bluuebunny/crossref_metadata_2025_split huggingface dataset:
Self Organized Compound Semiconductor Nanocrystallite Distributions in SiO2 on Silicon Synthesized by Ion Implantation
Authors: Karl H. , Groβhans I. , Stritzker B. 
Published: April 2011

ABSTRACTThe temporal and spatial evolution of sequentially and single ion implanted Cd and Se concentration distributions into thermally grown SiO2 on (001)-Si were investigated. Ex-situ rapid thermal annealing was performed to initiate the reaction-diffusion driven material transport, nanocrystal nucleation and growth. Finally this leads to the formation of buried distinct layers of CdSe nanocrystals. The spatiotemporal evolution of the concentration distributions were quantitatively analyzed by dynamic Secondary Ion Mass Spectrometry (SIMS). It will be shown, that there is a correlated diffusion of Cd and Se when both elements were implanted in overlapping concentration profiles, whereas the single implanted Cd and Se exhibit a completely different diffusion behaviour. In the region of the supersaturated solid solution reaction to thermodynamically stable CdSe clusters takes place. The steep concentration gradient provokes indiffusion of the stoichiometric compound. In the case of a surplus of Cd over Se and long annealing times self-organized, nearly periodic and correlated concentration variations of Cd and Se can be observed. Comparison of the profiles indicate that this pattern formation is controlled by the diffusion and precipitation of the over stoichiometric Cd.
Microanalysis of Self-assembled InAs Quantum Dot Structures Grown for Infrared Detector Applications
Authors: Sarney W.L. , Little J.W. , Svensson S. 
Published: April 2011

ABSTRACTIn an effort to develop materials that are sensitive to mid and far infrared radiation, we examine InAs quantum dot/GaAs matrix multilayer structures grown by molecular beam epitaxy (MBE). Customized electrical and optical properties result from nanoscale-level manipulation of the dots' physical dimensions. The MBE growth temperature can be set to yield dots having the desired lateral dimension; however this leads to dots of insufficient vertical height. It is therefore necessary to grow the dots in a manner that allows independent control of the lateral and vertical dimensions. In this experiment, the vertical dimension is controlled by growing the dots in a multilayer structure with GaAs matrix layers. An initial layer of InAs quantum dots was grown on top of GaAs, followed by a few seconds short growth of GaAs, and then followed by the growth of another layer of InAs dots. The GaAs laterally surrounds, but does not bury, the InAs quantum dots. When the second layer of InAs dots is grown, they tend to self-organize directly on top of the exposed first layer of dots. We then grew a third layer of dots in the same manner. This effectively results in a pseudo-single layer of dots of the desired height which is then completely buried in GaAs. The goal is to develop structures that can be integrated into high operating temperature quantum dot infrared detectors (QDIPs) that have maximum sensitivity, robustness, and portability.
On the Manipulation of Nanoscale Self-Assembly by Elastic Field
Authors: Gao Y.F. 
Published: April 2011

ABSTRACTMorphological and compositional self-assembly can be manipulated by the long-range elastic field. This paper gives a universal formulation that determines the dependence of energetically favored orientation of those self-assembled structures on the elastic interaction. Elasticity anisotropy can lead to symmetry breaking and herringbone structures. A layered substrate can tune the feature size by modulus mismatch, or tune the orientation if the layers have different orientation preference, or guide the self-assembly by embedded structures. A closed-form result is derived for elastically isotropic layers by using Dundurs parameters. The self-assembled structures can also be affected by a nonuniform residual stress field or external force field. Higher order (nonlinear) perturbation theory, coupling between morphology and composition, and other issues are also addressed in the discussion.
Second- and third-harmonic generation spectroscopy of coupled microcavities formed from all-silicon photonic crystals
Authors: Gusev D. G. , Soboleva I. V. , Martemyanov M. G. , Dolgova T. V. , Fedyanin A. A. , Aktsipetrov O. A. 
Published: April 2011

ABSTRACTThe enhancement of second- and third-harmonic generation (SHG and THG) in all-silicon coupled microcavities (CMC) formed from mesoporous silicon photonic crystals are observed at the resonance of the fundamental radiation with the CMC eigenmodes. Angular splitting of the peaks in intensity spectra of SHG and THG shows monotonous dependence on magnitude of coupling between two identical microcavity spacers controlled by the reflectivity of the intermediate Bragg reflector.
Bias-Voltage Dependence in Atomic-Scale Spin Polarized Scanning Tunneling Microscopy of Mn3N2 (010)
Authors: Smith Arthur R. , Yang Rong , Yang Haiqiang 
Published: April 2011

ABSTRACTAtomic-scale spin-polarized scanning tunneling microscopy results on the manganese nitride Mn3N2 (010) surface are presented. The images show the row-wise antiferromagnetic structure of the surface. It is shown that the bias voltage between tip and sample affects both the magnetic and non-magnetic components of the height profile. In particular, a reversal of the magnetic contrast is shown to occur at a certain bias voltage.
Neutron Studies of Magnetic Recording Media
Authors: Lee S. L. , Thomson T. , Ogrin F. Y. , Oates C. , Wismayer M. , Dewhurst C. , Cubitt R. , Harkness S. 
Published: April 2011

ABSTRACTSmall-angle neutron studies have been performed on samples of continuous inhomogeneous magnetic recording media. This has allowed the local magnetic structure to be probed at a sub-nanometre resolution, revealing some interesting information about the size and shape of the magnetic grains and their relation to the physical grains.
Heteroepitaxy of InSe/GaSe on Si(111) Substrates
Authors: Jasinski J. , Liliental-Weber Z. , Chaiken A. , Gibson G.A. , Nauka K. , Yang C.C. , Bicknell R. 
Published: April 2011

ABSTRACTHigh quality growth of InSe on Si(111) was achieved by insertion of GaSe buffer layer. Rhombohedral polytypes were formed in both the InSe and GaSe layers. Twinning and stacking disorder was often detected in these materials due to their layered structure. Moreover, in samples with a thin GaSe layer, strong interdiffusion of indium into the GaSe layer was detected that resulted in the formation of an InxGaySe phase. The dominant threading defects present in these InSe/GaSe heterostructures were screw dislocations, which may act as nonradiative recombination centers.
Amorphous-to-polycrystal transition in GeSbTe thin films
Authors: Privitera S. , Bongiomo C. , Rimini E. , Zonca R. , Pirovano A. , Bez R. 
Published: April 2011

ABSTRACTThe amorphous-to-polycrystal transition has been studied in Ge2+xSb2Te5 (x = 0.0 and 0.5) films through X ray diffraction analysis and in situ electrical measurements. Phase separation has been observed in samples with excess of Ge, which cannot be completely converted into thence phase at temperatures lower than 170 °C.By using in situ transmission electron microscopy, the growth velocity and the nucleation rate in Ge2Sb2Te5 films have been measured at different annealing temperatures. Activation energies of 2.8 eV and 2.4 eV have been obtained for the nucleation rate and the growth velocity, respectively. The barrier energy for the nucleation of a critical nucleus ΔG* has been evaluated.
Application of High Throughput Methods to the Development of Materials For Non-Magnetic Storage
Authors: Ramberg C. Eric , Wang Y. , Fan Q. , McDermott E. , Wang J. , Kenyon K. , Field M. , Hornbostel M. , Guan S. , Nguyen S. 
Published: April 2011

ABSTRACTHigh throughput, thin film synthesis methods have been used to make libraries of diverse metallic and metal-chalcogenide compositions. These libraries have been subject to a variety of screening protocols, including X-ray diffraction (XRD) after repeated annealing steps, and the measurement of temperature dependent electrical properties. The application of these methods for the development of materials for non-magnetic storage media is presented.
Study on a Decision Making Methodology with Uncertainties in the Selection Process of Preliminary Investigation Areas
Authors: Tsuchi Hiroyuki , Seo Toshihiro , Metcalfe Richard , Kawano Kenji , Takase Hiroyasu , Bowden Andrew , Suyama Yasuhiro , Toida Masaru , Furuichi Mitsuaki , Matsumura Atsushi , Yoshimura Miyoshi 
Published: April 2011

ABSTRACTThe selection of Preliminary Investigation Areas (PIAs) to be considered in the siting procedure for a Japanese High Level Radioactive Waste (HLW) repository, will require Site-specific Evaluation Factors (SSEF) to be considered. Evaluation of these factors requires a methodology for taking into account various kinds of uncertainties in varied types of literature data. The study described here evaluated the application of Evidential Support Logic (ESL) for this purpose. The approach involves constructing hierarchical process models. Uncertainties are then propagated from the lowest processes, corresponding to data or information, through intermediate processes, to some top level process of interest, such as “assessing the existence of an active fault”. To evaluate the usefulness of ESL a hypothetical site was assessed. The results demonstrate the value of the approach to support decision-making in the selection of PIAs.
Aqueous Dissolution and Surface Alteration Studies of Nd-bearing Zirconolite in 0.001M Citric Acid at 90°C
Authors: McGlinn Peter J. , McLeod Terry , Leturcq Gilles , Aly Zaynab , Blackford Mark G. , Zhang Zhaoming , Li Huijun , Lumpkin Gregory R. 
Published: April 2011

ABSTRACTNd-bearing zirconolite was leached at 90°C for 6 months in 0.001M citric acid, and also in deionised water, to determine the effect of organic-bearing solutions on durability. The pH of the citric acid solution was adjusted to 5 using KOH, approximating that of the water in the parallel tests, to avoid the influence of pH on chemical durability of the zirconolite.Releases were incongruent in the tests carried out in water. Release rates of Ti, Zr and Nd were comparatively very low (commonly too low to be measured) over the first 80 days of leaching. Rates for Ca and Al were 2 to 4 orders of magnitude higher than Ti, Zr and Nd over this same period. At about 80 days, there was an anomalous decrease in pH from 6 to 4 which enhanced release rates of Ti and Nd in particular. There was development of titania crystals, and the suggestion of hydrolysed titania, on the surface after 6 months. Thermodynamic equilibrium between the leachates and hydrolysed species on the surface of the zirconolite may be the key to apparent cessation of alteration, at least during thefirst 80 days of leaching.By contrast, zirconolite leached in 0.001M citric acid maintained release rates of Ti, Zr and Nd 2 to 4 orders of magnitude greater than those in water for the first 80 days, values sustained, within an order of magnitude, for the remainder of the leach tests. Releases were congruent. The surface of the zirconolite showed no signs of secondary phase development. This suggests complexation by citrate ions prevented control by hydrolysed species on zirconolite solubility.
Radiation Effects in Murataite Ceramics
Authors: Lian J. , Wang L. M. , Ewing R. C. , Yudintsev S. V. , Stefanovsky S. V. 
Published: April 2011

ABSTRACTSynthetic murataite, an isometric, derivative of the fluorite-structure, has been proposed as a potential host phase for the immobilization of rare earth elements (REE) and actinides. A 1 MeV Kr+ ion irradiation has been performed on synthetic murataite ceramics in the system Ca-Ti-U-Mn-Al-Zr-Ce-O for different structural multiples of the fluorite unit cell. The temperature dependence of the amorphization dose has been determined. A higher critical temperature was obtained for the disordered murataite as compared to that of murataite superstructures, suggesting that murataite becomes more “resistant” to ion beam-induced damage with increasing degrees of structural disorder.
A Comparison of Wasteforms and Processes for the Immobilisation of Iodine-129
Authors: Maddrell E. R. , Abraitis P. K. 
Published: April 2011

ABSTRACTA range of potential wasteforms for the immobilisation of iodine-129 have been synthesised and compared. The work used both iodosodalite and iodovanadinite, as identified in previous studies, as baseline iodine host phases. Syntheses of related compounds using alternative precursors had varying degrees of success. In addition it was shown that iodine could potentially be isolated in a simple composite wasteform of silver iodide particles in a rutile or anatase matrix. Preliminary leaching studies suggest that iodosodalite dissolves congruently whilst iodovanadinite shows preferential release of iodine at a rate approximately ten times that of matrix alteration.
Cs+ and Sr2+ Ion-Exchange Properties of Microporous Tungstates
Authors: Luca Vittorio , Griffith Christopher S. , Chronis Harriet , Widjaja Jonathan , Li Huijun , Scales Nicholas 
Published: April 2011

ABSTRACTThe hydrothermally prepared hexagonal tungsten bronze (HTB) phase displays promising distribution coefficients (KD) for both Cs+ (2 – 100 ppm) and Sr2+ (0.5 – 60 ppm) in acidic (1M HNO3) radioactive waste simulants. The development of an inorganic ion-exchanger that displays such selectivity has previously eluded researchers in this field. The selectivity for Cs+ and Sr2+ can be modulated by isomorphous substitution of molybdenum into the tungstate framework, and is optimum for material of nominal composition, Na0.2Mo0.03W0.97O3·zH2O (Mo-HTB). Both the parent HTB and Mo-HTB phases display fast ion-exchange kinetics for Cs+ and Sr2+ and cation exchange capacities ca. 50% that of the theoretical capacities of 0.9 and 0.45 mmol.g−1, respectively. The Mo-HTB adsorbent has a modest tolerance to alkali metal ions such as Na+ and K+ in acidic solutions with total Cs+ and Sr2+ uptake dropping by 66% as the concentration of Na+ increases from 9 mmol.L−1 to 1200 mmol L−1.
Phase Relations and Chemical Durability of Ceramics in the Pseudo-Binary System: CaZrTi2O7–GdAlO3
Authors: Mikhailenko N. P. , Ochkin A. V. , Stefanovsky S. V. , Kirjanova O. I. 
Published: April 2011

ABSTRACTPhase relations in a pseudo-binary system (1-x) CaZrTi2O7- x GdAlO3 suggested for immobilization of a zirconium - rare earth – actinide fraction of high level waste were studied with X-ray diffraction and electron microscopy. Zirconolite and perovskite were found to be major phases in the ceramic samples prepared by cold pressing and sintering at 1400 and 1500 °C. At relatively low perovskite content (x < 0.5) zirconolite is the major host for Gd, which is considered as a trivalent surrogate for Am and Cm. At higher perovskite content, perovskite becomes the major host for Gd. Zirconolite is the major host phase for corrosion products (Al, Fe, Ti, Zr). Leach rates of Gd, 238Pu, and 241Am from the ceramics studied are 10−4–10−5 g/(m2d).
Effect of Synthesis Conditions and Actinide Contents on Phase Composition of Actinide Bearing Ceramics
Authors: Ptashkin A. G. , Stefanovsky S. V. , Yudintsev S. V. , Perevalov S. A. 
Published: April 2011

ABSTRACTPu-bearing zirconolite and pyrochlore based ceramics were prepared by melting under oxidizing and reducing conditions at 1550 °C. 239Pu content in the samples ranged between ∼10 and ∼50 wt.%. Phase composition of the ceramics and Pu partitioning were studied using X-ray diffraction (XRD) and scanning electron microscopy with energy dispersive system (SEM/EDS). Major phases in the samples were found to be the target zirconolite and pyrochlore as well as a cubic fluorite structure oxide. Normally the Pu content in the Pu host phases was 10–12 wt.%. This corresponds to the Pu content recommended for matrices for immobilization of excess weapons plutonium. At higher Pu content (up to 50 wt.%) additional phases, such as a PuO2-based cubic fluorite-structured solid solution, perovskite, and rutile were found.
Modeling of the Effects of Radiolysis on UO2-dissolution Employing Recent Experimental Data
Authors: Jonsson Mats , Nielsen Fredrik , Ekeroth Ella , Eriksen Trygve E. 
Published: April 2011

ABSTRACTThis study examines the effect of water radiolysis on the dissolution of uranium dioxide. A model is created to describe the system of uranium dioxide fragments in water, and the production and reactions of radiolysis products (using recent kinetic data). The system is evaluated under different conditions using MAKSIMA-CHEMIST. Conditions examined include presence of carbonate in the water and effects of hydrogen. The simulations are compared to experimental results on spent fuel dissolution. Surprisingly, the simulated U(VI)-release agrees within a factor of three with the experimentally found U(VI)-release. The inhibiting effect of hydrogen is clearly demonstrated by the simulations. From the results of the simulations we are also able to conclude that the main inhibiting effect of H2 is the reaction with OH• and not the reduction of U(VI) to U(IV).
Understanding the Influence of Spatially Varying Retardation Effect on the Solute Transport
Authors: Niibori Yuichi , Shimoda Satoko , Tanaka Kouichi , Tochiyama Osamu 
Published: April 2011

ABSTRACTA two-dimensional approach to understanding the heterogeneity in retardation effect governing the solute transport was carried out. To express the simplified spatial distribution of retardation effect, this study prepared parallel flat boards packed with two kinds of solid materials, where these materials were not mixed, but arranged as two kinds of the layers in a direction parallel to the flow. The ratio of the width of the constituent layer to the total transport distance was assumed to be one of key parameters describing the solute release profile transported through the media. As a tracer, Eu3+ in HNO3 solution was used, and its breakthrough curve was monitored in the experiments. In order to determine the retardation coefficient of the each layer, the retardation coefficients was obtained from the separate column experiment. Moreover, the permeabilities of both layers were confirmed to be almost identical from the one-dimensional, column experiments. A mathematical model was constructed to express the two-dimensional advection and dispersion of the solute through the media with the distribution of retardation effect. The proposed mathematical model and the experimental results showed good agreements, and indicated that the solute release profile strongly depended on the ratio of the width of the constituent layers to the total transport distance and the standard deviation of the retardation.
An Approach to Sorption on Minerals Making Use of Surface Phase Thermodynamics
Authors: Emrén Allan T. 
Published: April 2011

ABSTRACTIn performance assessments for nuclear wastes repositories, Kdvalues are often used to describe sorption of radionuclides on fracture surfaces. The weakness of the Kdconcept is that values determined under certain conditions can only be used when the chemistry is similar to those. Alternatives include surface complexation models. The problem with such models is that the parameters required are not easily determined, and thus are missing for several systems.Another alternative is to use surface phase thermodynamics. Such a theory has been developed, in which the surface of a solid phase and the species adsorbed upon it are treated as a separate phase of variable composition. The composition is described in terms of pure end members. For each end member, the free enthalpy is described by a series expansion. To calculate coefficients, the theory makes use of the fact that at equilibrium, the chemical potential of a component has the same value in all phases. Thus, speciation of the bulk aqueous phase can be used. Making use of only the linear term in the expansion, one measured Kdvalue is enough to determine the corresponding coefficient.The theory has been applied to sorption of U(VI) on alumina with the aid of data from the literature. The coefficient was determined from the measured Kdvalues in the interval pH = 4 – 12. The resulting model curve was found to agree reasonably well with observed values, although the Kdvaries by a factor of 200.
Biologically Induced Clay Formation in Subsurface Granitic Environments
Authors: Tuck Victoria A. , West J. M. , Bateman K. , Coombs P. , Milodowski A. E. , Edyvean R. 
Published: April 2011

ABSTRACTExperiments were conducted to identify the rock-water and microbial interactions influencing accelerated smectite-clay formation. Packed columns and stirred batch reactors contained Äspö granodiorite, artificial groundwater mimicking that from Äspö and combinations of three types of subsurface chemolithotrophic bacteria, two of which were indigenous to the Äspö rocks. Results showed evidence that, within 5 days under anaerobic reducing conditions, all three of the bacterial types produced copious biofilamentous ‘meshes’ across porespaces, apparently using the larger grains as anchor points. The biofilaments quickly became encrusted with fine grained material and surrounded with neoformed clay-like deposits. In contrast, the abiotic controls showed little or no evidence of clay formation suggesting that this process is biologically induced or controlled. A second series of abiotic experiments to determine the effects of increased acidity showed evidence of mineral pitting and dissolution along with an increase in concentration of soluble species thought to be important in smectite formation (i.e. Si, Al, Mg, Fe, Ca, Na). However, there was no evidence of clay formation, and the biotic experiments showed no signs of bulk scale pH change, suggesting that either the bacteria are actively concentrating relevant chemical species at a local level or they are acting as templates or nucleation points for clay formation.
Threshold Voltage and Field for Metal Filament Formation in Hydrogenated Amorphous Silicon
Authors: Stradins P. , Branz H. M. , Jackson W. B. , Crandall R.S. , Hu J. , Wang Q. 
Published: April 2011

ABSTRACTElectrical switching due to metallic filament formation in hydrogenated amorphous silicon (a-Si:H) is studied in metal/a-Si:H/metal structures. We examine the effects of a-Si:H switch layer thickness, applied voltage and polarity, metal contact material, and contact interface properties. For switching, the voltage applied to the contacts must be large enough to establish: 1) a minimum threshold voltage of about 2V at the contacts and 2) a bias field of about 1 MV/cm in the bulk. Changing contact material and polarity strongly affects the switching behavior.