. Long alkyl substituents were required in heterocycle-containing compounds for sufficient solubility to conduct EFISH analysis. 2,4-Dinitro-substitution on these imine-linked materials gave the highest βμ in the series.
Electro-Optic and Nonlinear Optical Properties of 2, 6-Dibromo-N-Methyl-4-Nitroaniline (Dbnmna) Crystals
Authors: Nahata Ajay , Horn Keith A. , Yardley James T.
Published: March 2011

We report a new organic nonlinear optical crystal, 2, 6-dibromo-N-methyl-4-nitroaniline (DBNMNA). The refractive indices of DBNMNA were measured at several wavelengths between 500 and 1100 in and fit to a single oscillator Sellmeier equation. Second harmonic Maker fringe data yielded d33 values through comparison with y-cut crystalline quartz. We also report measurements of the electro-optic coefficients, (na3r13-nc3r33) r42, and r51 at several wavelengths. We find good agreement between the observed dispersion and that predicted by the simple two level dispersion model. However, the second order susceptibility is not well described by a single tensor component hyperpolarizability.
The Effect of Matrix Attachment on the Third Order Nonlinear Optical Properties of Dyes
Authors: Polis David W. , Bader Mamoun M. , Dalton Larry R.
Published: March 2011

In order to discern the source of the third order nonlinear optical (NLO) phenomenon both morphological and electronic considerations are required. A series of styrene copolymers with varying amounts of p-aminostyrene or p-chloromethylstyrene were prepared as anchoring sites for chemically reactive electrophilic and nucleophilic dyes. For comparison, the same dyes were incorporated into composites of polycarbonate. Preliminary degenerate four wave mixing results for all materials indicate that the copolymeric support allowed incorporation of greater amounts of electroactive units, versus composites, and hence allowed high third order nonlinear responses (X(3)/α of approximately 10−13 esu cm). Third order NLO responses were absent in some composite systems due to limited solubility and/or phase separation difficulties.
Synthesis and Properties of a Fully Conjugated Polydiacetylene: Poly(1,4-Bis (3-Quinolyl)-1,3-Butadiyne)
Authors: Talwar Satya S. , Kamath Manjunath B. , Babu K. N.
Published: March 2011

Synthesis of a new fully conjugated polydiacetylene i.e. poly(l,4-bis(3-quinolyl)-l,3-butadiyne) is described. Reflectance spectra of partially polymerised samples and the polymer are reported. The spectra show long wavelength absorption band at 750 nm. with the visible absorption edge above 800 nm. DC electrical conductivity measurements on pristine and Iodine doped Poly-DQ are reported. The results are discussed in terms of side group - backbone electronic interactions.
Large Cubic Nonlinear Optical Properties of Organic Semiconductor Superlattices
Authors: Jenekhe Samson A. , Chen Wen-Chang , Lo Saukwan , Flom Steven R.
Published: March 2011

We have measured extremely large second hyperpolarizabilities〈γxxxx〉 in solutions of two recently prepared organic polymer semiconductor superlattices. These block copolymers are of alternating aromatic and quinoidal moieties and structurally differ by a side group substituent. The values observed are 1.6 × 10−29 esu for the parent copolymer (PBTBQ) and 3.7 × 10−30 esu for its acetoxy derivative (PBTABQ). The corresponding values of χ(3) are estimated to be 2.7 × 10−7 esu and 4.5 × 108 esu. The measurements, made by picosecond degenerate four wave mixing at 532 nm, showed that the dynamics of the larger χ(3) valued copolymer were faster than the 30 ps resolution of the instrument while the derivative exhibited a slower response. The large magnitude and rapid response of the cubic optical nonlinearities in these novel materials suggest theiT potential for further development and photonic device applications.
Nonlinear Optical Properties of Two Thiophene-Based Polyconjugated Systems: Photoinduced Absorption and Third Harmonic Generation Spectroscopy
Authors: Zamboni R. , Taliani C. , Ruani G. , Pal A. J. , Kajzar F.
Published: March 2011

Nonlinear optical properties of two thiophene-based conjugated polymers (PTT and PDTB) were studied by the photoinduced absorption spectroscopy and the third harmonic generation spectroscopy. The results obtained with these two methods are used to estimate the value of χ(3) in these materials. Resonant χ(3) are (2.0 ± 0.2) × 10−11 e.s.u. and (1.0 ± 0.1) × 10−11 e.s.u. for PTT and PDTB, respectively. χ(3) is shown to be related to the width of the optical gap through a sixth-power law. In PTT a vibronic structure due to the C = C stretching mode appears in the χ(3) spectrum.
Rotational Diffusion of Chromophores Inside a Glassy Polymeric Film Studied By Electrooptical Interferometry
Authors: Meyrueix R. , Mignani G.
Published: March 2011

Perot Fabry interferometry under oblique incidence provides a powerful tool for the determination of the complex values of the independant components of the tensors χ2(−ω;ω,ο) and χ3(−ω;ω,ο,ο) of poled films. Deorientation of Disperse Red One chromophore in a poled film can be followed by the decrease with time of two order parameters. In the short term regime, the relaxation times of this process are spread over a broad spectrum. By comparing the chromophore dynamics in PMMA, PS and SAN at different temperatures, it appears that free volume and secondary transition concepts cannot fully explain the chromophore behavior. Chromophore dipole/Polymer dipole interactions are invoked in order to explain the slow deorientation rate in SAN.