bluuebunny/crossref_metadata_2025 huggingface dataset:
Sugar Coated Semiconductors: Model Surfaces to Study Biological Adhesion
Authors: Mastandrea Mark , Bednarski Mark D.
Published: March 2011

Certain molecules when placed in contact with a surface can bind to form well-ordered two dimensional arrays. This process is called molecular selfassembly (MSA), and it is emerging as an important method to control the interactions between a surface and its environment (interfacial properties). Molecular self-assembly uses the fundamental forces between molecules (Van der Waals interactions, hydrophobic effects and hydrogen bonding) to form highly ordered macromolecular systems. This process has been used to synthesize molecular films on a variety of surfaces including glass, gold, alumina, platinum, and silicon. The objective of this paper is to describe the application of molecular self-assembled films to the study of biological systems. Specifically, we will describe methods to synthesize and characterize surfaces that contain molecules that bind to bacteria and viruses. We will also evaluate the use of surface science techniques to characterize the physical and chemical properties of these surfaces, and we will attempt to correlate these properties with the adhesion of biological molecules.
Calcium Mineral-Peptide Interactions
Authors: Wheeler A. P. , Sikes C. Steven
Published: March 2011

Peptides have been synthesized by solid phase methods with structures which are in part based on experimentally-determined features of a major class of organic matrix phosphoproteins isolated from the calcium carbonate shell of the oyster. The matrix structures mimicked in the synthetic peptides included runs of aspartic acid (Asp), which were contrasted with peptides having other deployments of Asp with serine (Ser) and glycine (Gly). In addition, peptide-Ser was phosphorylated (PSer) and the hydrophobic carboxyterminus of natural matrix was mimicked using polyalanine tails. The interaction of the various peptides with CaCO3as well as calcium phosphates was determined using a variety of crystallization assays and studies of adsorption of radio-labelled peptides to crystal surfaces.

In general, peptides that include runs of Asp regulate crystal nucleation and growth more effectively than those which contain (Asp-X)nor (Asp-X-Y)nsequences with X and Y being either Gly or Ser. Further, CaCO3crystals have a much higher binding capacity for polyAsp than for peptides with other deployments of Asp. Phosphorylation increases the regulatory activity and the crystal capacities of Asp/Ser - containing peptides. PolyAsp peptides having terminal PSer's are especially effective as regulators of CaCO3nucleation and the conversion of amorphous calcium phosphate to apatite. The activity of Asp15molecules in CaCO3nucleation assays is markedly increased by the addition of polyalanine tails.
The Effects of Citrate and Phosphocitrate on the Kinetics of Mineralization of Calcium Oxalate Monohydrate.
Authors: Richardson C. F. , Johnsson M. , Bangash F. K. , Sharma V. K. , Sallis J. D. , Nancollas G. H.
Published: March 2011

The adsorption of citrate and phosphocitrate on calcium oxalate monohydrate (COM) surfaces has been measured in saturated solutions of calcium oxalate monohydrate at 37°C. In separate adsorption experiments, the uptake of phosphocitrate was markedly greater than that of citrate. When both additives were present, the adsorption of phosphocitrate was further increased. In constant composition studies of the crystallization of CON from supersaturated solution, phosphocitrate was more effective as an inhibitor than was citrate.
Organic, Organometallic and Polymeric Materials with Nonlinear Optical Properties
Authors: Marder S. R. , Perry J. W. , Schaefer W. P. , Ginsburg E. J. , Gorman C. B. , Grubbs R. H.
Published: March 2011

New approaches to both second-order and third-order nonlinear optical materials are presented. A series of organometallic and organic salts, in which the cation has been designed to have a large molecular hyperpolarizability, has been prepared and the SHG efficiencies were measured. Partially substituted derivatives of polyacetylene are synthesized via the ring-opening metathesis polymerization (ROMP) of cyclooctatetraene (COT) and its derivatives. Certain poly-COT derivatives afford soluble, highly conjugated polyacetylenes. These materials exhibit large third-order optical nonlinearities and low scattering losses.
Third-Order Optical Nonlinearity in a Polymer Composite
Authors: White K. M. , Harelstad R. E. , Francis C. V. , Gerbi D. J. , Stevens J. , Leung P. C.
Published: March 2011

Third-order optical nonlinearity in organic materials has generally been sought from molecules and polymers having extended i-electron delocalization in conjugated bonding schemes. In an alternative approach, we have investigated the third-order optical response of a polymeric composite containing charge transfer complexes in which the nonlinearity originates from intermolecular electron delocalization between π-electron clouds in charge transfer stacks. The material, which is composed of a polymer having electrondonating pendant side groups that complex with dopant electron-acceptor molecules, has been processed into an optically clear thin film. Nonlinear characterization of the film by means of third-harmonic generation suggests enhancement of the third-order response arising from charge transfer interactions.
Synthesis and Properties of Multifunctional Polymers
Authors: Goldberg H.A. , East A.J. , Kalnin I.L. , Johnson R.E. , Man H.T. , Keosian R.A. , Karim D.
Published: March 2011

Recent work aimed at developing new polymers which exhibit useful optical, electro-optical, and piezoelectric properties is presented. The materials under study are polymers with methacrylate backbones and oxynitrostilbene side chains. The synthesis is outlined, and pyro-electric, electro-optic, and thermal property data are reported and discussed.
Molecular Design of Synthetic Polypeptides for Nonlinear Optics
Authors: Ishii T. , Wada T. , Garito A. F. , Sasabe H. , Yamada A.
Published: March 2011

Second order molecular susceptibilities β of poly(γ – benzyl L–glutamate)(PBLG) and poly(γ – p–nitrobenzyl L–glutamate) (PNBLG) were determined by means of dc-induced second harmonic generation (dc-SHG technique in solutions at a wavelength of 1064nm as 1.5×10–−29 esu and −4.9×10−29 esu, respectively. Among PBLG, PNBLG and nitrobenzene, it was found that only PNBLG has negative value of β. It follows that the effect of nitrophenyl groups in side chains is dominant for β whereas the contribution of carbonyl groups in main chain is dominant for the permanent dipole moment μ in PNBLG.
Multifunctional Ceramic Materials–Review and Projections
Authors: Mackenzie John D.
Published: March 2011

Multifunctional engineering systems made up of different material components each providing primarily a single function are well known. Frequently, even for a monofunctional application, the material component must already have an optimum set of secondary properties to fulfill that function. It would be desirable to have multifunctional material components. In this paper some known multifunctional ceramic materials, mainly crystalline and glassy oxide systems, are reviewed. These are conveniently divided into molecular, ultrastructural and integrated materials systems. Projections are made regarding the future developments of multifunctional ceramics as well as nanocomposites with both inorganic and organic components based on the sol-gel technique.
Control of YBa2Cu3Oy Sol-Gel Solution Structure by Chemical Modification of Organic Acid and its Effects
Authors: Zheng Haixing , Mackenzie J. D.
Published: March 2011

2-ethylhexanoic acid (2EHA) has been applied to control the YBa2Cu3O7−x sol-gel solution. The experimental results prove that 2EHA functions as a sol-gel solution structure controlling and precipitation-prevention agent. The structure of the solution can be one, two or three dimensions of the network by using different concentration of 2EHA to modify the metal alkoxides. With decreasing 2EHA concentration, the homogeneity is improved due to increasing the network connectivity. This results in: (1) ease of the formation of YBa2Cu3O7−x; (2) denser microstructure with fine grains; and (3) narrower but lower superconducting transition.
Multi-Layers Thin Films of Acetalized Poly(Vinyl Alcohol) Derivatives Obtained by the LB Method and Their Opto-Electronic Properties
Authors: Oguchi Kiyoshi , Yokoh Yasuhiko , Sanui Kohei , Ogata Naoya
Published: March 2011

The formation of surface films of acetalized poly(vinyl alcohol)s at the air/water interface has been investigated in terms of the structure of the transferred films, after transfer of these surface films to solid substrates by means of the Langmuir-Blodgett technique. Furthermore, their electron beam exposure characteristics and non-linear optical properties were measured. It was found that the monolayers of acetalized poly(vinyl alcohol)s having aliphatic side chaines gave stable surface films with a limiting area of ca. 0.3nm2/average repeat unit, irrespective of the side-chain length and the degree of polymerization of the starting poly(vinyl alcohol). The surface films could be deposited onto various substrates with deposition ratios of 1.0. The resulting multilayers were Y type. The thickness of the multilayers was proportional to the number of layers, and the single-layer thickness increased with increasing sidechain length. The surface wettability of the multilayers changed alternatingly, depending on whether the number of layers was even or odd. These results indicated that the surface films were monolayers of polymers, with hydrophilic main chains spread over the air/water interface and hydrophobic side chains directed approximately normal to the interface. The transferred films maintained the oriented structure of the monolayers at the interface. The acetalized poly(vinyl alcohol)s prepared by the LB technique is adaptable as a high resolution negative-type EB resist. And the second harmonic generation (SHG) of some acetalized poly(vinyl alcohol)s was observed by LB method and by electric field poling method.
Dielectric, TSC and Electromechanical Measurements on some Prospective NLO Polymers
Authors: Carr Paul L. , Davies Geoff R. , Ward Ian M.
Published: March 2011

The pyroelectric coefficients of a range of polymers with a methacrylate backbone and nitrostilbene or nitrobipheny mesogens attached by a 3 or 6 carbon spacer have been measured in order to assess the efficiency of the poling process. It is found that the response is much lower than the guest-host system MNA in PMMA, suggesting that the polar mesogens pack anti-parallel and that this alignment is not broken by the applied field.

These strong interactions also provide an explanation for the absence of the β relaxation process in the experimental polymers and therefore the brittle nature of the films. They may also explain the stability of the polarisation achieved.
Vicrostructure and Electrical Properties of Kevlar/Polypyrrole Composite Fibers
Authors: Rector L. P. , DeGroot D. , Marks T. J. , Carr S. H.
Published: March 2011

Electrically conducting composite polypyrrole/poly(p-phenyleneterephthalamide) (PPTA or KEVLAR) fibers have been prepared by chemical polymerization of pyrrole within the interstices of the hydrogen-bonded gel structure of never-dried PPTA fibers. The resultant fibers contain a uniform dispersion of polypyrrole, as evidenced by scanning electron microscopy. The temperature dependence of the electrical conductivity of these hybrid fibers is presented. The conductivity is well described by the fluctuation-induced charge transport model over the entire temperature range of interest. However, the low temperature electrical conductivity also exhibits a hoppinglike temperature dependence, and an Arrhenius-like temperature dependence is observed in the high temperature limit. Measurements of the temperaturedependent tbermopower are indicative of a p-type carrier.
Photoactive Liquid Crystalline Polymers as Multifunctional Materials
Authors: Creed David , Griffin Anselm C. , Hoyle Charles E. , Venkataram Krishnan
Published: March 2011

UV-VIS spectral comparison with model compounds and isolation of the major product from preparative photolysis of one of the models has been used to show that the predominant photochemical reactions in the solid state of an aryl cinnamate polymer are 2+2 cycloaddition and photo-Fries rearrangement.
Enhancement of Third Order Nonlinearity on Phthalocyanine Compounds
Authors: Hosoda Masahiro , Wada Tatsuo , Yamada Akira , Garitoa Anthony F. , Sasabe Hiroyuki
Published: March 2011

The third order optical susceptibilities (−3ω; ω, ω ω,) for soluble metallophthalocyanine derivatives were determined by optical third harmonic generation measurements of molecularly doped polymer films at a wavelength of 1907nm. The X(3) value of tetra-tert-butylvanadylphthalocyanine is larger than that of metal-free derivative. We demonstrate experiment on modes of propagating light wave in molecularly doped films which exhibit excellent optical quality. The enhancement of third order optical nonlinear susceptibilities in phthalocyanine compounds are discussed in terms of molecular structure and molecular packing.
Thermochemistry and Structure of Model Waste Glass Compositions
Authors: Ellison Adam J. G. , Navrotsky Alexandra
Published: March 2011

Enthalpies of mixing of major oxide and waste components of proposed DWPF glasses are estimated. Several proposed glass compositions have very similar molar proportions of major structure-related components. Heats of mixing of major components are predicted to be small (glassy reference states), but may be endothermic or exothermic. Lanthanides are likely to form regions in the glasses rich in R-O-Si bonds but relatively depleted in Si-O-Si bonds. Measured enthalpies of solution of simple lanthanide-bearing glasses resemble those of mechanical mixtures of these end-members, with near-zero enthalpies of mixing for fairly large variations in lanthanide concentrations. DWPF glasses have alkalis in excess of those needed to charge-balance all T3+ cations in tetrahedral coordination. Electropositive +4, +5, and +6 cations are expected to use these excess alkalis to stabilize their own coordination polyhedra, forming complexes with effectively constant macroscopic stoichiometric ratios which contribute to enthalpies of solution in direct proportion to their concentration. Therefore, variations in the concentrations of high-valence cations in DWPF waste containment glasses are also predicted to result in near-zero enthalpies of mixing.
Effect of Curing Temperature on the Properties of Cementitious Waste Forms
Authors: Lokken Ryan O. , Shade John W. , Martin Paul F. C.
Published: March 2011

Current plans for disposing various low-level radioactive and/or hazardous liquid wastes include solidification of the waste using cementitious materials. One process, known as grouting, involves mixing liquid wastes with a blend of cementitious materials and pumping the resultant slurry to lined, underground concrete vaults. As the grout slurry begins to solidify and harden, the temperature within the grout increases due to exothermic hydration reactions. Depending on the the particular grout composition and on the disposal conditions, the grout may be exposed to temperatures of around 90°C for extended time periods. Studies are being conducted to determine the effects of high-temperature curing on selected properties of grouts prepared with a simulated low-level liquid waste. Grout samples cured at temperatures up to 950C in the laboratory absorbed water during curing. The resultant leach resistance and compressive strength of these grouts decreased with increases in curing temperature and curing time.
Thermokinetic Model of Borosilicate Glass Dissolution: Contextual Affinity
Authors: Advocat T. , Crovisier J.L. , Fritz B. , Vernaz E.
Published: March 2011

Short and long-term geochemical interactions of R7T7 nuclear glass with water at 100°C were simulated with the DISSOL thermokinetic computer code. Both the dissolved glass quantity and the resulting water composition, saturation states and mineral quantities produced were calculated as a function of time. The rate equation used in the simulation was first proposed by Aagaard and Hegelson: v = k+.S.a(H+)-n(l - e-(A/RT)). It simulates a gradually diminishing dissolution rate as the reaction affinity diminishes. The best agreement with 1-year experimental data was obtained with a reaction affinity calculated from silica activity (Grambow's hypothesis) rather than taking into account the activity of all the glass components as proposed by Jantzen and Plodinec. The concept of residual affinity was introduced by Grambow to express the fact that the glass dissolution rate does not cease. We prefer to replace the term “residual affinity” by “contextual affinity”, which expresses the influence on the dissolution rate of three factors: the solution chemistry, the metastability of SiO2(m), and the possible precipitation of certain aluminosilicates such as zeolites.
Effect of γ-Radiation on the Microstructure and Microchemistry of ggbfs/OPC Cemet Blends
Authors: Richardson I.G. , Groves G.W. , Wilding C.R.
Published: March 2011

Ground granulated blast-furnace slag (ggbfs)/OPC blends are among the materials being considered as possible encapsulating matrices for low and intermediate level radioactive wastes. It is therefore desirable to identify any microstructural modifications which may result in these systems frmn exposure to ionizing radiations. In order to investigate this, ggbfs/COC blends were γ-irradiated to >80M3y at 50°C over a period of 2 years. These were examined by electron optical, X-ray and thermal analysis techniques and the results ccmpared with controls subjected to a similar hydration regime. The morphological and ccmpositional similarities and differences revealed between the irradiated and control samples are presented and discussed.
Parametric Effects of Glass Reaction Under Unsaturated Conditions
Authors: Bates John K. , Gerding Thomas J. , Woodland Alan B.
Published: March 2011

Eventual liquid water contact of high-level waste glass stored under the unsaturated conditions anticipated at the Yucca Mountain site will be by slow intrusion of water into a breached container/canister assembly. The water flow patterns under these unsaturated conditions will vary, and the Unsaturated Test method has been developed by the YMP to study glass reaction. The results from seven different sets of tests done to investigate the effect of systematically varying parameters such as composition and degree of sensitization of 304L stainless steel, water input volume, and the interval of water contact are discussed. Glass reaction has been monitored over a period of five years, and the parametric effects can result in up to a ten-fold variance in the degree of glass reaction.
Behavior of Concrete as a Barrier Material for Nuclear Waste Disposal
Authors: James R. J. , Rashid Y. R.
Published: March 2011

The foundation necessary for a constitutive model to simulate the response of concrete at elevated temperature has been presented. A model including temperature dependent creep, material property degradation, and cracking is needed to evaluate the long term functional requirements of concrete as a barrier material for nuclear waste disposal. Since the stress due to thermal load is proportional to the modulus, the degradation of the modulus with time even at constant elevated temperatures requires continual redistribution of load. Furthermore, since this degradation is not recoverable, the response of the material at elevated temperatures exhibits a complex dependence not only on the temperature distribution, but on the prior thermal history of the structure.

This constitutive model for the response of concrete at elevated temperatures has been implemented into an implicit, finite element program called ANACAP [8]. Because of the direct coupling with temperature, both through thermal loads and material property dependency, ANACAP also contains a heat transfer module that includes thermal effects due to fluid flow and moving material boundaries. This program has been applied to problems involving underground waste storage tanks and grout vaults at the DOE Hanford site in Richland, Washington.
Alteration of Microstructure of West Valley Glass by Heat Treatment
Authors: Buechele A. C. , Feng X. , Gu H. , Pegg I. L.
Published: March 2011

Samples of West Valley reference glass WVCM-59 were subjected to isothermal heat treatment according to a systematic schedule of time-temperature combinations. Phases crystallizing during heat treatment were analyzed and quantified using an SEM equipped with an energy dispersive x-ray detector and image processing and analyzing capabilities. Only small amounts of noble metals (e.g. Rh, Pd) and RuO2 were present in the as-melted glass, but these frequently serve as nucleation sites during heat treatment. Iron-group spinels containing Fe, Ni, Cr, and Mn in variable proportions were the most common phases observed, appearing in quantities up to 3.5 vol% in heat treated glass. The formation of a thoria-ceria phase occurred at temperatures of 900°C and below. Acmites formed at temperatures of 800°C and below. A lithium phosphate phase with a particularly interesting morphology developed after prolonged heat treatment at temperatures between 600–750°C. The same phase appeared in a range of glass compositions. However, canister cooling curves preclude such a phase in production glass. Furthermore, no such phase was found in actual canister-cooled glass.
Constraints by Experimental Data for Modeling of Radionuclide Release from Spent Fuel
Authors: Grambow Bernd , Werme L.O. , Forsyth R.S. , Bruno J.
Published: March 2011

Comparison of spent fuel corrosion data from nuclear waste management projects in Canada, Sweden and the USA strongly suggests that the release of 90Sr to the leachant can be used as a measure of the degradation (oxidation/dissolution) of the fuel matrix. A surprisingly quantitative similarity in the 90 Sr release data for fuel of various types (BWR, PWR, Candu), linear power ratings and burnups leached under oxic conditions was observed in the comparison. After 1000 days of leachant contact, static or sequential, the fractional release rates for 90Sr (and for cesium nuclides) were of the order of 10−7/d.

The rate of spent fuel degradation (alteration) under oxic conditions can be considered to be controlled either by the growth rates of secondary alteration products, by oxygen diffusion through a product layer, by the rate of formation of radiolytic oxidants or by solubility-controlled dissolution of the matrix. These processes are discussed. Methods for determining upper limits for long-term 90Sr release, and hence fuel degradation, have been derived from the experimental data and consideration of radiolytic oxidant production.
Speciation of Pu(Vi) in Near-Neutral to Basic Solutions via Spectroscopy
Authors: Okajima Shigeo , Reed Donald T. , Mazer James J. , Sabau Carmen A.
Published: March 2011

The high sensitivity technique of laser photoacoustic spectroscopy and optical absorption spectroscopy were utilized to investigate the hydrolysis of Pu(VI) in perchlorate media. Absorption bands attributed to the hydrolysis of Pu(VI) were characterized in the pH = 6–8 regime which is of most interest to the proposed repository site at Yucca Mountain. Evidence was presented that supported the assignment of the polynuclear species (640 nm species) reported previously \1] as (PuO2)3(OH)5+1. Some temperature-dependent LPAS spectra are reported. The results obtained were compared to the predicted speciation of the geochemical code EQ3NR using the associated data base.
In-Situ Observation of the Alpha/beta Cristobalite Transition Using High Voltage Electron Microscopy
Authors: Meike A. , Glassley W. E.
Published: March 2011

A high temperature water vapor phase is expected to persist in the vicinity of high level radioactive waste packages for several hundreds of years. We have begun an investigation of the structural and chemical effects of water on cristobalite because of its abundance in the near field environment. A high voltage transmission electron microscope (HVEM) investigation of bulk synthesized α-cristobalite to be used in single phase dissolution and precipitation kinetics experiments revealed the presence β cristobalite, quartz and amorphous silica, in addition to α-cristobalite. Consequently, this apparent metastable persistence of β-cristobalite and amorphous silica during the synthesis of α-cristobalite was investigated using a heating stage and an environmental cell installed in the HVEM that allowed the introduction of either dry CO2or a CO2+ H2O vapor. Preliminary electron diffraction evidence suggests that the presence of water vapor affected the α-β transition temperature. Water vapor may also be responsible for the development of an amorphous silica phase at the transition that may persist over an interval of several tens of degrees. The amorphous phase was not documented during the dry heating experiments.
A Lagrangian Reactive Transport Simulator with Successive Paths and Stationary-States: Concepts, Implementation and Verification
Authors: Knapp R. B.
Published: March 2011

A geochemical software package which models static, single-path kinetic water-rock interactions, EQ3/6, has been modified to incorporate successive-paths and stationary states under high Peclet number transport conditions in a Lagrangian reference frame. These modifications permit calculation of reactive transport with reasonable computational requirements. Results from the new option in EQ3/6 have been compared with analytical results for the simple HC1 - SiO2 system; excellent agreements were achieved. Results have also been compared with published results for a portion of the A12O3 - HCI - K2O - SiO2 system. The results are in good qualitative and, in some cases, good quantitative agreement. However, the values of some variables differ substantially; these differences can be attributed to use of a different set of Al and Si aqueous species.
Modelling the in Situ Performance of Bentonite-Sand Buffer
Authors: Radhakrishna H.S. , Lau K.-C , Kjartanson B.H. , Cheung S.C.H.
Published: March 2011

In the Canadian nuclear fuel waste management concept, a number of engineered barriers, such as the bentonite-sand buffer which surrounds the waste container in the emplacement boreholes, are used to inhibit the transport of radionuclides. The buffer material is also required to effectively conduct heat from the fuel-waste containers to the surrounding rock. To a large extent, in situ buffer performance will depend on the degree of moisture within the buffer. The moisture content will in turn depend on temperature, temperature gradients, and buffer initial and moisture flux boundary conditions. Modelling of coupled heat and moisture transport in the buffer before resaturation is necessary to assess in situ buffer performance. This paper describes the results of a parametric study using the Philip and de Vries coupled heat and moisture transport model to assess the effects of variations in the moisture diffusivity parameters and the boundary conditions on buffer performance.

The results show that the thermal performance of the buffer is affected by heat-induced moisture movement. In particular, the thermal vapour diffusivity, DTvap, has the most significant effect on thermal drying in a closed system. Work is currently underway to improve our capability to model coupled heat and moisture transport in buffer. Laboratory experiments are in progress to more accurately define the moisture diffusivity parameters and the model is being modified to include the effects of boundary moisture fluxes and pressure potentials so that the resaturation process may be modelled. A full scale buffer/container experiment is currently being planned for conduct in AECL's Underground Research Laboratory to assess further the effects of scale and in situ boundary conditions on buffer performance and to qualify the model.
The Effect of Cracks on Diffusive Mass Transport through a Clay Barrier
Authors: Garisto Nava C. , Garisto Frank
Published: March 2011

Absract

Clay-based buffers are often proposed as engineered barriers for underground disposal vaults of used nuclear fuel. Thus, in the Canadian conceptual vault design, each used-fuel container is emplaced in a vertical borehole in rock and surrounded by a compacted buffer material, made up of a mixture of sodium bentonite and sand. There is some evidence, however, that the buffer may be susceptible to cracking due to, for example, cementation or moisture depletion.

In this paper we estimate numerically the consequences of cracking on the diffusion of uranium through a finite buffer layer. In particular, we study how the effects of cracks depend on the rock conditions at the edge of the vault.

For swept-away boundary conditions at the rock/buffer interface (e.g., representing a major fracture zone in granite), the total flux through the cracked buffer system is greater than through the corresponding uncracked buffer, particularly for buffers with a very small effective diffusion coefficient. On the other hand, for the case in which the rock at the rock/buffer interface is intact and, thus, the mass transport of material from the buffer into the rock is small, the effect of the cracks on the total release flux is negligible.
The Effects of Temperature on the Leaching Behavior of Cement Waste Forms - The Cement/Sodium Sulfate System
Authors: Fuhrmann Mark , Pietrzak Richard , Heiser John , Franz Eena-Mai , Colombo Peter
Published: March 2011

The leaching mechanisms of simulated low-level radioactive waste forms are being determined as support for development of an accelerated leach test. Two approaches are being used: (1) comparison of leaching data with results of a model that describes diffusion from a finite cylinder, and (2) observation of the leaching process at temperatures between 20°C and 65°C. To provide results that can be used for modeling, leaching at elevated temperatures must change neither the leaching mechanism nor the structural controls of leaching such as the porosity. Releases of 137Cs, 85Sr, calcium, sodium and potassium from portland cement containing sodium sulfate, as a simulated evaporator sludge, have been determined under a variety of experimental conditions. Data from the leach tests were compared to model results for diffusion from the finite cylinder. While most leaching appears to be diffusion controlled, notable exceptions occur. For all samples, activation energies ranging between 6 and 11 Kcal/mole have been calculated from the relationship of the effective diffusion coefficient to increasing temperature, close to the expected value of 5 Kcal/mole for diffusion.
Dynamic Rigidity Percolation in AOT Micelles and Microemulsions
Authors: Ye L. , Weitz D. A. , Sheng Ping , Huang J. S.
Published: March 2011

We study the acoustic properties of AOT micelles and microemulsions by measuring the velocity of sound as a function of droplet volume fraction and of frequency, using Brillouin scattering and ultrasonic techniques. These weakly attractive interparticle interactions lead to the formation of short–lived networks of droplets, which can support shear and result in a pronounced increase in the speed of sound at high frequencies. These networks do not persist for sufficiently long times to affect the sound velocity at lower frequencies. The increased rigidity due to the networks exhibits a percolation behavior with volume fraction, while the frequency dependence of the interactions depends on hydrocarbon chain length of the solvent. Increasing the water concentration results in an increase in interaction energy, but a decrease in the intrinsic droplet rigidity, which affects the magnitude and frequency dependence of the contribution of the microemulsion networks to the elastic constant of the suspension. A consistent picture of the viscoelastic behavior of these suspensions is obtained.
Role of Shear in the Isotropic to Lamellar Transition
Authors: Milner S. T. , Cates M. E.
Published: March 2011

In the isotropic to lamellar transition, nonlinear fluctuation terms lower the transition temperature τc and drive the transition first order. Here we show that steady shear, by suppressing the fluctuations, raises τc; in a certain temperature range the lamellar phase can be induced by applying shear. A study of the effective potential indicates that the transition remains first order, though becoming very weak at high shear rate. We argue heuristically that the lamellar ordering first occurs with wavevector normal to both the velocity and the velocity gradient. We estimate the characteristic shear rate for two current experimental systems.
Tracer-Diffusion in Weakly-Ordered Block Copolymers
Authors: Fredrickson Glenn H. , Milner Scott T.
Published: March 2011

We have investigated the self and tracer-diffusion properties of a labeled diblock copolymer in a weakly-ordered lamellar phase. This phase can be a pure copolymer of equal or different molecular weight, or might contain added homopolymer. The spatially-periodic chemical potential field presented by the lamellar phase is capable of strongly influencing the diffusive motion of the tracer. In general, this field serves to slow diffusion, although the manner in which it acts depends on the wavelength of the potential relative to the labeled copolymer radius-of-gyration and on the composition of the copolymer. In the extreme limit of compositional asymmetry of the diblock tracer, we obtain results for the tracer-diffusion coefficient of a homopolymer.
The Flow Properties of Concentrated Colloidal Suspensions
Authors: Goodwin J. W. , Hughes R. W.
Published: March 2011

The flow properties of dispersions are a function of both particle number density and interparticle potential. At high number densities suspensions change from fluid-like behaviour to solid-like. The number density where this transition occurs is controlled by the shape of the interparticle potential function. The material state is clearly indicated from the rheological measurements. Wave propagation, stress relaxation and continuous shear viscometry have been used to study a variety of suspensions of monodisperse particles. Hard sphere, weakly attractive and strongly repulsive systems are discussed.
Density Functional Theory of Interactions Between Charged Macroions in Solution
Authors: Stevens Mark J. , Robbins Mark O.
Published: March 2011

We apply density functional theory to the screened interactions between macroions in solution. The approach incorporates the strong correlations between screening ions at high densities, and reduces to the Poisson-Boltzmann equations at low densities. Local density functional theory results for the interactions between parallel planes are within ˜ 1% of Monte Carlo (MC) and inhomogeneous hypernetted chain (IHNC) values when the plane separation L ≥ 50Å. Non-local effects are important for divalent ions at small separations and high surface charge densities. A simple weighted density approximation qualitatively reproduces MC and IHNC results in this regime, and provides a simple explanation for the onset of attractive interactions between like-charged plates.
Structural Properties of Covalently Crosslinked Gels as Probed by Scattering Techniques
Authors: Canda Sauveur J. , Ilnai F. , Schosseler F. , Bastide J.
Published: March 2011

This paper reviews some characteristic results obtained by scattering techniques in two sorts of swollen covalently crosslinked networks : neutral networks swollen by a good solvent and weakly ionized gels. For neutral networks swollen at saturation, the local conformation of the chains was found to be the same as in semi-dilute solutions, whereas some concentration inhomogeneities are observed at larger scale. Ionized gels are characterized by a peak of the structure factor and the absence of long range stationary concentration fluctuations at the concentration of preparation of the gels.
Radial Creeping Flow Between Parallel Disks of Rod-like Nematic Liquid Crystals: Textures and Instabilities
Authors: Rey Alejandro D.
Published: March 2011

Four solutions to the Leslie-Ericksen equations for nematic liquid crystals are obtained for pressure-driven radial out-flow between concentric parallel disks and homeotropic director wall anchoring. At low pressure drops the in-plane mode is stable; the centerline director orientation is normal to the flow direction. For each radial distance from the entrance hole there is a critical pressure drop at which the elongational torque twist the director out-ofthe- plane of flow ; left and right rotations are possible. The transition results in the appearance of secondary flows in the azimuthal direction. The radius of the boundary between in-plane and out-of-the-plane modes increases with increasing pressure drops. At higher pressure drops a twist wall develops at the centerline. There is a second critical pressure drop at which the wall collapses with the nucleation and growth of a twist disclination loop. The resulting stable director field is in-plane and flow-aligned throughout the cell.
X-Ray Diffraction Studies of Protein Monolayers Bound to Self-Assembled Monolayers
Authors: Amador S. M. , Pachence J. M. , Fischetti R. , McCauley J. P. , Smith A. B. , Dutton P. L. , Blasie J. K.
Published: March 2011

X-ray interferometry was used to study monolayers of the protein yeast cytochrome c and a bimolecular cytochrome c/photosynthetic reaction center complex bound to self-assembled monolayers of 11-trichlorosilylundecyl thiol on inorganic substrates. Optical absorption spectroscopy and dissociation experiments show that the cytochrome c monolayer is covalently attached to the self-assembled monolayer via a disulfide bond and they are consistent with the cytochrome c and its bimolecular reaction center complex forming a close-packed array on the surface of the solid substrate. By sequentially forming these bio-organic monolayers on synthetic inorganic multilayers (“quantum wells”), we were able to determine the electron density profile of the protein layers to ∼13 Å resolution using x-ray interferometry and refinement techniques.
X-Ray Diffraction (Pole Figure) Study of the Epitaxy of Gold Thin Films on GaAs
Authors: Leung Siu , Milnes A. G. , Chung D. D. L.
Published: March 2011

X-ray diffraction (pole figure) measurements were made on gold thin films (300–2300 Å) evaporated on GaAs{111} and GaAs{001} to investigate the heteroepitaxy and twinning of the gold films and the chemoepitaxy of Au7Ga2on GaAs. For both GaAs orientations the epitaxial relationship (hkl)AU[hkl]Au/ (hkl)GaAs[hkl]GaAswas observed for all values of h, k and l. In addition, twin orientations were observed. For GaAs{111}, fourfold rotation twinning about the Au[l11] direction resulted in four azimuthal orientations: [112]Au// [112]GaAs, [112]Au// [112]GaAs, [112]Au// [110]GaAs, and [112]AU/ [110]GaAs. For GaAs{001}, reflection twinning with the four Au{111} planes as twinning planes resulted in four other orientations with Au(001) at approximately 71° from GaAs(001). The relative amounts of the twins depended on the substrate temperature, the film thickness and the deposition rate. Chemoepitaxy was observed for Au7Ga2on GaAs{111} the epitaxial relationship was (111)Au/ (0110)Au7Ga2/(111)GaAsand Au7Ga2[0001] was off by 10° from GaAs[110], toward GaAs[011], i.e. Au7Ga2[0001] was off by 10° from Au[110], toward Au[011]. This relationship corresponds to a perfect lattice match between Au7Ga2and gold.
How Epitaxial Are Pd2Si–Si Interfaces?
Authors: Liliental Z. , Carpenter R. W. , Tuenge R.
Published: March 2011

Pd2Si layers produced by evaporation or sputtering onto silicon substrates were examined by high resolution electron microscopy, microdiffraction, X-ray, energy loss and Auger spectroscopy. The Si-Pd2Si interfaces produced by evaporation were in all cases rougher and more polycrystalline than those produced by sputtering. X-ray microanalysis showed the predictable variation in palladium distribution across the interface but quantification did not produce the expected palladium–to–silicon ratios, primarily because of probe broadening and X-rayinduced fluorescence. Energy loss spectra showed plasmon energy shifts and changes in Si L edge shape due to bond formation with palladium. Auger data provided evidence for a small amount of oxygen at the Si-Pd2Si interface. Electrical measurements of the ideality factor for Schottky barriers made from these materials produced higher values for the rougher evaporation-formed interfaces consistent with interface-roughness-induced scattering and carrier recombination.
The Effects of PtxSi Growth on the Redistribution of P-Type Dopants in Silicon
Authors: Wei C. Y. , Katz W. , Smith G.
Published: March 2011

The redistribution of p-type dopants (boron and indium) during PtxSi growth was studied as a function of annealing time using secondary ion mass spectrometry. It was found that both boron and indium atoms redistribute into the silicide during a thermal anneal. Initially, the dopant becomes trapped at the PtxSi–Si interface and concomitantly getters to defect sites located at the moving Pt-PtxSi interface. Even after silicide formation is complete, the dopant continues to out-diffuse to the surface via an enhanced mechanism due to defects and/or grain boundaries. Finally, no evidence for a “snowplow” effect was observed for either boron or indium at the implant dose of 2 × 1013 ions cm−2.
Theory of Semiconductor Heterojunctions
Authors: Pollmann J. , Mazur A.
Published: March 2011

A short review of characteristic electronic properties of heterojunction interfaces is given. Band edge discontinuities and interface band structures for lattice-matched junctions are discussed in detail. The examples presented include non-polar and polar junctions as well as overlayer systems. The results of involved calculations are interpreted in terms of simple physically appealing pictures by directly relating the changes in bonds across an interface to the resulting bands in the interface band structure. The meaning of the results for the transport properties of semiconductor heterojunctions is briefly assessed.
Characterization of Ion-Beam-Sputtered Molybdenum Films on N-Type Silicon
Authors: Auret F. D. , Paz O. , Bojarczuk N. A.
Published: March 2011

The introduction of defect levels in the band gap of silicon (ND = 2.5×1015 cm−3), after ion beam sputtering of molybdenum contacts, was investigated with deep level transient spectroscopy and scanning electron microscopy (electron-beam-induced current mode). Molybdenum contacts were fabricated with beam voltages of 700, 1100 and 1500 V at a beam current density of 2.5 mA cm−2. Defect levels were observed at energies ranging from 0.18 to 0.55 eV below the conduction band. It was established that the introduction of these defect levels depends on the processing conditions and that they reside very close to the Mo-Si interface (less than 0.4 μtm). A correlation was observed between the fabrication conditions, the current-voltage and capacitance-voltage characteristics of the contacts, and the concentrations of the defects present. Charge collection micrographs confirmed the presence of a defective layer close to the surface.
Dynamics of Metal-SiOx and SiOx–Si Interfaces and the Associated Instabilities In Practical Metal/Insulator/Semiconductor Structures
Authors: Rajeswaran G. , Anderson W. A. , Jackson M. , Thayer M.
Published: March 2011

X-ray photoelectron spectroscopy, Auger electron spectroscopy and ellipsometry measurements were performed at Cr-SiOx, and Yb-SiOx interfaces, which are being considered for metal/insulator/semiconductor (MIS) solar cell applications. These measurements have led to a knowledge of instability mechanisms associated with MIS solar cells. The dynamics of the metal-oxide interface reduce the effective thickness of the insulating SiOx layer. Typically, in a 3 week period after fabrication the oxide thickness decreases by about 2 Å for ytterbium MIS structures and by less than 1 Å for chromium MIS structures. A structural equilibrium is reached thereafter. To explore further the dependence of MIS Schottky barrier heights on oxide thickness variations (from about 5 to 20 Å) a comprehensive charge balance analysis was performed at a general MIS interface. This theoretical study supports experimental data on barrier heights and also on instabilities. In addition, the application of the theoretical model to the experimental barrier heights has yielded quantitative information regarding the density of interface states at the SiOx,–Si interface.
Contact Resistance and Methods for its Determination
Authors: Cohen S. Simon
Published: March 2011

The problem of low resistance ohmic contacts to silicon has been of considerable technological interest. In recent years this problem has received special attention owing to the effect of scaling in very-large-scale integration (VLSI) technology. The field of ohmic contacts to semiconductors comprises two independent parts. First there exists the material science aspect. The choice of a suitable metallization system, the proper semiconductor parameters and the method of the contact formation is not obvious. Then there is the question of the proper definition of the contact resistance and the way it is measured.

Several methods for contact resistance determination have been introduced in the past. All seem to have some drawbacks that either limit their usefulness or raise doubts as to their validity in certain situations. We shall discuss the two-, three- and four-terminal resistor methods of measurement. Relevant theoretical considerations will also be included.

For conventional integrated circuits with a moderate junction depth of 1–2 μm, aluminum is uniquely suited as a single-element metallization system. However, for VLSI applications it may become obsolete because of several well-defined metallurgical problems. Thus, other metallization systems have to be investigated. We shall briefly discuss some recent data on several other metallization systems. Finally, the problem of size effects on the contact resistance will be discussed. Recent experimental results suggest important clues regarding the development of alternative metallization systems for VLSI circuits and also point to revisions of estimates of achievable design rules.
Ohmic Contacts to GaAs
Authors: Braslau Norman
Published: March 2011

The present capability of obtaining ohmic contacts to GaAs over a range of doping levels is reviewed. Possible models of transport across the metalsemiconductor interface are discussed and contact techniques are described. The widely used Au—Ge alloyed contact is seen to have a spatially inhomogeneous interface which appears to control its contact resistance. The most satisfactory process at this time is to alloy into a previously fabricated heavily doped layer.
Electrodeposition of Nanomodulated Ceramic Thin Films
Authors: Switzer Jay A. , Shane Michael J. , Phillips Richard J.
Published: March 2011

Electrochemistry can be used for the atomic-level architecture of ceramic materials. In this report, ceramic superlattices based on the TlaPbbOc/TldPbeOf system were electrodeposited with individual layer thicknesses as thin as 3nm. The superlattices were deposited from a single aqueous solution at room temperature, and the layer thicknesses were galvanostatically controlled. Substitution of Tl2O3 into PbO2 appears to stabilize a face-centered cubic structure with an average lattice parameter of 0.536nm. The lattice parameters for the T1aPbbOc. mixed oxides vary by less than 0.3% when the Pb/Tl ratio is varied from 0.84 to 7.3. Because the modulation wavelengths are of electron mean free path dimensions, this new class of degenerate semiconductor metal-oxide superlattices may show thickness-dependent quantum optical, electronic, or optoelectronic effects.