bluuebunny/crossref_metadata_2025_split huggingface dataset:
Testing the Grambow Glass Dissolution Model by Comparing it With Monte Carlo Simulation Results
Authors: Aertsens Marc 
Published: April 2011

AbstractWe have developed a Monte Carlo (simulation) model to describe glass dissolution. This model uses similar parameters to those used in the Grambow model, which has been the main glass dissolution model during the last decade. While the Grambow model is macroscopic, ours is microscopic. This assures that the value of our parameters is time independent and allows changes in the gel structure (not just concentrations) to be described.We relate our parameters to those of the Grambow model and test whether the basic assumptions of the Grambow model are consistent with our simulation results. In these simulations, as the solution evolves towards silica saturation, the silica concentration in solution can become higher than the (final) silica saturation concentration. A possible explanation for this behavior, which is observed experimentally as well, is that the silica saturation concentration is not constant as a function of time. Initially, the silica saturation concentration is the glass saturation concentration. The glass saturation concentration is higher than the final silica saturation concentration, which corresponds to saturation of the gel. In the Grambow model, the initial dissolution rate (at the gel/water interface) and the diffusion coefficient of silica in the gel are not constant either. The existence of a final dissolution rate depends on the silica content of the glass and on the protection provided by the gel layer. In the simulations, a protective gel is mainly formed by the adsorption (precipitation) of dissolved silica particles from the solution in contact with the gel. This makes us expect that (1) the gel would be non protective for dynamic tests (with a low silica content in solution) and (2) the gel would be very protective in static tests with high surface to volume ratios.
Grain Size and Burnup Dependence of Spent Fuel Oxidation: Geological Repository Impact
Authors: Kansa E. J. , Hanson B. D. , Stout R. B. 
Published: April 2011

AbstractFurther refinements to the oxidation model of Stout et al. have been made. The present model incorporates the burnup dependence of the oxidation rate and an allowance for a distribution of grain sizes. The model was tested by comparing the model results with the oxidation histories of spent-fuel samples oxidized in thermogravimetric analysis (TGA) or oven dry-bath (ODB) experiments. The experimental and model results are remarkably close and confirm the assumption that grain-size distributions and activation energies are the important parameters to predicting oxidation behavior. The burnup dependence of the activation energy was shown to have a greater effect than decreasing the effective grain size in suppressing the rate of the reaction U4O9→U3O8. Model results predict that U3O8 formation of spent fuels exposed to oxygen will be suppressed even for high burnup fuels that have undergone restructuring in the rim region, provided the repository temperature is kept sufficiently low.
Migration Experiments in Compacted Ca-Bentonite
Authors: García-Gutiérrez M. , Missana T. , Molinero J. , Yllera A. , Mingarro M. 
Published: April 2011

AbstractMigration experiments were carried out in compacted Ca-bentonite as a complement of the FEBEX project large scale tests.Through diffusion and permeation experiments with tritiated water were used to perform a deep characterisation of the clay diffusion parameters (diffusion coefficient, effective porosity and permeability ). In through diffusion experiments, a variation of tracer concentration in both reservoirs was allowed. Since in these experimental conditions an analytical solution of the diffusion problem does not exist, an analytical approximation was used and the results compared with a numerical model which takes into account the presence of the sintered steel filters confining the clay plug.The migration behaviour of Se in this compacted bentonite has been studied and the retardatioci factor obtained. The calculated Kd is at least one order of magnitude lower than the one obtained by means of batch sorption experiments due to a lower availability of sorption sites when increasing the compaction degree.
New Data on the HyrkkÖlÄ Native Copper Mineralization: A Natural Analogue for the Long-Term Corrosion Of Copper Canisters
Authors: Marcos N. , Ahonen L. , Bros R. , Roos P. , Suksip J. , Oversby V. 
Published: April 2011

AbstractThe Hyrkkölä U-Cu mineralization located in south-western Finland is reassessed with reference to the corrosion mechanisms affecting the stability of native copper and the time-scales of corrosion processes. The mineral assemblage native copper – copper sulfide occurs in open fractures at several depth intervals within granite pegmatites (GP). The surfaces of these open fractures have accumulations of uranophane crystals and other unidentified uranyl compounds. The secondary uranium minerals are mainly distributed around copper sulfide grains. Microscopic intergrowths of copper sulfides and uranyl compounds also have been observed. Groundwater samples were collected from the vicinity of the Cu samples. The hydrogeochemical features of these samples indicate that the present conditions are oxidising. The minimum age of U(VI) transport and deposition is about 200 000 years. This age is indicated by 234U/238U and 230Th/234U activity ratios of uranophane. The age of the hexavalent uranium precipitation may be somewhat later than the last influxes and/or demobilisation of sulfur.The mineral assemblage native copper – copper oxide (cuprite) occurs only at one depth interval within altered granite pegmatite. The fracture surface was coated by smectite. The content of uranium in smectite was 69–75 ppm U. The 234U/238U and 230Th/234U activity ratios of smectite showed that it has been exposed to recent groundwaters (e.g., during the last million years). The pH of the groundwater at this interval was near neutral (6.9). The copper grains present at this fracture surface were as large as 1 mm in diameter and had rims of cuprite of 0.01 to 0.1 mm thick. The smallest grains were totally oxidised.
Passive Films and Blistering of Titanium
Authors: Bedrossian Peter J. , Farmer Joseph C. , McCright R. Daniel , Phinney Douglas L. , Estill John C. 
Published: April 2011

AbstractCoupons of titanium alloys under consideration as components of the Engineered Barrier System in the proposed repository at Yucca Mountain have been evaluatedfor their passive film composition and stability. Oxide depths and compositions on specimens exposed in long-term corrosion testing for one year were determined with x-ray photoemission spectroscopy. The specimens removed from long-term testing, as well as separate coupons polarized cathodically in an electrochemical cell, exhibited blistering associated with hydride formation in both scanning electron microscopy and atomic force microscopy.
Low Temperature Kinetics for the Growth and Decay of Band-Tallcarriers and Dangling Bonds in Hydrogenated Amorphous Silicon
Authors: Schultz Niko , Taylor P.C. 
Published: April 2011

AbstractIn hydrogenated amorphous silicon (a-Si:H), the kinetics of the light induced production of silicon dangling bonds and long-lived band-tail electrons and holes has been measured at temperatures between 65 and 340 K using light induced electron spin resonance (LESR). Below about 150 K the measurement of Si dangling bonds is masked by the accumulation of long-lived band-tail carriers. The kinetics of the growth and decay of these long-lived, trapped band-tail carriers consists of very fast components (τ < ms) and very long components (τ > h). Optical quenching of these long-lived carriers is not efficient at quenching energies of 0.6 eV. Afler removal of these long-lived band tail carriers by annealing at about 250 K we find that the total production of silicon dangling bonds at 65 K after 10 h of illumination is about a factor of five less than at 340 K. The dangling bond production resulting from 10 h of illumination is well fit to an underlying mechanism that, if thermally activated, exhibits an activation energy of approximately 10 meV.
Structural Changes and Hydrogen Motion in A-SI:H Observed by Proton Nmr
Authors: Baugh Jonathan , Han Daxing , Wang Qi , Wu Yue 
Published: April 2011

AbstractProton nuclear magnetic resonance (NMR) is applied to investigate hydrogen dynamics and microstructures in a-Si:H. In addition to the generic broad and narrow lines observed in all aSi:H, an additional narrow line (about 1 kHz wide) is observed as the temperature is raised above RT. This narrow line is shifted to the up-field by about 4 ppm with respect to the generic narrow line of a few kHz in width. Below 150°C, the change of the proton spectrum with temperature is reversible; the hydrogen associated with this additional narrow line is shown to originate from hydrogen originally associated with the broad line. The spin-lattice relaxation time T1 of this up-field shifted narrow line is about 0.4 s. This short T1, along with its small linewidth, suggests that this line is associated with molecular hydrogen, possibly trapped in sites of atomic dimensions.
Current Noise Measurements of Surface Defect States in Amorphous Silicon
Authors: West P. W. , Kakalios J. 
Published: April 2011

AbstractMeasurements of conductance fluctuations in coplanar hydrogenated amorphous silicon (a-Si:H) are reported as a function of surface etching treatments. The noise power spectrum displays a broadened Lorentzian peak, associated with surface damage by CF4 reactive ion etching (RIE), whereas surface etches using ion milling or wet chemicals remove the Lorentzian spectral feature and only a 1/f spectral form for frequency f is observed. The Lorentzian spectral feature can be explained by trapping-detrapping from surface states induced by the RIE etch, which cause fluctuations in the depletion width of the space charge region near the film surface. The thermally activated Lorentzian comer frequency is a measure of the degree of band bending and the Fermi energy at the thin film surface.
An Experimental Evaluation of Modulated Photocurrent Spectroscopy as A Density of States Probe
Authors: Reynolds S. , Main C. , Webb D.P. , Rose M.J. 
Published: April 2011

AbstractModulated and Fourier-transformed transient photocurrent (MPC and TPC-FT) spectroscopies have been evaluated through a study of the density and capture properties of localised states in as-prepared and light-soaked PECVD a-Si:H samples over a range of temperatures and optical excitations. Both techniques return a conduction band tail state characteristic energy of approximately 22 meV. However, defect state spectra differ in detail and are strongly influenced by dc optical excitation. A feature correlating with the quasi-Fermi level position is observed, but the capture coefficient implied (of order 10-6 cm3 s-1) is some two orders greater than that calculated from thermal activation of emission frequencies. Such a value would suggest an implausibly low absolute density of defects. Possible explanations are briefly discussed and additional investigations proposed.
Capacitance Spectroscopy of Defects in a-SI:H/c-SI Heterostructures
Authors: Rösch M. , Unold T. , Pointmayer R. , Bauer G.H. 
Published: April 2011

AbstractWe investigate defects at the interface in heterodiodes of hydrogenated amorphous silicon and monocrystalline silicon by frequency and temperature dependent capacitance measurements. The interpretation of the experimental results is supported by numerical simulations of capacitance experiments via transient calculations of defect charging and decharging in the diodes. A defined variation of waver surface treatments prior to amorphous silicon deposition shows a clear correlation of interface defects determined by capacitance measurements with current-voltage characteristics.
Hydrogen Dilution Effect on the Crystallinity of Silicon Films Grow by Hot Wire Cell Method
Authors: Ichikawa M. , Takeshita J. , Yamada A. , Konagai M. 
Published: April 2011

AbstractA new process, the Hot Wire Cell method, was developed and successfully used to grow polycrystalline silicon thin films at a low temperature and high growth rate. In the Hot Wire Cell method, reactant gases are decomposed as a result of reacting with a heated tungsten filament placed near to a substrate and polycrystalline silicon films can be deposited at a growth rate of 1.2nm/s without hydrogen dilution and 0.9nm/s with the use hydrogen dilution. The film crystallinity changed from amorphous to polycrystalline due to the addition of hydrogen, thus hydrogen dilution was effective for improving film crystallinity. Furthermore, we obtained (220) oriented polycrystalline silicon thin films with a 90% crystal fraction by the use of hydrogen dilution. These results showed that the Hot Wire Cell method is promising for the deposition of device-grade polycrystalline silicon films for photovoltaic applications.
Growth and Properties of Microcrystalline Germanium-Carbide Alloys
Authors: Herrold Jason , Dalal Vlkram L. 
Published: April 2011

AbstractWe report on the preparation and properties of microcrystalline (Ge,C) alloys grown using a remote, reactive H plasma beam deposition technique. The plasma beam was generated using an ECR reactor. The films were grown at low temperatures (300 - 400°C) on glass, stainless steel and c-Si substrates. The optical properties of the films were measured using spectrophotometer and two-beam photoconductivity techniques. The C content was measured using XPS techniques. We find up to 3% C incorporation in the lattice. The degree of crystallinity determined using Raman spectroscopy was very good. X-ray diffraction measurements indicated grain size in the range of a few tens of nm. The best crystallinity was obtained on conducting substrates, indicating the importance of H ion bombardment in promoting crystallinity. We find that the absorption curves for increasing C content remain similar to the curves for c-Ge, but are shifted to higher energies. Thus, the absorption curve is sharper than for c-Si in the same energy range. The defect densities remain low for the range of C content measured. Because of its sharper absorption curve compared with c-Si, the material may be attractive for photovoltaic energy conversion.
Resistless Patterning of Hydrogenated Amorphous Silicon Films
Authors: Hollingsworth Russell E. , Hemdon Mary K. , Collins Reuben T. , Benson J.D. , Dinan J.H. , Johnson J.N. 
Published: April 2011

AbstractPractical methods for directly patterning hydrogenated amorphous silicon (a-Si:H) films have been developed. Direct patterning involves selectively oxidizing the hydrogen passivated a-Si:H surface or laser crystallization of the bulk. The oxide or polycrystalline layer formed in this way then becomes a mask for subsequent hydrogen plasma etching. Methods for selective oxidation of the a-Si:H surface have been extensively studied. Examination of the pattern generation threshold dose for excitation wavelengths from 248 to 633nm provides indirect evidence for electron-hole recombination breaking of the silicon-hydrogen bond. An additional hydrogen removal mechanism was observed whereby simple proximity of a tapered fiber optic probe less than 30nm from the sample surface resulted in pattern generation. Patterns were generated in both intrinsic and doped a-Si:H films by several means, including contact printing with a mask aligner, in situ projection lithography with an excimer laser, and direct writing with a near-field scanning optical microscope (NSOM). Direct patterning of a-Si:H films has a wide range of potential applications. We have demonstrated a-Si:H as an in situ photoresist material for patterning HgCdTe infrared detector arrays with all process steps done in vacuum. We have also demonstrated 100nm line widths using NSOM writing with a photolithography goal. Direct patterning of a-Si:H could simplify the manufacturing of thin film transistors, or other devices that require patterned silicon films.
Near Infrared Response of Amorphous Silicon Detector Grown with Microcompensated Absorber Layer
Authors: Caputo D. , Cesare G. De , Nascetti A. , Palma F. , Tucci M. 
Published: April 2011

AbstractIn this work we demonstrate that radiation up to 2 μm induces photocurrent in a single junction amorphous silicon structure at room temperature. The absorber layer is a microcompensated film deposited using very low concentrations of dopant species. Device operation is based on optical excitation of thermal generated carriers from trap states toward valence and conduction band in the high electric field region of the structure. Transient and frequency response under different bias voltages and illuminations conditions are presented. The possibility to use the infrared sensor in low bit rate communication systems has been demostrated by including our detector in a front-end system and measuring its frequency responce.Quantum efficiency measurement have been reproduced with a numerical model, able to take into account sub-band gap absorption into single films. Model results indicate the presence of a large valence band tail and a high number of dangling bonds and shallow defects ascribed to the presence of dopant atoms.
A High-Voltage Hydrogenated Amorphous Silicon Thin-Film Transistor for Reflective Active-Matrix Cholesteric LCD
Authors: Nahm J.Y. , Lan J.H. , Kanicki J. 
Published: April 2011

ABSTRACTA high-voltage hydrogenated amorphous silicon thin film transistor (H-V a-Si:H TFT) with thick double layer gate insulator (∼0.95 μm) has been developed for reflective active-matrix cholesteric liquid crystal displays. The double layer gate insulator consists of 0.85 and 0.10 μm thick benzocyclobutene and hydrogenated amorphous silicon nitride, respectively. This HV a-Si:H TFT operates at the gate-tosource and drain-to-source biases up to 100V without any serious leakage current degradation and device breakdown.
Melting and resolidification dynamics of a-Si and poly-Si thin films during excimer laser annealing
Authors: Hatano Mutsuko , Moon Seungjae , Lee Minghong , Suzuki Kenkichi , Grigoropoulos Costas P. 
Published: April 2011

ABSTRACTThe liquid-solid interface motion and the temperature history of thin Si films during excimer laser annealing are observed by in-situ experiments combining time-resolved (∼Ins) electrical conductance, optical reflectance/transmittance at visible and near-IR wavelength, and thermal emission measurements. The existence of partial and complete melting regimes is elucidated. In the partial melting regime, the maximum temperature remains close to the melting point of aSi, since the laser energy is consumed on the latent heat of phase-change. In the complete melting regime, substantial supercooling, followed by homogeneous nucleation is observed. These phase transformations are consistent with the recrystallized poly-Si morphologies.
Physical Characteristics of Very Low Temperature Anodic Oxides of Polycrystalline Si Films
Authors: Plantier H. , Pelletier J. , Devine R. A. B. , Vincent G. 
Published: April 2011

ABSTRACTControlled oxidation of polycrystalline and single crystal silicon has been carried out at temperatures < 100 °C using microwave excited, plasma assisted anodisation. Oxide thicknesses up to 30 nm have been obtained in times ∼ 15 minutes. The growth kinetics are similar for both types of Si. The results of infrared absorption measurements clearly indicate that the anodic oxides have a network structure significantly different to that of high temperature, thermally grown oxides and this is partly due to ultra-violet radiation present in the plasma during growth. Electrical measurements (CV, IV) are underway on simple MOS capacitors. The results indicate that the plasma oxides have acceptable levels of fixed oxide charge but that the breakdown electric fields are presently low. Preliminary data suggests that these very low temperature oxides are suitable for TFT applications though some technical problems need to be addressed. Given these reservations the processing of large area flat panel displays using this type of plasma assisted oxidation is perfectly feasible.
Exciton Dissociation and Mobility in Conducting Polymers and Oligomers
Authors: Jain S. C. , Geens W. , Poortmans J. , Mehra A. , Nijs J. , Mertens R. 
Published: April 2011

ABSTRACTA survey of the literature shows that reverse bias current IL of an illuminated conducting polymer Schottky diode increases with voltage. We suggest that this increase in IL with applied reverse bias is due to a combination of two factors: (1) increase of mobility, and (2) dissociation of excitons. The experimental results agree with the values of IL calculated using either of the two mechanisms. Therefore it is difficult to determine the relative importance of the two mechanisms. The relative importance can be determined only if reliable values of material parameters are available. We have fabricated Schottky diodes and FETs using 5-ring n-octyloxy-substituted oligo[p-phenylene vinylene](Ooct-OPV5) and C60. The mobility of the oligomer derived from the measured characteristics of the diode is 3.29×10−7cm2/Vs and from the FET data, 3.24 × 10−4 cm2/Vs. These results show that the mobility (and other material parameters) depend strongly on the structure of the device. Therefore for interpreting the IL data it is important to measure the material parameters on the same structure on which IL measurements are made.
Surface Treatment Effects on the Electron Emission Characteristics of Ultra Thin AIN Coated Molybdenum Tips
Authors: Kang D. H. , Zhirnov V. V. , Wojak G. J. , Sanwald R. C. , Park M. , Hren J. J. , Cuomo J. J. 
Published: April 2011

AstractAlthough plasma surface treatment has proven useful for both metal and diamond field emitters, there is at this time no study of the effect of plasma treatment on the field emission from a thin layer of AIN. In this study a 7 nm film of AIN deposited on a molybdenum emitter tip was treated with different plasmas (H2, O2, and N2). All surface treatments and measurements were carried out by using an in-situ technique inside the magnetron sputtering chamber. Changes in the measured I-V curves were not observed from the emitter after treatment with either hydrogen or nitrogen plasmas, but were observed after oxygen plasma treatment. In addition, it was found that a very thin coating of aluminum over the AIN further enhanced the emission characteristics. We propose that the lowering of the surface barrier is due to the electronegativity difference of the species forming the surface layer.
Mechanism of Efficient Field Emission from Carbon Nanotubes
Authors: Zhu W. , Bower C. , Zhou O. , Kochanski G. P. , Jin S. 
Published: April 2011

ABSTRACTWe report observation of electron emission from individual carbon nanotubes. Two classes of emitters are observed, one emitting electrons with momentum nearly parallel to the nanotube axis, the other emitting electrons with nonzero momentum perpendicular to the tube axis. The emission pattern reflects the electronic structure of a particular tube and allows us to distinguish between structurally different nanotubes. These nanotube emitters exhibit excellent macroscopic emission properties; they can operate at a very large current density, as high as 4 A/cm2. At electric fields as low as 4-7 V/μm, they emit technologically useful current densities, e.g. 10 mA/cm2. The emission characteristics and durability of the carbon nanotube cold cathodes offer promising applications for vacuum microelectronic devices.