bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of Alpha Radiolysis on UO2Dissolution under Reducing Conditions
Authors: Mennecart T. , Grambow B. , Fattahi M. , Blondiaux G. , Andriambololona Z. 
Published: April 2011

ABSTRACTEffects of water radiolysis on the dissolution rate of UO2were studied by irradiating UO2colloids with an alpha particle beam of a cyclotron. The solution was kept under reducing conditions by applying a current of -10 or -50 nA and an ultrahigh purity argon bubbling. The solution pH was fixed at 6 during experiment. The particle flux was 1.1×1011α.cm−2.s−1entering in solution with an energy of 5 – 6 MeV. Despite initial reducing conditions water radiolysis increased the dissolution rate of uranium dioxide due to reaction with oxidizing radiolytic species such as H2O2, O2, OH•, HO2•, ClO3−. The monitoring of the redox potential showed that the solutions became rapidly oxidizing. The dissolution rate values were between 0.01 and 26 mg·m−2·d−1depending on the ratio of the irradiated UO2mass to the solution volume. This dependency is caused by hydrogen peroxide consumption at the UO2surface. The rate of hydrogen peroxide consumption by reaction with colloids corresponds to an equivalent rate of UO2oxidation/dissolution between 2 and 60 mg.m−2.d−1indicating that only a small fraction of produced H2O2is consumed by the dissolution reaction.
KBS-TR-90 Twenty-five Years On - Progress in the Understanding of the Long-term Corrosion Behaviour of Copper Canisters
Authors: Werme Lars , King Fraser , Ahonen Lasse , Taxén Claes , Vuorinen Ulla 
Published: April 2011

ABSTRACTIn 1978, the Swedish Corrosion Institute published a report describing an assessment of the long-term corrosion behaviour of copper canisters for nuclear waste disposal. They concluded that the canisters would remain intact for a period exceeding 100,000 years in a deep underground repository in the Fennoscandian bedrock. In the intervening 25 years a great deal has been learnt about the corrosion of copper in the expected repository environment. In 2001, SKB and Posiva reviewed this new information and re-assessed the predicted canister lifetime [1]. It was concluded that the original prediction made in 1978 of canister lifetimes exceeding 100,000 years remains valid.
A Weld that Lasts for 100,000 Years: Friction Stir Welding of Copper Canisters
Authors: Cederqvist Lars 
Published: April 2011

ABSTRACTFriction Stir Welding (FSW) is a novel solid-state joining process where the work pieces are joined together using a rotating non-consumable tool. The process has mainly been used for joining aluminium alloys, and has not yet been used in production for any other metal. However, the results from the development program confirm that FSW can consistently seal 50mm thick copper canisters without creating defects. A new machine is now installed at SKB's Canister Laboratory to further automate the process to production level.
Earthquake Induced Rock Shear Through a Deposition Hole. Effect on the Canister and Buffer
Authors: Börgesson L. , Johannesson L.-E. , Hernelind J. 
Published: April 2011

ABSTRACTExisting fractures crossing a deposition hole may be activated and sheared by an earthquake. The effect of such a rock shear has been investigated in a project that includes both laboratory tests and finite element calculations.A number of laboratory tests have been performed with shearing of water-saturated bentonite samples at different densities and shear rates. From those tests a material model of the buffer that takes into account the shear rate has been formulated. Shear rates up to 6 m/s have been tested.The rock shear has been modelled with finite element calculations with the code ABAQUS. A 3D finite element mesh of the buffer and the canister has been created and a number of calculations with simulation of a rock shear have been performed. The rock shear has been assumed to take place perpendicular to the canister axis in either the centre of the deposition hole or at the ¼ point. The shear calculations have been driven to a total shear of 20 cm. Buffer densities at water saturation between 1950 and 2100 kg/m3 and shear rates between 0.0001 and 1000 mm/s have been modelled. The influence of buffer density, shear plane location, the shear rate and the magnitude of the shear displacement are analysed and discussed.The results show that the influence of especially the density of the buffer and the location of the shear plane are very strong but also that the shear rate and the magnitude of the shear displacement have a significant effect.
Adsorption and Retention of U-238 and Th-232 from Groundwater Using BIOS
Authors: Anderson Craig R. , Pedersen Karsten 
Published: April 2011

ABSTRACTBiofilms were grown in situ 296 metres below sea level in the Äspö Hard Rock Laboratory. The prominent organism in these biofilms wasGallionella ferruginea, which is an iron oxidising chemolithotrophic microorganism that grows in low oxygen conditions. This organism grows an organic stalk structure capable of binding and concentrating trace metals. This stalk structure also allows amorphous ferric iron oxyhydroxides, or BIOS, (bacteriogenic iron oxides) to precipitate. The pH of the groundwater within the system was between 7.4 and 7.6, with Eh potential between 150 and 190 mV and oxygen saturation between 3 and 15%. Biofilms developed within two weeks and were sampled every two weeks for three months. Cell number and stalk length was recorded for each sample. The concentration of Cr, Ni, Cu, Zn, Mo, REE (rare earth elements), U-238 and Th-232 was measured by ICP-MS. Early results suggested thatGallionellabiofilms and associated BIOS could potentially concentrate trace metals up to 1000 fold higher than levels within the host rock and over 1 000 000 times the levels in the groundwater over a period of years. These new experiments indicate thatGallionellabiofilms and BIOS can rapidly attenuate metals to levels over 1000 fold higher than the levels in the groundwater. This process can occur anywhere where reduced groundwater enters the waste repository tunnel, open cavities or where groundwater extrudes at the surface. Because of this, there is huge potential to use biofilms and BIOS for retention of radionuclides and pollution control.
Site Investigations of Potential Repository Sites in Sweden
Authors: Wikberg Peter , Ahlbom Kaj , Olsson Olle 
Published: April 2011

ABSTRACTThe Swedish nuclear waste management programme has entered the site investigation phase. Early 2002 SKB received permission from the municipalities of Östhammar and Oskarshamn to perform site investigations for a potential deep geologic repository for spent nuclear fuel. The goal of the site investigation phase is to obtain a permit to build the deep repository for spent nuclear fuel. In parallel with the investigations, consultations will be held with county administrative boards, regulatory authorities and municipalities, as well as with members of the public.
A Preliminary Chemical Toxicity Assessment for the Nirex Disposal Concept
Authors: Askarieh M. M. , Atkinson R. , Baker A. J. , Chambers A. V. , Heath T. G. , Williams S. J. 
Published: April 2011

ABSTRACTThe role of Nirex is to provide the United Kingdom with safe, environmentally sound and publicly acceptable options for the long-term management of all intermediate level and some low level radioactive waste. Nirex has developed its Phased Disposal Concept as one option for the long-term management of radioactive materials. The Phased Disposal Concept represents a stepwise and reversible approach to the disposal of radioactive waste within a deep geological repository that involves the immobilisation of wastes in containers (mainly fabricated from stainless steel) that are surrounded by a cementitious backfill.The wastes for potential disposal contain materials that may require consideration on the basis of their potential non-radiological hazards. This paper describes a preliminary two-stage methodology for assessing the post-closure impact of the disposal of chemically toxic materials to a conceptual Nirex repository. The study suggests some materials either exceeded current estimates of safe levels, or their impact could not be quantified at this stage but was considered to be of concern. These materials included beryllium, phenol, benzene, and nitrite.
Analogues for the Corrosion-induced Expansion of Iron in HLW containers
Authors: Smart Nicholas R. , Adams Rachel , Werme Lars 
Published: April 2011

ABSTRACTIn Sweden, spent nuclear fuel will be encapsulated in sealed cylindrical canisters, consisting of a cast iron insert and a copper outer container. The canisters will be placed in a deep geologic repository and surrounded by bentonite. If a breach of the outer copper container were to occur the cast iron insert would undergo anaerobic corrosion, forming a magnetite film whose volume would be greater than that of the base metal. In principle there is a possibility that accumulation of iron corrosion product could cause expansion of the copper canister. Anaerobic corrosion rates are very slow, so in the work described in this paper reference was made to analogous archaeological materials that had been corroding for long periods in natural anoxic aqueous environments. This paper describes a number of archaeological artefacts containing iron and copper corroding in constrained geometries in anoxic natural waters. No evidence has been obtained which would suggest that severe damage is likely to occur to waste canisters as a result of expansive corrosion of cast iron under repository conditions.
Amorphous Silicon Backplane with Polymer MEMS Structures for Electrophoretic Displays
Authors: Daniel J.H. , Krusor B.S. , Chopra N. , Street R.A. , Kazmaier P.M. , Ready S.E. , Ho J.H. 
Published: April 2011

ABSTRACTThe development of electronic paper has been a long-term goal and electrophoretic displays are a promising candidate for this application. Apart from developing the electrophoretic display medium there are important issues to solve regarding the overall system. The importance of the electronic addressing method increases with the demand for arbitrary images or text. We have developed and tested active-matrix backplanes based on amorphous silicon technology, as well as the driver electronics. The electrophoretic ink is combined with the backplane employing polymer MEMS cell structures. This system allows us to display high-resolution images and it is a good test bed for investigating various parameters of the electrophoretic display medium and of the electronics.
Tritium Induced Defects in Amorphous Silicon
Authors: Whitaker J. , Viner J. , Zukotynski S. , Johnson E. , Taylor P.C. , Stradins P. 
Published: April 2011

ABSTRACTWe report the growth of tritium induced defects in tritium doped hydrogenated amorphous silicon (a-Si:H,T) as measured by electron spin resonance (ESR) and photothermal deflection spectroscopy (PDS). The measurements allow one to examine the accumulation of defects in a-Si:H,T where the defect production mechanism is known. Defects produced by tritium decay are found to be much less numerous than the number of decayed tritium atoms and they are metastable like Staebler-Wronski defects. These results provide new insight into the metastable defect creation and the role of hydrogen motion.
H Evolution from Nano-Crystalline Silicon- Comparison of Simulation and Experiment
Authors: Biswas R. , Pan B. C. 
Published: April 2011

ABSTRACTThe temperature dependent H evolution from a-Si:H provides unique information on the H-bonding and microstructure. Traditional undiluted a-Si:H films show a high temperature H-evolution peak near 600°C. However device-quality compact nanocrystalline silicon films grown near the phase boundary of amorphous and microcrystalline growth show a new low temperature H- evolution peak near 400°C in addition to a second high temperature peak near 600°C. The origin of this peak cannot be attributed to microvoids or a substantial density of dihydride species typical of porous low-temperature films. We have simulated the H evolution using a molecular dynamics generated model of nanocrystalline silicon, where nano-crystallites reside in a background amorphous matrix. An excess density of H occurs at the crystallite surface. We find a low temperature evolution peak at 250-400°C, where the H-evolution starts from the surface of the nano-crystallite. In addition there is a higher temperature peak at 700-800°C providing good agreement with H-evolution measurements. The mobile H is found to exist in both the bond-centered type of species and H2 molecules – which has implications for H-diffusion models.
The p-channel a-Si:H Thin Film Transistor with Plasma Etched Copper Electrodes
Authors: Nominanda Helinda , Liu Guojun , Lee Hyun Ho , Kuo Yue 
Published: April 2011

ABSTRACTP-channel thin film transistors (TFTs) with a copper (Cu) gate, source, and drain electrodes, prepared by a novel plasma etching process, have been fabricated and studied. The p-channel TFT characteristics are similar to those of the p-channel TFT with Mo electrodes. The influence of the channel length on the TFT characteristics, such as mobility, threshold voltage, and on-off current ratio, was examined. In spite of its low mobility, good device characteristics, such as ohmic contacts, were obtained. Most of the TFT characteristics, except the threshold voltage, were not affected by an extended high-temperature annealing step. The increase of the threshold voltage was probably due to the lack of a diffusion barrier between the gate Cu and the gate SiNx layer.
Intrinsic and Doped m c-Si:H TFT Layers using 13.56 MHz PECVD at 250°C
Authors: Lee Czang-Ho , Striakhilev Denis , Nathan Arokia 
Published: April 2011

ABSTRACTUndoped and n+ hydrogenated microcrystalline silicon (μc-Si:H) films for thin film transistors (TFTs) were deposited at a temperature of 250°C with 99 ∼ 99.6 % hydrogen dilution of silane by standard 13.56 MHz plasma enhanced chemical vapor deposition (PECVD). High crystallinity m c-Si:H films were achieved at 99.6 % hydrogen dilution and at low rf power. An undoped 80 nm thick m c-Si:H film showed a dark conductivity of the order of 10−7 S/cm, the photosensitivity of an order of 102, and a crystalline volume fraction of 80 %. However, a 60 nm thick n+ μc-Si:H film deposited using a seed layer showed a high dark conductivity of 35 S/cm and a crystalline volume fraction of 60 %. Using n+ μc-Si:H films as drain and source contact layers in a-Si:H TFTs provides substantial performance improvement over n+ a-Si:H contacts. Finally, fully μ c-Si:H TFTs incorporating intrinsic m c-Si:H films as channel layers and n+ μc-Si:H films as contact layers have been fabricated and characterized. These TFTs exhibit a low threshold voltage and a field effect mobility of 0.85 cm2/Vs, and are far more stable under gate bias stress than a-Si:H TFTs.
Aluminum-Induced Crystallization of PECVD Amorphous Silicon
Authors: Jenq Kenneth , Chang Shawn S. , Lian Yaguang , Pan Grant Z. , Rahmat-Samii Yahya 
Published: April 2011

ABSTRACTAluminum-induced crystallization (AIC) of amorphous silicon (a-Si) in a conventional furnace with N2 protection has been studied at reaction temperatures ranging from 200 to 500°C by using optical microscopy, and transmission and scanning electron microscopy. The a-Si and Al layers were deposited with plasma-enhanced chemical vapor deposition (PECVD) and electron beam evaporation, respectively. The structures in the study are Al/a-Si and a-Si/Al on Si or glass wafers coated with 3000 Å PECVD SiO2. It was found that Al induces crystallization of a-Si for both Al/a-Si and a-Si/Al structures by exchanging positions of Al and Si layer through diffusion of Si into Al and the grain size of crystallized Si (c-Si) increases with the decrease of AIC temperature. AIC for Al/a-Si structures starts at a temperature as low as 200°C, which is 100°C lower than that for a-Si/Al structures. Kinetics analysis found that the activation energies are 1.76 eV and 1.65 eV for both Al/a-Si and a-Si/Al structures, respectively. The quality of AIC c-Si depends on the order, thickness and thickness ratio of a-Si to Al. Microstructural observations indicated that the c-Si for Al/a-Si structures is better and more suitable for use in fabrication of thin film transistors (TFTs) than that for a-Si/Al structures.
Initial Interaction of Crystalline Al/Amorphous Si Bilayer during Annealing
Authors: Zhao Yonghao , Wang Jiangyong , Mittemeijer Eric J. 
Published: April 2011

ABSTRACTInitial interaction of a magnetron sputter deposited Al(100 nm, {111} fibre textured)/Si(150 nm, amorphous) bilayer, induced by isothermally annealing at 523 K for 60 min in a vacuum of 2.0×10−4 Pa, was studied by X-ray diffraction, Auger electron microscopy and focused-ion beam imaging techniques. Upon annealing, the crystalline Si had grown into the grain boundaries of the Al layer with a {111} texture, a crystallite size of approximate 12 nm and a tensile stress of +138 MPa. Simultaneously, the Al grains had grown into the Si layer from the original interface of the a-Si and Al sublayers with the lateral grain growth. The stress parallel to the surface of the Al layer had changed from +27 MPa to +232 MPa after annealing.
In-Situ Aluminum-Induced Crystallization of Si Thin-Films on Glass Substrates above the Eutectic Temperature using HW-CVD
Authors: Ebil Ozgenc , Aparicio Roger , Birkmire Robert 
Published: April 2011

ABSTRACTThe growth of poly-Si films on glass substrates using an in-situ aluminum-induced crystallization (AIC) process above the Si-Al eutectic temperature of 577°C is discussed. Silicon films were deposited by Hot-Wire Chemical Vapor Deposition (HW-CVD) onto Al coated Corning 7059 glass substrates. The back surface coverage and the average grain size of the films were compared as a function of growth rate and the Si/Al thickness ratio. SEM and EDS analysis of samples with a Si/Al ratio of 1 revealed two domains in the films which varied in morphology and composition; rougher areas containing a mixture of Si and Al with Al content up to 35%, and relatively smoother areas composed of almost entirely Si. This non-uniform morphology seems to be the result of the absence of a native oxide layer when a liquid phase is formed during the deposition. Si grains as large as 50 m m in diameter and back surface coverage up to 90% were obtained for both the Si/Al ratios of 1 and 5. However, no continuous Si films were obtained. The sample with a Si/Al ratio of 1 had columnar grains reaching to the film surface, whereas on the Si/Al ratio of 5 large Si grains did not extend to the film surface.
A real-time optical signal and image processing p-i-n/p-i-n device
Authors: Vieira M. , Louro P. , Fernandes M. , Fantoni A. , Mendes C. , Martins J. 
Published: April 2011

ABSTRACTLarge area (4x4 cm2) optical signal and image processing (OSIP) devices were produced at low temperatures (110°C) by PE-CVD. The OSIP device consists of two stacked sensing/switching diodes (p(SiC:H)/i(Si:H)/n(SiC:H)) with or without an internal blocking layer between them and two semitransparent contacts. An optical scanner is used for charge readout. In this work the main emphasis will be put on the analysis of the optical characteristics. The use of a metal grid (290x290 μm2 Cr pixels with 40 m m spacing) between the two diodes, working as light screening layer or as floating anode via an a-SiN insulator layer, is analyzed. Its influence on the transfer functions, resolution, responsivity and response time of the sensor is presented. The various design parameters trade-offs are discussed. The optical-to-electrical transfer characteristics show high quantum efficiency, broad spectral response, and reciprocity between the optical and the electrical images. When the light screening floating anode is present an effective optical decoupling from both photodiodes is achieved while maintaining a good electrical conductivity and an increased light-to-dark sensitivity. A trade-off is established between sensor design and light pattern and scanner wavelengths in order to minimize the cross talk between the write and the read beams and to improve the light to dark sensitivity.
Detection Limits of a nip a-Si:H Linear Array Position Sensitive Detector
Authors: Martins R. , Costa D. , Águas H. , Soares F. , Marques A. , Ferreira I. , Borges P. , Fortunato E. 
Published: April 2011

ABSTRACTThis paper presents results of the spatial and frequency detection limits of an integrated array of 32 one-dimensional amorphous silicon thin film position sensitive detectors with a nip structure, under continuous and pulsed laser operation conditions. The data obtained show that 0.45×0.06 cm arrays, occupying a total active area of about 1 cm2 have a spatial resolution better than 10 m m (modulation transfer function of about 0.2), with a cut-off frequency of about 6.8 KHz. Besides that, under pulsed laser conditions the device non-linearity has its minimum (about 1.6%), for a frequency of about 200Hz. Up to the limits of the cut-off frequency, the device nonlinearity increases to values above 4%.
Comparison of Phase Diagrams for vhf and rf Plasma-Enhanced Chemical Vapor Deposition of Si:H Films
Authors: Ferreira G.M. , Ferlauto A.S. , Pearce J.M. , Wronski C.R. , Ross C. , Collins R.W. 
Published: April 2011

ABSTRACTDeposition phase diagrams are convenient for categorizing the evolution of the surface microstructure and phase with accumulated thickness for hydrogenated silicon (Si:H) films during plasma-enhanced chemical vapor deposition (PECVD). They can also be used to assess the electronic quality and device suitability of Si:H, based on previous correlations. In this study, phase diagrams have been applied in a comparison of Si:H PECVD using two different plasma excitation frequencies (rf: 13.56 MHz; and vhf: 60 MHz). Smooth crystalline Si (c-Si) wafer substrates have been used to obtain the surface roughness evolution with maximum sensitivity in the amorphous silicon (a-Si:H) growth regime. This study has shown that under all explored conditions of plasma power, frequency, and gas pressure, yielding deposition rates of 0.5-20 Å/s, a-Si:H exhibits improved microstructural characteristics with increasing H2-to-SiH4 flow ratio R right up to the amorphous-to-(mixed-phase microcrystalline) [a→(a+μc)] boundary of the phase diagram. For depositions at R values much lower than the a→(a+μc) transition for a thick film, vhf PECVD can provide a significant improvement in microstructural evolution over rf PECVD, for a given deposition rate. For optimum R just below the a→(a+μc) transition, however, vhf and rf a-Si:H films exhibit remarkably similar structural evolution for a given rate.
Identification of Possible Bonding Sites for Post Deposition Oxygen Absorption in Microcrystalline Silicon
Authors: Gedvilas L. M. , Mahan A. H. 
Published: April 2011

ABSTRACTUsing infrared (IR) spectroscopy and x-ray diffraction, the nature of the grain boundaries in twom c-Si films deposited by hot wire CVD, displaying similar crystalline volume fractionsbut very different behavior upon exposure to atmospheric contaminants, is analyzed. For the film exhibiting significant post deposition oxidation, the IR spectrum in the 2100 cm−1 Si-H stretch mode region contains two sharp and very narrow peaks, suggesting that the crystallites have been incorporated into them c-Si films with their hydrogenated surfaces relatively intact.By comparing these peak frequencies to those in the literature for Si-H bonding on c-Si surfaces, we identify certain crystallite orientations which, when comprising the c-Si grain boundaries, are particularly susceptible to oxidation. We further suggest that the distribution of H in this grain boundary/crystallite surface region is crucial for depositing c-Si films with good electronic properties and minimal post deposition oxidation.