bluuebunny/crossref_metadata_2025_split huggingface dataset:
Radiation-Induced Nanostructures in an Iron Phosphate Glass
Authors: Sun K. , Ding T. , Wang L.M. , Ewing R.C. 
Published: April 2011

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

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

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

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

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

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

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

ABSTRACTThe aim of this work is to provide credibility to the radiolytic models developed for performance assessment studies. Nowadays, there is a tendency to consider them useful tools for predicting the behaviour of spent fuel matrix under repository conditions, although they still suffer of limitations due, among others, to the following reasons: limited availability of kinetic data, difficulty to handle heterogeneous systems, lack of model validation.A kinetics-based model to predict the dissolution of UO2 α-doped pellets under initial anoxic conditions is presented and compared with experimental results previously obtained. The uranium and plutonium concentrations in solution are predicted by considering the presence of an α-radiation field and its influence due to radiolysis of water on the pellet surface oxidation and subsequent dissolution.The initial parameters required by the model in order to reproduce the pellet alteration process are: system geometry, chemical composition of the leachant, physico-chemical characteristics of the leachate and oxidation conditions of the pellet surface (expressed in terms of U(VI)/U(IV) ratio). The last one is the key parameter in the model for simulating the initial quick dissolution process. The results obtained are compared with experimental data. The agreement between the predictions obtained and the experimental published data is good.The influence on the matrix oxidation – dissolution process due to the α-radiation field as well as the release of Pu are reproducible by the model. The Pu concentration trends as a function of time are explained in connection with the matrix dissolution process and are controlled by the formation of the secondary phase “Pu(OH)4(s)”.
Pitting Studies Under Anoxic Conditions on Candidate Container Materials AISI 316L hMo and UHB 904L for The Disposal of HLW in Argillaceous Formations
Authors: Kursten Bruno , Druyts Frank 
Published: April 2011

ABSTRACTStainless steel is being envisaged as the primary candidate container material for the final disposal of vitrified HLW in deep geological argillaceous formations in Belgium. The impact of an evolving underground repository environment, i.e. a progressive change from oxic to anoxic conditions (due to the consumption of entrapped oxygen), on the pitting behaviour of austenitic stainless steels AISI 316L hMo and UHB 904L was studied. CPP-experiments were performed in synthetic solutions, which are representative for the near-field chemistry of an underground repository. The solutions contained various amounts of Cl- (100–50,000 mg/L) at near-neutral pH. Experiments were conducted at 16 and 90°C.AISI 316L hMo and UHB 904L will not be subjected to immediate pitting problems neither under oxic, nor under anoxic conditions. However, AISI 316L hMo could present long-term pitting problems under oxic conditions. Pits are much easier initiated on AISI 316L hMo, for both oxic and anoxic conditions. The pits propagate in a rather similar manner under oxic conditions for both alloys, whereas under anoxic conditions the pits formed on AISI 316L hMo are much deeper. AISI 316L hMo is more susceptible to crevice attack.
Assessment of Redox Conditions in the Near Field of Nuclear Waste Repositories: Application to the Swiss high-level and intermediate level waste disposal concept
Authors: Wersin Paul , Johnson Lawrence H. , Schwyn Bernhard 
Published: April 2011

ABSTRACTRedox conditions were assessed for a spent fuel and high-level waste (SF/HLW) and an intermediate-level waste (ILW) repository. For both cases our analysis indicates permanently reducing conditions after a relatively short oxic period. The canister-bentonite near field in the HLW case displays a high redox buffering capacity because of expected high activity of dissolved and surface-bound Fe(II). This is contrary to the cementitious near field in the ILW case where concentrations of dissolved reduced species are low and redox reactions occur primarily via solid phase transformation processes.For the bentonite-canister near field, redox potentials of about -100 to -300 mV (SHE) are estimated, which is supported by recent kinetic data on U, Tc and Se interaction with reduced iron systems. For the cementitious near field, redox potentials of about -200 to -800 mV are estimated, which reflects the large uncertainties related to this alkaline environment.
Monitoring Disturbances in the Repository System during Construction Process: Experiences from Natural Decay Series Studies at the Pyhäsalmi Mine (Central Finland)
Authors: Marcos N. , Suksi J. , Rasilainen K. , Antikainen J. 
Published: April 2011

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

ABSTRACTUse of compacted bentonite buffers is frequently planned in radioactive waste repositories to isolate waste canisters from the geological environment. When gas is generated from the wastes or their containers, it will need to migrate through the bentonite if pressure rises local to the canisters are to be avoided. Assessment of the effect of gas produced from waste canisters in bentonite buffers requires both experimental data on and models of gas migration through initially water-saturated bentonite. Several different approaches to modelling gas migration through bentonite are described. Some example comparison of model results with experimental data are provided, and some general discussion about the modelling approaches is offered.
Water and Gas Movement in Mx80 Bentonite Buffer Clay
Authors: Horseman Stephen T. , Harrington Jon F. , Sellin P. 
Published: April 2011

ABSTRACTThis paper describes a long-term laboratory test designed to examine the sensitivity of gas flow in Mx80 buffer bentonite subject to a constant volume boundary condition. A constant volume and radial flow (CVRF) apparatus was designed to enable gas flow from a centrally located injection filter to be independently monitored at three sink-filter arrays mounted around the circumference of the clay specimen. Axial and radial total stresses and internal porewater pressure were continuously monitored. Gas entry, breakthrough and peak gas pressures were found to be systematically higher under constant volume boundary conditions than under previously reported constant stress and radially-constrained test conditions [6, 9, 10]. The observation that gas pressures are sensitive to test boundary conditions supports the hypothesis that gas entry is accompanied by dilation of the bentonite fabric. Gas penetration of the clay caused a substantial increase in total stress and internal porewater pressure. Abrupt drops in gas pressure, accompanied by similar drops in total stress, were interpreted as fracture propagation events. The outflow of gas was always non-uniformly distributed between the sinks. Furthermore, the distribution of flow between sinks often changed abruptly during the course of an experiment indicating that gas pathways were very unstable. When gas injection stopped, the gas pressure and rate of outflow spontaneously declined with time. Under constant volume conditions, the gas pressure at the asymptote exceeded the internal porewater pressure by an amount equal to the capillary pressure. In constant volume tests on clay with high water saturation, capillary pressure has a value close to the measured swelling pressure of the clay.
The Uptake of Strontium by Calcium Silicate Hydrates under High pH Conditions: An Experimental Approach to Distinguish Adsorption from Co-precipitation Processes
Authors: Tits J. , Wieland E. , Dobler J.-P. , Kunz D. 
Published: April 2011

ABSTRACTThe interaction of Sr(II) with CSH phases has been investigated to distinguish adsorption from co-precipitation processes and to assess the relevance of these processes for performance assessments. Batch-type sorption experiments were carried out to study the adsorption of Sr(II) on synthetic CSH phases at different C:S ratios. Co-precipitation experiments were conducted by precipitating CSH phases in the presence of Sr(II) at two different precipitation rates.Distribution ratios (Rd) of Sr(II) obtained from the sorption and co-precipitation studies were found to be similar in value. The results indicate that co-precipitation processes do not enhance Sr(II) uptake by CSH compared to adsorption. In both the co-precipitation and adsorption experiments the same sorption sites are accessible to Sr(II). The precipitation rate of the CSH phases has no significant influence on the Rd values.
Low Temperature a-Si:H TFTs with a SiO2 Gate Insulator Deposited by Liquid Phase Deposition
Authors: Cross Richard B. M. , Oxley David P. , Manhas Meenakshi , Narayanan Ekkanath. M. Sankara 
Published: April 2011

ABSTRACTA systematic study has been made of the influence of the deposition conditions on the properties of SiO2 grown by liquid phase deposition (LPD), and a-Si:H manufactured by plasma enhanced chemical vapour deposition (PECVD) with the novel facility of source-gas heating. It is demonstrated that LPD-SiO2 can be grown at 50°C with good dielectric properties. Material has been produced with a resistivity of 1015 &cm and a dielectric strength of 9 MVcm-1.The oxide was found to have a negative fixed oxide charge of 4 × 1011 cm−2, with a dielectric constant of 3.08 and a refractive index of 1.44. In the case of a-Si:H, pre-heating the source gases has enabled material to be grown at 125°C with a hydrogen content of ∼ 10 at%, with a predominance of monohydride bonding and a photosensitivity of ∼ 104. Inverted-staggered thin film transistors have been fabricated incorporating these films with an On/Off ratio of five orders of magnitude, a sub-threshold slope of 1.3 Vdecade−1 and a field effect mobility of 0.20 cm2V−1s−1
The effect of substrate temperature and interface oxide layer on aluminum induced crystallization of sputtered amorphous silicon
Authors: Hossain Maruf , Abu-Safe Husam , Barghouti Marwan , Naseem Hameed , Brown William D. 
Published: April 2011

ABSTRACTThe effect of substrate temperature and interface oxide layer on aluminum induced crystallization (AIC) of amorphous silicon (a-Si) is investigated. The effect of substrate temperature on the AIC process was studied by changing the deposition temperate of a-Si from 200 to 300°C in a Al/a-Si/glass configuration. To study the effect of interface oxide on AIC, samples with a-Si/Al/glass, a-Si/Al-oxide/Al/glass, and Al/Si-oxide/a-Si/glass configurations were prepared at a fixed substrate temperature. The samples were annealed in the temperature range from 300°C to 525°C for different periods of time. The X-ray diffraction (XRD) patterns confirmed the crystallization of the a-Si films in the various configurations. From the analysis, we report that crystallization of a-Si happen at 350°C annealing temperature in the Al/a-Si/glass configuration. However, with or without the presence of Si-oxide at the interface, crystallization saturated after annealing for 20 minutes at 400°C. On the other hand, when Al-oxide is present at the interface, higher annealing temperatures and longer annealing times are required to saturate the crystallization of a-Si. Environmental Scanning Electron Microscope (ESEM) and Energy Dispersive X-Ray (EDX) mapping were used to study the surface morphology as well as the layer sequence after crystallization. This analysis revealed that Si-Al layer-exchange happens regardless of the deposited film configuration.
The Role of Charged Gap States in Light-Induced Degradation of Single-Junction a-Si:H Solar Cells
Authors: Zeman M. , Nádazdy V. , Metselaar J.W. 
Published: April 2011

ABSTRACTComputer simulations of single-junction hydrogenated amorphous silicon (a-Si:H) solar cells with different thickness of the intrinsic layer were carried out in order to study the role of charge gap states in their light-induced degradation. It is demonstrated that it is the decrease of positively charged states above midgap, Dh, and the increase of neutral states around midgap,Dz, and negatively charged states below midgap, De in the intrinsic layer that result in a drop of performance of the solar cells due to light soaking. These changes in the gap states are in accordance with our recent experimental results from the charge deep-level transient spectroscopy on undoped a-Si:H. The experimentally observed changes in the dark and illuminated J-V curves and spectral response could not be simulated with the same set of input parameters by only increasing the defect-state density in the intrinsic layer.
The Influence of Light-Soaking and Atmospheric Adsorption on Microcrystalline Silicon Films studied by Coplanar Transient Photoconductivity
Authors: Smirnov V. , Reynolds S. , Finger F. , Main C. , Carius R. 
Published: April 2011

ABSTRACTA study of the effects of light-soaking and atmospheric adsorption (aging) on the dark- and photo-conductivity of a series of microcrystalline silicon films of varying crystallinity is presented. Light-soaking in vacuum slightly reduces photoconductivity in films close to the amorphous – microcrystalline transition, and there is also a reduction in dark current. Aging increases the dark current, and thus unless due care is taken during light-soaking experiments to eliminate or compensate for aging, the apparent effect of light-soaking may be reduced or even reversed in sign. Transient photocurrent decays confirm the presence of a large density of metastable light-induced defects. A shift in the apparent distribution of defects occurs on prolonged aging, which may be due either to changes in the DOS or a shift in the Fermi level.
Device Characteristics of Ultra-shallow Junctions Formed by fRTP Annealing
Authors: Satta A. , Lindsay R. , Severi S. , Henson K. , Maex K. , McCoy S. , Gelpey J. , Elliott K. 
Published: April 2011

ABSTRACTThe creation of ultra-shallow junction for CMOS devices at the sub-100 nm node is driving significant efforts in developing thermal processing to give rise to high dopant activation in combination with limited diffusion. Flash-assist Rapid Thermal Annealing™ (fRTP™) is a promising new annealing technique, which involves the heating of the bulk of the wafer to an intermediate temperature using rather conventional spike RTP, followed by a short and intense pulse of light localized on the implanted wafer surface.In this work, we have systematically investigated the junction formation of different implants under fRTP anneals in terms of profile and devices. Co-implanted Ge and F species provide more box-like profiles with improved activation. Although leakage currents are higher for fRTP-annealed junctions than for spike-annealed junctions, appropriate fRTP process parameters and correct process conditions provide a critical tool to control and reduce the leakage current of co-implanted fRTP junctions to acceptable levels. Proper implant and anneal are requested for minimizing pattern effect and improving device performance.