bluuebunny/crossref_metadata_2025_split huggingface dataset:
Application of Diluted Magnetic Semiconductors and Quantum Dots to Spin Polarized Light Sources
Authors: Bhattacharya Pallab , Fathpour Sasan , Chakrabarti Subhananda , Holub Michael , Ghosh Siddhartha 
Published: April 2011

ABSTRACTThe magnetic properties of single and multiple layers of GaMnAs, grown by molecular beam epitaxy, have been investigated for application as spin injector layers in spin polarized lights sources. Curie temperatures, TC, as high as 150K have been measured in 15nm Ga0.95Mn0.05As films and similar results are obtained for multiple thin layers of GaMnAs separated by 5nm thick GaAs layers. We have also investigated the properties of self-organized InMnAs quantum dots buried in a GaAs or GaMnAs matrix. Magnetization measurements indicate TC >300K in the dot heterostructures. Light-emitting diode heterostructures with 150nm Ga0.95Mn0.05As spin injector layers and In0.4Ga0.6As quantum dot active regions were grown and fabricated into 600μm diameter mesa-shaped surface-emitting devices. Polarized light at 1.05μm is observed with an output polarization efficiency of 26% at a record high temperature.
Strong light confinement in microporous photonic silicon structures
Authors: Lérondel G. , Reece P. , Bruyant A. , Gal M. 
Published: April 2011

ABSTRACTWe have recently reported the fabrication of Si based subnanometer linewidth microcavities and omnidirectionnal mirrors. The structures were made of microporous silicon by electrochemical anodization. The structure high quality and the observation of omnidirectionnal stop bands have been made possible by the optimisation of the starting material, the etching conditions, and the structure design. In this paper we discuss more specifically the choice of these parameters considering the material intrinsic limitations.
Optical devices based on anisotropically nanostructured silicon
Authors: Diener J. , Künzner N. , Gross E. , Kovalev D. , Fujii M. 
Published: April 2011

ABSTRACTAnisotropic nanostructuring of bulk silicon (Si) leads to a significant optical anisotropy of single porous silicon (PSi) layers. A variation of the etching current in time allows a controlled modification of the porosity along the growth direction and therefore a three-dimensional variation of the refractive index (in plane an in depth). This technique can be important for photonic applications since it is the basis of a development of a variety of novel, polarization sensitive, silicon-based optical devices: retarders, dichroic Bragg Reflectors, dichroic microcavities and Si based polarizers.
Interaction of Periodically Arranged Point Defects in a Two Dimensional Photonic Crystal -The Photonic Analogue to a Doped Semiconductor
Authors: Richter S. , Schweizer S. L. , Hillebrand R. , Jamois C. , Wehrspohn R. B. , Zacharias M. , Goesele U. 
Published: April 2011

ABSTRACTWe present and characterize hexagonal point defects in a two dimensional photonic crystal based on macroporous silicon. These point defects are prepatterned periodically, forming a superstructure within the photonic crystal after electrochemical etching. Spatially resolved, optical investigations related to morphological properties, like defect concentration and pore radius, are compared to bandstructure calculations. The confined defect states are identified and their interaction is evaluated quantitatively.
Innovation Providing New Multiple Functions in Phase-Change Materials To Achieve Cognitive Computing
Authors: Ovshinsky Stanford R. , Pashmakov Boil 
Published: April 2011

ABSTRACTThis paper describes a basic new scientific and technological approach for information and computing use. It is based on Ovonic cognitive devices that utilize an atomically engineered Ovonic chalcogenide material as the active medium. We demonstrate how such a device possesses many unique functions including an intrinsic neurosynaptic functionality that permits the processing of information in a manner analogous to that of biological neurons and synapses. Our Ovonic cognitive devices can not only accomplish conventional binary computing, but are capable of non-binary generation of information, storage, encryption, higher mathematics, modular arithmetic and factoring. Uniquely, almost all of these functions can be accomplished in a single nanosized device. These devices and systems are robust at room temperature (and above). They are non-volatile and also can include other volatile devices such as the Ovonic Threshold Switch and Ovonic multi-terminal threshold and memory devices that can replace transistors.
Key Technology for Ultra Density Optical
Authors: Somekh Robert E. , Davies Clare E. 
Published: April 2011

ABSTRACTUltra Density Optical (UDO) has been designed as the Phase Change successor to 5¼-inch Magneto Optic data storage products, with a UDO road map spanning three product generations leading to 120GB capacity. First generation UDO will utilise 405nm wavelength, 0.7NA drive optics with 100 micron cover layer media construction in a robust, double-sided cartridged format with 30GB capacity. There will be two types of UDO, both aimed at the professional market: UDO Write Once for high density, high data rate, archival data storage applications, and high cyclability UDO Rewritable. The features of UDO and the underlying Media Engineering optimisation strategies are discussed.
Mechanisms of Initialization of Doped Sb-Te Phase-Change Media
Authors: Towlson Samantha J. , Elwell Clifford A. , Davies Clare E. , Greer A. Lindsay 
Published: April 2011

ABSTRACTLaser initialization of the chalcogenide optical-recording medium Ag-In-Sb-Te is investigated using transmission electron microscopy of the resulting microstructure. Initialization beam power and velocity are varied. The average inhomogeneous strain of the chalcogenide is estimated from X-ray peak broadening. At high power and low velocity a clearly defined columnar grain structure with low strain is produced, typical of directional solidification. At low power and high velocity the initialized structure has a high density of defects and high strain; this is attributed to crystallization from the amorphous rather than the liquid state. The beam power and linear velocity of laser initialization may therefore be used to control the microstructure.
Nonlinear characteristics of super resolution chalcogenide thin film
Authors: Kim Se-Young , Kang Myung-jin , Choi Se-Young 
Published: April 2011

ABSTRACTA third order nonlinear optical material, As2Se3 was proposed for super resolution near field structure disk. As2Se3 was deposited by thermal evaporation technique. Composition, phase, surface morphology, linear/non-linear optical properties were obtained from EPMA, XRD, AFM, UV-VIS-NIR spectrophotometer and VASE. As2Se3 thin film showed large non-linear optical characteristics (XR(3) =7.42×10-7 m2/w, γ=1.268×10-5m2/w) and self-focusing phenomenon. Super resolution effects of the As2Se3 thin films were measured by using the laser beam profiler. As a result, recording density can be enhanced by 2.3 times, in case of 350nm As2Se3 thin film was deposited as super-RENS.
Synthesis, Characterization and Study of the Radiation Effects on Hollandite Ceramics Developed for Cesium Immobilization
Authors: Aubin Virginie , Caurant Daniel , Gourier Didier , Baffier Noël , Advocat Thierry , Bart Florence , Leturcq Gilles , Costantini Jean M. 
Published: April 2011

ABSTRACTProgress on separating the long-lived fission products has notably implied basic research on specific host matrices, especially for the immobilization of cesium. Barium hollandite (BaAl2Ti6O16) ceramics have received considerable interest because of their high cesium incorporation ability and chemical stability. This study deals with the preparation of hollandite in the BaxCsy(Al,Fe)2x+yTi8–2x-yO16 (x+y<2) compositional range by an oxide route. Different parameters such as the grain size of the precursor or the temperature and duration of sintering were changed in order to optimize ceramics synthesis. To estimate the hollandite radiation resistance, external electron irradiation experiments (simulating the β particles emitted by radioactive cesium) were performed on hollandite of simple composition. The irradiation-induced defects were studied by Electron Paramagnetic Resonance (EPR) spectroscopy and their nature is discussed.
Quantitative Assessment of the Instant Release Fraction (IRF) for Fission Gases and Volatile Elements as a Function of Burnup and Time under Geological Disposal Conditions
Authors: Ferry Cécile , Lovera Patrick , Poinssot Christophe , Johnson Lawrence 
Published: April 2011

ABSTRACTThe Instant Release Fraction at container failure time, IRF(t), is here considered as being the sum of (i) the initial labile fraction, corresponding to the sum of gap and grain boundary inventories of certain radionuclides on exit from the reactor, with a further possible contribution from segregation in the rim region and (ii) the time-dependent fraction of radionuclides accumulating at grain boundaries due to a self-irradiation enhanced diffusion through the grains. The initial labile fraction of radionuclides such as 14C, 36Cl, 79Se, 129I, and 135Cs has been estimated based on leaching experiments, post-irradiation fission gas release measurements and studies of solid-state chemistry of spent fuel, along with estimates of fission product segregation in the rim zone. The contribution of the a self-irradiation enhanced diffusion has also been estimated based on a diffusion coefficient decreasing with time proportionally with the volume α-activity of the spent fuel. Its contribution to the IRF is limited for UO2 fuels. The proposed bounding values of the IRF for fuel with a burnup of 55 GWd/tIHM for 14C, 36Cl, 79Se, 129I, and 135Cs are 11 % at t=0 and close to 15 % at a container failure time of 10,000 y.
Microstructure Development in Copper Welded by the FSW-Process
Authors: Källgren Therese , Sandström Rolf 
Published: April 2011

ABSTRACTTo ensure safe storage of nuclear fuel waste, copper canisters are proposed as corrosion barrier. One alternative for sealing the copper canisters is Friction Stir Welding (FSW). During the joining process friction heat and mechanical deformation appear between the rotating tool and the material being welded. Liquid metal will not form, since this is a solid state welding process. Three distinct microstructural zones are developed namely the nugget, the thermo-mechanically affected zone (TMAZ) and heat-affected zone (HAZ). The nugget is in the centre of the weld, where the pin is located and where severe plastic deformation occurs that leads to recrystallisation. Surrounding the nugget, the TMAZ is only partially recrystallised, due to lower temperature increase and deformation compared to the nugget. The third zone, HAZ, surrounds the TMAZ. The initial nugget can have a classic round aluminium nugget image, when the welding conditions are cold, but the steady state nugget, is wider near the shoulder and shorter in the weld root.
On Pressure Pulse Techniques for Testing Low Permeability Geological Materials and Formations
Authors: Zhang M. , Takeda M. 
Published: April 2011

ABSTRACTThe accurate hydraulic characterization of low permeability geological materials and formations has important practical implications, such as the geological disposal of radioactive nuclear waste. In this paper, we discuss pressure pulse techniques, which are methods that are commonly adopted both in the laboratory and in situ for testing low permeability geological materials and formations. The results obtained in this study illustrate that: 1) the use of nominal values for water compressibility will lead to significant underestimation of permeability from the pressure pulse tests; 2) specific storage is also an important parameter that should be evaluated simultaneously with permeability; 3) to shorten the time required to measure low permeability in the laboratory, it is advisable to use disk-shaped specimens; 4) when a geological formation is anisotropic, the value of permeability calculated using an isotropic model is between the maximum and minimum permeabilities of the geological formation; 5) the values of permeability and specific storage derived from an in situ pressure pulse test may only reflect the hydraulic properties of the domain closely surrounding the test well. Caution should be exercised when interpreting data derived from the pressure pulse tests for the purpose of safety assessment.
Harmonisation of Site Characterisation and Performance Assessment Modelling - The Relative Importance of Surface Sorption and Matrix Interaction Phenomena
Authors: Crawford James , Moreno Luis , Neretnieks Ivars 
Published: April 2011

ABSTRACTIn the context of geological repositories for nuclear waste disposal, the goal of site characterisation (SC) is to obtain input data that can later be used as a basis for performance assessment calculations (PA). Performance assessment is required to give an indication as to whether the repository will behave as intended over the geological timescales relevant for risk analysis.Processes that may be important in a PA setting for constraining radionuclide transport may not necessarily be dominating, or indeed may not even be observable during SC investigations.In this paper it is shown that the migration of sorbing tracers is governed largely by surface sorption phenomena in typical SC-type field experiments whereas in a PA scenario, matrix interaction instead can be expected to play an overwhelmingly important role. This study uses data and settings that are representative for fractured rocks in Sweden, but the method used and the conclusions may have more general applicability.
The Feasibility of USD Method in Tracking Past Hydrogeochemical Changes in the Fennoscandian Shield
Authors: Rasilainen Kari , Suksi Juhani , Ruskeeniemi Timo , Pitkänen Petteri 
Published: April 2011

ABSTRACTUranium-series disequilibrium (USD) method is the only paleohydrogeological method that for the time scale relevant for performance assessments can detect and directly date past hydrogeochemical changes. Such changes cause U mobility which is seen as uranium-series disequilibrium. We have reviewed the method taking into account experimental and interpretation aspects and identified pros seem to outweigh identified cons. Reported USD studies in Finland and Sweden have earlier been mostly qualitative but a quantitative methodology has been developed for future studies.
Study of the Uranium Heterogeneous Diffusion through Crystalline Rocks and Effects of the “Clay-Mediated” Transport
Authors: Alonso U. , Missana T. , García-Gutiérrez M. , Patelli A. , Ravagnan J. , Rigato V. 
Published: April 2011

ABSTRACTRock matrix diffusion is one of the possible mechanisms for radionuclide retardation in a deep geological high-level radioactive waste repository, and it is usually considered that radionuclides diffuse as solutes through the rock. Nonetheless, the potential effects that clay, from the bentonite barrier, may induce on the radionuclides migration should be taken into account. Furthermore, transport models generally assume that the whole mineral surface is accessible to transport, whereas transport is highly conditioned by the heterogeneous mineral distribution, since different minerals may act as preferential pathways, while others may present higher sorption capability. It is therefore necessary to determine the actual surface area accessible to transport.The aim of the present work is the identification of the uranium preferential pathways to the granite, both in presence or absence of bentonite clay. Results showed that uranium as solute diffused in specific mineral areas, indicating that the actual surface area accessible to matrix diffusion, and/or sorption on the surface, is significantly lower than the whole mineral surface. By the other hand, the uranium in presence of the clay was randomly distributed on the surface, and penetrated into the granite mainly through “defects” (as fractures or grain boundaries); its migration being enhanced on specially fractured or disturbed areas.
A Conceivable Technique of Measuring Sorption Coefficients in Intact Rock Using an Electrical Potential Gradient as the Driving Force for Migration
Authors: Löfgren Martin , Neretnieks Ivars 
Published: April 2011

ABSTRACTSorption coefficients are traditionally obtained in batch experiments if the sorbent is strongly or intermediately sorbing. In a batch experiment the rock is crushed and this could increase the surface area as well as induce new and fresh surfaces. Therefore there is some concern whether sorption coefficients obtained in batch experiments represents those of intact rock. Performing sorption experiment by diffusion in intact rock with intermediately and strongly sorbing species seems impossible in practice due to extremely long experimental times. In this paper the possibility of increasing the migration rate in the rock by two of three orders, thus enabling KD measurements of intermediately sorbing species in intact rock, is discussed. The increase in migration ratehas already been achieved successfully in so called through electromigration experiments using non-sorbing species. Here a potential gradient acts as the main driving force. In our experiments the migration rate was increased 320 times by using a potential drop of only 9 volts.
Modification of the Tournemire Argilite in Contact with Simplified Concrete Fluid
Authors: Devol-Brown Isabelle , Stammose Denise , Ahamdach Noureddine , Geiss Olivier 
Published: April 2011

ABSTRACTArgillaceous rocks are considered as potential host rocks for radioactive waste repositories. The design of an underground disposal often includes large amounts of concrete which are proposed as waste matrix, backfill material and structural components. The leaching of concrete by groundwater produces alkaline solutions that will react with the host rock inducing modifications of the geological barrier performances. In order to examine the effects of an alkaline plume on the properties of claystone, an experimental program is being developed in our institute involving batch, diffusion and percolation experiments. This paper presents the results obtained with first batch studies performed at 25°C and 70°C over 3 months. The effect of high pH solutions (corresponding to the early period of leaching) on the composition of a claystone (originating from Tournemire - France) was examined. The changes in solutions composition were monitored as a function of temperature and V/m ratio. In spite of the short contact time between solution and solid, some modifications in these two phases were noticed. The interactions between solids and solutions were more pronounced at 70°C than at 25°C, resulting in pH and potassium concentration decrease, while the sodium concentration remained constant. Moreover, the dissolution of mineral phases such as dolomite and kaolinite was proposed.
iCONNECTClub: Integrated CONtinuum and NEtwork Approach to Groundwater Flow and Contaminant Transport
Authors: Holton David , Hartley Lee J , Hautojärvi Aimo , Marschall Paul , Selroos Jan-Olof 
Published: April 2011

ABSTRACTModels of groundwater flow and transport are routinely used as part of the safety assessment of a site, and increasingly to aid the site investigation strategy and design of a proposed repository. This emphasis puts greater demands on those models to reflect a higher level of realism to incorporate additional information in the vicinity of the repository. This paper describes a successful approach to incorporate these different scales, from canister- to regional-scale, within one model. Such an approach is able to resolve the details of groundwater flow around the waste packages in the overall hydrological setting of the site.
Hyperalkaline Cement Leachate-Rock Interaction and Radionuclide Transport in a Fractured Host Rock (HPF Project)
Authors: Mäder Urs , Frieg Bernd , Puigdomenech Ignasi , Decombarieu Michel , Yui Mikazu 
Published: April 2011

ABSTRACTThe HPF project (Hyperalkaline Plume in Fractured rock) at the Grimsel Test Site comprises an underground long-term field experiment in a shear zone, in-situ radionuclide transport experiments, two laboratory core infiltration experiments, sophisticated reactive transport modeling exercises, studies on radionuclide stability and solubility, innovative on-line measurement techniques and development of equipment for high-pH conditions (K-Na-Ca-OH, pH = 13.4 at 15 °C). Results to date indicate a decrease in the overall transmissivity of the tested shear zone over a duration of 2 years accompanied by channeling of flow as evidenced by repeat dipole tracer testing with Na-fluorescein, 82Br, 131I, 24Na, and 85Sr. The associated evolution in fluid chemistry indicates the in situ formation of Ca-Si-hydrates. Tracer transport modeling of dipole tests are based either on a heterogeneous porous medium approach or on discrete fracture models. Reactive transport modeling is achieving reasonable agreement with a laboratory core infiltration experiment. Integral to the project are supporting sorption / stability studies, colloid measurements, and development of analytical and measurement techniques.
Location Control of Crystal Grains in Excimer Laser Crystallization of Silicon Thin Films for Single-Grain TFTs
Authors: Kumomi Hideya , Wakiyama Hiroaki , Nakagawa Gou , Makihira Kenji , Asano Tanemasa 
Published: April 2011

ABSTRACTLocation of crystal grains is controlled in excimer laser crystallization (ELC) of amorphous Si (a-Si) thin films, aiming at a high-performance single-grain thin film transistor (TFT) whose channel is inside a single crystal grain with no grain boundary in the channel. The location control is achieved by manipulating seed-crystal forming sites in the starting thin film. The sites are small portions of the a-Si thin film, typically 1 μm in diameter, only in which nanometer-sized crystallites are embedded in the amorphous matrix. During the ELC, at least one crystallite survives the melting duration and serves as a seed crystal for the resolidification of the surrounding molten silicon. As a result, large crystal grains are formed at the predetermined sites. The TFTs whose channels are fabricated at the location-controlled crystal grains exhibit higher performance than the random polycrystalline Si (poly-Si) TFTs.
Are the Current Models Helpful to Understanding Staebler-Wronski Degradation?
Authors: Roedern Bolko von 
Published: April 2011

ABSTRACTThis contribution reviews the compatibility of Staebler-Wronski models with experimental data and observations. The review will show that neither the “bond-breaking models” (originally proposed by Dersch and Stutzmann) nor the “defect conversion” models (originally proposed by Adler) can explain all observations on films and/or solar cells. It has been well accepted for some time that experimental stress and recovery phenomena, both on films and devices, always identify both “slow” and “fast” degradation and recovery mechanisms. It is argued that the quintessential understanding of the Staebler-Wronski mechanisms will come from identifying a fundamental physical process that provides a quantitative understanding of the “coupling” between the slow and fast mechanisms.