bluuebunny/crossref_metadata_2025_split huggingface dataset:
Materials Engineering For Polarized Light Emitting Diodes
Authors: Wegner G. , Neher D. , Remmers M. , Cimrova V. , Schulze M. 
Published: April 2011

ABSTRACTElectroluminescent devices have been made from organo-soluble derivatives of poly(pphenylene). Solubility and processibility by the LB-technique is achieved by attaching alkoxy side groups to the backbone-p-phenylene units. These polymers are of the hairy-rod (HR) type. If transferred as monolayers from the air-water-interface, monodomain multilayers with large order parameters of chain orientation are obtained. A 130 nm thick LB-film of poly(2,5-diisopentoxy-pphenylene) shows blue photoluminescence at λmax = 3.08 eV (404 nm) with a tail extending to 2 eV. The anisotropy was (lII- l1)/ (l11, + l11)= 0.5. This LB-film between a transparent gold and an evaporated Al-electrode shows polarized light emission at E ≤ 6.107 V cm−1 with am=a λmax2.2 eV and an in-plane anisotropy of 0.54. Thin films obtained by spincoating of the same polymer show isotropic electroluminescence between ITO and Al-electrodes with an external quantum efficiency of about 0.03 %. Higher efficiencies up to 4 % were realized optimizing the device architecture and the electrodes. Photocrosslinkable sites are introduced as side groups to the poly(pphenylene) chain. This allows patterning of the LEDs. General features of the supramolecular architecture and typical defect structures occurring in films of polyconjugated macromolecules are discussed using prototypical polymers as examples. Important effects are chain segregation according to chain length and formation of disclinations.
Evidence Of Photo-Oxidation In Photobleaching Process Of Nonlinear Optical Polymer
Authors: Lee M. H. , Lee H. J. , Han S. G. , Kim H. -Y. , Won Y. H. 
Published: April 2011

ABSTRACTThe photobleaching mechanism of nonlinear optical polymers has been investigated; the PMMA based polymers with nonlinear optical chromophores, 4-dimethylamino-4'-nitro-stilbene (DANS), 4-dimethylamino-4'-hexylsulfone-stilbene (DASS), and 4'-(2-hexyloxyethyl) ethyl amino-4-nitro azobenzene (DR-16). The photobleaching was carried out using near-UV lines. FTIR spectra and UV-VIS absorption spectra were obtained after each photobleaching. Refractive indices were measured in the photobleaching processes. The results suggest that the photobleaching mechanism of two PMMA based side-chain polymers with DANS and DASS chromophores results from the photo-oxidation and that of the PMMA based host-guest polymer with DR-16 chromophore results from the combination of the photo-degradation and the trans-cis conformational transformation.
Observation Of Photorefractive Effect In A Second Order Nonlinear Optical Chromophore Functionalized Polythiophene Derivative
Authors: Chittibabu K. G. , Li L. , Chen Z. , Kumar J. , Tripathy S. K. 
Published: April 2011

ABSTRACTWe report the observation of photorefractive (PR) effect in a solution processable, thiophene copolymer with a side chain nonlinear optical (NLO) chromophore, poly(3- octylthiophene-co-N-(3-thenyl)-4-amino-2-nitrophenol) [POMDT]. The copolymer exhibits moderately fast photoconductivity. When doped with second order NLO active azo dye, this copolymer exhibited large second order NLO activity, and low asymmetric two beam coupling (TBC) gain. Enhanced TBC gain was observed, when this composite material was plasticized. The observed photorefractive response time is of the order of seconds. The slower response is attributed to the presence of large volume fraction of the plasticizer in the composition, which reduces the charge carrier mobility. The results from photoconductivity, second harmonic generation and two beam coupling experiments are discussed.
Experimental studies of surface relief gratings on polymer Films
Authors: Jiang X. L. , Kim D. Y. , Li L. , Shivshankar V. , Kumar J. , Tripathy S. K. 
Published: April 2011

ABSTRACTWe report our investigation on the recording of surface relief gratings on azobenzene containing polymer films by laser beams with different polarizations. Experimental evidence shows that it is necessary to have spatial variations of both magnitude and direction of net electric field in the films to record surface relief gratings. Large surface modulation (> 3500 Å) and high diffraction efficiency (about 30%) were obtained under optimized recording conditions. In addition, polarization dependent erasure of the gratings by a single laser beam has been studied.
Ferrimagnets made by assembling high- spin organic polyradicals by mean of complexation with magnetic metal ions. Vii. One- dimensional chains made by an alternating array of mn(ll)(hfac)2 and 1,3- bis(n- oxy- tert-butylamino)benzenes
Authors: Inoue Katsuya , lwamura Hiizu 
Published: April 2011

ABSTRACTManganese bis(hexafluoroacetylacetonate), Mn(hfac)2, reacts with a series of bisnitroxide radicals, 5- R- 1,3- bis(N- oxy- tert- butylamino)benzene 1R (R = H, Cl, and Br), to give 1:1 polymeric complexes of formula [Mn(hfac)2·1R]n. The X- ray crystal structure of the 1H complex reveals that it crystallizes in the monoclinic system, space group P21/n, with a= 9.212(3) Å, b= 16.620(3) Å, c= 20.088(2) Å, β= 98.46(1)°, V= 3042(1)Å3, and Z= 4. The manganese(II) ion and 1H molecule makes onedimensional chains by ligation of the latter serving as a bis(monodentate) ligand to the former. The crystals of the 1H complex undergo transition to a metamagnet at 5.5 K. Similar 1cl and 1Br complexes behave as ferrimagnets with transition temperatures of 5.2 and 5.0 K, respectively.
Stability of PPV Derivatives: The Effect of Side Group Functionalities
Authors: Cumpston B. H. , Jensen K. F. , Klavettert F. , Staring E. G. J. , Demand R. C. J. E. 
Published: April 2011

ABSTRACTWe have identified excited-state singlet oxygen as a reactive intermediate in the solid state photo-oxidation of two poly(p-phenylene vinylene) (PPV) derivatives, poly(2,5-bis(5,6- cholestanoxy)-1,4-phenylene vinylene) (BCHA-PPV) and poly(2-methoxy,5-(2'-ethyl-hexoxy)- 1,4-phenylene vinylene) (MEH-PPV). Singlet oxygen is photosensitized via energy transfer from the polymer and undergoes 1,2-cycloaddition across the electron-rich vinyl double bond in the backbone of the polymer resulting in the formation of highly oxidized species such as esters. Volatile carbonyl species are also formed, and, consequently, the film thins. This degradation pathway occurs when the polymer film is exposed in air to light having energy above the bandgap of the polymer, from either a low-pressure UV mercury lamp or an Ar+ laser operating at 514 or 457 nm. Interestingly, the singlet oxygen reaction does not take place in model compounds with similar structures such as trans-stilbene. In an effort to understand which properties of the polymer make it susceptible to singlet oxygen attack, we have studied the effect of conjugation length and side groups on the reactivity of thin polymer films. Specifically, the role of electron withdrawing groups, steric protection of the vinyl double bond, and conjugation length effects have been investigated using both FrIR spectroscopy and semi-empirical computational chemistry calculations.
Solid-Phase Synthesis of Potential Molecular Wires. Attachment of Molecular Alligator Clips
Authors: Jones LeRoy , Tour James M. 
Published: April 2011

ABSTRACTDescribed is the solid-phase and solution-phase synthesis of oligo(2-dodecylphenyleneethynylene) s via an iterative divergent/convergent approach. Synthesized were the monomer, dimer, tetramer, octamer and 16-mer of the oligo(2-dodecylphenylene-thynylene)s. The synthetic protocol for the synthesis and attachment of protected thiol-containing end groups is also described which may serve as molecular alligator clips for adhesion to gold surfaces. These oligomers may act as molecular wires in molecular electronic devices.
The Influence of Film Morphology on the Photovoltaic Effect in α-Sexithienyl Thin Film Devices
Authors: Marks R. N. , Zamboni R. , Taliani C. 
Published: April 2011

ABSTRACTWe report measurements made on the photovoltaic effect in devices fabricated with thin films of α-sexithienyl (αT6) as the active layer. aT6 was sublimed onto glass/ITO substrates (as the positive contact), and the substrate temperature was varied between room temperature and 156°C during sublimation to control the film morphology. As the substrate temperature increases, the average size of the αT6 grains increases, from ˜200nm at 22° C to ˜1500nm at 150°C, and order within the grains increases. Aluminium metal was evaporated onto the αT6 as the top (negative) contact.The dark current-voltage (I-V) curve is strongly rectifying, whereas under illumination it becomes almost symmetrical about ˜0.7V on the voltage axis, which represents the maximum open-circuit voltage. This behaviour indicates that the efficiency of charge separation is strongly bias dependent, and that charges are separated by the bulk field rather than at, for example, a Schottky barrier. The spectral response of the photocurrent is independent of the film morphology, which is surprising since the environment in which excitons recombine radiatively in αT6 is known to depend on the morphology of the film. The spectral response is consistent with previous measurements on photoconductivity, indicating that the efficiency of charge separation increases with increasing photon energy. There is also a significant photocurrent at energies well below the absorption edge of αT6, suggesting an exponential distribution of defect states extending at least 0.6eV into the optical gap, which may be a distribution of X-traps below the absorption edge. As the substrate temperature during growth increases from 28C to 150C the efficiency of charge separation decreases by an order of magnitude, suggesting that exciton dissocation is assisted by traps or defects which are present in smaller numbers in the more ordered films.
A New Approach to Synthesize Polyphenylene Dendrimers
Authors: Mandal Braja K. , Sinha Arun K. , Li Xiaofang , Walsh Christopher J. , Lamb David R. , Smith Jonathan O. 
Published: April 2011

ABSTRACTA new type of dendritic molecules containing p-phenylene repeat units has been synthesized. Preliminary results on linear and nonlinear optical properties are discussed.
Chromic Polydiacetylene Single Crystals: Atomic Force Microscopy Studies
Authors: Shivshankar V. , Sung C. , Kumar J. , Tripathy S. K. , Sandman D. J. 
Published: April 2011

ABSTRACTWe have studied the surface morphology of free standing single crystals of thermochromic polydiacetylenes (PDAs), namely, ETCD and IPUDO (respectively, the ethyl and isopropyl urethanes of 5,7-dodecadiyn-1,12-diol), by Atomic Force Microscopy (AFM) under ambient conditions. Micron scale as well as molecularly resolved images were obtained. The micron scale images indicate a variable surface, and the molecularly resolved images show a well defined 2-D lattice that is interpreted in terms of molecular models and known crystallographic data. Thereby information about surface morphology, which is crucial to potential optical device or chromic sensor performance is available. We also report the observation of a “macroscopic shattering” of the IPUDO monomer crystal during in-situ UV polymerization studies.
Optical Properties and Dynamics of Molecular Excitons in Oligothiophenes
Authors: Tubino R. , Bongiovanni G. , Mura A. , Bosisio R. , Botfa C. , Silvestrot G. Di 
Published: April 2011

ABSTRACTCW absorption and emission spectra as well as time-resolved photoemission dynamics have been employed to detect the evolution of the first excited electronic states and the associated spectroscopical changes in passing from the isolated molecules to the aggregated state in thiophene oligomers. To this end a novel form of inclusion compound in PHTP in which the molecules are electronically decoupled in the solid state has been studied, thus avoiding the complications associated with the change in conformation occurring upon dissolution. The experimental data are interpreted in terms of the molecular exciton model.
Optical Properties of Oriented Crystalline Oligothiophene Thin Films
Authors: Suzuki K. , Shimizu N. , Shiraishi Y. , Kuroda M. , Kanemitsu Y. 
Published: April 2011

ABSTRACTWe have studied optical properties of oriented crystalline oligothiophene (T4-T6) thin films to analyze the correlation between optical properties and microstructures in organic films. By using conventional vacuum deposition and organic molecular beam deposition techniques, we fabricated oriented crystalline oligothiophene thin films on fused silica glasses. Luminescence spectrum and dynamic. depend on the thickness of the crystalline films. X-ray and scanning electron microscope analyses show that with an increase of film thickness, the average size of microcrystals increases and then saturates to a constant (∼300 nm). The anisotropy of absorption and luminescence spectra show the orientation of molecules in thick films.
Thermally Stabilized Polyaniline With m-Xylylenedisulfonic Acid And Its Application For A Counter Electrode Of A Tantalum Capacitor
Authors: Ishikawa H. , Yageta H. , Amano K. , Satoh M. , Hasegawa E. 
Published: April 2011

ABSTRACTWe have succeeded in preparing a conductive polyaniline (PAn) with improved thermal stability from a chemical oxidative polymerization of aniline by using an oxidant and a novel protonic acid, m-xylylenedisulfonic acid (XDSA). The acid was synthesized from dibromoxylene and characterized by elemental analysis, IR and NMR spectroscopies. The polymer which is doped with XDSA shows a high conductivity of 5 S/cm. The conductivity does not change with annealing at 125°C in air for over 1000 hours. This polymer exhibits good thermal stability, and this stability is attributed to XDSA dopant, which consists of a bi-functional sulfonic group bonded to a polymer chain. By immersing an anodized tantalum pellet into a reactive solution, PAn doped with XDSA film is formed on the dielectric surface. The tantalum capacitor using PAn doped with XDSA as a counter electrode shows the improved characteristics: high apparent capacitance (90%), and small series resistance (<200mΩ at 100kHz). The capacitor demonstrates an excellent thermal stability due to because of the exceptional heat-resistance of PAn doped with XDSA formed in the capacitor.
Electrically Conducting Polymer Blends Based On Polyaniline
Authors: Passiniemi P. , Laakso J. , Ruohonen H. , Väkiparta Kimmo 
Published: April 2011

ABSTRACTPolyaniline offers a promissing possibility to make electrically conducting polymer blends with tailorable surface and bulk conductivities. The matrix polymer can be a thermoplast or a thermo- set. Different commonly used polymer processing methods are applicable to the blends; e.g. injection moulding, film blowing, compression moulding and fiber spinning. Also commonly used thermoset resins processings are possible. The key feature in making all this feasible is the co- solvent/plasticizer technology developed recently in the industry. Typically, the antistatic conduc- tivity level is reached in melt-processing with a polyaniline complex amount of 5 to 10 wt-% and in solution processing with 0.5 to 5 wt-% complex amounts. The maximum conductivity is in the range of 10 to 100 mS/cm for blends.
Fabrication of New Multilayer Heterostructures Based on Self-Assembled Layers of Poly(amic acid) with Various Electroactive Polymers
Authors: Baur J. W. , Besson P. , O'Connor S. A. , Rubner M. F. 
Published: April 2011

ABSTRACTSelf-assembled films of pyromellitic dianhydride oxydianiline (PMDA-ODA) were fabricated through the alternate adsorption of poly(amic acid) and various polycations including poly(allyl amine) (PAH), polyaniline (PAni), and the tetrahydrothiophene precursor of poly(p-phenylene vinylene) (PPV). In all cases, a linear build-up in thickness with increasing number of bilayers was observed with a high sensitivity of the average bilayer thickness to the ionic strength of the poly(amic acid) solution. By controlling the ionic strength of the PAA solution, the bilayer thickness could be varied from 10 to 100 Å, depending on the polycation used. Examination of the self-assembled films of poly(amic acid) and PAni showed that a conductivity of 0.5 S/cm could be achieved prior to conversion of the polyimide, but that the conductivity was drastically reduced when either the ionic strength of the poly(amic acid) solution was increased or when the poly(amic acid) was converted to polyimide. The self-assembly of poly(amic acid) with precursor PPV demonstrated that it was possible to produce a film which can be self-assembled as two ionic precursor polymers and then thermally converted into a film composed of two non- ionic polymers. Advancing sessile water drop contact angle measurements revealed that very hydrophobic surfaces can be generated upon conversion of the PAA/precursor PPV films.
Photoexcitation Dynamics In Polymeric Heterostructures
Authors: Bongiovanni G. , Destri S. , Mura A. , Piaggi A. , Tubino R 
Published: April 2011

ABSTRACTWe investigate the dynamics of photoexcitations in thiophene-based copolymers by site-selective and time-resolved photoluminescence spectroscopies. We attribute the large Stokes-shift observed between the absorption and luminescence peaks to spectral relaxation of excitons within an inhomogeneously broadened density of states. The non exponential decay of the photoluminescence intensity is explained through the interplay between spectral diffusion, thermally activated jumps and slow transfer to non nearest neighbour sites.
Schottky Barrier Diodes From Electrochemically Generated Polypyrrole-Aluminium Junctions
Authors: Rodriguez J , Moliton J. P. , Trigaud T , Otero T. F. , Grande H. 
Published: April 2011

ABSTRACTPolypyrrole films were electrogenerated and electrochemically compacted at high cathodic potentials on aluminium. Films removed from the electrode after polarization at -2000 mV show stable bulk conductivities of 10-6 S/cm for months. Planar structures metal/polymer/metal present rectifying properties. The presence of a thin oxidized surface layer having a higher conductivity than that of the bulk polymer can be deduced remaining reduced the polymer mass.
Optical Properties of Poly[(3-Pentyl-5-Oxyazobenzene) Thiophene]
Authors: Luzzati S. , Viera W. , Catellani M. 
Published: April 2011

ABSTRACTWe report a study of the optical and photoexcitation properties of a new polyalkylthiophene:poly[(3-pentyl-5-oxoazobenzene)thiophene]. UV-Vis absorption and emission, IR absorption, Raman scattering, indicate that the steric hindrance of the side chain induces some rotational disorder of the backbone but the π electron delocalization is not substantially differing from other polyalkylthiophenes. Long lived photoexcitations have been characterized by photoinduced absorption. The spectral features are intrinsic to the polyconjugated thiophene chain, even when the backbone and the azo chromophore are both photoexcited by UV light.
Aggregate Formation in Pyridine-Based Polymers
Authors: Blatchford J. W. , Jessen S. W. , Lin L. B. , Gustafson T. L. , Epsteint A. J. , Fu D. K , Wang H. L. , Swager T. M. , Macdiarmid A. G. 
Published: April 2011

ABSTRACTThe spectroscopic properties of the pyridine-based polymer poly(p-pyridyl vinylene p-phenylene vinylene) (PPyVPV) are examined. The emission of PPyVPV in solution has small intrinsic Stokes shift with some vibronic structure. In contrast, emission from thick film samples is featureless, with a strong redshift of ˜0.5 eV versus solution. We attribute these observations to the formation of aggregate states in film samples. Time-resolved photoluminescence measurements are in accord with the diffusion of excitons to the aggregate sites. Photoinduced absorption also originates from excitons in aggregate states.
Selective Luminescence Spectroscopy of Poly(p-Phenylene) Thin Films at Room Temperature
Authors: Drobizhev M. A. , Sapozhnikov M. N. , KobryanskII V. M. 
Published: April 2011

ABSTRACTSelectively excited room-temperature luminescence spectra are reported for thin films of poly(p-phenylene) (PPP) deposited onto quartz substrata. The spectra exhibit a localization threshold in the low-energy tail of the luminescence excitation band at vloc.= 22400 cm−1, 2200 cm−1 below the maximum of the excitation spectrum. Upon laser excitation at Vex < Vloc., the maximum Vem of the luminescence spectrum shifts linearly with Vex due to selective excitation of polymer segments. It was found that there exists the frequency range where the slope of the Vem vs Vex dependence is smaller than unity, which corresponds to our previous model calculations for the case of selective excitation of chromophores through broad phonon bands. At vex > vloc,, the luminescence spectrum is independent of Vex. This behavior can be explained if one assumes that upon excitation below the localization threshold the luminescence is related to polymer segments directly excited by laser, whereas upon exciting above the threshold the fast energy relaxation takes place from initially excited states to lower-lying states, from which uminescence occurs.
Two-Photon Absorption of Biexcitons for a Truncated Potential
Authors: Gallagher F. B. , Spano F. C. 
Published: April 2011

ABSTRACTA tight binding, one dimensional, two-band model is used to investigate the formation and nonlinear optical properties of biexcitons in conjugated polymers. The full single and double electron-hole pair basis sets are explicitly considered for a Hamiltonian which includes an electron and hole transfer parameter (t) along with a truncated potential with only on-site (V0 ) and nearest neighbor (V1) Coulombic interactions. The biexciton phase space is determined to be a function of only two parameters α and βwhere α ≅V1/V0 and β ≅t/V0. Due to the truncated potential only a single biexciton eigenstate is formed in the region limited by 0.64 < α≤ 1 and 0 ≤ β< 0.33. The two-photon absorption spectra in the range 0 < hω < δ, where δ is the one photon gap, are found to contain at most two types of peaks: one arising from a biexciton and another due to a charge-transfer, single-exciton. The polymer limit is obtained and used to investigate polymers with large alternation such as polysilane.
Novel ElectrolUminescence Enhancement in Poly(3-ALKYLTHIOPHENE) Light Emitting Diode Doped With Fluorescent Dye
Authors: Ohmori Y. , YOSHIDA M. , HIRONAKA Y. , FUJII A. , TADA N. , YOSHINO K. 
Published: April 2011

ABSTRACTElectroluminescent diodes utilizing poly(3-alkylthiophene) (PAT) containing fluorescent dyes have been fabricated and their unique enhancement of emission efficiency has been studied for PAT diodes doped with different fluorescent dye materials. Remarkable enhancement of electroluminescent efficiency has been observed, and the mechanism of emission enhancement in PAT diode by doping of fluorescent dye has been discussed in PAT with different aLkyl-side-chain length.
The Microstructure and Properties of Layered Oxide Thin Films Fabricated by MOCVD
Authors: Li Tingkai , Zhu Yongfei , Desu Seshu B. , Nagata Masaya 
Published: April 2011

ABSTRACTFor the first time, layered oxide thin films of SrBi2Ta2O9 (SBT) with very good ferroelectric properties have been prepared by direct-liquid-injection MOCVD technique. The SBT films were deposited onto both Pt/Ti/SiO2/Si wafers and single-crystal sapphire substrates to measure their phase formation, microstructure and ferroelectric properties. Crystalline SBT phase had been observed at temperatures as low as 500°C. With increasing deposition temperature above 500°C, the grain size of SBT thin films was increased from 0.01 μ m to 0.2 μm. The films were found to be dense and homogenous. Typically, SBT thin films of 200 nm thick with grain size about 0. 1μm have 2Pr around 10 μC/cm2 at 5V, Ec 55.7 kV/cm, and dielectric constant around 100. The leakage 9 2 currents were as low as 8 × 10−9 A/cm2 at 150 kV/cm. The films also showed fatigue-free characteristics: no fatigue was observed up to 1.4 × 1010 switching cycles. This development of MOCVD technique for good quality SBT films make their integration into high density nonvolatile memories relatively easy.