bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of Redox Condition on Waste Glass Corrosion in the Presence of Magnetite
Authors: Ylnagaki  , Ogata A. , Furuya H. , Idemitsu K. , Banba T. , Maeda T.
Published: April 2011

Static corrosion tests of a powdered simulated waste glass were performed in the presence of magnetite under oxic and anoxic conditions, respectively. The corrosion tests under oxic conditions were performed in air, and those under anoxic conditions were performed in a glove box purged with mixed gas(Ar+5%H2). The experimental results showed that the presence of magnetite can enhance glass corrosion under both oxic and anoxic conditions, and the enhancement under anoxic conditions was small compared to that under oxic conditions. A large portion of the Si and insoluble elements were sorbed onto the magnetite surface, and the sorption under anoxic conditions was small compared to that under oxic conditions.

It was suggested that the enhancement of glass corrosion by magnetite results from the sorption or precipitation of silica on the magnetite surface, which can be greatly affected by redox condition. Under anoxic conditions, it was suggested that precipitation of amorphous silica on the magnetite surface may be the dominant process for enhancement of glass corrosion in addition to sorption.
The Indefinite Containment of Nuclear Fuel Wastes
Authors: Shoesmith D. W. , King F. , Ikeda B. M.
Published: April 2011

The safe disposal of used fuel or vitrified reprocessed waste could be guaranteed if the containers remained intact indefinitely (> 106 a). Justification of indefinite containment may be possible if two criteria are met; (i) a sound mechanistic understanding of the corrosion and mechanical behaviour of the container material is available, and (ii) the disposal environment and its evolution with time can be confidently predicted. In disposal vaults in which the environmental conditions evolve from a short aggressive period to a long-term benign period, long container lifetimes are achievable. This approach is illustrated by discussing the possibility of indefinite containment of used fuel in a Canadian disposal vault using Ti alloys or Cu.
Spectroscopy of Plutonium-Organic Complexes
Authors: Richmann M. K. , Reed D. T.
Published: April 2011

Information on the spectroscopy of plutonium-organic complexes is needed to help establish the speciation of these complexes under environmentally relevant conditions. Laser photoacoustic spectroscopy (LPAS) and absorption spectrometry were used to characterize the Pu(IV)-citrate and Pu(IV)-nitrilotriacetic acid (NTA) complexes at concentrations of 1−3 – 10−7 M in aqueous solution. Good agreement was observed between the band shape of the LPAS and absorption spectra for the Pu(IV)-NTA complex. Agreement for the Pu(IV)-citrate complex was not quite as good. In both cases, a linear dependence of the LPAS signal on laser power and total concentration of the complexes was noted. This work is part of an ongoing research effort to study key subsurface interactions of plutonium-organic complexes.
Effect of Swelling Pressure on Local Volume Change in Unsaturated Sand-Bentonite Buffer Material
Authors: I Shooshpasha , A.M.O Mohamed , Yong R. N.
Published: April 2011

This study was designed to investigate the effect of swelling pressure on local volume changes in unsaturated sand-bentonite based buffer material. A laboratory mixture of sodium bentonite and graded silica sand in equal proportion by dry weight was used in both ambient and elevated temperatures experiments. At high water content locations within the tested specimens, the density was reduced by 3.57% from its initial values due to swelling. The swelling pressure as a function of distance was calculated by 4 different models. The calculated results have indicated that the density distribution within the specimen is affected by swelling potential distribution. The calculated swelling pressure values vary as a function of water content, reaching 1 MPa at the source of water intake, i.e., at high water content zone, and 2 MPa at the heater side, i.e., at low water content zone.
Diffusion of Uranium in Compacted Bentonites in the Reducing Condition with Corrosion Products of Iron
Authors: Idemitsu Kazuya , Tachi Y. , Furuya H. , Inagaki Y. , Arima T.
Published: April 2011

In high-level waste repository, a carbon steel overpack will be corroded after closure. This will create a reducing environment in the vicinity of the repository. Reducing conditions are expected to retard the migration of redox-sensitive radionuclides such as uranium.

The apparent diffusion coefficients of uranium were measured in compacted bentonites (Kunigel VI® and Kunipia F®, JAPAN) in contact with carbon steel and its corrosion products under reducing conditions or without carbon steel under oxidizing conditions for comparison. The apparent diffusion coefficients measured were 10-12 to 10-14 m2/s under oxidizing conditions and 10-13 to 10-14 m2/s under reducing conditions. There were significant effects of redox conditions, dry density (0.8 to 2.0 g/cm3) and montmorillonite contents (60% for Kunigel VI or 100% for Kunipia F) on the apparent diffusion coefficients. The sorption of uranium on corrosion products of iron was smaller than that on montmorillonite. Montmorillonite density could be a good index to explain density dependence of the diffusion coefficients under the reducing conditions. Uranium would diffuse in free pore water with diffusion coefficients greater than 10-13 m2/s in low density bentonites under both redox conditions because the diffusion coefficients depended on sorption coefficients. Since diffusion coefficients were independent of sorption coefficients in high density bentonites where free pore water is scarce, surface diffusion might occur with coefficients were of about 10-13 m2/s.
Theoretical Relationships Between Reactivity and Permeability for Monomineralic Porous Media
Authors: Smith Robert W. , Schafer Annette L. , Tompson Andrew F. B.
Published: April 2011

The release of contaminants to the subsurface has lead to potential or actual contamination of groundwater resources. The remediation of these plumes requires improved capability for the prediction of contaminant fate and transport. Key to improving predictive capabilities is an increased understanding of natural chemical (or reactive) heterogeneity in subsurface media and how chemical and physical heterogeneity are related. Although the effects of physical heterogeneity on transport has received significant attention, similar investigations of chemical heterogeneity, and the correlation of chemical and physical heterogeneity are in their infancy.

Theoretical considerations for unconsolidated porous media composed of sand-sized grains of a single reactive phase suggest that chemical reactivity and permeability are inversely related. This correlation is consistent with measured permeability, porosity, and surface area data for unconsolidated sands. The correlation arises because both reactivity and permeability are functions of the surface area of the porous media. This relationship suggests that for a heterogeneous porous media, significant contaminant transport will occur in zones of minimal reactivity.
Improved Radionuclide Transport Models for a Nuclear Waste Repository
Authors: Codell Richard B.
Published: April 2011

NRC is developing improved models for transport of chain decay radionuclides in porous and fractured/porous media using finite-difference for spatial discretization, and numerical inversion of Laplace transforms for time. This hybrid technique allows great flexibility for spatial variability, flow rate changes and boundary conditions that are difficult with analytical solutions, and are much faster than solutions fully in the time domain. This paper presents the status of NRC's development of a method for transport through fractured porous media at the proposed Yucca Mountain repository, building on the work of a number of authors.
Predicted Behavior of Technetium in a Geological Disposal Vault For Used Nuclear Fuel - Ramifications of a Recent Determination of the Enthalpy of Formation of TcO2(cr)
Authors: Lemire R. J. , Jobe D. J.
Published: April 2011

Recently, we reported a value of ΔH°(TcO2(cr)) = -(458 ± 6) kJ·mol-1based on heat of solution measurements. The implications of this value on the database used in the Canadian Nuclear Fuel Waste Management Program for the evaluation of the technetium released by congruent dissolution of used UO2fuel have now been assessed.

It is probable that the Tc(IV) oxides are more stable than previously predicted and, hence, they are less likely to be oxidized to TcO4(aq) under moderately reducing conditions. We have revised earlier calculations done to predict the solution concentrations of technetium species in a vault as a function of the oxidation conditions in model groundwaters.
Bulk Self-Assembled Films for Photonics
Authors: Tripathy S. K. , Kim D. Y. , Kim W. H. , Kumar J.
Published: April 2011

Recently we have reported, significant second harmonic generation from spin coated and bulk films of a soluble polydiacetylene (PDA), namely poly{8-[[[butoxy carbonyl] methyl]urethanyl]-1-(5-pyrimidyl)-octa-l,3,-diyne}} (BPOD) without recourse to poling. Poly(BPOD) is an asymmetrically substituted PDA in which a polarizable heteroaromatic pyrimidyl group is attached as one of the side groups. In addition to reviewing the earlier results, we report a series of new soluble PDAs of the same class with further functionalization, elaborating on the already defined design principle.

A second class of polymers with azo dye based NLO chromophores incorporated into the structure has been processed optically to fabricate holographic elements. Trans-cis-trans isomerization driven reorientation and macromolecular motion leads to the formation of surface relief gratings upon exposure to an interference pattern. Fabrication of optical elements based on these polymers will be elaborated.
The Synthesis And Optoelectronic Properties Of Oxadiazole-Based Polymers
Authors: Li X.-C. , Kraft A. , Cervini R. , Spencer G. C. W. , Cacialli F. , Friend R. H. , Gruener J. , Holmes A. B. , Mello J. C. De , Moratti S. C.
Published: April 2011

New oxadiazole-based polymeric materials have been synthesized either as side chain copolymers with polymethacrylate or as main chain copolymers carrying solubilizing elements such as hexafluoropropylidene or meta-linked aromatic spacer units. Many of these materials exhibit blue luminescence in the solid state. The materials have been evaluated by photoluminescence and cyclic voltammetry studies, and as the electron transporting layer in a two-layer electroluminescent device with poly(p-phenylenevinylene) (PPV) as the emissive layer. The major conclusion is that these materials function by providing large heterojunction offsets at the Highest Occupied Molecular Orbital (HOMO) which block the passage of holes through the device.
Synthesis And Characterization Of 1,3-Bis(Dicyanomethylene)Indane (Bdmi) Derived Second Order Nlo Materials
Authors: Sunt Sam-Shajing , Harpert Aaron W. , Zhangt Cheng , Daltont Larry R. , Garner Sean M. , Chen Antao , Yacoubian Araz , Steier William H.
Published: April 2011

Difunctionalized aminophenylenethienylidene-1,3-bisdicyanomethyleneindane (BDMI) derived second order push-pull chromophores and polymers have been synthesized and characterized. Preliminary studies of doped polymeric composite thin films reveal large SHG signals as well as good chemical and thermal stabilities under poling conditions.
Photo-Induced Surface Alignment Of Nematic Liquid Crystals On Polyamide-Imide Layers
Authors: Rich David C. , Sichel Enid K. , Cebet Peggy
Published: April 2011

A technique for producing surface-induced liquid crystal nematic alignment is presented. The alignment film is a simple, inexpensive polyamide-imide, which is treated with linearly polarized short wavelength ultraviolet radiation (λ = 254 nm). The alignment performance of UV-aligned layers is shown by optical transmission of the liquid crystal cells to be comparable to that of brushed layers. Strong alignment is produced within minutes of UV exposure and is maintained with long exposures.
Demonstration Set-Up for Fast Switchable Diffraction of Laser Light Using the Computer Controlled Diffraction Grating Based on Ferroelectric Liquid Crystal
Authors: Beresnev L. A. , Hossfeld J. , Dultz W. , Onokhov A. P. , Haase W.
Published: April 2011

Switchable diffraction grating with 80 “idependently drived transparent stripe electrodes with spatial resolution 40 l/mm based on ferroelectric liquid crystal is presented. The switching of the diffraction angle till frequency 1kHz is demonstrated using the computer choise of assemblies of electrodes.
Growth of Organic Periodic Structures by Molecular Layer Deposition
Authors: Dietrich T. , Schlesser R. , Sitar Z. , Günter P.
Published: April 2011

Thin films of organic nonlinear optical materials have become of increasing interest for potential electro-optic and nonlinear optical applications. Organic molecular layer deposition (OMLD) consists of an alternating evaporation of suitable difunctional monomers under UHV conditions and allows self-terminating monolayer growth and in-situ polymerization of periodic structures. Film stability is increased due to chemical bonding between the alternating layers. Moreover, in contrast to epitaxial growth techniques, the choice of interesting inorganic substrates is not limited by lattice-matching conditions. We have investigated the xperimental requirements for OMLD in detail, with pyromellitic acid dianhydride (PAD), terephthalic acid dichloride (TOC), and 4,4′-diamino-diphenylether (DDE) as prototype precursors. After optimization of material fluxes and growth temperatures, covalently bonded monolayers were formed via a self-terminating surface reaction while excessive material was desorbed.
Contact Dependence of α-Sexithienyl Thin Film Transistor Characteristics
Authors: Lin Y. Y. , Gundlach D. J. , Jackson T. N.
Published: April 2011

We have fabricated thin film transistors (TFTs) using ca-sexithienyl (α-6T) as the active material and have investigated the dependence of transistor characteristics on the choice of source/drain contact metal. Using α-6T synthesized from terthiophene and purified by vacuum gradient sublimation, we have fabricated TFTs with material deposited by evaporation onto substrates held at both room and elevated temperature. We have studied devices fabricated by depositing the active material onto previously patterned source/drain contacts and also by depositing the source/drain contacts after the active layer deposition, in both cases with the gate contact and dielectric underneath the active material. For both device types we find a clear dependence on the choice of source/drain contact metal with correlation to the metal work function. For our devices the best performance is obtained using metals with largest work function (Pd, Pt, or Au), intermediate performance is obtained using a metal with somewhat smaller work function (Cr), and significantly degraded performance is obtained using a metal with relatively small work function (Al). Despite the apparent correlation to the metal work function, we cannot yet rule out oxidation or other chemical effects with the more reactive metals. We have also examined doping of the α-6T layer as a possible route to improved contacts and find that FeCI3 can be used to shift the threshold voltage of α-6T TFTs by more than 50 V.
Low Temiperature Band Transport in Alpha-Hexathienylene Thinfilm-Transistors
Authors: Torsi L. , Dodabalapur A. , Rothberg L. J. , Fung A. W. P. , Katz H. E.
Published: April 2011

We provide experimental evidence of a transition from thermally activated hopping of small polarons to band transport of delocalized polarons in polycrystalline oligothiophene fieldeffect transistors. We demonstrate that these transport mechanisms are intrinsic, i.e. governed by material-specific parameters such as the electronic overlap integral and the polaron binding energy. At high temperatures the field-effect mobility decreases with decreasing temperature and the transport mechanism is thermally activated hopping. Below a critical temperature Tτ, the field-effect mobility abruptly increases by more than two orders of magnitude and the transport becomes band-like. This behavior is consistent with the theory T. Holstein developed in 1959 for small polaron transport.
Bioactive Polypyrrole Thin Films with Conductimetric Response to Analyte
Authors: Guiseppi-Elie A. , Tour J. M. , Allarat D. L. , Sheppard N. F.
Published: April 2011

Thin films of electroconductive poly[pyrrole-co-3−(1−pyrrolyl)propionic acid] were prepared by electropolymerization onto 3-aminopropyltrimethoxysilane modified and 3−(1−pyrrolyl)propionic acid derivatized interdigitated microsensor electrode (IME) arrays. The ω−(1−pyrrolyl) moiety on the surface of the device provides for specific adhesion of the polymer film to the device and the (N-pyrrolyl)propionic acid moiety on the polymer backbone provides for covalent attachment of bioactive molecules, such as biotin and urease, to the polymer surface. The immobilized, bioactive urease produces an ON/OFF conductimetric response traceable to analyte concentration.
Poly(3′,4′-Dibutyl-α-Terthiophene-Phenylene-Vinylene), and Poly(3′,4′-Dibutyla-α-Terthiophene-Phenylene-Imine): Synthesis and Properties of Two New Isoelectronic Soluble Conjugated Polymers.
Authors: Wang Chenggang , Xie Xusheng , LeGoff Eugene , Kanatzidis Mercouri G.
Published: April 2011

A new soluble and dopable copolymer consisting of 3‘,4‘-dibutyl-2,2‘:5‘,2”-terthiophene and phenylene vinylene units has been designed and prepared via a Wittig reaction. This copolymer is soluble in common organic solvents such as THF and CHC13, and can be doped with various oxidants increasing its electrical conductivity by several orders of magnitude. Its films are electrochromic and turn reversibly and rapidly from red to green-blue upon doping and undoping electrochemically. If the phenylene vinylene units are replaced with phenylene imine units, another interesting new polymer forms which is not readily dopable with the same oxidants but is dopable with acids. The new material exhibits strong chemochromism with dramatic shifts in its optical absorption spectra. In the undoped state both copolymers show strong photoluminescence.
Strategies for Conducting Polymer Solutions: Solvato-Controlled Oxidative Doping Using Metal Cations
Authors: Lebedev M. , Holdcroft S.
Published: April 2011

Solutions of Ag(I) and poly(3-alkylthiophenes), which usually precipitate immediately upon contact, are stabilized with Ag(l)-coordinating ligands. Casting of polymer-Ag(I)-ligand solutions followed by evaporation of the ligand yields an electronically conducting polymer film. It is postulated that Ag(I) either undergoes nucleophillic addition to poly(3-alkylthiophenes), in a manner similar to which polythiophenes are protonated by acids, or forms a charge transfer complex with the polymer. The “doped” polymer exhibits enhanced stability over films oxidized using conventional oxidants. Ag(I)-doping of poly(3-alkylthiophenes) represents a new strategy for doping conjugated systems.
Degradation Studies Of Polypyrrole Coated Fibers For Microwave And Millimeterwave Obscurants
Authors: Buckley Leonard. J. , Eashoo Mark
Published: April 2011

Microwave and millimeterwave obscurants based on typical millimeterwave materials do not environmentally degrade with respect to their physical and electrical properties. The use of conductive polymer coated films and fibers with inherent environmental instabilities are being investigated as possible alternatives. Achieving the optimum electrical performance is highly dependent upon the polymer/dopant combination, deposition conditions, morphology, and volume of the coating that is used. Several conductive polymer coated fiber systems were investigated via thermal analysis. The effects of processing conditions on performance and stability were studied.
Femtosecond Optical Dynamics In A Poly(Para-Phenylene)-Type Ladderpolymer
Authors: Graupner W. , Petritsch K. , Leising G. , Lanzani G. , Nisoli M. , De Silvestri S. , Scherf U.
Published: April 2011

Time-resolved femtosecond pump and probe experiments were conducted on films and solutions of poly (para-phenylene)-type ladder-homopolymers featuring a high degree of intrachain order. We find photobleaching, stimulated emission and photoinduced absorption. The spectral separation of stimulated emission and photoinduced absorption makes this polymer a promising candidate for a solid state laser.
Positron Lifetime Studies of Polyaniline Conducting Polymers
Authors: Huang C. M. , Liu J. , Sandreczki T. C. , Jean Y. C.
Published: April 2011

Positron annihilation lifetime measurements are made in a series of polyaniline polymers with different chemical compositions and protonation ratios at room temperature. Two positron lifetimes are observed in these materials: one is assigned to annihilation in the bulk and the other to voids created due to protonation. A relationship between conductivities and positron annihilation probabilities is found.
Raman spectra of charge transfer organic compounds: Conductors And Semiconductors
Authors: Gómez R. , Ridaura R. , Quintana M. , Marquina M. L. , Marquina V. , Jiménez M. , Aburto S. , Gómez-Lara J. , González-Rolón B.
Published: April 2011

A series of coordination compounds -macrocycle tetraaza derivatives with extended electronic conjugations- as molecular solids have been synthesized and analyzed by Raman spectroscopy. Their resistivity vs. temperature characteristics, measured in thin films, show three types of behavior: metallic, semiconductor and, in some cases, semiconductor with a transition to metallic below certain temperature. Room temperature Raman spectra were obtained in a FT-IR spectrometer and some stretching modes show different Raman shifts depending on the reactants. We relate these shifts with the degree of charge transfer between donor and acceptor radicals.
Characterization Of Heattreated Polyparaphenylene-Based Carbons
Authors: Matthewsa M. J. , Endo M. , Takahashi T. , Nishimura Y. , Takamuku T. , Dresselhaus M. S.
Published: April 2011

Raman spectroscopy and TEM measurements were recently performed on a series of polyparaphenylene (PPP)-based carbon samples which were heat-treated to temperatures between 600°C and 3000°C. Particular attention is focused on the development of carbonaceous structures at low heat-treatment temperatures (THT) in the range 600°C ≤ THT ≥ 800°C. PPP-based carbons heat treated in this temperature range have been found to have a very high affinity for the electrochemical introduction of lithium, which is of particular interest in ‘rocking-chair’ rechargeable Li batteries. Specific (Faradaic) capacities of up to 1120 mAh/g have been obtained for PPPbased carbon anodes with a THT of 700°C, which is about three times the capacity of GIC-based anode materials. At a heat-treatment temperature of 700° C, the PPPbased carbon has a disordered-granular appearance, as observed from TEM, while a ribbon-like graphitic structure is seen for heat treatment near 3000°C. Furthermore, Raman spectra show that, near a THT of 700° C, these PPP-based materials undergo a carbonization transformation from a mostly polymer-type extended lattice to a disordered carbon matrix, which undergoes partial graphitization at higher THT. Upon the introduction of small amounts of substitutionally-doped Boron (1% - 3% atomic), various properties are substantially modified. In this work we briefly discuss the effect of B-doping on the PPP-based carbon structure.
Erbium Tris(Amide) Compounds as Source Molecules FOR Rare Earth Doping of Semiconducting Materials
Authors: Just Oliver , Greenwald Anton C. , Rees William S.
Published: April 2011

The homoleptic compound erbium{tris[bis (trimethylsilyl)]amide} displays high doping ability for incorporation of the rare earth element into epitaxially grown semiconducting host materials for fabrication of temperature-independent, monochromatic solid state optoelectronic devices. Electronic characteristics derived from erbium doped semiconducting films have been obtained. Several more volatile and lower melting representatives of this class of compounds have been synthesized, characterized by various analytical techniques and examined for their suitability to incorporate optically-active erbium centers into a semiconducting environment.
Liquid Delivery MOCVD of Ferroelectric PZT
Authors: Roeder J. F. , Vaartstra B. A. , Buskirk P. C. Van , Beratan H. R.
Published: April 2011

Ferroelectric PbZrxTi1-x O3 (PZT) films have been deposited by chemical vapor deposition using flash vaporized metalorganic precursors. Crystalline perovskite films approximately 3000Å thick were deposited on Pt/Si substrates at 550–590°C and had dielectric coefficients in the range of 600–1900. Dielectric constant was found to increase with increasing Zr/Ti ratio, rising to the largest values near the morphotropic phase boundary. Remanent polarizations of the PZT were between 20–27 μC/cm2 and the coercive field decreased with increasing Zr/Ti ratio from 43 to 21 kV/cm. Pyroelectric coefficients were measured using the Byer-Roundy technique and ranged from 20–30 nC/cm2K. At 550°C, a direct relationship was observed between precursor composition and film composition. At 590°C, volatility of PbO became appreciable and composition of films with Zr/(Zr+Ti) = 0.3 remained near stoichiometry over a wide range of excess Pb in the precursor. However, this effect was found to diminish for higher ratios of Zr/Ti. The orientation of the PZT films deposited over a range of precursor compositions was similar with some [100] preferred orientation. In contrast, the orientation of a PbTiO3 films could be manipulated by the Pb/Ti ratio in the precursor, with [111] preferred orientations predominating at lower Pb/Ti and [ 100/001]–[111] mixed orientations at higher Pb/Ti ratios.
MOCVD OF SrS and SrS:Ce Thin Films for Eelctroluminescent Flat Panel displays
Authors: Samuels John A. , Smith David C. , Siebein Kerry N. , Salazar Kenny , Tuenge Richard T. , Schaus Christian F. , King Christopher N. , Le H. , Hitt J. , Thuemler R. L. , Wager J. F.
Published: April 2011

High quality SrS and SrS:Ce thin films were deposited from Sr(thd)2, Ce(thd)4 and H2S via a low pressure MOCVD process. Film characteristics were found to be insensitive to the presence of the cerium dopant in the concentration range investigated. Depositions were carried out for a wide temperature range (250–550° C). Deposition rates were found to be relatively insensitive for the temperature range investigated. The films produced were found to be highly crystalline at all temperatures investigated. Deposited material showed texturing as a function of substrate material and temperature. FWHM of the <111> reflections were found to have a 2Θ values of 0.15–0.18 deg. for all temperatures. RBS and AES shows stoichiometric 1:1 SrS with less than 2% carbon and oxygen contaminates. ERD indicates the films to have 1 – 2.5% hydrogen. Films doped with 0.019 – 0.043 atom – 250 volts.
MOCVD of Very thin Films of Lead Lanthanum Titanate
Authors: Beach David B. , Vallet Catherine E.
Published: April 2011

Films of lead lanthanum titanate were deposited using metal-organic chemical vapor deposition (MOCVD) at temperatures between 500 and 550°C in a hot-wall reactor. The precursors used were Pb(THD)2, La(THD)3, and Ti(THD)2(I-OPr)2where THD = 2,2,6,6-tetramethyl-3,5-heptanedionate, O2C11H19, and I-OPr = isopropoxide, OC3H7. The three precursors were delivered to the reactor using a single solution containing all three precursors dissolved in tetraglyme and the precursor solution was volatilized at 225°C. Films were deposited on Si and Si/Ti/Pt substrates, and characterized using Rutherford Backscattering Spectroscopy (RBS) and X-ray diffraction(XRD). Films deposited at 550°C had a composition which was close to that of the precursor solution while films deposited at 500°C were deficient in lanthanum. Even at 500°C, the desired perovskite phase is readily observed by XRD. Subsequent rapid thermal processing of the film deposited at 500°C showed an increase in the intensity of the X-ray lines, but did not change the width of these lines, implying that grain sizes had remained unchanged.
Liquid Source Mocvd of High Quality Yba2Cu3O7−x Films on Polycrystalline And Amorphous Substrates
Authors: Studebaker D.B. , Doubinina G. , Zhang J. , Wang Y.Y. , Dravid V.P. , Marks T.J.
Published: April 2011

High temperature superconducting Yba2Cu3O7−x films were grown by liquid delivery metal-organic chemical vapor deposition (LDMOCVD) on silver-coated stainless steel substrates. The films are c-axis oriented, and exhibit a very low surface resistance of 110 μΩ at 77 K and 3 GHz. A two-step LDMOCVD method for growth of oriented (200) CeO2 films on amorphous substrates was also developed. Films of CeO2 for YBCO buffer layers were grown on fused silica (SiO2), polycrystalline alumina (Al2O3), and sapphire (A12O3). A highly c-axis oriented film of YBCO was grown on a fused silica substrate with a CeO2 buffer layer.
Barrier Modification In Au/IIb Semiconducting Diamond Contacts
Authors: Teklu M. , Das K.
Published: April 2011

Rectifying contacts on semiconducting type IIb diamond crystals are readily established with any conducting material system including elemental metals, highly doped semiconductors, silicides and carbides. However, for a given surface preparation using oxidizing wet chemicals and in the absence of a surface reaction, barrier heights are observed to be constant regardless of the metal work function. In this report it is demonstrated that an adjustment of the barrier height can be achieved by employing a premetallization low-dose low-energy ion-implantation step.
Esr Of Defects In Surface Conduction Layer On Cvd Diamond Films
Authors: Show Y. , Iwase M. , Izumi T.
Published: April 2011

Defects in the surface conductive layer of CVD-diamond films have been investigated by ESR method. ESR analysis revealed that defect center ( Pac-center: g=2.003, ΔΔ Hpp=8 Oe ) in the non-diamond phase carbon region exists in the surface conductive layer. The Pac-center with a spin density of the order of 1020spins/cm3 or above was formed in the surface layer by hydrogen radical irradiation during the diamond deposition. Formation of the Pac-center causes the resistivity of CVD-diamond to decrease ( from 9 × 108 Ω to 1.8 × 106 Ω )
Reaction Of Diamond Surfaces With Halogen-Containing Species
Authors: Larsson K.
Published: April 2011

An energetic and structural comparison has been made concerning adsorption processes on a diamond (111) surface from a hydrogen (H)-, halogen (X)- or H/X-carrying carbon precursors. The halogens X examined were F, Cl and Br. The quantum mechanical methods used in the investigation were the ab initio MO method as well as the LDA method. F, Cl, and H, were all shown to be able to sustain the sp3 structural configuration of the surface carbon atoms. For Br large sterical hindrances were induced and the diamond (111) surface could not be stabilized. The calculated adsorption energy of CF3 to a H-terminated diamond (111) surface was found to be numerically the largest one (489 kJ/mol on the MP2 level of theory) in comparison to the other adsorption processes studied in the present investigation. It was, in particular, much larger than the corresponding adsorption energy of CH3 (418 kJ/mol). The calculated adsorption energies do support the initial step in the growth process (adsorption) to be energetically more favourable for systems incorporating a mixture of halogen and hydrogen in the growth vapor than for corresponding systems involving unmixed halogen or hydrogen in the carbon containing precursor.
Fluoroalkyl Iodide Photodecomposition on Diamond (100) - an Efficient Route to The Fluorination of Diamond Surfaces
Authors: Smentkowski V. S. , Yates J. T.
Published: April 2011

The photodecomposition of CF3I and C4F9I overlayers at 119 K on diamond (100) surfaces has been shown to be an efficient route to fluorination of the diamond surface. X-ray photoelectron spectroscopy (XPS) has been used for photoactivation as well as for studies of the following processes: the photodecomposition of the fluoroalkyl iodide molecules: the attachment of the photofragments to the diamond surface; and the thermal decomposition of the fluoroalkyl ligands. Chemisorbed CF3groups on diamond (100) decompose by 300 K whereas C4F9groups decompose over the temperature range of 300 K to ∼ 700 K. Both of these thermal decomposition processes produce surface C-F bonds on the diamond surface which thermally decompose over a wide temperature range extending up to 1500 K. Hydrogen passivation of the diamond surface is ineffective in preventing free radical attack from the photodissociated products of the fluoroalkyl iodides. The use of photoactivation of fluoroalkyl iodides for the fluorination of diamond surfaces provides a convenient route compared to other methods involving the direct production of atomic F, molecular fluorine, XeF2, and F containing plasmas.
Electrical Properties Of Undoped Polycrystalline Diamond Thin Films On Silicon
Authors: Jauhiainen Anders , Bengtsson Stefan , Engström Olof
Published: April 2011

We have investigated the electrical properties of undoped polycrystalline diamond thin films deposited on (100)-oriented n-type and p-type silicon substrates. The films, intended for electronic applications, were manufactured using hot filament chemical vapour deposition (HFCVD). To a large extent the capacitance-voltage characteristics are influenced by traps located close to the interface between the diamond layer and the silicon substrate. These traps play an important role for voltage sharing between the diamond layer and the silicon space charge region. The DC current density through the diamond film has the same functional dependence on the electric field for films deposited on both n- and p-Si. The field dependency agrees with a Frenkel-Poole transport model. Further, although the DC current transport is thermally activated, it does not follow an Arrhenius relation. A possible reason is that traps within a broad range of energy levels are involved in the charge transport. Finally, current transients resulting from stepwise changes in the applied voltage follow a power law time dependence where the kinetics depend only weakly on temperature.
High Field Electrical Conductivity and Breakdown in Heteroepitaxial Diamond Films
Authors: Schröppel S. , Hessmer R. , Schreck M. , Stritzker B.
Published: April 2011

Nominally undoped, heteroepitaxially nucleated diamond films have been grown on Si(001). For different temperatures ranging between room temperature and 490°C the DCconductivity through the films has been measured for field strengths up to 600kV/cm. In the framework of the Poole-Frenkel theory a fit of the curves is possible for the model of isolated as well as for the model of overlapping coulombic potentials yielding an activation energy of 1.03eV.

In addition the breakdown voltage of the films has been measured as a function of the temperature. A drastic linear decrease with temperature is observed. Starting at a dielectric strength of about 1 MV/cm at room temperature the breakdown field decreases by an order of magnitude for 400°C. This observed behaviour is consistent with thermal breakdown based on Poole-Frenkel conduction in the pre-breakdown region.
Determination of Hydrogen in CVD Diamond by Notched Neutron Spectrum Technique and Ftir
Authors: Golshani F. , Miller W. H. , Prelas M. A. , Sung T. , Popovici G. , Manning G. , Loyalka S. K. , Shahedipour F. , White H. W. , Brown W. D. , Malshe A. P. , Naseem H. A.
Published: April 2011

The hydrogen content of free-standing polycrystalline CVD diamond samples was determined by Fourier Transform Infrared (FTIR) measurements and was quantified by a notched neutron spectrum technique. The latter measures the total bonded and unbonded hydrogen. The concentration of total hydrogen in these samples was of the same order of magnitude. The FTIR measurements, which are sensitive to the bonded hydrogen, indicated different hydrogen to diamond peak ratios.
A High Performance UV Photodetector from Thin Film Diamond
Authors: Mckeag Robert D. , Whitfield Michael D. , Chan Simon Sm , Pang Lisa Ys , Jackman Richard B.
Published: April 2011

Thin film diamond has been used to fabricate a photodetector which displays high sensitivity to deep UV light, with an external quantum efficiency of greater than one, a dark current of less than 0.1nA and which is near ‘blind’ to visible light.
Photoelectron Emission from the Cesiated Diamond (110) Surface
Authors: Fox C. A. , Kelly M. A. , Hagstrom S. B. , Cao R. , Vergara G. , Pianetta P. , Pan L. S. , Hsu W. L.
Published: April 2011

Cesiation of type IIB diamond (110) crystals was studied using a combination of ultraviolet photoemission spectroscopy, x-ray photoemission spectroscopy, and low energy electron diffraction. The diamond (110) crystal was hydrogen treated by exposure to a hydrogen microwave discharge. Although cesium was largely unreactive with the hydrogenated diamond surface, cesiation yielded a large enhancement in the secondary electron yield of the diamond surface and the negative electron affinity (NEA) condition. An increase in the downwards band bending of approximately 0.75-0.9 eV was inferred from the shift in the valence band edge following cesiation. In addition, (lx 1) LEED patterns were observed at all cesium coverages. Exposure of the cesiated diamond surface to molecular oxygen significantly reduced the NEA peak (relative to the secondary electron background); however, recovery of the NEA peak was observed when the molecular oxygen source was removed.
On The Optimized Nucleation of Near-Single-Crystal Cvd Diamond Film
Authors: Chen L. C. , Juan C. C. , Wu J. Y. , Chen K. H. , Teng J. W.
Published: April 2011

Near-single-crystal diamond films have been obtained in a number of laboratories recently. The optimization of nucleation density by using a bias-enhanced nucleation (BEN) method is believed to be a critical step. However, the condition of optimized nucleation has never been clearly delineated. In the present report, a novel quantitative technique was established to monitor the nucleation of diamond in-situ. Specifically, the induced current was measured as a function of nucleation time during BEN. The timedependence of induced current was studied under various methane concentrations as well as substrate temperatures. The optimized nucleation condition can be unambiguously determined from the current-time plot. Besides the in-situ current probe, ex-situ x-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) were also used to investigate the chemical and morphological evolution. Characteristic XPS and AFM features of optimized nucleation is discussed.
Solid-Phase Thermal Decomposition of 2,4-Dinitroimidazole (2,4-DNI)
Authors: Minier Leanna , Behrens Richard , Bulusu Suryanarayana
Published: April 2011

The solid-phase thermal decomposition of the insensitive energetic aromatic heterocycle 2,4- dinitroimidazole (2,4-DNI: mp 265–274°C) is studied utilizing simultaneous thermogravimetric modulated beam mass spectrometry (STMBMS) between 200° and 247°C. The pyrolysis products have been identified using perdeuterated and N-labeled isotopomers. The products consist of low molecular-weight gases and a thermally stable solid residue. The major gaseous products are NO, CO2, CO, N2, HNCO and H2O. Minor gaseous products are HCN, C2N2, NO2, C3H4N2, C3H3N3O and NH3. The elemental formula of the residue is C2HN2O and FTIR analysis suggests that it is polyurea- and polycarbamate-like in nature. The rates of formation of the gaseous products and their respective quantities have been determined for a typical isothermal decomposition experiment at 235°C. The temporal behaviors of the gas formation rates indicate that the overall decomposition is characterized by a sequence of four events; 1) an early decomposition period induced by impurities and H2O, 2) an induction period where CO2 and NO are the primary products formed at relatively constant rates, 3) an autoacceleratory period that peaks when the sample is depleted and 4) a final period in which the residue decomposes. Arrhenius parameters for the induction period are Ea = 46.9 ± 0.7 kcal/mol and Log(A) = 16.3 ± 0.3. Decomposition pathways that are consistent with the data are presented.
Kinetics and Species of Flash Pyrolysis of Cellulose Acetate Butyrate: The Binder of Lova
Authors: Gongwer P. E. , Arisawa H. , Brill T. B.
Published: April 2011

The principal binder of many LOVA propellants is cellulose acetate butyrate (CAB). By the use of T-Jump/FTIR spectroscopy, CAB was flash-pyrolyzed to set temperatures in the 465–600°C range, while rapid-scan IR spectra were used to identify the main decomposition products and to measure the rate of formation of each product as a function of temperature. Eleven specific products, which include oligomers of CAB, acids, aldehydes, ketenes, esters, CO2 and CO, were quantified by chemometric procedures. The ketenes are the most novel products. The Arrhenius parameters reveal that below 510 ± 20°C, the rate of product evolution is controlled mainly by condensed phase reactions. Above 510 ± 20°C, the rate of product evolution is controlled by desorption/evaporation of the volatile products.
Atomic Force Microscopy of Hot Spot Reaction Sites in Impacted RDX and Laser Heated AP
Authors: Sharma J. , Coffey C. S. , Ramaswamy A. L. , Armstrong R. W.
Published: April 2011

An atomic force microscope (AFM) has been used to reveal residual sub-micron sized decomposition sites in drop weight impacted RDX and laser irradiated AP crystals. In impacted RDX, the small and early reaction sites observed are hemispherical craters, ranging in size from 20–300 nm. The smallest reaction site encompassed about 10,000 molecules with an expected energy evolution of 2 × 10−14 J. On a somewhat larger scale hillocks of 200–800 nm were observed, their shape giving evidence of internal reaction and hot spot melting. Dislocation densities as high as 5 × 1012 per cm2 were observed in sub-ignited RDX. High resolution AFM images of the RDX lattice structure indicate molecular rotation as well as displacements at dislocation sites. In AP, after nanosecond pulsed laser irradiation, reaction sites were trumpet shaped with a smallest size of approximately 50 nm. Most sites contained a crystallographically oriented central square lid formed above the surrounding crystal surface, probably relating to the orthorhombic to cubic phase transition documented in micron scale cracking patterns observed at the laser heated sites.
Probing Detonation Physics and Chemistry Using Molecular Dynamics and Quantum Chemistry Techniques
Authors: Cook M. D. , Fellows J. , Haskins P. J.
Published: April 2011

Modem quantum chemistry and molecular dynamics computer codes are powerful tools with which to study the physics and chemistry of energetic materials at the molecular level. Quantum chemistry calculations, on one or two energetic molecules, can give valuable information about the initial steps in their decomposition. Molecular dynamics calculations, even with empirical potentials, can yield important information about the physical processes involved in the initiation and growth of reaction of energetic materials. The combination of Molecular dynamics and quantum chemistry techniques offers the potential to probe energetic material reaction chemistry in real systems, in some detail, in the near future. Such an approach is vital if we are to be able to create new realistic macroscopic models within hydrocodes that can describe the initiation and growth of reaction in explosives. This paper gives an overview of the approach being adopted at DRA Fort Halstead to understanding energetic materials at the molecular level. In particular, the use of quantum chemistry and Molecular dynamics to help construct new macroscopic models will be discussed.
Hot Spots in a Molecular Solid Under Rapid Compression: Energy Sharing Among the T-R-V Degrees of Freedom.
Authors: Tsai D. H.
Published: April 2011

Sharing of the kinetic energy among the translational-rotational-vibrational (T-R-V) degrees of freedom in a molecular crystal, following excitation of the T degrees of freedom, has been studied by means of molecular dynamics. The model was similar to that employed in [2]. The Tdegrees of freedom were energized by adding a velocity distribution to the (100) molecular lattice planes so as to excite certain normal modes in the [100] direction. The kinetic energy components in TR, V and the rates of energy sharing between T-V and T-R were determined. The results were then compared with those from rapid compression of the same model, with or without defects.
Molecular Dynamics Calculations on the Properties of the Reaction Zone in Liquid Explosive
Authors: Soulard L
Published: April 2011

We present the results of molecular dynamics calculations concerning the structure and the thermodynamic state of the reaction zone in the liquid explosive NO under shock sollicitation.We show that the compression of explosive is due to inertial shock followed by endothermic decomposition. Then exothermic reactions occur and cause a slow decreasing of pressure until the end of the reaction zone. Analysis of particle velocities distribution and interatomic forces shows that only a partial equilibrium is reached in the reaction zone. As the relaxation time of particles velocities is very small compared to the characteristic time of chemical reactions, thermal equilibrium is always reached and the various molecular species are isothermal. It is not the case of interparticle forces and pressure in the usual thermodynamic way cannot be defined: the reaction zone is not isobaric. Our conclusion is that an equation of state cannot be defined in the reaction zone.
Simulations of Ozone Detonation Using a Reactive Empirical Bond Order (REBO) Potential for the Oxygen System
Authors: Barrett J. J. C. , Robertson D. H. , Brenner D. W. , White C. T.
Published: April 2011

The short length and time scales associated with chemical detonations make these processes excellent candidates for study by MD simulation. Potentials used in these simulations must have sufficient flexibility to describe gas-phase properties of isolated reactant and product molecules, high density material generated under shock compression, and allow smooth adjustment of bonding forces during chemical reaction. The REBO formalism has been shown to provide these characteristics and allow the treatment of a sufficient number atoms for sufficiently long times to demonstrate a chemically-sustained shock wave (CSSW). In this paper we present a REBO potential describing the oxygen system for use in MD simulation of detonation in an ozone molecular solid. The potential reproduces spectroscopic properties of isolated gas-phase O2 and O3. It also describes an ozone molecular solid with density and speed of sound within physical norms. We observe detonation characteristics that depend on crystallographic orientation in simulations using a three dimensional ozone molecular crystal.
Vibrational Energy Transfer in High Explosives: Nitromethane
Authors: Hong Xiaoyu , Hill Jeffrey R. , Dlott Dana D.
Published: April 2011

Time resolved vibrational spectroscopy with picosecond tunable mid-infrared pulses is used to measure the rates and investigate the detailed mechanisms of multiphonon up-pumping and vibrational cooling in a condensed high explosive, nitromethane. Both processes occur on the ˜100 ps time scale under ambient conditions. The mechanisms involve sequential climbing or descending the ladder of molecular vibrations. Efficient intermolecular vibrational energy transfer from various molecules to the symmetric stretching excitation of NO2 is observed. The implications of these measurements for understanding shock initiation to detonation and the sensitivities of energetic materials to shock initiation are discussed briefly.