bluuebunny/crossref_metadata_2025 huggingface dataset:
Tem Study of Radiation Damage and Annealing of Neutron Irradiated Zirconolite
Authors: Lumpkin Gregory R. , Smith Katherine L. , Blake Ron G.
Published: April 2011

Neutron irradiation was used to simulate alpha-decay damage in zirconolite, resulting in a transformation from the crystalline to the amorphous state at doses of 4–25 × 1019 n/cm2 (E ≥ 1 MeV). With increasing dose, the radiation damage microstructures resemble damage caused by: 1) alpha-decay of 232Th and 238U in natural zirconolites, 2) alpha-decay of 238Pu or 244Cm in synthetic samples, and 3) collision cascades in samples irradiated with heavy ions. Heavily damaged zirconolite recovers to a defect fluorite phase on annealing at temperatures up to 1000 °C. The main stage of structural recovery was found to occur at temperatures of 600–800 °C. The microstructures after heating depend on the initial level of damage: zirconolite grains with low to moderate levels of damage anneal to imperfect single crystals, whereas heavily damaged grains recrystallize to a polycrystalline microstructure. Complications encountered in this work include the production of fission tracks (due to trace amounts of U) and a non-uniform distribution of damage at higher dose levels (possibly due to electron beam heating).
Apatite- and Monazite-Bearing Glass-Crystal Composites for the Immobilization of Low-Level Nuclear and Hazardous Wastes
Authors: Wronkiewicz D. J. , Wolf S. F. , DiSanto T. S.
Published: April 2011

This study demonstrates that glass-crystal composite waste forms can be produced from waste streams containing high proportions of phosphorus, transition metals, and/or halides. The crystalline phases produced in crucible-scale melts include apatite, monazite, spinels, and a Zr-Si-Fe-Ti phase. These phases readily incorporated radionuclide and toxic metals into their crystal structures, while corrosion tests have demonstrated that glass-crystal composites can be up to 300-fold more durable than simulated high-level nuclear waste glasses, such as SRL 202U.
Sorption Mechanism of Carbon-14 by Hardened Cement Paste
Authors: Noshita K. , Nishi T. , Matsuda M. , Izumida T.
Published: April 2011

Carbon-14 sorption by cementitious materials should be enhanced to ensure the long term safety of radioactive waste repositories. The sorption mechanism of inorganic C- 14 (CO32- was investigated using batch sorption experiments and zeta potential measurements. The results suggested that C-14 was adsorbed onto the cement surface by an electrostatic force, due to the reaction between SiO2 and CaO contained in the cementitious composition. That is, SiO2 was originally negatively charged (SiO-) in cement, but became positively charged through the interaction of Ca2+. These positive sites on the SiO2 surface adsorbed inorganic C-14. Ordinary Portland cement (OPC) did not contain enough SiO2 compared with its CaO content to produce sufficient numbers of C-14 adsorption sites. The C-14 distribution coefficient (Kd) was increased from 2,000 to 7,000 mL/g by adding SiO2 to OPC.
Evaluation of Microbially-Influenced Degradation of Massive Concrete Structures
Authors: Hamilton M. A. , Rogers R. D. , Veeh R. , Zolynski M.
Published: April 2011

Corrosion of massive concrete structures is a costly and environmentally dangerous problem. Many low level waste disposal vaults, both above and below ground, are constructed of concrete. When the integrity of these structures is compromised, potential for soil and water contamination is significantly increased. There are literally thousands of massive concrete structures within the U.S. infrastructure that are in a serious state of disrepair due to corrosion. One potential contributing agent to the destruction of concrete structures is microbially-influenced degradation (MID). MID occurs when microorganisms in the environment produce mineral or organic acids that dissolve or disintegrate the cement matrix. Three groups of bacteria are known to create conditions that are conducive to destroying concrete integrity. They are sulfur oxidizing bacteria, nitrifying bacteria, and heterotrophic bacteria.

Research is being conducted at the Idaho National Engineering Laboratory to assess the extent of naturally occurring microbially influenced degradation (MID) and its contribution to the deterioration of massive concrete structures. The preliminary steps to understanding the extent of MID, require assessing the microbial communities present on degrading concrete surfaces. Ultimately such information can be used to develop guidelines for preventive or corrective treatments for MID and aid in formulation of new materials to resist corrosion. An environmental study was conducted to determine the presence and activity of potential MID bacteria on degrading concrete surfaces of massive concrete structures. Scanning electron microscopy detected bacteria on the surfaces of concrete structures such as bridges and dams, where corrosion was evident. Enumeration of sulfur oxidizing thiobacilli and nitrogen oxidizingNitrosomonas sp.andNitrobacter sp.from surface samples was conducted. Bacterial community composition varied between sampling locations, and generally the presence of either sulfur oxidizers or nitrifiers dominated, although instances of both types of bacteria occurring together were encountered. No clear correlation between bacterial numbers and degree of degradation was exhibited.
Glass as a Waste Form for the Immobilization of Plutonium
Authors: Bates J. K. , Ellison A. J. G. , Emery J. W. , Hoh J. C.
Published: April 2011

Several alternatives for disposal of surplus plutonium are being considered. One method is incorporating Pu into glass and in this paper we discuss the development and corrosion behavior of an alkali-tin-silicate glass and update results in testing Pu doped Defense Waste Processing Facility (DWPF) reference glasses. The alkali-tin-silicate glass was engineered to accommodate a high Pu loading and to be durable under conditions likely to accelerate glass reaction. The glass dissolves about 7 wt% Pu together with the neutron absorber Gd, and under test conditions expected to accelerate the glass reaction with water, is resistant to corrosion. The Pu and the Gd are released from the glass at nearly the same rate in static corrosion tests in water, and are not segregated into surface alteration phases when the glass is reacted in water vapor. Similar results for the behavior of Pu and Gd are found for the DWPF reference glasses, although the long-term rate of reaction for the reference glasses is more rapid than for the alkalitin-silicate glass.
Humid-Air and Aqueous Corrosion Models for Corrosion-allowance Barrier Material
Authors: Lee J. H. , Atkins J. E. , Andrews R. W.
Published: April 2011

Humid-air and aqueous general and pitting corrosion models (including their uncertainties) for the carbon steel outer containment barrier were developed using the corrosion data from literature for a suite of cast irons and carbon steels which have similar corrosion behaviors to the outer barrier material. The corrosion data include the potential effects of various chemical species present in the testing environments. The atmospheric corrosion data also embed any effects of cyclic wetting and drying and salts that may form on the corroding specimen surface. The humid-air and aqueous general corrosion models are consistent in that the predicted humid-air general corrosion rates at relative humidities between 85 and 100% RH are close to the predicted aqueous general corrosion rates. Using the expected values of the model parameters, the model predicts that aqueous pitting corrosion is the most likely failure mode for the carbon steel outer barrier, and an earliest failure (or initial pit penetration) of the 100-mm thick barrier may occur as early as about 500 years if it is exposed continuously to an aqueous condition at between 60 and 70°C.
Stochastic Simulation of Pitting Degradation of Multi-Barrier Waste Container in the Potential Repository at Yucca Mountain
Authors: Lee J. H. , Atkins J. E. , Andrews R. W.
Published: April 2011

A detailed stochastic waste package degradation simulation model was developed incorporating the humid-air and aqueous general and pitting corrosion models for the carbon steel corrosion-allowance outer barrier and aqueous pitting corrosion model for the Alloy 825 corrosion-resistant inner barrier. The uncertainties in the individual corrosion models were also incorporated to capture the variability in the corrosion degradation among waste packages and among pits in the same waste package. Within the scope of assumptions employed in the simulations, the corrosion modes considered, and the near-field conditions from the drift-scale thermohydrologic model, the results of the waste package performance analyses show that the current waste package design appears to meet the ‘controlled design assumption’ requirement of waste package performance, which is currently defined as having less than 1% of waste packages breached at 1,000 years [1]. It was shown that, except for the waste packages that fail early, pitting corrosion of the corrosion-resistant inner barrier has a greater control on the failure of waste packages and their subsequent degradation than the outer barrier. Further improvement and substantiation of the inner barrier pitting model (currently based on an elicitation) is necessary in future waste package performance simulation model.
A Phenomenological Approach to Simulating the Evolution of Radioactive-Waste Container Damage Due to Pitting Corrosion
Authors: Henshall G. A.
Published: April 2011

The damage to high-level radioactive-waste containers by pitting corrosion is an important design and performance assessment consideration. It is desirable to calculate the evolution of the pit depth distribution, not just the time required for initial penetration of the containers, so that the area available for release of radionuclides through the container can be estimated. A phenomenological approach for computing the time evolution of these distributions is presented which combines elements of the deterministic and stochastic aspects of pit growth. The consistency of this approach with the mechanisms believed to control the evolution of the pit depth distribution is discussed. Qualitative comparisons of preliminary model predictions with a variety of experimental data from the literature are shown to be generally favorable. The sensitivity of the simulated distributions to changes in the input parameters is discussed. Finally, the results of the current model are compared to those of existing approaches based on extremevalue statistics, particularly regarding the extrapolation of laboratory data to large exposed surface areas.
Microautoradiography in Studies of Pu(V) Sorption by Trace and Fracture Minerals in Tuff
Authors: Vaniman D. , Furlano A. , Chipera S. , Thompson J. , Triay I.
Published: April 2011

Microautoradiography was used to evaluate the mineralogic basis of Pu(V) retention by tuffs from Yucca Mountain, Nevada. Altered orthopyroxenes and oxide minerals are associated with high Pu retention, but are limited to specific stratigraphic horizons. A weaker but more general association of Pu with smectite occurs in most samples. Thinsections that cross fractures allow comparative studies of Pu retention by fracturelining versus matrix minerals. Using Ag metal in emulsions as a measure of underlying Pu concentration, electron-microprobe (EMP) analysis can quantify Pu retention along fracture walls and provide mineral/mineral Pu retention factors. For smectite-lined microfractures in zeolitized tuff, the smectite/clinoptilolite Pu retention factor is <80.
Localized Dryout: an Approach for Managing the Thermal-Hydrological Effects of Decay Heat at Yucca Mountain
Authors: Buscheck Thomas A. , Nitao John J. , Ramspot Lawrence D.
Published: April 2011

For a nuclear waste repository in the unsaturated zone at Yucca Mountain, there are two thermal loading approaches to using decay heat constructively-that is, to substantially reduce relative humidity and liquid flow near waste packages for a considerable time, and thereby limit waste package degradation and radionuclide dissolution and release. “Extended dryout” achieves these effects with a thermal load high enough to generate large-scale (coalesced) rock dryout. “Localized dryout”(which uses wide drift spacing and a thermal load too low for coalesced dryout) achieves them by maintaining a large temperature difference between the waste package and drift wail; this is done with close waste package spacing (generating a high line-heat load) and/or low-thermal-conductivity backfill in the drift. Backfill can greatly reduce relative humidity on the waste package in both the localized and extended dryout approaches. Besides using decay heat constructively, localized dryout reduces the possibility that far-field temperature rise and condensate buildup above the drifts might adversely affect waste isolation.
First-Passage-Time Modeling of Transport in Fractured Rock
Authors: Becker M. W.
Published: April 2011

This paper presents theory intended for the design and interpretation of tracer tests in fractured rock. The objective is to provide an understanding of experiments in which particulate and solute tracers are injected simultaneously. In such experiments, it is expected that the solute tracer will diffuse into the rock matrix, while the particulates will be confined to the fractures. The theory allows information about matrix diffusion to be extracted from the breakthrough curve. Furthermore, it can accommodate tests in which a non-ideal source is used, and where some of the withdrawn fluid is re-injected. The solution is performed in Laplace space and transformed to the time domain using a commercial spreadsheet.
Low-Impact Sampling Under an Active Solid Low-Level Radioactive Waste Disposal Unit Using Horizontal Drilling Technology
Authors: Puglisi C. V. , Vold E. L.
Published: April 2011

The purpose of this project was to determine the performance of a 5.5 year old active solid low-level radioactive waste disposal unit (Pit 37) located on a mesa top at Los Alamos National Laboratory (LANL), Los Alamos, NM, and to provide in-situ (vadose zone) site characterization information to Technical Area 54, Material Disposal Area (MDA) G's Performance Assessment. The vadose zone beneath Pit 37 was accessed by utilizing low-impact, air-rotary horizontal drilling technology. Core was sampled at approximately 5-foot intervals via wire-line core method in 3 horizontal holes fanning out below Pit 37. Samples were screened and prepared in-field following LANL Environmental Restoration Project guidelines. Samples were transferred from the field to the Mobile Radiation Analysis Laboratory for initial radiological screening. Following screening, samples were delivered to an analytical lab for analyses including moisture content, 23 inorganic compounds, 60 volatile organic compounds, 68 semivolatile organic compounds, tritium, lead 210, radium 226 's Pit 37 is performing well and no significant liquid phase migration of contaminants has occurred.
Deformation Mechanism of Basic Rock During Long-Term Compression: Area of Hlw Repository Design, Chelyabinsk District, Russia
Authors: Petrov V. A. , Zviagintsev L. I. , Poluektov V. V.
Published: April 2011

A combination of ultrasound, mechanical and petrographic results for long-term experimental compression of greenschist facies porphyritic andesite tuffs indicate a deformation mechanism that depends upon the mineral composition, textural-structural features of the rocks and the orientation of compression relative to the rock textures. Three dry samples of rock were investigated. Coaxial compression of a massive sample for 816 hours and a foliated sample for 1176 hours (pressure orthogonal to foliation) is characterized by solidification when the rocks are temporarily metastable. Compressive strength of the first sample is 850 kg/cm2 and of the second one, 800 kg/cm2. Experimentally, the rock behavior changes from a plastic to a brittle regime of deformation. In contrast, compression of the foliated sample parallel to foliation causes disintegration along the foliation within 480 hours without solidification. The rock is liable to brittle deformation and its compressive strength is 500 kg/cm2. These results may have implications for characterization of near-field processes in connection with numerous subhorizontal zones of schistosity within the strata that are targeted for underground disposal of high-level wastes (HLW) in the Mayak radiochemical complex area.
Mechanism of Saleeite Formation at the Koongarra Secondary Ore Deposit
Authors: Murakami Takashi , Isobe Hiroshi , Ohnuki Toshihiko , Sato Tsutomu , Yanase Nobuyuki , Kiyoshige Junko
Published: April 2011

Rock samples in the secondary ore deposit at Koongarra, Australia, were examined mineralogically to clarify the formation mechanism of saléeite (Mg(UO2)2(PO4)2.10H2O), a major secondary uranium mineral in the secondary ore deposit. Sklodowskite (MgSi2U2O11.7H2O) veinlets, present upstream of the ore deposit, are partially replaced by saléeite. Most grains of apatite (Ca5(P04)3F), an accessory mineral of the host rock, are also replaced by saléeite. Thermodynamic calculations by EQ3NR showed that the present Koongarra ground waters are undersaturated with respect to saléeite and also suggested that saléeite can be precipitated under the condition of higher U or P concentrations. Such conditions can be created at the reaction interfaces of dissolving sklodowskite, which releases U, or dissolving apatite, which releases P. The present study indicates that saléeite is formed by local microscale saturation upstream of the secondary ore deposit, which is different from the formation mechanism of saléeite downstream of the ore deposit, where saléeite microcrystals of 1 – 20 nm in size form by catalysis on iron minerals, the weathering products of the host rock.
Trace Element Distribution Patterns in Magnetically Separated Fractions of Fracture Filling Material
Authors: Cui D. , Eriksen T. E.
Published: April 2011

The distribution patterns of trace elements in magnetically separated fractions of a granite fracture filling material have been studied using instrumental neutron activation analysis. The distribution patterns of trace elements with similar ionic radii and the same charge, Fe-Co, Rb-Cs, Hf-Zr, U-Th, and light REE, were found to be similar. Whereas most of the elements are found in higher concentrations in the more clay rich fractions, Rb and Cs display a more homogeneous distribution.
Optical Degradation of Poly(P-PHENYLENE VINYLENE)
Authors: So S. K. , Chan M. H. , Hon C. S. , Leung Louis M.
Published: April 2011

The influence of laser irradiation on an electroluminescent polymer, poly(2,5-di-n-hexyloxy-l,4- phenylene vinylene) is studied. Photoluminescence, infrared spectroscopy, and photothermal deflection spectroscopy were used to identify changes in the optical properties of the polymer after laser irradiation. It is found that optical irradiation leads to the opening of the vinyl double bond and decrease in conjugation length. Photo-oxidation of the polymer is believed to be responsible for the optical degradation of the polymer.
New Developments in Thermally and Chemically Stable Nonlinear Optical Chromophores for E-O Device Applications
Authors: Rao Varanasi Pushkara , Jen Alex K-Y. , Drost Kevin J. , Cai Y. M.
Published: April 2011

A new class of second order nonlinear optical chromophores resulted from the replacement of the most reactive CN group in tricyanovinylthiophene derivatives with aryl units, have been designed and synthesized. It was shown that these chromophores provide excellent tradeoffs among many relevant properties such as molecular nonlinearity, linear absorption at 830 nm, inherent thermal stability, chemical stability in processing solvents as well as host polymer matrices at high temperatures and attenuation at 830 nm.
Materials Engineering For Polarized Light Emitting Diodes
Authors: Wegner G. , Neher D. , Remmers M. , Cimrova V. , Schulze M.
Published: April 2011

Electroluminescent 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

The 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

We 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

We 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

Manganese 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

We 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

Described 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

We 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

A 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

We 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

CW 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

We 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

We 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

Polyaniline 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

Self-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

We 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

Polypyrrole 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

We 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

The 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

Selectively 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

A 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

Electroluminescent 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

For 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.
Preparation and Properties of ferroelectric Bi2SrTa2O9 thin films for FeRAM using Flash-MOCVD
Authors: Ami T. , Hironaka K. , Isobel C. , Nagel N. , Sugiyama M. , Ikeda Y. , Watanabe K. , Machida A. , Miura K. , Tanaka M.
Published: April 2011

Ferroelectric Bi2 SrTa2 O9 thin films were successfully prepared by liquid delivery MOCVD, and structural and electrical properties were investigated. As-deposited films showed sharp distinct peaks, which were indexed assuming a fluorite-type structure. These precursors were transformed to bismuth-layered structures by annealing at 800 °C in flowing oxygen. Reasonable ferroelectric properties were observed in a film with 170 nm-thickness. Remanent polarization and coercive field were estimated to be 5.2 μC/cm2 and 52 kV/cm, respectively, at 5V.
The Microstructure of SrBi2Ta2O9 Films
Authors: Gutleben C.D. , Ikeda Y. , Isobe C. , Machida A. , Ami T. , Hironaka K. , Morita E.
Published: April 2011

We present the results of an investigation of the microstructural properties of layered-structure perovskite SrBi2Ta2O9 films grown by Flash-MOCVD, conventional CVD, and MOD. The films grown by Flash-MOCVD on Pt electrode layers, were polycrystalline and showed acceptable ferroelectric properties and low leakage. TEM showed that the individual crystallites were of high quality and, on average about 300nm in diameter. TEM also gave some indications of a disordered phase interspersed amongst the crystallites.

A complete, high-resolution set of XPS spectra gathered from these films confirmed that the basic perovskite structures were predominately single phased but that they were, in all cases, accompanied by a significant amount of mobil clusters of Bi metal. We speculate that this Bi metal corresponds to the disordered phase seen by TEM and show that appropriate ozone annealing is able to remove all evidence of it.
High Temperature X-Ray Diffraction Study of PbTio3 Thin Films Grown on Mgo(001) by MOCVD
Authors: Batzer R.S. , Yen Biming , Liu Donhang , Kubo H. , Bai G.R. , Chen Haydn
Published: April 2011

Lead titanate (PT) is ferroelectric in its tetragonal phase (c/a=1.06). The domain formation is coupled to the relaxation of internal stress generated by a combination of lattice mismatch, transformation strain and differential thermal stress. The mechanism of domain formation in an epitaxially grown PT film is related to the substrate type and the growth temperature. In this study, PT films have been deposited on MgO(001) in a coldwall, horizontal metal organic chemical vapor deposition (MOCVD) system. The structure of domains and their evolution have been measured as a function of temperature by the x-ray diffraction method using a hot stage. Domain structure changes were observed by θ−2θ scans, ω scans, as well as in-plane φ scans. Effect of film stress on the ferroelectric transition temperature is discussed. Reproducibility of domain formation as a result of temperature cycling both below and above Tc is assessed.
Chemical Vapor Deposition of Oxides From Alkoxides
Authors: Xu R.
Published: April 2011

MOCVD of oxides can be achieved through deposition reaction schemes such as oxidation, thermal pyrolysis, plasma assisted pyrolysis, radiation-assisted pyrolysis or any combinations of these free-radical processes. Chemically mild and clean reaction schemes such as the hydrolysis-polycondensation and the hydrolysis-assisted pyrolysis reactions are found favorable for stoichiometric depositions using alkoxide complex precursors. We review the various reaction schemes and try to point out comparatively the advantages and disadvantages of each. Experiments in the deposition of lithium tantalate from alkoxide complex precursors are presented. Low deposition temperature, high deposition rate and autostoichiometry capabilities are demonstrated in the experiments.