bluuebunny/crossref_metadata_2025 huggingface dataset:
Dielectric and Optical Properties of Perovskite-type Artificial Superlattices
Authors: Harigai Takakiyo , Nam Song-Min , Kakemoto Hirofumi , Wada Satoshi , Saito Keisuke , Tsurumi Takaaki
Published: April 2011

BaTiO3/SrTiO3, BaTiO3/BaZrO3, and SrZrO3/SrTiO3 artificial superlattices were fabricated on SrTiO3 substrates by the molecular beam epitaxy (MBE) process. The stacking periodicity of each layer was varied from 1 unit cell to 40 unit cells, and the total thickness was fixed at 80 unit cells. In-situ reflection high-energy electron diffraction (RHEED) and x-ray diffraction (XRD) clearly shows the formation of the superlattice structure. Their lattice parameters obtained from the reciprocal space mapping measurement indicated that the lattice distortion was dependent on the stacking periodicity. The capacitance and the complex admittance of the superlattices were measured with interdigital electrodes by an impedance analyzer up to 110 MHz. It was found that the dielectric permittivity changed with the superlattice periodicity. The Q-V measurement results showed clear hysteresis curves and this suggested that ferroelectricity was induced into the SrZrO3/SrTiO3 superlattices despite a combination between paraelectrics/paraelectrics.
Artificially Induced Perturbations in Chirped Magneto-Optical Bragg Gratings
Authors: Jonsson Fredrik , Flytzanis Christos
Published: April 2011

We report on theoretical analysis of magneto-optically induced longitudinal perturbations in chirped magneto-optical Bragg gratings. The induced perturbations considered are of Lorentzian shape, with a spatial extent considerably larger than the spatial grating period but at least an order of magnitude less than the geometrical length of the grating. In the numerical simulation of the proposed device, we show on a high polarization state selectivity in the region of the perturbation, with resonance peaks of transmission for circularly polarized orthogonal components possessing a full width at half maximum as narrow as 0.18 nm, meanwhile being separated by 0.6 nm.
Novel Magneto-Optic Layers Based on Semiconductor Nanostructures for Kerr Microscopy.
Authors: Gourdon C. , Jeudy V. , Karczewski G. , André R. , Ivchenko E.L.
Published: April 2011

A novel type of magneto-optic layers based on CdMnTe quantum wells is used to image the magnetic flux pattern at the surface of type I superconductors. The magneto-optic layer is designed as an anti-reflecting optical cavity. The quantum wells are arranged in a Bragg structure and placed at maxima of the electric field in the cavity in order to enhance Faraday rotation.
Sodium Ion Conduction in Plastic Phases: Dynamic Coupling of Cations and Anions in the Picosecond Range
Authors: Wilmer D. , Feldmann H. , Lechner R.E. , Combet J.
Published: April 2011

Results of simple computer simulations and model calculations for ion conducting rotor phases are compared to quasi-elastic neutron scattering data from solid solutions of sodium orthophosphate and sodium sulphate, xNa2SO4 · (1 — x)Na3PO4. These materials are not only sodium fast-ion conductors in their high-temperature cubic phases but also show considerable dynamic reorientation disorder of their tetrahedral anions.

At an elastic energy resolution of about 100 μeV, neutron spectrometry monitored oxygen scattering due to anion reorientation which occurs on the picosecond time scale. This thermally activated process exhibits activation energies between 0.184 eV (x = 0. 0) and 0.052 eV (x = 0.5). Analysis of the quasielastic intensities as a function of scattering vector Q gives clear evidence of the involvement of cations in the anion reorientation.

Increasing the elastic resolution to about 1 μeV FWHM (thereby shifting the dynamic window to the nanosecond scale) allowed to examine sodium diffusion in x Na2SO4 · (1 — x)Na3PO4. This process consists predominantly of thermally-activated jumps between tetrahedrally coordinated sites, the activation energies ranging from 0.64 eV for x = 0.0 to 0.30 eV for x = 0.5.
Oxide-Ion Transport in Gadolinium Zirconate - Titanates under High Pressure
Authors: Takamura Hitoshi , Kakuta Hirofumi , Kamegawa Atsunori , Okada Masuo , Tuller Harry L.
Published: April 2011

The oxide-ion conduction of gadolinium zirconate - titanates, Gd2(Ti1−xZrx)2O7 (GTZ), has been investigated under high pressure in the range of 2 to 6 GPa with the aid of a cubic-anvil-type apparatus. For these pyrochlore compounds, the oxide-ion conductivity at elevated temperatures in the range of 750 to 960 °C decreased with increasing pressure, indicating the presence of a positive activation volume, ΔV. The activation volumes ΔV of GZ (x = 1.0) and GTZ (x = 0.95) were 2.0 and 1.3 cm3/mol, respectively, at 750 °C and decreased with increasing temperature.
Exploration of Electrophoretic Deposition of YSZ Electrolyte for Solid Oxide Fuel Cells
Authors: Xu Zhigang , Rajaram Gukan , Sankar Jag
Published: April 2011

The suspensions of yttria stabilized zirconia (YSZ) were prepared in pure acetylacetone and ethanol and their mixtures. In all of the suspensions, YSZ thin films were obtained using electrophoretic deposition technique on the substrates of stainless steel and porous strontium-doped lanthanum manganite (LSM) which is a typical cathode materials used in solid oxide fuel cells (SOFCs). The deposition behavior in the different suspensions was studied. The deposited films were dried at room temperature and then sintered at high temperature. Observation with scanning electron microscopy (SEM) showed the sintered YSZ were of high density.
Dye Sensitized Solar Cells Incorporating Polyelectrolyte Multilayer Composites
Authors: Lowman Geoffrey M. , Tokuhisa Hiroaki , Lutkenhaus Jodie L. , Hammond Paula T.
Published: April 2011

Dye sensitized solar cells (DSSC's) are constructed using TiO2 electrodes synthesized by aqueous liquid phase deposition in combination with microcontact printing techniques or porous thin film template methods. Layer-by-layer deposition of polyelectrolytes is used to produce an ionic conducting solid-state electrolyte thin film, which is enhanced by post-processing in oligoethylene glycol diacid (OEGDA). The impact of TiO2 film architecture, as well as the thin film electrolyte, on device performance is discussed.
Nano-Columnar Mg Thin Films Created by Plasma Sputter Deposition for Improved Hydrogen Kinetics and Storage Properties
Authors: Zandbergen M. W. , Eijt S. W. H. , Legerstee W. J. , Schut H. , Svetchnikov V. L.
Published: April 2011

The hydrogen storage properties of nanostructured Mg and MgH2 thin films were studied as created by Ar and Ar+H2 plasma sputter deposition. Columnar structures with typical widths of ∼120 nm are observed with their long columnar axis extending throughout the thickness of the films. Applying substrate bias voltages during deposition results in narrower columns. A concomitant reduction in hydrogen desorption temperature from 400 °C to 360 °C is observed. Capping the Mg films with a ∼100 nm thin Pd layer leads to significantly reduced hydrogen desorption temperatures of ∼200 °C induced by the catalytic activity of the Pd cap layer. Also, hydrogen permeation of the films is strongly improved. The rate-determining factor is found to be the dissociation of the hydrogen molecules. Optimum hydrogen loading conditions of the Pd/Mg films were obtained just above ∼200 °C at hydrogen pressures of 0.25–1.0 MPa, resulting in hydrogen storage capacities in the range of 4–7 wt%.
Nanoscale Elastic-Property Mapping with Contact-Resonance-Frequency AFM
Authors: Hurley D. C. , Kos A. B. , Rice P.
Published: April 2011

We describe a dynamic atomic force microscopy (AFM) method to map the nanoscale elastic properties of surfaces, thin films, and nanostructures. Our approach is based on atomic force acoustic microscopy (AFAM) techniques previously used for quantitative measurements of elastic properties at a fixed sample position. AFAM measurements determine the resonant frequencies of an AFM cantilever in contact mode to calculate the tip-sample contact stiffness k*. Local values for elastic properties such as the indentation modulus M can be determined from k* with the appropriate contact-mechanics models. To enable imaging at practical rates, we have developed a frequency-tracking circuit based on digital signal processor architecture to rapidly locate the contact-resonance frequencies at each image position. We present contact-resonance frequency images obtained using both flexural and torsional cantilever images as well as the corresponding vertical contact-stiffness (k*) image calculated from flexural frequency images. Methods to obtain elastic-modulus images of M from vertical contact-stiffness images are also discussed.
Structure and Dynamics of Propylene Oxide and Trimethylene Oxide Clathrate Hydrates
Authors: Peral Inmaculada , Curtis Joseph E. , Chakoumakos Bryan C. , Jones Camille Y.
Published: April 2011

We present results from studies of the structure and dynamics of clathrate hydrates of three cyclic ethers by neutron diffraction and preliminary results on molecular dynamics simulations. Recent results from neutron powder diffraction and quasielastic neutron scattering of studies of propylene oxide (PO, C3H6O) and its isomer trimethyelene oxide (TMO, C3H6O), are compared with structural results obtained previously for tetrahydrofuran (THF, C3H5O). Experimental evidence of distortions of the host structures with temperature is discussed in light of the findings from quasielastic neutron scattering, which indicate distinct regions of high-temperature and low-temperature rotational dynamics and a temperature dependence related to the size of the guest. Preliminary MD results indicate a general expansion of the lattice with temperature resulting in increased volume available to PO.
On The Mechanics of Indentation Induced Lateral Cracking
Authors: Chen Xi
Published: April 2011

The mechanics governing the lateral cracks that form when a hard object plastically penetrates a ceramic is presented. The roles of indentation load, penetration depth and work of indentation are all highlighted, as are the influences of the mechanical properties of the substrate. The three dimensional axisymmetric problem for an annular crack driven by a rigid spherical or conical indenter pushed into a semi-infinite half-space of elastic-perfectly plastic material is solved using numerical methods. The region of highest tensile stress is identified corresponding to the location where a crack is most likely to nucleate. This location coincides with the depth below the surface where the crack will expand parallel to the surface under mode I conditions. The solutions have been validated by comparison with measurements of the cracks that form upon Vickers indentation. The basic formula for the crack radius has been used to predict trends in cracking upon static penetration.
MODELING OF NANOINDENTATION AND MICROSTRUCTURAL DUCTILE BEHAVIOR IN METALLIC MATERIAL SYSTEMS
Authors: Ma Jeong Beom , Ashmawi W. , Zikry M. A. , Schall D. , Brenner D. W.
Published: April 2011

Specialized large-scale computational finite-element and molecular dynamic models have been used to understand and predict how dislocation density emission and contact stress fields due to nanoindentation affect inelastic deformation evolution at scales that span the molecular to the continuum level in ductile crystalline systems. Dislocation density distributions and local stress fields have been obtained for different crystalline slip-system and grain-boundary orientations. The interrelated effects of grain-boundary interfaces and orientations, dislocation density evolution and crystalline structure on indentation inelastic regions have been investigated.
Nanomechanical Testing of Hydrated Biomaterials: Sample Preparation, Data Validation and Analysis
Authors: Kaufman Jessica D. , Klapperich Catherine M.
Published: April 2011

Implants, tissue engineering scaffold materials, drug delivery and bio-micro electromechanical systems (BioMEMs) all use polymer or hydrogel materials. These applications require both mechanical performance and successful integration of the material into a biological environment. Mechanical strength, storage and loss moduli, wear resistance and surface adhesion properties are all critical in biomedical device design and can be determined using nanoindentation. The difficulty of obtaining large samples of specialized materials, and the complexity of testing soft materials in traditional materials testing apparatus, make nanoindentation an attractive alternative. Our previous research using nanoindentation to measure the surface mechanical properties of non-hydrated polymers led to improvement in nanoindentation testing protocols. One of the major challenges in using this technique for hydrogels and tissues is maintaining and controlling hydration of the materials during the test. Here we describe the design of a microfluidic platform for nanoindentation that facilitates continuous hydration of hydrogel samples and high throughput nanomechanical testing. Data from creep experiments on synthetic, hydrated poly-2-hydroxyethyl methacrylate (poly-HEMA) are presented. In addition, we show data to validate the materials properties determined from nanomechanical testing by complementary testing. Finally, the data is fitted to a phenomenological model for viscoelastic materials, specifically the three-element standard linear solid model used by Cheng et al. [1].
Measurements of Viscoelastic Properties of SWNT/Polymer Composite Films Using Nanoindentation
Authors: Lu Hongbing , Huang Gang , Wang Bo , Mamedov Arif , Gupta Sachin
Published: April 2011

Methods for measuring the mechanical properties of linear viscoelastic materials in both time and frequency domains have been presented using the nanoindentation technique. In the time domain, the viscoelastic functions of materials were measured through the direct differentiation method using the load-displacement curve or the material parameter extraction method by fitting the load-displacement curve. In the frequency domain, the complex creep functions of materials were measured in terms of dynamic load-displacement data under a harmonic loading superimposed upon a ramp loading. As an application, these methods were used to determine the material properties for single-wall carbon nanotube (SWNT)/polyelectrolyte mutilayer films and the neat resin film made of polyelectrolyte under nanoindentation tests. The uniaxial relaxation moduli as a function of time for both SWNT/polymer composite films and the neat resin film have been obtained from quasi-static nanoindentation tests. The complex compliance as a function of frequency for SWNT/polyelectrolyte composite films has been obtained from dynamic nanoindentation tests.
High Temperature Nanoindentation for the Study of Flow Defects
Authors: Schuh C. A. , Mason J. K. , Lund A. C. , Hodge A. M.
Published: April 2011

Our recent progress in elevated temperature nanoindentation is reviewed, with an emphasis on the study of discrete events (i.e., pop-in phenomena) observed during nanoindentation. For crystalline materials the incipient plasticity problem is associated with the nucleation of dislocations, an effect which we show to be significantly temperature dependent. For metallic glasses it is the operation of individual shear bands beneath the indenter that gives rise to pop-in events; here we also show this to be a temperature dependent phenomenon. Approaches to extract the activation volume and energy of defects involved in plastic flow beneath the indenter are also briefly described.
Effects of Surface Stress on the Load-Depth Curves of Depth-Sensing Indentation
Authors: Wang Q. , Ozaki K.
Published: April 2011

Based on the effects of residual surface stress on the unloading curves of indentation load-depth responses, an experimental scheme for determination of the residual stress by depth-sensing indentation is proposed. From the point that the elastic unloading portion of the load-depth curves can be expected to be unaffected by the residual stresses, the formula for evaluating surface stress by indentation is derived based on energy method. The proposed formula is verified by using FEM simulated indentation load-depth responses for different surface stress levels. The levels of surface stress evaluated by the proposed formula show a good agreement with the ones used as input parameters in FEM simulation.
Abnormal deformation behavior in Polysynthetically-twinned TiAl crystals with A and N orientations——an AFM study
Authors: Chen Yali , Pope David P.
Published: April 2011

Polysynthetically-twinned TiAl crystals were deformed by compression with loading axis parallel and perpendicular to the lamellar interfaces. The deformation structures on the free surfaces were scanned using a dimension AFM with scan directions parallel and perpendicular to the lamellar interfaces. Abnormal deformation behaviors were observed to occur in both orientations. When the compression axis is parallel to the lamellar interfaces, the gamma and alpha lamellae deform primarily by shear in planes inclined with the lamellar interface, while the shear vectors lie in the interface. However, in-plane shear, shear in slip planes parallel to the lamellar interfaces, also occurs along the lamellar interfaces. When the loading axis is perpendicular to the lamellar interface, in-plane shear was found to be dominant at the beginning stage of plastic deformation and contributes more to the macroscopic strain. These behaviors are controversial to the Schmid's Law since the applied resolved shear stress for these deformation systems is zero. The abnormal phenomenon was explained by the large coherency stresses along the lamellar interfaces.
Identification of the chirality of intermetallic compounds by electron diffraction
Authors: Fujio S. , Sakamoto H. , Tanaka K. , Inui H.
Published: April 2011

A new CBED method is proposed for the identification of the chirality of enantiomorphic crystals, in which asymmetry in the intensity of the reflections of Bijvoet pairs in an experimental symmetrical zone-axis CBED pattern is compared with that of a computer-simulated CBED pattern. The intensity difference for reflections of these Bijvoet pairs results from multiple scattering among relevant Bijvoet pairs of reflections, each pair of which has identical amplitude and different phase angles. With the method, a single CBED pattern is sufficient and chiral identification can be made for all possible enantiomorphic crystals that are allowed to exist in crystallography. The method is successfully applied to some chiral intermetallic compounds.
TEM Analysis of Long-Period Superstructures in TiAl Single Crystal with Composition Gradient
Authors: Hata S. , Shiraishi K. , Kuwano N. , Itakura M. , Tomokiyo Y. , Nakano T. , Umakoshi Y.
Published: April 2011

The ordering mechanism of long-period superstructures (LPSs) in Al-rich Ti-Al alloys was studied using a TiAl single crystal with a composition gradient. A TiAl single crystal with gradient compositions from 55 to 75 at.% Al was prepared by annealing in a molten Al at 1234°C. The single crystal exhibits long-period ordering into different LPSs depending on the Al concentration as follows: an Al5Ti3 type short-range order, h-Al2Ti and one-dimensional antiphase domain structures. These LPSs show an orientation relationship in which Al (002) layers of the LPSs are parallel to those of the TiAl matrix. The atomic arrangements of the LPSs are characterized in common as the alternate stacking of the Al (002) layers and Ti-Al (002) layers. It is thus concluded that the ordering of this type of LPSs and the phase transition between these LPSs are explained as structural changes in Ti-Al (002) layers of the Al-rich L10-TiAl crystal.
Nanomechanical and Microstructural Properties of Bombyx mori Silk Films
Authors: Ebenstein Donna M. , Park Jaehyung , Kaplan David L. , Wahl Kathryn J.
Published: April 2011

Instrumented indentation and micro-Raman spectroscopy were used to investigate the mechanical and structural properties of Bombyx mori silk films. Twelve different films were prepared from B. mori silk fibroin protein using a variety of post-deposition processing treatments (e.g. soaking in methanol, soaking in water, stretching, and/or enzymatic etching). The results show that different treatments lead to changes in both the conformation of the silk fibroin protein and the mechanical properties of the films.
Photoinduced Memory Effects based on Poly(3-hexylthiophene) and Al Interface
Authors: Kaneto Keiichi , Ujimoto Mitsuru , Takashima Wataru
Published: April 2011

Organic memory cells have been constructed utilizing conducting polymer, poly(3-hexylthiophene), PHT. The PHT film with Au electrodes at the bottom was coated with ultra thin Al having the thickness of 1 nm on the top. The cell showed the large photoconductivity, which was measured between Au bottom electrodes. The photoconductivity lasted for several hours after turn off the illumination, indicating photo induced memory effect. The phenomenon is discussed in terms of the persistent photoconduction, which is resulted from the electron trapping at Al donor sites in the depletion layer formed near the top of film.
Simulations of Organic-tethered Silsesquioxane Nanocube Assemblies
Authors: Zhang Xi , Chan Elaine R. , Ho Lin C. , Glotzer Sharon C.
Published: April 2011

Polyhedral oligomeric silsesquioxane (POSS) based materials are a class of organic/inorganic hybrid nanomaterials with many interesting properties. Recent experiments have demonstrated that self-assembly of tethered POSS nanocubes is a promising route to the synthesis of novel materials with highly ordered, complex nanostructures. Using a coarsegrained model developed for tethered POSS, we perform molecular simulations of POSS molecules tethered by short polymers to investigate how the novel architecture of these hybrid building blocks can be exploited to achieve useful structures via self-assembly. We systematically explore the parameters that control the assembly process and the resulting equilibrium structures, including concentration, temperature, tethered POSS molecular topology, and solvent conditions. We report preliminary results of lamellar and cylindrical structures that are typically found in conventional block copolymer and surfactant systems, but with interesting modifications of the phase behavior caused by the bulkiness and cubic geometry of the POSS molecules.
Characterization of Dendrimer-Gold Nanocomposite Materials
Authors: Balogh Lajos P. , Rose Ganser T. , Shi Xiangyang
Published: April 2011

Gold-dendrimer nanocomposite materials have various applications in catalysis, optics, biological sensing, cancer therapeutics, as well as building blocks to assemble functional films. Primary amine-terminated poly(amidoamine) (PAMAM) dendrimers of different generations (generation 2 through 6) were used as templates to synthesize gold-dendrimer hybrid nanocomposites. UV-Vis spectrometry, fluorescence, transmission electron microscope (TEM), zeta-potential, and polyacrylamide gel electrophoresis (PAGE) were used to extensively characterize these nanocomposite materials. Results indicate that the structure of gold-dendrimer nanocomposites changes as the function of generation and their size decreases with the increase of the generation number of dendrimer templates. TEM shows that aggregated gold-dendrimer nanocomposites are polycrystalline. These nanocomposites are fluorescent and display a stronger emission intensity (458 nm) than commercially available gold nanoparticles of similar size do. PAGE analysis shows that the gold-dendrimer nanocomposites have electrophoretic migration patterns that are similar to those of the corresponding dendrimer templates. The combination of applied different analytical techniques provides new insights into the structure and properties of gold-dendrimer nanocomposite materials.
Pentacene Transistors with Polymer Gate Dielectrics on Metallized Optical Fibers
Authors: Granstrom Jimmy , Katz Howard E.
Published: April 2011

It is difficult to deposit a very thin polymer layer onto a fiber-shaped substrate from solution because the high interfacial energy can lead to dewetting. This difficulty presents itself when attempting to apply a gate dielectric to conductive fiber substrates during the fabrication of fiber transistors for use in applications such as “electrotextiles” and optical switches. We present a dip coating process that applies a gate dielectric to metal-coated optical fibers with high uniformity and reproducibility, resulting in pentacene field-effect transistors (FETs) with excellent transistor characteristics including mobilities up to 0.4 cm2/Vs and on/off ratios up to 7000. In one case, a memory effect was demonstrated. Several gate dielectrics were successfully applied to the optical fibers, suggesting a baseline set of suitable materials for this purpose. A thorough study of the dip coating conditions is presented, including proposed explanations of the effects of different coating procedures and solution physical properties.
Self-Extinguishing Polymer Nanocomposites
Authors: Si Mayu , Chu Hsinchou , Hefter Daniel , Sokolov Aryeh , Hefter Jonathan , Smith Michael , Sokolov Jonathan , Rafailovich Miriam
Published: April 2011

Self-extinguishing PMMA/Clay nanocomposites with conventional flame retardant agents, decabromodiphenyl oxide (DB) and antimony trioxide (AO) have been prepared by melt blending using Brabender. The combustion behavior was first investigated by subjecting slabs of the polymer to UL-94 V0 testing. We found that the polymers with only the retardant agents or the clay could not pass. On the other hand all polymers with both components were self-extinguishing. DMA results show that the introduction of 5 wt% clay improves PMMA bending modulus by 28 % and increases Tg by 8 °C. the addition of clay can effectively avoid dripping during burning test. Based on the cone calorimeter data, the general mechanism is proposed that the synergy between the char formation promoted by the clay in condense phase and free radical capture in gas phase due to the DB and AO makes the material become self-extinguishing.
Air-Liquid Foams, Concentrated Direct Emulsion and Soft Chemistry Toward Hierarchically Organized Porous Silica Monoliths
Authors: Carn F. , Colin A. , Achard M.-F. , Backov R.
Published: April 2011

Hierarchically organized matter appears today a strong and highly competitive field of research mainly induced by the wide scope of applications expected. In this context, chemistry of shapes appears as a strong interdisciplinary field of research combining soft chemistry and soft matter. Hierarchical inorganic porous monoliths can be obtained using either air-liquid foams or biliquid foams as macroscopic patterns while lyotropic mesophases are employed to promote porosity at the mesoscale. By controlling the air-liquid foam's water liquid fraction or the emulsions oil fraction we can design the inorganic porous texture at the macroscale (i.e. cell sizes and shapes as well as the Plateau borders thickness). Those stategies lead to the formation of materials with characteristics that resemble aerogels.
COLLAPSE OF POROSITY DURING DRYING OF ALKYLENE-BRIDGED POLYSILSESQUIOXANE GELS. INFLUENCE OF THE BRIDGING GROUP LENGTH
Authors: Loy Douglas A. , Small James H. , DeFriend Kimberly A. , Wilson Kennard V. , Minke McKenzie , Baugher Brigitta M. , Baugher Colleen R. , Schneider Duane A. , Shea Kenneth J.
Published: April 2011

The introduction of organic substituents into sol-gel materials can often result in networks that collapse during drying to afford non-porous xerogels. This can prove useful if non-porous coatings or membranes are the ultimate objectives. Collapse of porosity is also manifested in bridged polysilsesquioxanes with flexible bridging groups. Alkylene-bridged polysilsesquioxanes are hybrid xerogels whose organic bridging group is an integral constituent of the network polymer that can be systematically varied to probe the influence of its length on the xerogels' porosity and morphology. Our previous studies have shown that hexylene-bridged polysilsesquioxane xerogels prepared from 1, 6-bis(triethoxysilyl)hexane under acidic conditions are nonporous while the pentylene-bridged polysilsesquioxanes prepared under the same conditions are porous. We also discovered that the more reactive 1, 6-bis(trimethoxysilyl)hexane monomer could polymerize under acidic conditions to afford porous xerogels. Here, we have extended our study of bis(trimethoxysilyl)alkanes to include the heptylene (C7), octylene (C8), nonylene(C9) and decylene (C10) bridges so as to ascertain at what bridging group length the porosity collapses. The morphology of the resulting xerogels was characterized by nitrogen sorption porosimetry and electron microscopy. Solid state NMR was used to structurally characterize the materials.
Suppression of Reaction between Si Substrate and Obliquely Deposited Fe Atoms
Authors: Jomori S. , Suzuki M. , Nakajima K. , Kimura K.
Published: April 2011

We have investigated the initial stage of the growth of obliquely deposited Fe on a Si substrate held at 470 °C with atomic force microscopy (AFM) and high resolution Rutherford backscattering spectroscopy (HRBS). During the deposition from the normal direction, many Si atoms are displaced from their lattice position due to the reaction with the deposited Fe. On the contrary, the number of displaced Si atoms decreases significantly, and the nanoislands of a few 10 nm in diameter grow selectively when Fe is deposited at 85°. This is clear evidence that the local nucleation processes for the Fe silicide formation is modified by the geometrical deposition conditions.
Solid State NMR Measurements for Preliminary Lifetime Assessments in λ-Irradiated and Thermally Aged Siloxane Elastomers
Authors: Chinn Sarah C. , Herberg Julie L. , Sawvel April M. , Maxwell Robert S.
Published: April 2011

Siloxanes have a wide variety of applications throughout the aerospace industry which take advantage of their exceptional insulating and adhesive properties and general resilience. They also offer a wide range of tailorable engineering properties with changes in composition and filler content. They are, however, subject to degradation in radiatively and thermally harsh environments. We are using solid state nuclear magnetic resonance techniques to investigate changes in network and interfacial structure in siloxane elastomers and their correlations to changes in engineering performance in a series of degraded materials. Nuclear magnetic resonance (NMR) parameters such as transverse (T2) relaxation times, cross relaxation rates, and residual dipolar coupling constants provide excellent probes of changes crosslink density and motional dynamics of the polymers caused by multi-mechanism degradation. The results of NMR studies on aged siloxanes are being used in conjunction with other mechanical tests to provide insight into component failure and degradation kinetics necessary for preliminary lifetime assessments of these materials as well as into the structure-property relationships of the polymers. NMR and magnetic resonance imaging (MRI) results obtained both from high resolution NMR spectrometers as well as low resolution benchtop NMR screening tools will be presented.
Energetics of Oxygen Interstitials in Cr and V
Authors: Good Brian S. , Copland Evan
Published: April 2011

Dissolved oxygen in group IIIA-VA (Nb, Ti, Zr, Y) based alloys is a fundamental problem, affecting both mechanical properties and oxidation resistance, yet details of the phenomenon are poorly understood. In these alloys, oxygen is more stable dissolved in the metal than as an oxide-compound. In contrast, alloys based on Ni, Fe, Al and Cr exhibit almost no oxygen solubility. To improve the performance of Nb and Ti based alloys it is necessary to understand the differences in oxygen solubility between these two groups of metals. As a first step we considered the energetics of interstitial oxygen in α-V and α-Cr. Both of these metals have a BCC structure, yet the oxygen solubility in V is much higher than that in Cr. We obtain total energies, densities of states and population analyses using the CASTEP plane-wave pseudopotential density functional computer code. The differences in the energetics and electronic structures of the two materials, particularly the partial densities of states associated with the interstitial oxygen, are discussed.
Volatile Evolution from Polymer Materials Induced by Irradiation with Accelerated He++ Ions
Authors: Murphy Julian.J. , Wetteland Christopher.J.
Published: April 2011

Experimentally investigating ageing caused by irradiation with energetic particles is very difficult. Radioactive sources can be employed but these are difficult to handle and contaminate the material being irradiated precluding subsequent chemical and physical characterisation. The penetration of energetic particles also tends to be small so any change is localised in the near surface region so only a small amount of material is irradiated. Analysing changes in such thin layers causes a number of problems. To simulate ageing induced by particle radiation polymer samples have been exposed to fast He++ ions in an accelerated ion beam. The ions pass through a 10μm thick window of Havar foil before impacting upon the sample. Volatile species evolved from the materials upon bombardment are contained within the irradiation chamber by the foil window. Analysis of such species is shown to be a highly sensitive probe for investigating chemical changes in the exposed materials. A number of important chemical changes induced in polymer materials have been identified. Trends in the relative rates of volatile evolution have been identified which correlate with chemical changes identified in other radiation experiments. As these experiments are performed at far slower irradiation rates the large acceleration factors used in ion beam irradiation are discussed along with the implications for using ion beams to simulate alpha particle irradiation.
The Application of Modern Metallurgical Principles And Knowledge to the Manufacture of Mokumé Gane (Wood-Grain Metal) Decorative Alloy
Authors: Ferguson Ian T. , Derby Brian , Thompson G. E.
Published: April 2011

Mokumé Gane layered metal is a 300-year old decorative metal laminate technique peculiar to the isolated culture of the Japanese Shogunate. Like many complex craft practices handed down through individual experience, the manufacture and development of Mokumé Gane has changed minimally over time. The application of contemporary metallurgical knowledge and solid state bonding techniques such as Hot Press Diffusion Bonding and Hot Roll Bonding provide for further development of Mokumé Gane: bonding success rates are improved, and manufacturing times are reduced. In addition, the range of possible metal combinations is substantially increased; 42 different combinations to date have been successfully bonded, including a new type of Mokumé Gane employing aluminium alloys. This research has allowed a very large increase in the variety of colours, patterns, and visual effects, available to contemporary metalsmiths and jewellers.
Magnetic and Structural Properties of Mn-implanted Si
Authors: Bolduc M. , Awo-Affouda C. , Stollenwerk A. , Huang M. B. , Ramos F. , Agnello G. , LaBella V. P.
Published: April 2011

P-type Si wafers (∼1019 cm−3) were implanted with 300 keV Mn+ ions at 350°C to a dose of 1×1016 cm−2, and then annealed at 800°C for 5 min. The magnetic properties with dependence upon temperature were measured by using a Superconducting Quantum Interference Device (SQUID) magnetometer. The Mn-implanted Si compound shows ferromagnetic ordering above room temperature. The saturation magnetization increases by ∼ 2 × after annealing and the Curie temperature is TC > 400 K. The structural properties have been investigated by means of Secondary Ion Mass Spectroscopy (SIMS) depth profiling and Transmission Electron Microscope (TEM) imaging. Measurements showed that the Mn atoms redistribute in the Si crystal due to the thermal annealing and form a band layer composed of nanoscale structures such as crystallites or defects.
Effective Modulus and Stress Relaxation of Freestanding Aluminum Microtensile Beams
Authors: El-Deiry P. A. , Barbosa N. , Brown W. L. , Vinci R. P.
Published: April 2011

Freestanding Al thin film microtensile beams 600 μm long, 100 μm wide, and with thicknesses of 0.25 μm, 0.50 μm, 0.75 μm, and 1.00 μm were tested under uniaxial tension with a custom-built microtensile system. Displacement controlled experiments employing five strain rates between 8.3 × 10−4 s−1 and 8.3 × 10−1 s−1 were performed. Three crosshead displacements of 1.00 μm (0.17% strain), 2.60 μm (0.43%), and 3.60 μm (0.60% strain) were exercised in order to investigate behavior in the elastic, anelastic, and the inelastic sections of the stress/strain curve.

At a 0.17% strain amplitude, the 0.50 μm thick microtensile beams exhibit an effective modulus that increases with increasing strain rate. The 1.00 μm, 0.75 μm, and 0.25 μm microtensile beams do not show a similar trend. The 0.25 μm and the 0.75 μm thick microtensile beams have similar grain sizes and similar moduli; the 0.50 μm and the 1.00 μm microtensile beams have similar but smaller grain sizes and higher effective moduli. This suggests that grain size is more significant than film thickness in determining the effective modulus of freestanding Al thin films. Furthermore, no stress relaxation behavior was identified for any of the films during the hold at the 0.17% strain amplitude.

At a strain amplitude of 0.43%, the effective moduli are very similar to the values measured at a 0.17% strain amplitude; however, the 0.50 μm and 1.00 μm thick microtensile beams show measurable stress relaxation while the 0.25 μm and 0.75 μm microtensile beams do not. This result combined with a lower observed modulus suggests that the particular anelastic mechanisms operating in these films at these time scales activate sooner and provide a faster stress relaxation process in the larger grained films.
Effect of Stress-induced Magnetic Anisotropy on the Properties of Giant Magnetostrictive Single Layer and Multilayer Thin Films
Authors: Tan J. H. , Guerrero V. H. , Wetherhold R. C. , Anderson W. A.
Published: April 2011

Giant magnetostrictive thin films deposited on nonmagnetic substrates can constitute effective sensors and actuators for microdevices. In this work, we investigated the effects of a stress-induced anisotropy on the magnetic properties of Tb0.4Fe0.6, Fe0.5Co0.5 single layer films and [Tb0.4Fe0.6/Fe0.5Co0.5]n multilayers deposited on Si substrates. The magnetostrictive thin films were fabricated by means of RF sputtering and were subjected to a post-deposition annealing treatment. The uniaxial magnetic anisotropy was induced by bending the substrate before deposition and then allowing it to resume its original flat shape after depositing the film. The heat treatment was performed in a vacuum system with a vacuum of 10−6 Torr. The magnetic properties of the fabricated specimens were measured using a SQUID. SEM and XRD analyses were performed to ensure that the thermal treatment would relax the internal stresses induced during the deposition process without crystallizing the film. The thickness of the single layer thin films studied was between 300 and 800 nm while multilayer samples consisted of 6 layers with each layer thickness ranged from about 20 to 40 nm. Compared to single layer samples, multilayer samples with stress anneal growth exhibited an improvement in magnetic saturation by a factor of two while maintaining a low coercive field. Manipulations of the magnitude and direction of magnetic anisotropy was observed by introducing various values of tensile and compressive stress into the film.
Magnetostrictive Microcantilever as Micro-Biosensor Platform
Authors: Li Suiqiong , Li Zhimin , Orona Lisa , Cheng Z.-Y.
Published: April 2011

In this paper, a novel micro-biosensor platform - magnetostrictive microcantilever (MSMC) - is reported. The resonance behavior and the sensitivity of MSMC as sensor platform were characterized and compared to the theoretical calculation. The detection of yeast cells using the biosensor made of MSMC was reported. The results demonstrate the feasibility of MSMC as a high performance biosensor platform. Compare to current microcantilevers, which is widely considered as the state-of-art sensor platform, the MSMCs have following advantages: 1) remote/wireless driving and sensing; 2) easy to fabricate. More importantly, it is experimentally found that the quality merit factor (Q value) of MSMC can reach more than 250, which is much higher than other cantilevers.
Evaluation of the Corrosivity of Dust Deposited on Waste Packages at Yucca Mountain, Nevada
Authors: Bryan Charles , Jarek Russell , Wolery Thomas , Shields David , Sutton Mark , Hardin Ernest , Barr Deborah
Published: April 2011

Potentially corrosive brines can form during post-closure by deliquescence of salt minerals in dust deposited on the surface of waste packages at Yucca Mountain during operations and the pre-closure ventilation period. Although thermodynamic modeling and experimental studies of brine deliquescence indicates that brines are likely to form, they will be nitrate-rich and noncorrosive. Processes that modify the brines following deliquescence are beneficial with respect to inhibition of corrosion. For example, acid degassing (HCl, HNO3) could dry out brines, but kinetic limitations are likely to limit the effect to increasing their passivity by raising the pH and increasing the NO3/Cl ratio.

Predicted dust quantities and maximum brine volumes on the waste package surface are small, and physical isolation of salt minerals in the dust may inhibit formation of eutectic brines and decrease brine volumes. If brines do contact the WP surface, small droplet volumes and layer thicknesses do not support development of diffusive gradients necessary for formation on separate anodic-cathodic zones required for localized corrosion. Finally, should localized corrosion initiate, corrosion product buildup will stifle corrosion, by limiting oxygen access to the metal surface, by capillary retention of brine in corrosion product porosity, or by consumption of brine components (Cl−).
A Study on Gas Migration Behavior in Buffer Material using X-ray CT Method
Authors: Tanai K. , Yui M.
Published: April 2011

This paper presents a study on gas migration behavior in a bentonite specimen with the aid of X-ray computer tomography (CT) scan data. The laboratory experiment was carried out to clarify gas migration behavior through saturated, compacted bentonite. X-ray CT was used to estimate the spatial distribution of gas and water saturation during gas migration test in the bentonite. For the gas migration test, the controlled flow rate of gas injection was adopted for pre-compacted samples of Kunigel V1 bentonite using helium gas, which is safer than hydrogen gas.A specimen was isotropically consolidated and saturated by synthetic seawater, simultaneously, by applying a backpressure. This was followed by injecting the gas using a syringe pump. Inlet and outlet gas fluxes were monitored. This test exhibited a significant threshold pressure for breakthrough, somewhat larger than the sum of the swelling pressure and the backpressure.

The procedure of the X-ray CT measurement is as follows; i) measurement of the initial condition (saturated condition) of the compacted bentonite, ii) measurement of the gas injection condition as a function of time. The digital data obtained from the X-ray CT usually includes some noise. The stacking method can reduce the noise in CT values and enables to identify the gas migration area. The results indicate that gas is transported through preferential pathways in compacted bentonite, and is not homogenous.
The Belgian Demonstration Programme for the Disposal of High-Level and Long-Lived Radioactive Waste
Authors: Frédéric Bernier , Marc Demarche , Johan Bel
Published: April 2011

The EIG EURIDICE is responsible for performing large-scale tests, technical demonstrations and experiments so as to assess the feasibility of a final disposal of vitrified radioactive waste in deep clay layers. This programme is part of the Belgian Research and Development programme managed by ONDRAF/NIRAS. The research infrastructure includes the Underground Research Facilities HADES (URF HADES) in the Boom Clay geological formation and surface facilities. The achievements of the demonstration programme are the demonstration of the construction of shafts and galleries at industrial scale, the characterisation of the hydro-mechanical response of the host rock, and the “OPHELIE mock-up” a large scale hydration test under thermal load of pre-fabricated bentonite blocks. The future works will consist mainly in the realisation of the “PRACLAY experiments” including a large scale heater test. The large scale heater test has to demonstrate that Boom Clay is suitable, in terms of performance of the disposal system, to undergo the thermal load induced by the vitrified waste. The combined effect of the excavation and the thermal load will be investigated. A long term (more than 10 years) large scale heater test would be representative of the most penalizing conditions that could be encountered in the real disposal. The results of this test will constitute an important input for the Safety and Feasibility Cases 1 (SFC-1, 2013) and 2 (SFC-2, 2020).
Importance of the Excavation Damaged Zone (EDZ) in the General Performance of the Near-Field of a Geological Disposal System; Input of the EDZ Component to the EC Integrated Project on the Near-Field (NF-PRO)
Authors: Aranyossy Jean François , Blümling Peter , Alheid Hans Joachim , Geet Maarten Van , Mayor Juan Carlos , Marschall Paul , Plas Frederic
Published: April 2011

In order to tackle the particular issues presented by the existence of an Excavation Damaged Zone (EDZ) along disposal cells and tunnels and the subsequent potential occurrence of preferential flow paths and radionuclide migration, a specific Component on the EDZ has been incorporated into the EC Integrated Project on the Near-Field (NF-PRO)1. This Component is organised into several Work Packages matching the foreseeable EDZ evolution during the repository lifetime: (i) the “initial phase”, corresponding to EDZ development induced by underground excavations and rock stress release; (ii) the “transient phase”, corresponding to the repository operating phase, mainly characterised by desaturation, temperature increase and resaturation processes; (iii) the “long-term phase”, corresponding to the post-closure repository period, mainly characterised by EDZ self-sealing / self-healing and gas transport processes.

The scientific results obtained through the numerous tasks included in the Component cover various aspects of EDZ investigation (desk studies, experimental work on representative rock samples, in situ experiments in URLs, numerical modelling) and are integrated into a global EDZ impact evaluation to be forwarded to the Component of the project devoted to process coupling and integration in the general performance assessment of the near-field.
Atmospheric Stress Corrosion Cracking (ASCC) Susceptibility of Stainless Alloys for Metallic Containers
Authors: Nakayama Gen
Published: April 2011

Metallic canisters placed in concrete casks and containing spent nuclear fuel elements, will be exposed to a moist oceanic atmosphere while the decay heat generated in the fuel elements cools for more than fifty years. Thus, the surface environment of the metallic canisters will be wet and covered with chloride compounds. The canisters may suffer atmospheric stress corrosion cracking. Therefore, corrosion tests for some potential alloys were conducted in an aqueous bittern solution, containing 22% enriched chloride compounds simulating the expected surface conditions of the canisters, to aid in selecting appropriate alloys based on corrosion resistance. The results suggest that the corrosion resistance of ordinary stainless steels, such as SUS304 and SUS316, is not high enough to avoid ASCC (atmospheric stress corrosion cracking) in the environment. Thus, a higher-grade stainless steel, namely, NSSC270 (20Cr-18Ni-6Mo-0.2N-Low C)or SUS836L (23.5Cr-25Ni-5.5Mo-0.2N-Low C, equivalent to AL-6XN) has been selected for this application.