bluuebunny/crossref_metadata_2025_split huggingface dataset:
Large-Area Film Structure Consisted by Aggregation of Zinc Oxide Micro-Whiskers
Authors: Tokita Shuji , Ohshi Shigeo , Saitoh Hidetoshi 
Published: April 2011

ABSTRACTWe developed a chemical-vapor deposition (CVD) apparatus with a 0.5×240 mm2 slit-type nozzle that scans at an area of 240×315 mm2 in the atmosphere. This apparatus forms uniform oxide crystals on substrates through the decomposition process of precursors emitted from the nozzle. In this study, ZnO whiskers were synthesized on a single-crystalline 8-inch wafer of (100)-oriented silicon using this apparatus. Morphological and crystallographic properties of the samples were evaluated using scanning electron microscopy and X-ray diffractometry.
Molecular-Dynamics Simulation of the Initial Period of Cluster Deposition
Authors: Shintani K. , Nakajima T. , Taniguchi Y. 
Published: April 2011

ABSTRACTThe initial periods of deposition process of metal clusters in the soft-landing regime are investigated by the molecular-dynamics simulation. The embedded-atom method potential is adopted for calculation of the interaction between metallic atoms. The predictor-corrector method for second-order differential equations is employed for integration of the equations of motion. A simulation begins with equilibration of clusters and a substrate at a specified temperature. The lowest atomic layer in the substrate is fixed and the next few atomic layers are set to be velocity-scaling layers during the deposition process. The periodic boundary conditions are imposed in the horizontal directions. A single cluster with no velocity is deposited on the substrate. The simulations are performed at different temperatures of the clusters and substrate and for different sizes of clusters. How the morphological transition of the deposited nanostructures is affected by these parameters is discussed.
Stress evolution during deposition and during annealing of TixAly-alloy films
Authors: Lackner St. , Abermann R. 
Published: April 2011

ABSTRACTThe main objective of this paper is a series of experiments designed to elucidate the origin of large fluctuations in the growth stress of aluminium rich TixAly-alloy films found in earlier experiments. The internal stress of the various alloy films was measured in situ under UHV-conditions during as well as after deposition, using a cantilever beam technique. In parallel experiments the microstructure of the different films was investigated by TEM.The experiments were started assuming that the fluctuations in the stress vs. thickness curve of aluminium rich TixAly-alloy films indicate unstable films. In order to test this hypothesis, we have performed annealing experiments with alloy films of which the aluminium content was varied from 50% to 75%. The films were formed by evaporating the alloy components from two separate evaporation sources onto alumina substrate films at 27°C substrate temperature.The growth stress of the Ti50Al50-alloy film exhibits a large tensile stress, which increases linearly with film thickness and a negligible stress change after deposition. Increasing the aluminium content lowers the tensile stress built up and the average stress in the Ti25Al75-alloy film is compressive but stress changes after deposition are still very small. This experimental evidence is interpreted to indicate that layer by layer growth is the representative growth mode for these films. The origin of the growth stress of these films is assumed to be the grain boundary relaxation mechanism proposed by R.W. Hoffman. The differences in the growth stress in films with varying aluminium content are assumed to originate from changes in the magnitude of the attractive forces in the grain boundaries, defects etc‥Annealing these films gives rise to irreversible tensile stress changes. These stress changes in the Ti25Al75-alloy film are about four times that measured during annealing of the Ti50Al50-alloy film. A pronounced tensile stress feature in the temperature range between 230°C and 260°C is interpreted to be due to segregation of aluminium in the alloy film and to the alloy film surface. This aluminium segregation is negligible in alloy films with an aluminum content lower than 67%. With the experimental evidence presented in this paper we are able to show that aluminium segregation is the reason for the large fluctuations in the stress vs. thickness curves of aluminium rich alloy films when the two alloy components are evaporated simultaneously from two separate evaporation sources.
Surface Roughness Evolution in Amorphous Tantalum Oxide Films Deposited by Pulsed Reactive Sputtering
Authors: Jain Pushkar , Juneja Jasbir S. , Karabacak Tansel , Rymaszewski Eugene J. , Lu Toh –Ming 
Published: April 2011

ABSTRACTThe growth front roughness of Ta2O5 amorphous films grown by pulsed plasma d.c. reactive sputtering has been investigated using atomic force microscopy. Film deposition during reactive sputter deposition is explained based on dynamic scaling hypothesis in which both time and space scaling are considered simultaneously. The interface width w increases as a power law with deposition time t, w ∼ tβ, with β = 0.45 ± 0.03. The lateral correlation length ξ grows as ξ ∼ t1/z, with 1/z = 0.61 ± 0.07. The roughness exponent extracted from the slope of height-height correlation analysis is α = 0.79 ± 0.04. The results are similar to that obtained by sputtering of elemental materials, and do not fit to any of the presently known growth models. Monte Carlo simulations were carried out based on a recently developed re-emission model, where incident flux distribution, shadowing, sticking coefficient, and surface diffusion mechanisms were accounted for in the deposition process. An important finding is that sticking coefficient must be less than unity to obtain the observed β value (∼0.45).
Segregation of Yttrium Ions as to the Surfaces of t-ZrO2
Authors: Redfern S.E. , Stanek C. R. , Grimes R.W. , Rawlings R.D. 
Published: April 2011

ABSTRACTAtomistic simulation has been used to predict the segregation of defect clusters containing two substitutional Y3+ ions and one charge compensating oxygen vacancy to the (100) and (101) surfaces of t-ZrO2. The most stable orientation of the defect cluster depends on its distance from the surface. Significantly, segregation energies vary greatly between surfaces. For example, the defect cluster is equally stable up to a depth of 9Å from the (100) surface but only to a depth of 4Å below the (101) surface. In both cases, segregation energies are negligible 12Å beneath the surface.
The Properties of a Na-Doped Twist Boundary in SrTiO3 from First Principles
Authors: Astala Roope K. , Bristowe Paul D. 
Published: April 2011

ABSTRACTThe segregation of Nasr impurities to a Σ = 5 [001] twist boundary in SrTiO3 is studied using DFT-based plane-wave pseudopotential techniques. The formation energies of the impurities are calculated as a function of oxygen chemical potential and electron chemical potential. The results indicate a strong driving force for segregation to the boundary and that the Na impurities exhibit acceptor-like behaviour. The atomic displacements caused by the impurities are small both in the bulk and at the grain boundary. Based on the results a model is suggested in which Nasr segregation is driven by soft relaxation of the electronic structure.
Effect of Thin Y-O and Si-O Films on In-situ Formed CaO Coatings on V-4%Cr-4%Ti in Liquid 2.8 at.% Ca-Li
Authors: Park Jong-Hee , Sawada A. , Kestle B. , Rink D. , Natesan K. , Mattas R. F. 
Published: April 2011

ABSTRACTWe are developing electrically insulated coatings for the liquid-metal/structural-material interface of the breeder blanket for magnetic fusion reactors. Our earlier experimental studies indicated that sintered Y2O3 is compatible with liquid Li. In continuing studies, we have deposited thin (0.2 and 0.8 μm) yttrium films on V-4Cr-4Ti structural material by physical vapor deposition (PVD). Annealing the thin Y-metallic PVD film on O-charged V-4Cr-4Ti at 750°C for 17 h formed an oxide film by the solid-state reaction between O and Y. Both energy dispersive spectroscopy (EDS) and X-ray diffraction indicated that the Y-metallic films converted to either YVO3 or Y8V2O17 after annealing. When these samples were exposed in 2.8 at.% Ca-Li at temperatures of 700°C for 99 h, a uniformly microstructured CaO layer was formed on the top of the Y-V oxides, but localized Y was not detected by cross-sectional EDS analysis. The addition of Si was found to minimize the V incorporation in the in-situ forming film.
Molecular Dynamics Computer Simulations of Calcium-Alumino-Silicate Intergranular Films between the basal and prism planes of α-Al2O3
Authors: Garofalini Stephen H. , Zhang Shenghong 
Published: April 2011

ABSTRACTMolecular dynamics computer simulations using a robust multibody potential were used to study the structure of the intergranular films (IGFs) formed between two different crystallographic orientations of α-Al2O3crystals. The simulations show a localized ordering of the IGF at the interface of both the basal and prism planes caused by preferential adsorption of specific ions from the IGF onto the crystal planes. However, the results of the adsorption have significantly different effects on crystal growth of the specific orientations. The preferential adsorption of Ca ions from the IGF onto the (0001) surface inhibit growth in the <0001> direction. However, Ca does not affect adsorption of O and Al from the IGF onto the (1120) surface and potential growth of this orientation in the <1120> direction. The results are consistent with experimental data regarding anisotropic grain growth in this system and provide an atomistic view of this behavior.
Interface Conduction between Conductive ReO3 Thin Film and NdBa2Cu3O6 Thin Film
Authors: Ohkubo Manabu , Fukai Kumiko , Matsuo Kohji , Iwata Nobuyuki , Yamamoto Hiroshi 
Published: April 2011

ABSTRACTThe Re oxide films were deposited on quartz glasses by RF reactive sputtering from a Re metal target. The lowest resistivity was observed in the film in-situ annealed at 200?C in Ar atmosphere and showed the order of 10-4 Ωcm of which the value was still about 10 times as large as that of a single crystal ReO3. The temperature dependence of the resistivity revealed a metallic behavior. A superconductivity did not take place in the bilayered film of ReO3 / NdBa2Cu3O6. In the interface region the resistivity minimum probably caused by the Kondo effect was observed in the neighborhood of 120K.
Synthesis and Properties of High-Manganese Iron-Based Bulk Amorphous Metals as Non-Ferromagnetic Amorphous Steel Alloys
Authors: Joseph S. , Shiflet Gary J. , Ponnambalam V. , Keppens Veerle M. , Taylor R. , Petculescu G. 
Published: April 2011

ABSTRACTHigh-manganese ferrous-based alloys containing 10–20 at. % Mn have been investigated as prospective iron-based structural amorphous metals with magnetic transition temperatures far below the ambient temperature. Many of these alloys are found to have a high reduced glass transition temperature of 0.6–0.63 and large supercooled liquid region of 40–90 °C. Rod-shaped amorphous samples with diameters reaching 4 mm are obtained by employing simple injection casting. The search for good glass-forming alloys has been guided by an atomistic approach coupled with the realization of low-lying liquidus temperatures via proper alloying. The tensile yield strengths and Vickers hardness of the new amorphous metals far exceed those known in high-strength steel alloys, and the elastic moduli are comparable to those reported for super-austenitic steels. The present high-manganese amorphous Fe-alloys also show promise as very good corrosion-resistant materials.
Magnetostriction and Coercivity of Soft Magnetic Fe-(Al, Ga)-(P, C, B, Si) Bulk Glassy Alloys
Authors: Makino Akihiro , Bitoh Teruo , Inoue Akihisa 
Published: April 2011

ABSTRACTThe relationship between coercivity (Hc) and magnetostriction (λs) of the glassy Fe-(Al, Ga)-(P, C, B, Si) alloys has been discussed. The glassy Fe-(Al, Ga)-(P, C, B, Si) alloys exhibit lower Hc and lower Is compared with the conventional Fe-based amorphous alloys with the same λs and Fe content, respectively. Theoretical analysis on the basis of domain-wall movement suggests that the low Hc results from the long-range homogeneous structure of the glassy alloys, which realizes a low density of pinning centers. The good combination of high glass-forming ability and good soft magnetic properties (especially low Hc) indicates the possibility of future development as new bulk glassy soft magnetic materials.
Crystallization Behavior of Mechanically Alloyed Zr-Cu-Al-Ni Glass Composites Containing Second-Phase ZrC Particles
Authors: Deledda S. , Eckert J. , Schultz L. 
Published: April 2011

ABSTRACTWe report on mechanical alloying of elemental powders with nominal composition Zr55Cu30Al10Ni5 together with up to 30 vol.% of ZrC particles which results in the formation of a metallic glass matrix in which the carbide particles are homogeneously dispersed and, at the same time, reduced to nanometer size. The thermal stability is investigated by isochronal differential scanning calorimetry and is found to be strongly affected by increasing the ZrC volume fraction. Comparison with calorimetric data for single-phase mechanically alloyed Zr-Cu-Al-Ni-C glassy powders suggests that dissolved carbon, originating from non-negligible ZrC-dissolution processes during mechanical alloying, is responsible for the changes in the glass transition and the crystallization behavior. Isothermal calorimetric data are also presented and discussed in the framework of the Johnson-Mehl-Avrami model. The carbon atoms dissolved in the glassy phase are suggested to slow down the kinetics of overall crystallization. On the other hand, for large ZrC volume fractions nucleation of crystalline phases is promoted by the second-phase particles and changes in the Avrami exponent from n = 4 to n = 3 suggest that the nucleation rate approaches zero after the early stages of crystallization.
The Effect of Atomic-Scale Open-Volume on Flow and Fracture Processes in a Zr-Ti-Ni-Cu-Be Bulk Metallic Glass
Authors: Suh Daewoong , Dauskardt Reinhold H. 
Published: April 2011

ABSTRACTEffects of atomic-scale open-volume regions in metallic glass structure on the flow and fracture behavior of a Zr-Ti-Ni-Cu-Be bulk metallic glass were examined. Studies of relaxation time scales showed that atomic arrangement processes for viscous flow were significantly retarded with annealing. Plane strain fracture toughness was significantly decreased and fatigue crack crack-growth rates were dramatically increased, indicating degradation of resistance to crack extension as a result of annealing. Fracture morphology completely changed from vein patterns to cleavage-like features with little evidence of plasticity with annealing. The positron lifetime and Doppler broadening experiments revealed decreased open-volume regions as a result of annealing. The loss of stress relief ability by retarded crack tip viscous flow as a result of the anneal-out of open-volume regions is believed to contribute to observed annealing embrittlement.
Systematic Trends and Empirical Modeling of Lead Uptake by Cements and Cement Minerals
Authors: Ochs Michael , Talerico Caterina , Lothenbach Barbara , Giffaut Eric 
Published: April 2011

ABSTRACTUptake of Pb was investigated for different hydrated fresh and leached Portland and high-alumina cements, different CSH phases including tobermorite, portlandite, as well as for several relevant cement Al-minerals. Except for highly degraded cement, CSH minerals are the most important phases for Pb uptake. A systematic analysis of our data and a comparison with recent literature data for CSH phases [1] shows that Pb uptake is characterized by three trends: 1) between pH 10–13, Pb uptake decreases with increasing pH, 2) Pb uptake increases with increasing Fe content in the clinker, and 3) Pb uptake is dependent on the Pb concentration in the solution. Following these findings, an empirical model was developed based on regression analyses of uptake vs. Pb concentration, pH, and Fe content in the clinker. The resulting relation can predict Kd values for a large range of fresh and leached cements, as well as for individual cement minerals under different experimental conditions. Model application to independent data on cement phases, whole cement, and mortar gave very good agreements.
Evaporative Evolution of Brines from Synthetic Topopah Spring Tuff Pore Water, Yucca Mountain, NV
Authors: Alai Maureen , Carroll Susan 
Published: April 2011

ABSTRACTWe are investigating the evaporation of pore water representative of the designated high-level-nuclear-waste repository at Yucca Mountain, NV to predict the range of brine compositions that may contact waste containers. These brines could form potentially corrosive thin films on the containers and impact their long-term integrity. Here we report the geochemistry of a relatively complex synthetic Topopah Spring Tuff pore water that was progressively evaporated in a series of experiments. The experiments were conducted in a vented vessel in which HEPA filtered air flowed over the 95°C solution. Samples of the evaporating solution and the condensed vapor were taken and analyzed to determine the evolving water chemistry and gas volatility. The final solid was analyzed by X-ray diffraction.The synthetic Topopah Spring Tuff water evolved towards a complex brine that contained about 45 mol % Cl, 7 mol% NO3, 43 mol% Na, 4 mol % K, and less than 1 mol % each of SO4, Ca, Mg, HCO3 and Si. Trends in the solution data and identification of CaSO4 solids suggest that fluorite, carbonate, sulfate, and Mg-silicate precipitation minimize the corrosion potential of “sulfate type pore water” by removing F, Ca, and Mg during the early stages of evaporation.
New Developments in Field Studies of Low Activity Waste Glass Corrosion and Contaminant Transport
Authors: McGrail B. P. , Bacon D. H. , Meyer P. D. , Ojovan M. I. , Strachan D. M. , Ojovan N. V. , Startceva I. V. 
Published: April 2011

ABSTRACTPerformance assessment calculations for low-activity waste glass to be disposed at the Hanford site depend on simulations of long-term glass corrosion behavior and contaminant transport that are being performed via reactive chemical transport modeling. Confidence in the underlying physical and chemical processes that are being approximated by the computer model could be significantly enhanced through carefully-controlled field testing, which includes studies of buried ancient glasses. Field tests with simulated low-activity waste glasses have been initiated on the Hanford site and at the Ballidon site in the United Kingdom. In addition, a joint PNNL – SIA RADON research project has been initiated to analyze a unique data set collected over 12+ years during a Russian in-situ testing program with actual low-activity waste glass. The glasses buried at Hanford are scaled down cylinders (45 kg mass) and include a representative glass composition for Hanford low-activity waste and a glass designed to be highly reactive. Each glass was doped with chemical analog tracers (Re, Se, and Mo). Design of the lysimeter test facility and sampling locations were done with aid of predictive calculations performed with the STORM code. These same glasses were also buried at Ballidon but in the form of small glass coupons. The coupons will be retrieved over a period of several years for detailed analysis along with core samples of the surrounding limestone, which will be analyzed for contaminant transport profiles. Analysis of porewater from underneath the Russian burial site ha s been compared with modeling calculations. Good agreement between the model and the field data has been obtained so far using estimated parameters for the glass corrosion. Independent laboratory tests are in progress to parameterize the STORM model for quantitative comparisons.
The effect of uncertainties in stability constants on speciation diagrams
Authors: Ödegaard-Jensen Arvid , Ekberg Christian , Meinrath Gunther 
Published: April 2011

ABSTRACTSpeciation calculations are one of the more common ways to describe a chemical system. Speciation diagrams is a convenient way to display such calculations and may also be the basis on which experiments in neighbouring fields of interest, such as sorption are based. In earlier days only very simple problems could be described, e.g. hydroxide species dominance diagrams versus pH. With the aid of computers, however, more complicated systems such as groundwater chemistry may be used. However, as the complexity increase, so does the effect of uncertainties. In this paper we focus on the effect uncertainties in stability constants may have on speciation calculations. The common belief is that the curves will be replaced by narrow bands, while the truth is far from that. In many cases one or several species cover the entire region between 0 and 100%.
Influence of organic matter in the prediction of iodine migration in natural environment
Authors: Reiller Pascal , Moulin Valérie 
Published: April 2011

ABSTRACTHalogenation of phenolic moieties is one of the most important reactions between humic substances (HS) and iodine or chlorine. These reactions were studied in order to assess the importance of these interactions with reduced (I−) and oxidised (I2) form of iodine. I−was fixed by the addition of Na2S2O3. After separation of HS and I−by ultrafiltration, no significant uptake was evidenced in the time framework of this study. The consumption of I2(aq) by HS was followed by the decay of I−3absorbance (351 nm). It comes out that (i) when I−is fixed by Na2S2O3, no interaction with HS could be quantified; (ii) I2(aq) does react with HS but the kinetics cannot be linearalised. This study confirms the significance of iodine-organic matter interactions as a governing process for iodine migration in surface environment. More studies are on going to develop predictive models of iodination kinetics.
Characterization of the Corrosion Behavior of Alloy 22 after Five Years Immersion in Multi-ionic Solutions
Authors: Wong Lana L. , Fix David V. , Estill John C. , Daniel McCright R. , Rebak Raúl B. 
Published: April 2011

ABSTRACTAlloy 22 (N06022) is the candidate material for the corrosion resistant, outer barrier of the nuclear waste container. Two of the potential corrosion degradation modes of the container are uniform corrosion and localized corrosion. A testing program is under way at the Lawrence Livermore National Laboratory to determine the susceptibility of Alloy 22 to these two forms of corrosion using immersion tests. Metallic coupons are being exposed to several electrolyte solutions simulating concentrated underground water from pH 3 to 10 at 60°C and 90°C. This paper describes the results obtained after more than a five-year exposure of 122 specimens to the testing electrolyte solutions. Results show little general corrosion and the absence of localized corrosion. The maximum general corrosion rate was 23 nm/yr.
Vapour Phase Hydration of Magnox Waste Glass
Authors: Hyatt Neil C. , Lee William E. , Hand Russell J. , Ojovan Michael I. , Abraitis Paul K. , Scales Charlie R. 
Published: April 2011

ABSTRACTVapour phase hydration studies of simulant Magnox waste glass have been undertaken at 200°C, over periods of 5 – 25 days. Electron microscopy studies reveal a thin uniform hydration layer (∼10 μm thick) on 5, 10 and 25 day specimens. The formation of isolated surface alteration products occurs between 5 and 10 days at 200°C. The formation of extensive surface alteration products, in the form of a magnesium sodium aluminosilicate, is observed only in the case of the 25 day specimen. The significance of these observations in the context of the composition of Magnox waste glass, is discussed.