bluuebunny/crossref_metadata_2025 huggingface dataset:
Calculations of the Structure and Properties of Rapidly Quenched Ni/Zr Alloys
Authors: Cherne F. J. , Baskes M. I. , Schwarz R. B. , Srinivasan S. G.
Published: April 2011

Using molecular dynamics and a modified embedded atom potential developed by our group we studied the diffusivity and viscosity of molten Ni1-xZrx alloys as a function of composition, temperature, and cooling rate. Previous results indicate that these potentials represent the Ni-Zr system quite well. Liquid alloys were quenched at rates of 5 × 1011 and 1012 K/s. For x > 0.04 the solidified alloys were crystalline. For higher x values, the solidified alloys were amorphous. For the amorphous alloys, the composition dependence of the calculated glass transition temperature Tg follows the general trend of experimental Tg values. The calculated viscosity and diffusivity show systematic variation with composition. For the undercooled Ni-6 at.% Zr melt the calculated viscosity shows the Vogel-Fulcher-Tammann (VFT) behavior characteristic of a “fragile” glass.
Effect of temperature on formation of murataite and murataite-pyrochlore ceramics
Authors: Kirjanova O. I. , Stefanovsky S. V. , Yudintsev S. V.
Published: April 2011

Processes of phases formation in the ceramic mixtures with basic compositions (wt.%) 10 CaO, 10 MnO, 5 Al2O3, 5 Fe2O3, 55 TiO2, 5 ZrO2, 10 UO2 (M1) and 8 CaO, 8 MnO, 4 Al2O3, 4 Fe2O3, 20 Gd2O3, 44 TiO2, 4 ZrO2, 8 UO2 (M4) were studied using X-ray diffraction, scanning and transmission electron microscopy. The batches were milled, compacted in pellets at 200 MPa, and heat-treated in a resistive furnace at 1100 °C, 1300 °C, 1400 °C, and 1500 °C as well as melted in a cold crucible at ∼1600 °C. Reactions in the mixtures heat-treated at 1100 °C were not completed and samples contained significant amount of unreacted and intermediate (altered rutile, cubic oxide solid solution, perovskite) phases. Within the temperature range 1100–1300 °C reactions are mainly completed and ceramics sintered at 1300 °C are composed of major murataite and minor rutile (M1) or major murataite and pyrochlore and minor zirconolite and perovskite (M4). However full homogenization at 1300 °C has not been reached yet and to obtain the ceramics with uniform compositions of the phases sintering at 1400 °C or melting at 1500–1600 °C were required.

In the ceramic sample M1 two murataite varieties with five- (murataite-5C) and eight-fold (mu-rataite-8C) fluorite-type unit cells were found. The sample M4 is composed of pyrochlore, murataite-8C and zirconolite-3O. In the sample M1 murataite-5C is enriched with U and Ca and depleted with iron group elements as compared to murataite-8C. Fraction of murataite-5C concentrates about 80% of total U and about 70% of Mn+Fe (corrosion products). Waste elements partitioning among the phases in the M4 sample depends significantly on temperature of heat-treatment.
The effect of pH on chlorite dissolution rates at 25°C
Authors: Gustafsson Åsa B. , Puigdomenech Ignasi
Published: April 2011

The Swedish nuclear industry is planing to dispose spent nuclear fuel encapsulated in copper canisters in granitic bedrock at a depth of approx. 500 m. The reducing capacity of the geo-sphere is important for canister corrosion and radionuclide migration. The main inorganic reduc-tants are Fe(II)-containing minerals: biotite in the bedrock, and pyrite and chlorite in the fracture filling minerals as well as in the buffer and backfill. As a consequence, the dissolution of chlorite is an important parameter when considering the reducing capacity available to groundwaters around the repository.

The weathering rates of a chlorite sample from Taberg in central Sweden has been studied in 0.01 M NaCl media at (25±1)°C in the pH region 2–12. The chlorite was characterized before and after grinding and sieving, and was found to have a relatively low Fe-content, with the formula (Mg9.44 FeII0.72Al1.68)(Si6.47Al1.4FeIII0.13)O20(OH)16. Kinetic experiments were performed using a thin-film continuous flow-through technique with flow rates of 5 mL/h or 2.7 mL/h. This technique prevents the precipitation of secondary phases such as iron(III) hydroxides. Solution samples were taken after a reaction time of 0–30 days. The contents of released Al, Fe, Mg and Si were analyzed using an Inductively Coupled Plasma emission spectroscopy (ICP-AES) technique and then normalized to the Brunauer-Emmet-Teller (BET) surface area and flow-rate in order to obtain rates of dissolution. The dissolution rate of the chlorite studied was pH-dependent, and a minimum was observed in the neutral pH region. The dissolution rate (based on Si data) decreased from 7×10-11 mol/(m2 s) at pH=2 to 4×10-13 mol/(m2 s) at pH≈7 and then in-creased to 3×10-12 mol(m2 s) at pH=12.
Ab-initio Studies of Plutonium with Relevance to Nuclear Waste Management
Authors: Setty Arun K. , Cooper B. R. , Price D. L.
Published: April 2011

Plutonium, well known for its unusual nuclear and material properties, has remained an unsolved problem for over a half century. Due to the continuing issue of safe, longterm nuclear waste storage, gaining an understanding of plutonium and its compounds cannot be overstated. Self-irradiation in plutonium leads to vacancy formation [1], and our computations indicate that the electronic structure we predict for pure delta plutonium is preserved in the presence of vacancies, and that vacancies do stabilize the delta phase. A preliminary study of self-diffusive properties of plutonium, and of diffusion at the interface of plutonium and iron indicates that plutonium atoms readily diffuse across the interface with steel. This has relevance in nuclear waste storage in steel containers for assessing the depth of penetration to be dealt with in surface treatment for decontamination. The effect of thermomigration (Soret effect) in the plutonium-steel system appears to facilitate the movement of plutonium atoms into the bulk steel.
Accounting for EBR-II Metallic Waste Form Degradation in TSPA
Authors: Ebert W. L. , Lewis M. A. , Barber T. L. , Johnson S. G.
Published: April 2011

A metallic waste form (MWF) will be used to immobilize cladding hulls from spent sodium-bonded nuclear fuel rods. Laboratory tests were conducted to determine if the HLW glass degradation rate model used in Total System Performance Assessment (TSPA) calculations can be used as an upper bound for the degradation rate of the MWF. Static tests were conducted with monolithic MWF samples in pH buffer solutions to measure the degradation rates at 50, 70, and 90°C. The measured degradation rates of the MWF were compared to the rates calculated with the HLW glass degradation model. The degradation rates were calculated as the product of the specific dissolution rates and the anticipated exposed surface areas of glass and MWF in a breeched canister. This comparison showed that the rate calculated using the HLW glass degradation model bounds the rates measured for the MWF at all pH values and temperatures. These results support the potential use of HLW glass as a surrogate for MWF degradation for the purpose of performance assessment.
Alteration of Si-B-Na-Al model glass in water at 90°C: experiments and thermodynamic modelling
Authors: Munier Isabelle , Crovisier Jean-Louis
Published: April 2011

An attempt to model the alteration process of a model glass (Si-B-Al-Na), similar to the French reference SON68 glass, by using the geochemical code KINDIS, was developed. This simulation study was compared with experiments carried out in parallel: glass samples were placed at 90°C in pure water for 30 to 180 days, at two different S/V ratios (1 and 80 cm-1).

The formation of the alteration layer was simulated by the precipitation of an ideal solid solution. The cases of oxides, hydroxides and metasilicates as end-members were tested. The considered solid solution always contains a siliceous end-member, which consists of amorphous silica, chalcedony or quartz.

The relative thermodynamic stability of the chosen end-members (especially siliceous ones) influences directly the composition of the predicted gel and thus the composition of the solution. The results obtained by using chalcedony and hydroxides as end-members show a good agreement between the experimental and modelled silicon contents in solutions and in alteration gels, whatever the S/V ratio.

The gel layer of the glass contains significant amounts of Na and Al, which are equimolar on average, what would probably correspond to the compensation of AlO4- charges by Na+.
Redox properties of MX-80 and Montigel bentonite-water systems
Authors: Lazo Cecilia , Karnland Ola , Tullborg Eva-Lena , Puigdomenech Ignasi
Published: April 2011

The uptake of dissolved oxygen (O2) has been studied in bentonite suspensions in 0.1 M NaCl media at (25±2)°C. MX-80 and Montigel bentonites were used in concentrations varying from 18 to 73 g/L. The experiments were performed in a magnetically stirred closed glass vessel, in an N2-glove box. Redox potentials where measured with Pt-wires, and dissolved O2 was measured both with a membrane electrode and with an optode. The experiments with MX-80 show that dissolved O2 disappears in ∼5 days under these conditions. Redox potentials decreased from ∼ +500 to ∼ +125 mVSHE (versus Standard Hydrogen Electrode). The data for the Montigel bentonite show similar time scales for O2 uptake but lower redox potentials at the end of the experiments ∼ −175 mVSHE. Pyrite oxidation is perhaps not the main process for O2 uptake, as MX-80 contains 0.3% FeS2 while Montigel bentonite only has a negligible amount.
Redox Reactions of Iron and Uranium Dioxide in Simulated Cement Pore Water Under Anoxic Conditions
Authors: Cui Daqing , Spahiu Kastriot , Wersin Paul
Published: April 2011

Results on the chemical behavior of Fe(0) and UO2(s), as well as the interaction between fresh and corroded iron with U(VI) in simulated cement contacting alkaline solution are reported. Batch experiments were conducted under anoxic conditions at different alkalinities and salt concentrations to investigate: (a) the corrosion of iron foils (b) the U(VI) removal by fresh, aged and pre-treated (with FeS or Fe3O4 layers) iron surfaces in a simulated cement pore fluid, (c) the dissolution rates of newly reduced UO2.00 slices in simulated cement pore fluid and KOH solutions (pH 12.7) and (d) the isotope exchange reactions between dissolved 235U(VI) and 238UO2(s). The reacted iron and UO2(s) surfaces were analyzed by X-ray diffraction (XRD), scanning electron microscopy-energy dispersive spectra (SEM-EDS), laser Raman spectroscopy and X-ray photoelectron, spectroscopy (XPS).
Interfacial Layer Effects in Ba1-xSrxTiO3 Thick Films prepared by Plasma Spray
Authors: Ahn Kipyung , Wessels Bruce W. , Sampath Sanjay
Published: April 2011

The dielectric properties of high k dielectric thick films prepared by thermal spray were investigated. BaTiO3 and Ba0.68Sr0.32TiO3 thick films were deposited using plasma spray on Ag-Pd screen-printed alumina substrates. The sprayed films were predominantly polycrystalline but contained an amorphous second phase. The dielectric constants of the films decreased with decreasing film thickness in 10 ∼ 60 μm range. This was attributed to the presence of an interfacial layer between the film and the substrate as determined by capacitance measurements. The capacitance density of the interfacial layer was determined to be ∼ 2.7 nF/cm2. The capacitance density of the interfacial layer increased to 12 nF/cm2 after post heat treatment at 500 °C for 20 hours.
Characterization of Electrostatic Micromembrane Actuator Performance Using a Mass Probing Method
Authors: Wu Xingtao , Hui Jeremy , Kayatta Pat , Kenneth Dedeian , Young Mariam , Warde Cardinal
Published: April 2011

We describe a mass probing technique for characterizing the electro-mechanical behavior of micromembrane array actuators under electrostatic loads. The technique utilizes one or more arrays of center-positioned posts as a joint-link between an array of micro membrane actuators and a top movable rigid mass plate to generate 1D motion of the top mass owing to motion transfer from the deformed membranes. The micromembrane actuator arrays are fabricated using a stacked architecture similar to MUMPs in which the poly-Si structure material is replaced by metal-over-polymer composite, and final release is accomplished by a dry etch of a-Si sacrificial material. The mass probing technique is implemented by hybrid integrating a thick (100∼650-μm), heavy, and rigid mass plate (with a polished surface as a reflective mirror) onto the membrane array in which individual membrane actuators have a center interface post to act as mechanical linkage. A preliminary test of a 40-um pitch membrane array shows a 1st natural frequency of 2.1MHz of the membrane actuator. This was scaled down to ∼50KHz by a 2.7mmx2.7mm 200-μm thick mass load weighting 3.3-mg. Ignoring the small membrane mass, the lumped spring stiffness is estimated to be ∼70-μN/μm per actuator (3248 40-μm actuators embedded beneath the probing mass). Thus, motion transfer principle from micro size actuators to macro size components was demonstrated.
Interface Adhesion and Reliability of Microsystem Packaging
Authors: Francis Marvin I. , Wadach Kellen , Walwadkar Satyajit , Cho Junghyun
Published: April 2011

Flip-chip technology is becoming one of the most promising packaging techniques for high performance packages. Solder balls are used as the connection technique in the flip-chip method and the connections are reinforced by filling in the spacing between the chip and substrate with underfill. The function of the underfill is to reduce the stresses in the solder joints caused by a coefficient of thermal expansion (CTE) mismatch. The presence of polymeric underfill material will, however, make the flip-chip packaging system susceptible to interfacial failure. Thus, the purpose of this study is to examine the interfacial delamination between the dissimilar materials in order to increase the reliability of the flip-chip interconnection method, and to understand the effect of underfill curing conditions on the interface adhesion. In particular, we use a linear elastic fracture mechanics (LEFM) approach to assess interfacial toughness. For this purpose, four-point bending testing is performed to determine a critical strain energy release rate, Gc. In addition, nano-indentation testing equipped with atomic force microscope (AFM) is employed to determine structure and properties of the underfill layer.
Application of FIB/SEM and TEM to Bit Failure Analyses in SRAM Arrays
Authors: Qin Wentao , Volinsky Alex , Rice Larry , Johnston Lorraine , Theodore David
Published: April 2011

Many microelectronic chips contain embedded memory arrays. A single SRAM bit-cell contains several transistors. Failure of any of the transistors makes the entire bit-cell inoperable. Dual-beam Focused Ion Beam (FIB) combines the slicing capability of FIB with in-situ SEM imaging. The combination offers unparalleled precision in looking for root causes of failures in microelectronic devices. Once a failure site is located, an FIB lift-off method can be used to prepare a TEM sample containing the area of interest. Further structural, elemental information can then be acquired from the failure site. We report here analyses of single and multiple bit failures in SRAM arrays carried out using FIB/SEM, and in two cases TEM imaging and EDS/PEELS. Root causes of bit failures including remnant seed-layer metal between stacked vias have been identified.
Formation of a Ba-Te Surface on GaAs
Authors: Boulais Kevin A. , Santiago Francisco , Long Karen J. , Gehman Victor H.
Published: April 2011

The formation of a Ba-Te surface on GaAs has been investigated. The surface was created using molecular beam epitaxy (MRS). A GaAs (100) surface was first exposed to Te and characterized using x-ray photoelectron spectroscopy (XPS), reflective high energy electron diffraction (RHEED) and low energy electron diffraction (LEED). The Te-reacted surface was then exposed to BaF2 flux producing a second reaction. In this reaction, the BaF2 dissociated leaving barium on the surface but no fluorine. This is in contrast to the clean (no tellurium) GaAs (100) surface in which BaF2 has been shown to grow single crystal. Although high order exists during early stages of the Ba-Te growth, further exposure gives way to a polycrystalline form. This paper discusses the formation and analysis of the Ba-Te surface.
Potentiometric Detection of DNA Molecules Hybridization Using Gene Field Effect Transistor and Intercalator
Authors: Sakata Toshiya , Otsuka Hidenori , Miyahara Yuji
Published: April 2011

We propose a new concept of a gene field effect transistor (FET) for detection of allele specific oligonucleotide hybridization, which is in principle based on charge density change at the gate insulator. The electrical characteristics of the gene FET were found to shift after specific binding of biomolecules at the surface of the gate insulator. Allele specific oligonucleotide hybridization and reaction between double-stranded DNA and intercalator were successfully detected with gene FETs because they have intrinsic charges in an aqueous solution. Ability to discriminate single nucleotide polymorphism (SNP) was also examined using the gene FET. Our results show that control of hybridization temperature and utilization of intercalator lead to more precise SNP analysis using the gene FET.
Nanocomposites with functionalized carbon nanotubes
Authors: Mhetre Shamal K. , Kim Yong. K. , Warner Steven. B. , Patra Prabir. K. , Katangur Phaneshwar , Dhanote Autumn.
Published: April 2011

The main issues related with preparation of nanocomposites are dispersion, alignment and adhesion between carbon nanotubes and matrix. We are designing an approach where these issues are fully addressed. We combined a functionalization approach with in-situ technique of nanocomposites preparation. A good dispersion and intercalation of carbon nanotubes were observed in the prepared nanocomposites. A presence of strong interfacial region was also noted. It is also found that orientation of carbon nanotubes inside matrix can be done by mechanically stretching of nanocomposites. DSC analysis shows that inclusion of carbon nanotubes affects crystallization behavior of nylon 6 significantly and it is found that CNTs acts as nucleating agents.
Virtual Synthesis of Sub-Nanoscale Materials With Prescribed Physical Properties
Authors: Pozhar Liudmila A. , Yeates Alan T. , Szmulowicz Frank , Mitchel William C.
Published: April 2011

Properties of electronic energy spectra of several small virtual clusters (known as small quantum dots, or QDs) composed of In, Ga and As atoms are investigated for the further use in nanoheterostructure (NHS) units of pre-designed electronic properties. Modern quantum statistical physics methods relate these properties to electronic transport properties of such systems and therefore, lead to realization of a virtual (i.e., fundamental theory- based, computational) approach to synthesis of sub-nanoscale electronic materials with pre-designed electronic properties[1].
Microstructure of Precipitated Au Nanoclusters in TiO2
Authors: Wang C. M. , Shutthanandan V. , Zhang Y. , Baer D. R. , Thomas L. E. , Thevuthasan S.
Published: April 2011

Gold nanoclusters dispersed in single crystal TiO2 (110) have been formed by 2MeV Au2+ implantation to an ion fluence of 1×1017 cm-2 at 300 K and 975 K followed by annealing at 1275 K for 10 hours. The morphological features, size and crystallographic orientation of the Au nanoclusters with respect to the TiO2 matrix have been investigated using conventional transmission electron microscopy and electron diffractions. In particular, the interface structure between the Au nanoclusters and TiO2 was investigated. Atomic structural model of interface between Au and TiO2 was established based on high-resolution transmission electron microscopy (HRTEM) imaging and HRTEM image simulations. Two types of orientation relationship can be identified, Au<110>//TiO2[001] and Au{111}//TiO2(200), and Au<110>//TiO2[001] and Au{111}//TiO2(110). Au clusters are faceted along Au{112}and Au{111} or Au{220} and Au{002} planes. The precipitated Au clusters show extensive (111) twins. These orientation relationships are the same for Au clusters grown on TiO2(110) surface, indicating that lowering interfacial energy to be a governing factor for setting the orientation relationship.
HSA-Cercanam®: A New Material with a Continuous Nanopore Network
Authors: Akash A. , Nair B. , Minnick K. , Wilson M. , Hartvigsen J.
Published: April 2011

A novel nano-ceramic material, called HSA-CERCANAM®, which has a very high surface area with a nanopore network has been developed. HSA-CERCANAM® can be casted in various shapes and forms resulting in a monolithic piece that has surface area as high as 80–100 m2/g. The surface area and the nanopore network of HSA-CERCANAM® remains stable at temperatures as high as 1000°C. Furthermore, the unique nature of HSA-CERCANAM® allows it to be casted on and around features, either sacrificial or permanent. Using sacrificial features, microchannels can be incorporated internally into the monolithic HSA-CERCANAM® piece in a simple, one-step process. Further, this monolithic ceramic component, which has an intrinsically high surface area and a nanopore network, can be infiltrated with a desired catalyst. This could offer clear technological advantages over currently available microreactors. The surface area, porosity, catalyst type and infiltration levels are some of the ways in which tailored microstructures can be realized in components such as mixers, heat exchangers, extractors, filters or reaction chambers thereby leading to highly efficient, multi-functional ceramic micro-devices.
A Model of New VUV NLO Materials Based on Borate: A Novel Noncentrosymmetric Borophosphate Compound Be3BPO7
Authors: He Zhangzhen , Moriyama Hiroshi
Published: April 2011

A favorable borate anionic group can be selected as the basic structural unit for VUV NLO materials, in terms of the properties of known inorganic NLO crystals and the features of their anionic groups, based on anionic group theory from SHG coefficients, UV absorption edge and moderate birefringence. Considering the coordination chemistry of atoms in some inorganic compounds, and the relationship between a noncentrosymmetric structural arrangement and the composition of compounds, a suitable theoretical model that aids the search for new VUV NLO materials has been proposed. The model compounds, formulated as MxA1,2(BO3)1,2Oy, may be prospective candidates for new VUV NLO materials considering their SHG coefficients, UV absorption edge, and moderate birefringence. The model suggests that investigation for a new VUV NLO material would be profitably conducted by focusing on boroberylate, boroaluminate, and borophosphate, on the basis of anionic group theory. For example, a novel noncentrosymmetric beryllium borophosphate compound, Be3BPO7 was synthesized by solidstate reaction. Microcrystalline Be3BPO7 has a hexagonal system and contains the BO3 anionic group as its basic structural unit, which should play an important role for SHG coefficients. In fact, Be3BPO7 powder was found to have a significant SHG effect.
In-situ Observation of Formation Processes of Anodic Porous Alumina on a Si Substrate Using Infrared Absorption Spectroscopy
Authors: Kimura Yasuo , Shiraki Hirokazu , Ishii Hisao , Ono Sachiko , Itaya Kingo , Niwano Michio
Published: April 2011

We investigated formation processes of a porous anodic alumina film on a p-type silicon (Si) substrate using infrared absorption spectroscopy in the multiple internal reflection geometry (MIR-IRAS). We observed drastic IR spectral changes when porous anodic alumina film approached interfaces between an aluminum (Al) layer and a Si substrate. The intensity of the IR absorption peaks due to water (H2O) molecules and silicon oxides (SiO2) increased simultaneously with a spike of anodic current density. The IR spectral changes indicated that the penetration of electrolytes brought about inhomogeneous oxidation of a Si substrate surface. We observed that the arrangement of the SiO2 nanodots closely reflected that of pores of a porous anodic alumina film. IR absorption peaks due to porous anodic alumina finally disappeared. The formation of SiO2 nanodots on a Si substrate promoted penetration of electrolytes to peel the porous anodic alumina film off it.
MODELLING TWO–PHASE FLOW IN MICROFLUIDIC DEVICES
Authors: Menech Mario De
Published: April 2011

A phase–field method is used to model two–phase flow in microfluidic devices, where capillary and viscous stresses dominate over inertial forces. Dissipative and reactive couplings in the hydrodynamic equations are derived from a Cahn–Hilliard–van der Waals free energy, which accounts for the equilibrium thermodynamics of the fluid system, including phase behavior, interfacial tension and wetting properties. The singularities inherent to the free boundary description are smoothed out by the presence of a diffuse interface over which interfacial stresses are distributed, such that complex phenomena like droplet breakup and coalescence or contact line dynamics can be resolved numerically. The reliability of the scheme used to solve the discretized transport equations is tested against different benchmarks for free flow conditions. The model is then applied to the simulation of the flow of droplets in microdevices, resulting in a satisfactory agreement with the behavior observed in experiments.
INFLUENCE OF CONFINEMENT ON POLYMER-ELECTROLYTE RELAXATIONAL DYNAMICS
Authors: Zanotti J.-M. , Smith L.J. , Price D.L. , Saboungi M.-L.
Published: April 2011

Conception and industrial production of viable high specific energy/power batteries is a central issue for the development of non-polluting vehicles. In terms of stored energy and safety, solid-state devices using polymer electrolytes are highly desirable. One of the most studied systems is PEO (polyethylene oxide) complexed by Li salts. Polymer segmental motions and ionic conductivity are closely related. Bulk PEO is actually a biphasic system where an amorphous and a crystalline state (Tg ≈ 213 K, Tm ≈ 335 K) coexist. To improve ionic conduction in those systems requires a significant increase of the amorphous phase fraction where lithium conduction is known to mainly take place. Confinement strongly affects properties of condensed matter and in particular the collective phenomena inducing crystallization. Confinement of the polymer matrix is therefore a possible alternative route to the impractical use of high temperature.

Results of a quasi-elastic incoherent neutron scattering study of the influence of confinement on polyethylene oxide (PEO) and (PEO)8Li+[(CF3SO2)2N]− (or (POE)8LiTFSI) dynamics are presented. The nano-confining media is Vycor, a silica based hydrophilic porous glass (characteristic size of the 3D pore network ≈ 50 Å). As expected, the presence of Li salt slows down the bulk polymer dynamics. The confinement also affects dramatically the apparent mean-square displacement of the polymer. Local relaxational PEO dynamics is described KWW model. We also present an alternate model and show how the detailed polymer dynamics (correlation times and local geometry of the motions) can be described without the use of such stretched exponentials so as to access a rheology-related meaningful physical quantity: the monomeric friction coefficient.
Effect of Thin Film Confinement on the Transport Properties of Ultra-Thin Polymer Films
Authors: Singh Lovejeet , Ludovice Peter J. , Henderson Clifford L.
Published: April 2011

The influence of film thickness and polymer molecular weight on the diffusion coefficient of a series of small molecule penetrants (including water, benzene, and trifluoroacetic acid) in thin films of two different model photoresist polymers (poly(p-hydroxystyrene) and bis-triflouromethyl carbinol substituted poly(norbornene)) has been studied using vapor sorption experiments via quartz crystal microbalance (QCM) methods. Diffusion coefficients for films ranging in thickness from approximately 1 μm to 50 nm were determined. It is observed that the diffusion coefficient of small molecules in a thin polymer film is a strong function of film thickness, and that the diffusion coefficient decreases drastically as film thickness is reduced below a critical thickness value. This critical thickness value is found to be a function of both the type of polymer used and the polymer molecular weight.
Improvement of Crystallization and Mechanical Properties of PLA by Means of Clay Nanocomposite
Authors: Okamoto Hirotaka , Nakano Mitsuru , Ouchi Makoto , Usuki Arimitsu , Kageyama Yuji
Published: April 2011

Some composite materials of poly (lactic acid) (PLA) with organophilic clays and an organic crystal accelerator (OCA) were prepared by melt compounding method to improve the rate of crystallization and mechanical properties, especially heat distortion temperature (HDT). The PLA/clay nanocomposite with 2.9wt% of finely dispersed organophilic clay and 1wt% of the OCA showed an exothermic peak corresponding to its crystallization at 1.9 minutes in the isothermal measurement of DSC at 100°C from its molten state, although PLA itself did not show a clear peak in the same procedure. Crystallized specimens of the nanocomposite were well obtained by injection molding when the hold time was set at more than 90 seconds. The HDT of the specimens that were held for more than 120 seconds in the mold exceeded 120°C. It is about 65°C higher than amorphous PLA. The crystallized specimen with 1wt% of the clay showed higher tensile modulus and Izod impact strength than the amorphous one.
Mechanical Properties of Superhard Nanocomposites with High Thermal Stability
Authors: Veprek Stan , Argon Ali S.
Published: April 2011

Abstract Superhard nanocomposites, nc-MnN/a-XxNy (M = Ti, W, V, Zr, (Al1-xTix)N; X = Si, B) with hardness of 40–100 GPa are prepared by plasma CVD or PVD under a sufficiently high nitrogen activity and deposition temperature that allow the formation of a stable nanostructure by self-organization upon strong thermodynamically driven, spinodal phase segregation. These nanocomposites display an extraordinary combination of a high hardness, high elastic recovery, high resistance against brittle fracture and tensile strength of 5 to 40 GPa approaching the ideal strength of flaw-free materials. These properties can be understood in terms of conventional fracture physics scaled appropriately down to crystallite sizes of few nm. The interfacial monolayer of Si3N4 or BN with strong bonding to the nanocrystallites and high structural flexibility avoids grain boundary sliding. With increasing thickness of this interface the hardness decreases, possibly due to an increase of this “liquid-like” component in which plastic transformation can be triggered.
The Microstrain Generation in Cryomilled Nickel by Impurity Nitrogen Atoms
Authors: Chung Kyung H. , Lavernia Enrique J.
Published: April 2011

The residual microstrains in cryomilled Ni powders, processed under various cryomilling conditions, are measured by XRD and analyzed using a single line approximation (SLA) method. The results show that the average residual microstrains are in the range of 2×10-3 ∼ 6×10-3, and the residual microstrain on the (200) plane is higher than those on the other planes by 33 %. The measured microstrain is proposed to evolve from the introduction of N as impurity atoms in Ni lattice may be attributed to the evolution of the residual microstrain. The N atoms tend to stay in the octahedral sites of Ni, and the diameter of N atom is larger than that of the octahedral site of Ni by 48 %. Accordingly, a lattice strain field is expected around interstitial N atoms that are located at octahedral sites. By comparing the crystal structure around the octahedral site of Ni with that of Ni3N structure, the lattice strains are estimated to be in the range of 5 ∼ 15 %. The results show that the (200) plane has the lattice strains that are two times higher than those in other planes, and this is argued to be the reason for the measured anisotropy of residual microstrain in Ni after cryomilling.
Surface porosity development on metal substrates by helium implantation and annealing.
Authors: Escobar Galindo R. , van Veen A. , Schut H. , Evans J.H. , Fedorov A.V. , Hou P.Y. , de Hosson J.Th.M.
Published: April 2011

The effects of helium implantation parameters and heating schemes on the formation of surface porosity have been studied. Confinement of the implanted helium by a coating on the metal leads to a prolonged development of the bubble structure. Finally, delamination and blistering occurs and rather open surface structures remain.
Radiation-Induced Nanostructures in an Iron Phosphate Glass
Authors: Sun K. , Ding T. , Wang L.M. , Ewing R.C.
Published: April 2011

Electron and ion irradiation-induced nanostructures in an iron phosphate glass with a composition of 45 mol%Fe2O3-55 mol%P2O5 have been characterized by advanced electron microbeam techniques. Analysis by energy-filtered transmission electron microscopy indicated that Fe-rich and P-rich nanophases were formed when the glass was irradiated under a broad (with a diameter of 1.2μm) electron beam [give the dose range]. Phase separation developed with the increase in electron dose (from 1.0×1026e/m2 to 4.8×1026e/m2) as a result of the formation of an Fe-rich phase and pure P-phase. The formation of the Fe-rich and the P-phases are thought to be due to mainly ionization process. Under a low energy ion beam irradiation, Fe/FeO nanoparticles were formed, as confirmed by selected-area electron diffraction analysis. However, no nanoparticles were observed under a high-energy high-dose ion irradiation. The ion beam-irradiation results suggest that the formation of the Fe/FeO nanoparticles was due to preferential sputtering during ion irradiation and that the nanoparticles lie within the surface layers of the glass.
Molecular dynamics simulation of point defect accumulation in 3C-SiC
Authors: Devanathan R. , Gao F. , Weber W. J.
Published: April 2011

Defect accumulation in silicon carbide has been simulated by molecular dynamics using a Brenner-type potential connected smoothly to the Ziegler-Biersack-Littmark potential. Displacement damage in 3C-SiC, which is known to consist of point defects, vacancy and interstitial clusters and anti-site defects, was modelled by introducing random displacements on the Si or C sublattice. SiC was amorphized by Si displacements at a damage level corresponding to 0.15 displacements per atom (dpa) and by C displacements at 0.25 dpa. In both cases, the damage consists of Si and C Frenkel pairs as well as anti-site defects. The results provide evidence that SiC can be amorphized by displacing C atoms exclusively and suggest that short-range disorder provides the driving force for amorphization of SiC.
Formation of Au-nanocrystals in TiO2 and SrTiO3 by ion implantation in restricted volumes
Authors: Fromknecht R. , Linker G. , Sun K. , Zhu S. , Wang L.M. , van Veen A. , van Huis M.A. , Weimann T. , Wang J. , Niemeyer J. , Eichhorn F. , Wang T.
Published: April 2011

Au-ions were implanted at RT conventionally and through a mask into TiO2- and SrTiO3-single crystals with doses in the range from 1×1015Au+/cm2 to 1×1017Au+/cm2, and dose rates of ∼1011ions/sec and ∼3×1013ions/sec, at an energy of 260keV; some samples subsequently were annealed at temperatures up to 1100K. The Au-atoms precipitated to nanocrystals during implantation with an average particle size of 1.5nm. HRTEM investigations revealed that the Au-nanocrystals, embedded in amorphous TiO2-regions, have a broad size distribution varying from large sizes in the near surface region to smaller sizes at larger depths. In the annealing process a coarsening and a reorientation of the Au-nanocrystals is observed. At 1000K the particle size of the textured Au-implant was evaluated to be ∼6nm. Implantation with a high dose rate performed through a metal mask with holes of 120μm diameter and without annealing resulted in an almost equidistant arrangement of the Au-nanocrystals with a narrow size distribution of 2–6nm in TiO2 and 3–5nm in SrTiO3 in the near surface region. Au-ion implantation through an e-beam resist mask (50nm × 50nm holes), with doses ranging from 1×1015Au+/cm2 to 4×1015Au+/cm2 at the low dose rate and annealed at 1000K, lead to a periodic structure of the Au-nanocrystals. The nanocrystal size, evaluated from TEM analysis, in the as-implanted state was ∼5nm and after annealing at 1000K sizes of several nanometers to several tens of nanometers were observed.
Site-Control Technology for InAs Quantum Dot Formation by Direct Deposition of Indium Nano-Dots with a Nano-Jet Probe
Authors: Ohkouchi Shunsuke , Nakamura Yusui , Nakamura Hitoshi , Asakawa Kiyoshi
Published: April 2011

We propose a new nano-probe-assisted technique which enables the formation of site-controlled InAs quantum dots (QDs). High-density two-dimensional indium (In) nano-dot arrays on a GaAs substrate were fabricated by using a specially designed atomic-force-microscope (AFM) probe (the Nano-Jet Probe). This developed probe has a hollow pyramidal tip with a sub-micron size aperture on the apex and an In-reservoir tank within the stylus. By applying a voltage pulse between the pyramidal tip and the sample, In clusters were extracted from the reservoir tank within the stylus through the aperture, resulting in the In nano-dot formation. These In nano-dots can be directly converted to InAs QD arrays by subsequent irradiation of arsenic flux.
Self-Organized Superlattices in GaInAsSb Grown on Vicinal Substrates
Authors: Wang C.A. , Vineis C.J. , Calawa D.R.
Published: April 2011

Self-organized superlattices are observed in GaInAsSb epilayers grown lattice matched to vicinal GaSb substrates. The natural superlattice (NSL) is oriented at a slight angle of about 4° with respect to the vicinal (001) GaSb substrate. This vertical composition modulation is detected at the onset of growth. Layers in the NSL are continuous over the lateral extent of the substrate. Furthermore, the NSL persists throughout several microns of deposition. The NSLs have a period ranging from 10 to 30 nm, which is dependent on deposition temperature and GaInAsSb alloy composition. While the principle driving force for this type of phase separation is chemical, the mechanism for the self-organized microstructure is related to local strains associated with surface undulations. By using a substrate with surface undulations, the tilted NSL can be induced in layers with alloy compositions that normally do not exhibit this self-organized microstructure under typical growth conditions. These results underscore the complex interactions between compositional modulation and morphological perturbations.
Light Guiding in Low Index Materials using High-Index-Contrast Waveguides
Authors: Almeida Vilson R. , Xu Qianfan , Panepucci Roberto R. , Barrios Carlos A. , Lipson Michal
Published: April 2011

We propose a novel high-index-contrast waveguide structure capable of light strong confinement and guiding in low-refractive-index materials. The principle of operation of this structure relies on the electric field (E-field) discontinuity at the interface between high-index-contrast materials. We show that by using such a structure the E-field can be strongly confined in a 50-nm-wide low-index region with normalized average intensity of 20 μm−2. This intensity is approximately 20 times higher than that can be achieved in SiO2 with conventional rectangular or photonic crystal waveguides.
Resonant Inelastic Soft X-ray Scattering Studies of U(VI) Reduction on Iron Surfaces
Authors: Butorin S. M. , Shuh D. K. , Kvashnina K. , Soroka I. L. , Ollila K. , Roberts K. E. , Guo J.-H. , Werme L. , Nordgren J.
Published: April 2011

We report on the spectroscopic analysis of several samples relevant to the processes governing the behavior of oxidized uranium species in groundwater solutions under anoxic conditions. Both Fe samples with different times of exposure to the U(IV) solution and Fe metal-solution inetrfaces in the liquid cell ex-situ and in-situ, respectively. Resonant inelastic soft x-ray scattering is shown to be sensitive to the chemical state of uranium. The measurements were performed at a number of energies of the primary photon beam across the U 5d absorption edge. The results unambiguously indicate the reduction of U(VI) to U(IV) on the Fe surface.
Modelling of the (U1−y238Puy)O2+x Leaching Behaviour in Deionised Water under Anoxic Conditions
Authors: Quiñones J. , Cobos J. , Diaz-Arocas P. , Rondinella V. V.
Published: April 2011

The aim of this work is to provide credibility to the radiolytic models developed for performance assessment studies. Nowadays, there is a tendency to consider them useful tools for predicting the behaviour of spent fuel matrix under repository conditions, although they still suffer of limitations due, among others, to the following reasons: limited availability of kinetic data, difficulty to handle heterogeneous systems, lack of model validation.

A kinetics-based model to predict the dissolution of UO2 α-doped pellets under initial anoxic conditions is presented and compared with experimental results previously obtained. The uranium and plutonium concentrations in solution are predicted by considering the presence of an α-radiation field and its influence due to radiolysis of water on the pellet surface oxidation and subsequent dissolution.

The initial parameters required by the model in order to reproduce the pellet alteration process are: system geometry, chemical composition of the leachant, physico-chemical characteristics of the leachate and oxidation conditions of the pellet surface (expressed in terms of U(VI)/U(IV) ratio). The last one is the key parameter in the model for simulating the initial quick dissolution process. The results obtained are compared with experimental data. The agreement between the predictions obtained and the experimental published data is good.

The influence on the matrix oxidation – dissolution process due to the α-radiation field as well as the release of Pu are reproducible by the model. The Pu concentration trends as a function of time are explained in connection with the matrix dissolution process and are controlled by the formation of the secondary phase “Pu(OH)4(s)”.
Pitting Studies Under Anoxic Conditions on Candidate Container Materials AISI 316L hMo and UHB 904L for The Disposal of HLW in Argillaceous Formations
Authors: Kursten Bruno , Druyts Frank
Published: April 2011

Stainless steel is being envisaged as the primary candidate container material for the final disposal of vitrified HLW in deep geological argillaceous formations in Belgium. The impact of an evolving underground repository environment, i.e. a progressive change from oxic to anoxic conditions (due to the consumption of entrapped oxygen), on the pitting behaviour of austenitic stainless steels AISI 316L hMo and UHB 904L was studied. CPP-experiments were performed in synthetic solutions, which are representative for the near-field chemistry of an underground repository. The solutions contained various amounts of Cl- (100–50,000 mg/L) at near-neutral pH. Experiments were conducted at 16 and 90°C.

AISI 316L hMo and UHB 904L will not be subjected to immediate pitting problems neither under oxic, nor under anoxic conditions. However, AISI 316L hMo could present long-term pitting problems under oxic conditions. Pits are much easier initiated on AISI 316L hMo, for both oxic and anoxic conditions. The pits propagate in a rather similar manner under oxic conditions for both alloys, whereas under anoxic conditions the pits formed on AISI 316L hMo are much deeper. AISI 316L hMo is more susceptible to crevice attack.
Assessment of Redox Conditions in the Near Field of Nuclear Waste Repositories: Application to the Swiss high-level and intermediate level waste disposal concept
Authors: Wersin Paul , Johnson Lawrence H. , Schwyn Bernhard
Published: April 2011

Redox conditions were assessed for a spent fuel and high-level waste (SF/HLW) and an intermediate-level waste (ILW) repository. For both cases our analysis indicates permanently reducing conditions after a relatively short oxic period. The canister-bentonite near field in the HLW case displays a high redox buffering capacity because of expected high activity of dissolved and surface-bound Fe(II). This is contrary to the cementitious near field in the ILW case where concentrations of dissolved reduced species are low and redox reactions occur primarily via solid phase transformation processes.

For the bentonite-canister near field, redox potentials of about -100 to -300 mV (SHE) are estimated, which is supported by recent kinetic data on U, Tc and Se interaction with reduced iron systems. For the cementitious near field, redox potentials of about -200 to -800 mV are estimated, which reflects the large uncertainties related to this alkaline environment.
Monitoring Disturbances in the Repository System during Construction Process: Experiences from Natural Decay Series Studies at the Pyhäsalmi Mine (Central Finland)
Authors: Marcos N. , Suksi J. , Rasilainen K. , Antikainen J.
Published: April 2011

Prior to the selection of the site for nuclear waste disposal, the performance of the repository is assessed based on general geological data of sites under investigation. Once the site has been selected, the results of the site investigations are used to establish the baseline condition to monitor and evaluate the induced processes during the construction of the repository. One of the processes considered is the change in hydraulic properties in the bedrock due to excavation of tunnels and other open spaces. Within this framework, the results of natural decay series studies in rock samples from the Pyhäsalmi mine collected in the nearby of a water-conducting fracture at the depths of 1275 and 1325 m may give insights on the influence of the excavation-induced changes, if any, in the groundwater flow. The spatial and temporal scale of these changes is also evaluated. The methodology used in this work could be applied to add confidence in the establishment of the baseline conditions to better assess the evolution of changes in groundwater flow patterns during and after construction of a repository system.
The Modelling of Gas Migration through Compacted Bentonite Buffers in Radioactive Waste Repositories: the Work of the GAMBIT Club
Authors: Rodwell William R , Hoch Andrew R , Swift Ben T
Published: April 2011

Use of compacted bentonite buffers is frequently planned in radioactive waste repositories to isolate waste canisters from the geological environment. When gas is generated from the wastes or their containers, it will need to migrate through the bentonite if pressure rises local to the canisters are to be avoided. Assessment of the effect of gas produced from waste canisters in bentonite buffers requires both experimental data on and models of gas migration through initially water-saturated bentonite. Several different approaches to modelling gas migration through bentonite are described. Some example comparison of model results with experimental data are provided, and some general discussion about the modelling approaches is offered.