bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Study of Rock Matrix Diffusion Properties by Electrical Conductivity Measurements
Authors: Ohlsson Y. , Neretnieks I. 
Published: April 2011

AbstractTraditional rock matrix diffusion experiments on crystalline rock are very time consuming due to the low porosity and extensive analysis requirements. Electrical conductivity measurements are, on the other hand, very fast and larger samples can be used than are practical in ordinary diffusion experiments. The effective diffusivity of a non-charged molecule is readily evaluated from the measurements, and influences from surface conductivity on diffusion of cations can be studied. A large number of samples of varying thickness can be measured within a short period, and the changes in transport properties with position in a rock core can be examined.In this study the formation factor of a large number of Äspö diorite samples is determined by electrical conductivity measurements. The formation factor is a geometric factor defined as the ratio between the effective diffusivity of a non-charged molecule, to that of the same molecule in free liquid. The variation of this factor with position along a borecore and with sample length, and its coupling to the porosity of the sample is studied. Also the surface conductivity is studied. This was determined as the residual conductivity after leaching of the pore solution ions. The formation factor of most of the samples is in the range 1E-5 to 1E-4, with a mean value of about 5E-5. Even large samples (4-13 cm) give such values. The formation factor increases with increasing porosity and the change in both formation factor and porosity with position in the borecore can be large, even for samples close to each other.The surface conductivity increases with increasing formation factor for the various samples but the influence on the pore diffusion seems to be higher for samples of lower formation factor. This suggests that the relation between the pore surface area and the pore volume is larger for samples of low formation factor.
Bedrock Characterisation of Four Candidate Repository Sites in Finland As Determined by He-Gas Methods
Authors: Hartikainen J. , Hartikainen K. , Timonen J. , Hautojärvi A. 
Published: April 2011

AbstractAt the end of the year 2000, one of four sites will be chosen as the final repository site in Finland. Therefore accurate and comprehensive statistics of the bedrock characteristics such as porosity [% ] and effective diffusion coefficient [m2/s ] of these sites are of importance. Altogether 115 rock samples from the four sites were measured by different He-gas methods to achieve this goal.The results obtained indicate that the average bedrock properties at these sites are quite similar. Variations among individual samples and different rock types within one repository site were larger than variations among the averaged values of the four sites. Some indication of increased microfracturing was also found in samples of small size.
Investigation of the Long -Term Performance of Betafite and Zirconolite in Hydrothermal Veins From Adamello, Italy
Authors: Lumpkin G. R. , Day R. A. , McGlinn P. J. , Payne T. E. , GierÉ R. , Williams C. T. 
Published: April 2011

AbstractBetafite and zirconolite occur in Ti-rich hydrothermal veins emplaced within dolomite marble in the contact aureole of the Adamello batholith, northern Italy. Zirconolite contains up to 18 wt% ThO2 and 24 wt% UO2, and exhibits strong compositional zoning. Some zirconolite grains were corroded by the hydrothermal fluid. Betafite, the Ti-rich member of the pyrochlore group, often occurs as overgrowths on zirconolite. The betafite is weakly zoned and contains 29-34 wt% UO2. In terms of end -members, betafite contains approximately 50 mole percent CaUTi2O7 and is the closest known natural composition to the pyrochlore phase proposed for use in titanate waste forms. Amorphization and volume expansion of the betafite caused cracks to form in the enclosing silicate mineral grains. Backscattered electron images reveal that betafite was subsequently altered along crystal rims, particularly near the cracks. EPMA data reveal little difference in composition between altered and unaltered areas, except for lower totals, suggesting that alteration is primarily due to hydration. The available evidence demonstrates that both betafite and zirconolite retained actinides for approximately 40 million years after the final stage of vein formation. During this time, betafite and zirconolite accumulated a total alpha -decay dose of 3-4 x 1016 and 0.2-2 x 1016 α/mg, respectively.
Nuclear Waste Package Corrosion Behavior in the Proposed Yucca Mountain Repository
Authors: Sagüés A. A. 
Published: April 2011

AbstractThe corrosion performance of spent nuclear fuel waste packages is becoming increasingly important in establishing the viability of the proposed Yucca Mountain repository system. Current package concepts propose the use of a 2 cm thick nickel-base superalloy (Alloy 22) shell as the main barrier to prevent corrosion penetration over many thousands of years. The expected package service conditions, as well as their variability and uncertainty, are discussed. The electrochemical conditions known to be responsible for passive behavior and its breakdown in Alloy 22 and similar alloys are examined in the light of the predicted repository environment. Durability prediction approaches and their conclusions are considered. Efforts to determine the relative impact of localized modes of failure and uniform passive dissolution on package durability are reviewed, along with open issues in need of resolution and alternative package designs. The basic question of the validity of extrapolating corrosion behavior over many times the duration of the present base of experience is addressed.
Open Site Tests on Corrosion of Carbon Steel:Containers for Radioactive Waste Forms
Authors: Barlnov A. S. , Ojovan M. I. , Ojovan N. V. , Startceva I. V. , Chujkova G. N. 
Published: April 2011

AbstractTesting of waste containers under open field conditions is a component part of the research program that is being carried out at SIA “Radon”for more than 20 years to understand the long-term behaviour of radioactive waste forms and waste packages. This paper presents the preliminary results of these ongoing studies. We used a typical NPP operational waste, containing 137Cs, 134Cs, and 60Co as the dominant radioactive constituents. Bituminized and vitrified waste samples with 30–50 wt.% waste loading were prepared. Combined effects of climatic factors on corrosion behaviour of carbon steel containers were estimated using gravimetric and chemical analyses. The observations suggest that uniform corrosion of containers prevails under open field conditions. The upper limits for the lifetime of containers were derived from calculations based on the model of atmospheric steel corrosion. Estimated lifetime values range from 300 to 600 years for carbon steel containers with the wall thickness of 2 mm containing vitrified waste, and from 450 to 500 years for containers with the wall thickness of 2.5 mm that were used for bituminized waste. However, following the most conservative method, pitting corrosion may cause container integrity failure after 60 to 90 years of exposure.
Microstructure and Leaching Characteristics of a Technetium Containing Metal Waste Form
Authors: Johnson S. G. , Keiser D. D. , Noy M. , O'Holleran T. , Frank S. M. 
Published: April 2011

AbstractArgonne National Laboratory is developing an electrometallurgical treatment for spent fuel from the experimental breeder reactor II. A product of this treatment process is a metal waste form that incorporates the stainless steel cladding hulls, zirconium from the fuel and the fission products that are noble to the process, i.e., Tc, Ru, Pd, Rh, Ag. The nominal composition of this waste form is stainless steel/15 wt% zirconium/ 1–4 wt% noble metal fission products. The behavior of technetium is of particular importance from a disposal point of view for this waste form due to its long half life, 2.14E5 years, and its mobility in groundwater. To address these concerns a limited number of spiked metal waste forms were produced containing Tc. These surrogate waste forms were then studied using scanning electron microscopy (SEM) and selected leaching tests.
Lead and Lead-Based Alloys as Waste Matrix Materials
Authors: Arustamov Arthur E. , Ojovan Michael I. , Kachalov Michael B. 
Published: April 2011

AbstractMetals and alloys with relatively low melting temperatures such as lead and lead-based alloys are considered in Russia as prospective matrices for encapsulation of spent nuclear fuel in containers in preparation for final disposal in underground repositories. Now lead and leadbased alloys are being used for conditioning spent sealed radioactive sources at radioactive waste disposal facilities.
Epr of Fe3+ and Cr3+ Ions in NZP Ceramics
Authors: Troole A. Y. , Stefanovsky S. V. , Bogomolova L. D. 
Published: April 2011

AbstractA new method to estimate the thermodynamic stability of crystalline host phases for radwaste is based on the determination of the degree of coordination polyhedra distortion. Analysis of the stability of sodium zirconium phosphate (NZP) structure containing Fe and Cr has been completed. The NZP structure can incorporate a limited amount of iron (∼2 mol. % Fe2o3). From the EPR study, Fe3+ and Cr3+ ions occupy two different structural positions substituting for Zr4+and Na+. Moreover, these ions can enter extra phases.
Fast Deposition of a-Si:H Layers and Solar Cells in a Large-Area (40×40 cm2) VHF-GD Reactor
Authors: Kroll U. , Fischer D. , Meier J. , Sansonnens L. , Howling A. , Shah A. 
Published: April 2011

AbstractLarge-area deposition of hydrogenated amorphous silicon has been investigated in a single-chamber industrial reactor with electrode dimensions of 40×40 cm2 in the plasma excitation frequency range of 60 to 120 MHz. The film thickness uniformity, analyzed by a light interferometry technique and a step profiler, has been compared with 2-dimensional interelectrode voltage measurements and calculations. The frequency of 80 MHz has been found to be a good compromise between the gain in deposition rate and the homogeneity requirements necessary for a-Si:H solar cells. Under these conditions and while using hydrogen dilution high deposition rates of 6-7 Å/s with a film uniformity of ±5% over a usable substrate size of 30×30 cm2 have been obtained.In the same single-chamber deposition system at 80 MHz, 0.4 gtm thick single-junction a-Si:H solar cells with high performance were fabricated in a total process time of 16 minutes applying a continuous deposition process. Spectral response measurements indicate a minor boron contamination of the i-layer. Initial cell efficiencies of 7.1 % could be achieved for such a fast-grown a-Si:H solar cell.
Assessment of Intrinsic-Layer Growth Temperature to High-Deposition-Rate a-Si:H n-i-p Solar Cells Deposited by Hot-Wire CVD
Authors: Wang Qi , Iwaniczko Eugene , Xu Yueqin , Nelson Brent P. , Mahan A. H. 
Published: April 2011

AbstractWe report progress in hydrogenated amorphous silicon n-i-p solar cells with the i-layer grown by the hot-wire chemical vapor deposition technique. Early research showed that we grew device-quality materials with low saturated defect density (2 × 106/cm3), high initial ambipolar diffusion length (~2000 Å) and low hydrogen content (<1%). One of the major barriers to implementing this material into solar cells is the high substrate temperature required (>400°C). We re-assess the effects of low substrate temperature on the property of the films and the performance of the solar cells as an alternative avenue to solving this problem. We find that the material grown at 300°C can have similar values of saturated defect density and ambipolar diffusion length as the one grown greater than 400°C. We also study the effect of i-layer substrate temperature ranging from 280° to 440°C for n-i-p solar cells. We now consistently grow devices with Fill Factor (FF) greater than 0.66, with the best close to 0.70 at lower substrate temperature. A collaboration with United Solar System, in where they grew the p-layer and top contact, produced devices with initial efficiencies as high as 9.8%. We produce n-i-p solar cells with initial efficiencies as high as 8% when we grow all the hydrogenated amorphous silicon and top contact layers. All these i-layers are grown at deposition rates of 16 to 18 Å/sec. We need to further improve our p-layer and transparent conductor layer to equal the collaborative cell efficiency. We also report light-soaking results of these devices.
A Novel Excimer Laser Crystallization Method of Poly-Si Thin Film by Grid Line Electron Beam Irradiation
Authors: Park C-M , Lee M-C , Jeon J-H , Han M-K 
Published: April 2011

AbstractExcimer laser annealing technique is proposed to increase the grain size and controlling the microstructure of polycrystalline silicon (poly-Si) thin film. Our method is based on the lateral grain growth during laser annealing. Our specific grid ion beam irradiation method was designed to maximize the lateral growth effect and arrange the location of grain boundaries. We observed well-arranged poly-Si grains up to micrometer order by transmission electron microscopy (TEM).
Structural Properties of Amorphous Silicon Produced by Electron Irradiation
Authors: Yamasaki J. , Takeda S. 
Published: April 2011

AbstractThe structural properties of the amorphous Si (a-Si), which was created from crystalline silicon by 2 MeV electron irradiation at low temperatures about 25 K, are examined in detail by means of transmission electron microscopy and transmission electron diffraction. The peak positions in the radial distribution function (RDF) of the a-Si correspond well to those of a-Si fabricated by other techniques. The electron-irradiation-induced a-Si returns to crystalline Si after annealing at 550°C.
Remote Silane Plasma Chemistry Effects and their Correlation with a-Si:H Film Properties
Authors: Kessels W.M.M. , Smets A.H.M. , Korevaar B.A. , Adriaenssens G.J. , Sanden M.C.M. Van de , Schram D.C. 
Published: April 2011

AbstractA remote silane plasma, capable of depositing solar grade a-Si:H at a rate of 10 nm/s and with an up to ten times higher hole drift mobility than standard a-Si:H, has been investigated by means of several plasma diagnostics. The creation of the different reactive species in the plasma and their contribution to film growth has been analyzed and is correlated with the film properties obtained under various conditions. Furthermore, the first results on a n-i-p solar cell with the intrinsic a-Si:H film deposited by this remote plasma are presented.
Microstructure and Hydrogen Dynamics in a-Si1-xCx:H
Authors: Shinar R. , Shinar J. , Williamson D. L. , Mitra S. , Kavak H. , Dalal V. L. 
Published: April 2011

AbstractSmall angle x-ray scattering (SAXS), IR spectroscopy, and deuterium secondary ion mass spectrometry (DSIMS) were used to study the microstructure and hydrogen dynamics of undoped and boron-doped if-sputter-deposited (RFS) and electron cyclotron resonance (ECR)-deposited hydrogenated amorphous silicon carbides (a-Si1-xCx:H) with x ≤ 19 at.%. The SAXS measurements indicated residual columnar-like features and roughly spherical nanovoids of total content CnV ≤ 1.0 vol.%. The growth of CnV with annealing was due largely to an increase in the average nanovoid radius. It was noticeably smaller than in RFS a-Si:H films. The IR spectra demonstrated H transfer by annealing from mostly bulk-like Si-H groups to C-bonds. The H diffusion and its temperature dependence in undoped films resembled those of a-Si:H and were consistent with the SAXS and IR data. Suppression of long-range motion of most of the H atoms, consistent with increased CnV was observed in B-doped ECR films. However, a small fraction of the H atoms appeared to undergo fast diffusion, reminiscent of the fast diffusion in doped a-Si:H. The results are consistent with impeded relaxation processes of the Si network, caused by the presence of C atoms, and H trapping at C-H bonds.
Hydrogen Flip Model for Metastable Structural Changes in Amorphous Silicon
Authors: Biswas R. , Li Y.-P. 
Published: April 2011

AbstractWe propose a new metastable defect associated with hydrogen atoms in amorphous silicon. A higher energy metastable state is formed when H is flipped to the backside of the Si-H bond at monohydride sites. This defect is described by a double-well potential energy and occurs in addition to metastable dangling bonds. The dipole moment of this “H-flip” defect is larger and increases the infrared absorption. This defect accounts for large structural changes observed on light soaking including larger absorption and volume dilation.
Photoconductivity Transient Response from the Steady State in Amorphous Semiconductors
Authors: Main C. , Reynolds S. , Zollondz J.- H. , Bruggemann R. 
Published: April 2011

AbstractWe present analysis, computer modelling and experimental measurements of the photoconductive decay which occurs on cessation of illumination, in amorphous semiconductors. We explore the processes of relaxation of the excess carrier distributions, and examine the relative rôles of re-trapping and recombination in a model case of an exponential trapping state profile, with monomolecular recombination. A variety of possible decay behaviour is revealed. We examine several plausible intuitive explanations of the decay process, including (a) the assumption that the rate limiting step in the decay process is the thermal release of trapped carriers from the vicinity of the quasi - Fermi level, and (b) multiple re-trapping at the quasi -Fermi level prior to recombination. Actual decay rates, however are often much faster than that predicted by these assumptions, and the generation rate dependencies do not follow the relation expected. These explanations are shown in detail to be largely erroneous. Results of experimental measurements of the decay from steady state and TPC in films of a-Si1-xCx:H are presented. While these appear initially to be at variance with the predictions of the present work, we demonstrate that the observations can be reconciled fully with theory.
Vibrational Properties of a-Si:H Films Containing Voids: Experiment and Modeling
Authors: Barriquand N. , Paillard V. , Cabarrocas P. Roca i , Landa G. , Djafari-Rouhani M. 
Published: April 2011

AbstractIn this paper, we present results about the vibrational properties of hydrogenated amorphous silicon films. We expect to explain the slight differences observed in the Raman spectra using atomic-scale modeling. In particular, we focuse on the correlation of our results to the density of samples. This should give quantitative structural information which could be correlated to both macroscopic properties and elaboration conditions.
Polymorphous Silicon: Transport Properties and Solar Cell Applications
Authors: Longeaud C. , Kleider J. P. , Gauthier M. , Brtiggemann R. , Poissant Y. , Cabarrocas P. Roca i 
Published: April 2011

AbstractTransport properties of hydrogenated polymorphous silicon layers (pm-Si:H) deposited at 150°C under various pressures in the range 80-293 Pa in sandwich (Schottky and p-i-n diodes) and coplanar structures have been compared to those of hydrogenated amorphous silicon (a-Si:H) samples deposited at the same temperature in standard conditions. The layers have been studied as-deposited, annealed and after light-soaking. With increasing pressure up to 240 Pa: i) the density of states above the Fermi level decreases as determined by means of the modulated photocurrent technique, ii) the mobility-lifetime products of electrons and holes measured by means of steady-state photoconductivity and photocarrier grating techniques both increase. The highest values for the diffusion length of minority carriers exceed 200 nm. Capacitance measurements as a function of frequency and temperature show that the density of states at the Fermi level is lower in the pm-Si:H than in the a-Si:H films. After light-soaking the diffusion length of minority carriers in a-Si:H is reduced by a factor oftwo whereas it is less reduced or not affected in the pm-Si:H layers. Solar cells including this new material present an excellent stability.
Use of A GAS Jet Technique to Prepare Microcrystalline Silicon Based Solar Cells at High I-Layer Deposition Rates
Authors: Jones S.J. , Crucet R. , Deng X. , Doehler J. , Kopf R. , Myatt A. , Tsu D.V. , Izu M. 
Published: April 2011

AbstractUsing a Gas Jet thin film deposition technique, microcrystalline silicon (μc-Si) materials were prepared at rates as high as 15-20 Å/s. The technique involves the use of a gas jet flow that is subjected to a high intensity microwave source. The quality of the material has been optimized through the variation of a number of deposition conditions including the substrate temperature, the gas flows, and the applied microwave power. The best films were made using deposition rates near 16 Å/s. These materials have been used as i-layers for red light absorbing, nip single-junction solar cells. Using a 610nm cutoff filter which only allows red light to strike the device, pre-light soaked currents as high as 10 mA/cm2 and 2.2-2.3% red-light pre-light soaked peak power outputs have been obtained for cells with i-layer thicknesses near 1 micron. This compares with currents of 10-11 mA/cm2 and 4% initial red-light peak power outputs obtained for high efficiency amorphous silicon germanium alloy (a-SiGe:H) devices. The AM1.5 white light efficiencies for these microcrystalline cells are 5.9-6.0%. While the efficiencies for the a-SiGe:H cells degrade by 15-20% after long term light exposure, the efficiencies for the microcrystalline cells before and after prolonged light exposure are similar, within measurement error. Considering these results, the Gas Jet deposition method is a promising technique for the deposition of μc-Si solar cells due to the ability to achieve reasonable stable efficiencies for cells at i-layer deposition rates (16 Å/s) which make large-scale production economically feasible.
Microstructural Defects of Device Quality Hot-Wire Cvd Poly-Silicon Films
Authors: Rath J.K. , Tichelaar F.D. , Schropp R.E.I. 
Published: April 2011

AbstractTwo types of poly-Si:H thin films made by Hot Wire CVD have been evaluated with respect to utilisation in solar cells. Poly-Si:H films made at high hydrogen dilution are highly porous and have large interconnected voids. The void density is 25000/μm-3 as determined by XTEM. On the other hand, poly-Si:H layers made at low hydrogen dilution have a compact structure and a much smaller density of voids. In these films, two types of voids exist: globular voids smaller than 15 nm, and elongated voids, often located between columns of large crystals of 150-250 nm wide at the top. The density for the 5 - 15 nm spherical voids is usually -50/μm3, but larger concentrations often occur locally, up to 1000/pm3, i.e., 0.05% volume fraction. High oxygen content in the poly-Si films made at high hydrogen dilution is largely due to post deposition intrusion of water vapour through the interconnected voids. Profiled layers are made by depositing device quality poly-Si:H layers (low hydrogen dilution) on top of a seed layer (high hydrogen dilution) of high nucleation density. Cells incorporating profiled poly-Si:H films as i-layers at a deposition rate of 0.5 nm/s were made on stainless steel substrates in the configuration SS/n-μc-Si:H(PECVD)/i-poly-Si:H(HWCVD)/p-μc-Si:H(PECVD)/ITO. For our n-i-p solar cell with poly-Si i-layer we obtained an efficiency of 4.41% and a FF of 0.607. Due to native surface texture a current density of 19.95 mA/cm2 is generated in only ~1.22 μm thick i-layer without back reflector.