Resonant Raman Scattering in the Polyacetylene System

The amplitude mode approach for describing the resonant raman scattering in dimerized chains is reviewed and applied to the polyacetylene system. trans-(CH)_x is disordered with a variable electron-phonon coupling constant. cis-(CH) _x is ordered with an extrinsic gap of ～ 5% of the full gap. A distribution of extrinsic gaps is shown to exist In trans-(CH) _x chains in partially isomerized polyacetylene.     

Measurements of Soliton Trapping and Motion in Trans-Polyacetylene Using Dynamic Nuclear Polarization

Abstract

The motion of solitons in undoped trans-(CH)_x is studied over the temperature range 1.5–300 K using dynamic nuclear polarization. The results of a theoretical model for the combined solid state and Overhauser effects in terms of the time dependence of the electron nuclear interaction due to motion of electrons is presented. Its application to the experiment shows that most of the solitons are trapped below 30 K and that the mobile solitons above 30 K have a diffusion coefficient that is approximately proportional to the square root of the temperature. At 300 K the time for a soliton to diffuse its length is greater than or equal to 1.7 × 10^?11 seconds.     

Electrochemical Cells Employing (Ch)x -Cathodes In A Nonaqueous Electrolyte

Polyacetylene films have been used as cathodes in electrochemical cells of the type A1/Li/LiC10₄(l…2M) - PC/ (CH)_X/Pt. Their performance characteristics have been measured. The results show that these cells can be cycled 10 to 15 times at deep discharges, over 300 times at shallow discharges and over 1000 times at very light discharges. Due to the instability of the oxidized (CH)_X the charge retention of the cells is poor.     

In Situ Raman and Epr Investigations of A Cis-(Ch)X Electrode

Abstract

In situ Raman and EPR experiments have been performed on a cis-(CH)_x electrode in an electrochemical cell {(CH)_x/1M L1C10₄ in THF/Li}. After a n-type doping with Li, the Raman spectra exhibit new features at = 1600 cm^?1 and 1270 cm^?1, comparable to those obtained with [CH)_X films Li doped via a chemical treatment. The evolution of the EPR signal is followed in a doping-dedoping cycle, showing both the reversibility of the process as well as the evidence for a metallic behavior at the maximum doping concentration.     

Morphology and Dopant Distribution in Polyacetylene

We report the results of scanning electron microscopic stadies of the morpology and dopant distribution in polyacetylene, (CH)_x. A variety of fibrillar and rod-like morphologies were observed for trans-(CH)_x and (CH)_x doped with iodine and AsF₅. Results show that iodine and atrsenic distributions are uniform across the surface of the films to a resolution of 5000 A, with no significatn difference in the concentration observed on the dull and shiny sides of the film. Hence any inhomogenieties in the dopant distribution must be on a finer scale. The fiberillar morphology was observed through the bulk of a film even after doping with iodine. Swelling of the fibrils is seen upon doping, with larger effects observed in the AsF₅ doped samples.     

Polyacetylene and Relativistic Field Theory Models

Connections between continuum, mean-field, adiabatic Peierls-fröhlich theory in the half-filled band limit and known field theory results are discussed. Particular attention is gi en to the Φ⁴ model and to the solvable N +2 Gross-Neveu model. The later is equivalent to the Peierls system at a static, semi- classical level. Based on this equivalence we note the prediction of both kink and polaron solitions in models of trans-(CH)_x. Polarons in cis-(CH) are compared with those in the trans isomer. Optical absorption from polarons is described, and general experimental consequences of polarons in (CH)_x and other conjugated polymers is discussed.     

An Insight on the Polyacetylene Properties Through Resonant Raman Scattering Spectra Analysis

Resonant Raman Scattering spectra of trans polyace-tylene (CH)_X and (CD)_X are interpreted in terms of a model based on a bimodal distribution of conjugation length segments. Such a theory takes into account the electronic and lattice dynamics properties of different conjugation length segments, together with the electronic dipole moments from the transitions and the electron vibration interactions in the excited electronic states. This model accounts also for the Resonant Raman Scattering spectra taken during the isomerization process and from cis rich samples.     

Properties of Well-Aligned Polyacetylene Obtained with a Shear Proceure

We have developed a procedure to polyerize acetylene under shear conditions and graphoepitaxially in a couette type arrangement. With this procedure (CH)_n is obtained in the form of thin films consisting of highly aligned fibers. Electron diffraction patterns evidence that thepolymer chain axis is oriented parallel to the fiber direction in the (CH)_n film plane. From striations appearing perpendicular to the fiber during e-beam irradiation, from staining experiments and from dark field imaging in strong reflections of the fiber pattern it is concluded, that the (CH)_n fibers consist of lamellae with a periodicity of about 110 Å.     

Proton Magnetic Resonance in Partially Deuterated Trans - Polyacetylene

Proton NMR measurements as a function of ^l H concentration in partially deuterated trans-(CH_zD_1-z)_x show that at high ¹H content the proton relaxation is ^{z 1-z x}homogeneous and reflects the dynamics of electronic spins. At low concentration, protons of residual catalyst (about 6% per CH unit) dominate the NMR results, misleading earlier analysis.     

Solitons in Polyacetylene Induced and Probed by Positive Mupons

Abstract

Positive muons were injected into both trans- and cis- (CH) as well as (CD)_x. In cis-polyacetylene, the μ⁺ was found to form a radical state with an unpaired electron localized near the μ⁺ In trans-polyacetylene, the longitudinal μ⁺ spin relaxation rate at 293 K showed H^?1/2 dependence on the applied field H. After considering possible mechanisms, we concluded that it is due to the soliton-like one-dimensional motion of induced unpaired electron.     

Resonance Raman Scattering of Undoped Trans-Polyacetylene in the Region of the Absorption Edge

Resonance Ranan Scattering of undoped CH)_X was studied for excitation wavelength λ_L between 700 and 1064 nm. Scattering is entirely due to long conjugated chains, but with evidence of disorder. Positions and shapes of the Raman lines are studied as a function of λ_L. The action spectrum shows a maximm near 1.4 eV, with a width > 0.2 eV at 2 K and no other structure.     

Surface Chemistry of Polyacetylene: Adhesion to Silica,Derivatization With Nickel And Catalytic Activity

Adhesion of (CH)_x film prepared by the Luttinger method to glass can be improved by silylation in order to more closely match dispersive surface energies. Treatment of n-type (CH) films with NiBr₂/HMPA/THF affords (CH)_x -supported N° which shows selectivity in hydrogenation of phenyl acetylene.     

Development of performance‐improved global positioning system (GPS) patch antenna based on sol‐gel‐synthesized dual‐phase (Bi4Ti3O12)X – (CaCu3Ti4O12)1–X composites

As a first attempt, a series of composite materials of general formula (Bi₄Ti₃O₁₂)_X – (CaCu₃Ti₄O₁₂)_1–X (BTO_X – CCTO_1–X) (X = 0–1.0) is synthesized by a sol‐gel combustion method. The phase changes, including their formation and evolution during the gradual substitution of BTO into CCTO are analyzed from the X‐ray diffraction pattern. The Jana2006 refinement plotting method proves that formation of an ideal dual‐phase composite system with separate orthorhombic and cubic phases occurs. A surface morphological study revealed that the BTO_X – CCTO_1–X composites are composed of small CCTO grains embedded in large BTO grains and both coexisted with a bimodal distribution. The possible vibrational modes of interactions between the constituent phases are determined from Raman spectra. Our inexpensive, combustion method for BTO_0.2 – CCTO_0.8 gives a high dielectric constant (ε′ = 3232) at 100 Hz at room temperature. The nature behind these data is revealed that the BTO‐CCTO composite can be applicable for the fabrication of miniaturized global positioning system (GPS) patch antennas. The fabricated GPS patch antenna shows optimum results of small size (2.37 mm × 1.18 mm), return loss (‐14.419) and wide bandwidth (350 MHz) to be operated at 1.57 GHz.     

The Crystallisation of Aluminium Trihydroxide (Gibbsite) from Sodium Hydroxide Solution Onto Fine Seeds: Physico-chemical Studies on the Internal Structure and Agglomeration of Different Crystal Fractions

A batch of Bayer gibbsite crystals (particle size range 3 to 70 μm) was prepared by crystal growth onto fine seeds (1 to 3 μm) from sodium hydroxoaluminate/sodium hydroxid-solution. The internal structures and seed agglomeration of different fractions were examined by optical microscopy, infra-red spectrophotometry, thermal analysis and chemical dissolution analysis. These physico-chemical studies confirmed that crystal growth occurs with some seed agglomeration in the early stages, followed by growth onto the ‘agglomerates’. The agglomerated seeds contents (X) were as follows: for fraction DiD (l₀ = 6.3 μm), X = 0.44; for fraction Gi C (l₀ = 20 μm), X = 0.41; for fraction Gi B (l₀ = 38 μm), X = 0.31 and for fraction Gi A (l₀ = 55 μm), X = 0.24.     

In Situ Deposition of Highly C-axis Oriented Lanthanum Modified Lead Titanate Thin Films by Multi-Ion-Beam Reactive Co-sputtering Technique

Highly c-axis oriented La-modified PbTiO₃ (PLT) thin films were in situ grown on Pt(100)/MgO(100) and MgO(100) substrates by multi-ion-beam reactive co-sputtering (MIBRECS) technique at the substrate temperature range of 450°C-540°C. The orientation degree a of the films is more than 90%. The chemical composition is in good agreement with the designed one and is almost uniform across the surface of the substrates. The remanent polarization (P_r) and coercive field (E_c) were found to be 5.3 μC/cm² and 78 kV/cm, respectively.     

Optical properties and chemical bonding characteristics of amorphous SiNX:H thin films grown by the plasma enhanced chemical vapor deposition method

Amorphous silicon nitride (SiN_X:H) thin films grown by the plasma enhanced chemical vapor deposition (PECVD) method are presently the most important antireflection coatings for crystalline silicon solar cells. In this work, we investigated the optical properties and chemical bonding characteristics of the amorphous SiN_X:H thin films deposited by PECVD. Silane (SiH₄) and ammonia (NH₃) were used as the reactive precursors. The dependence of the growth rate and refractive index of the SiN_X:H thin films on the SiH₄/NH₃ gas flow ratio was studied. The chemical bonding characteristics and the surface morphologies of the SiN_X:H thin films were studied using the Fourier transform infrared spectroscopy and atomic force microscopy, respectively. We also investigated the effect of rapid thermal processing on the optical properties and surface morphologies of the SiN_X:H thin films. It was found that the rapid thermal processing resulted in a decrease in the thickness, increase in the refractive index, and coarser surfaces for the SiN_X:H thin films.     

Phase‐selective crystallization of nickel phosphate VSB‐5 with (2‐hydroxyethyl) trimethylammonium hydroxide as template

Several nickel phosphate molecular sieves were synthesized by conventional heating (CH) and microwave assisted hydrothermal (MAH). Nickel phosphate VSB‐5 (Versailles Santa Barbara‐5) was synthesized with conventional oven for 72 h or with microwave for 1 h and followed by conventional oven for 48 h in the presence of (2‐hydroxyethyl) trimethylammonium hydroxide as template. The phase transformation is observed by variation of CH time for the synthesis of nickel phosphate molecular sieves. At CH time of 24 h, the VSB‐5 crystal together α‐Ni₂P₂O₇, Ni₂P₄O₁₂ and unknown phases were produced but the pure VSB‐5 crystal was obtained in the CH time of 48 h or more. At high content of nickel, a mixture of α‐Ni₂P₂O₇, Ni₂P₄O₁₂ phases and small amount of VSB‐5 crystal, was achieved but pure VSB‐5 crystal was obtained in the lower level of nickel and other phases are vanished. An efficient ultrasonic‐assisted aging was found for the synthesis of nickel phosphate molecular sieve, in which by ultrasonic mixing of 0.5 h followed microwave of 1 h, the CH time is significantly reduced from 48 to 24 h. The morphology of nickel phosphate crystals is highly influenced in the presence of ethylene glycol as co‐solvent. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Frequency Dependent Conductivity of Polyacetylene

We report on an extensive study of the frequency and temperature dependent conductivity of largely cis- (CH)_x trans- (CH)_x, and NH₃ compensated and iodine doped materials. The results reveal a strongly temperature (T) dependent dc conductivity and weakly T-dependent ac conductivity for largely cis- (CH)_x and for NH₃ compensated samples, similar to the behavior that is observed in many crystalline and amorphous semiconductors. The trans- (CH)_x and lightly iodine doped trans- (CH)_x have larger dc and ac conductivity and a strongly T-dependent ac conductivity. These latter results contrast with the usual expectations of variable range hopping and polaronic hopping, but are in good agreement with the predictions of Kivelson's Theory of charge transport via intersoliton electron hopping.     

Liquid Phase Epitaxy (LPE) of YB2Cu3O7-δ High Tc Superconductors

YBa₂Cu₃O_7-δ films were grown by liquid phase epitaxy in Y-ZrO₂ crucibles on (110)NdGaO₃ substrates. A change in the preferred crystallographic growth direction was observed reproducibly. The growth mode changes from pure c-axis oriented over mixed c/a-axis oriented films to pure a-axis oriented films with increasing undercooling. X-ray diffraction measurements and atomic force microscopy investigations with c-axis oriented as well as a-axis oriented films are presented. It will be shown that atomically smooth steps with 0.2-0.8 μM width can be achieved by LPE, which are free from melt remnants. Furthermore the values for the enthalpy of dissolution from literature, which are varying in a wide range, will be combined and a new value will be calculated in terms of a multi particle model.     

Orientational Order and Linear Dichroism of a Water Soluble Porphine in a Lyotropic Nematic Liquid Crystal

Aqueous lyotropic nematic liquid crystals can be homogeneously oriented by magnetic fields and are therefore well suited to be used as anisotropic solvents for optical polarization studies of water soluble dye molecules. The potassium laurate (KL)/KCl/H₂O nematic phase, composed of rod-like or cylindrical micelles, was used as a matrix for the study of orientational order and linear dichroism of a substituted free-base porphine (TPPS₄). The results indicate that a significant portion of porphine molecules are incorporated into the micelles with their planes on the average perpendicular to the optic axis of the lyotropic rods. The order parameter of TPPS₄ is much higher in this system than in other nematic lyophases such as KL/decanol/H₂O in which preferential hydrogen bonding occurs between TPPS₄ molecules and the hydroxyl groups of decanol molecules which presumably occupy the surface of the cylindrical micelles. All observed electronic transitions in the 350-700 nm range are found to be polarized in the plane of the porphine ring.