bluuebunny/crossref_metadata_2025_split huggingface dataset:
Factors Influencing Mass Diffusion in Bentonite and Mixtures of Bentonite and Sand
Authors: Cheung S.C.H. , Oscarson D.W. , Lopez R.S. 
Published: March 2011

ABSTRACTA model, based on the relative volumes of surface and interstitial water in soil, has been developed to study the effective mass diffusion coefficient in bentonite and mixtures of bentonite and sand. The results show that, when the surface water layer is fully developed to a thickness of 0.25 nm, the theoretical effective mass diffusion coefficient decreases with increasing dry density andbentonite content in a mixture of bentonite and sand. The development of surface water depends on the initial water content, the conversion of interstitial water to surface water, and the dry density. When the surface water layer is not fully developed, the effective mass diffusion coefficientdoes not necessarily decrease as the dry density increases.Considering the magnitude of measured mass diffusion coefficients in bentonite compacted to a dry density of 1.75 Mg/m], the model indicates that in this system there is significant conversion of interstitial to surface water. This suggests that mass diffusion coefficients in compacted bentonite are mainly influenced by the relative volumes of interstitial and surface water.
Porosities of and Diffusivities in Crystalline Rock and Fissure Coating Materials
Authors: Skagius Kristina , Neretnieks Ivars 
Published: March 2011

ABSTRACTThe diffusion of non-sorbing species in different rock materials and fissure coating materials have been studied. The results show that the effective diffusivity of iodide in granites with fissure coating materials is of the same magnitude or higher as the effective diffusivity for iodide in granites without fissure coating material. Also the porosities of the granites with fissure coating material were higher. The effective diffusivity for iodide in rock materials without fissure coating material was determined to be from 1.i0-14 m2/s to about 7.10-13 m2/s.To simulate the stress that exists in the bedrock at large depths diffusion experiments with iodide in rock materials under mechanical stress, and electrical resistivity measurements in salt-water-saturated rock cores under stress have been started. Electrical resistivity measurements is an indirect method to determine the diffusivity.Results from some initial measurements show that the effective diffusivity is reduced to about 40 % of the value for unstressed samples at pressures of 230-280 bar. This is the expected stress at repository depths.
Rock Properties Input to the Site Screening Process
Authors: Bauer Arthur A. , Ratigan Joe E. 
Published: March 2011

ABSTRACTThe site-screening process is designed to provide information on rock formations that will serve as the basis for recoximnding potentially suitable sites for locating a nuclear waste repository. While the application of criteria to extrinsic characteristics of the host rock, such as minimum depth and areal extent, are based on requiremnts associated with repository design and waste isolation, the significance of intrinsic characteristics (e.g., thermal conductivity, heat capacity, Young's modulus) is less firmly based. This is of particular importance with crystalline or grantitic-type rocks since they exhibit a wide range of canpositions and properties.The range of crystalline rock property variations has been defined and results describing the impact of these variations on repository thermal, mechanical, chemical, and hydrological performance constraints obtained. Results also are presented for various repository design options (emplacement mode, thermal loading, package power/pitch). For the analysis, rock properties and repository design elements are treated as stochastic parameters by statistical methods. The output range of a performance parameter is determined with respect to the range of stochastic parameters to establish their importance in site selection.
A Natural Analogue Approach for Estimating the Health Risks from Release and Migration of Radionuclides from Radioactive Waste.
Authors: Gilbert Thomas L. 
Published: March 2011

ABSTRACTThe health risks from radioactive waste may be expressed as a sum of products of transfer factors that characterize the causal chain of events between disposal of radionuclides in a waste field and the consequent health effects. “Model” estimates for the transfer factors are commonly obtained by modeling transport and other mechanisms in the subsystems that form the links in the causal chain. “Natural” estimates of some transfer factors for naturally occurring radionuclides can be obtained from data on the concentrations of naturally occurring radionuclides in soil, food, and the human body. These “model” and “natural” estimates can be used with scaling procedures to estimate the uncertainties and to obtain better estimates of the transfer factors. The scaling procedures take into account the differences in the source characteristics for radionuclides in a waste field of limited size and for radionuclides generally distributed in the natural environment. The ratios of the natural estimates to the model estimates for several transfer factors and several radionuclides belonging to the U-238 decay series have been determined. These ratios range from 1/8 to 4/1 for food-concentration/sourceconcentration transfer factors for the food pathways and from 1 to 77 for dose-rate/source-concentration transfer factors for the internal radiation dose pathways to various organs.
Prediction of Waste Performance in a Geologic Repository
Authors: Chambre' Paul L. , Pigford Thomas H. 
Published: March 2011

ABSTRACTThe rate of dissolution of low-solubility species from waste forms in a geologic repository can be calculated from a theoretical analysis of the time-dependent rate of mass transfer by diffusion and convection Into the groundwater surrounding the waste, assuming a concentration at the waste-form surface eanal to the solubility of the radioelement. The analytical solutions for time-dependent mass transfer are reduced to asymptotic steady-state approximations valid over specified ranges of repository conditions. The predicted steady-state dissolution rates are considerably below those observed in laboratory leaching experiments with borosilicate glass and with other waste forms, indicating that the solid-liquid chemical reaction rates measured in the laboratory experiments are greater than the rates of diffusive-convective mass transfer in the concentration boundary layer surrounding the waste form in a geologic repository. It is shown that the time to reach steady-state dissolution can be as short as a few years, if convective mass transfer in the concentration boundary layer is important, to many thousands of years, If mass transfer is mainly by diffusion in the groundwater. The steady-state mass transfer rate can be Increased, and the time to reach steady state decreased, by sufficiently short half lives of the dissolving species. The theory has been extended to Include the effect of backfill on the steady-state mass transfer from the waste-form surface into moving groundwater.The mass-transfer theory has been extended to include the effect of time-dependent solubilities, diffusion coefficients, and retardation coefficients, which provides a means of calculating the time-dependent dissolution of lowsolubility species from waste exDosed to groundwater during the Period of repository heating. The effects of timetemperature transient dissolution on far-field concentrations and cumulative release are calculated.The transient and steady-state diffusion of radionuclides through a finite backfill layer separating a finite waste solid and porous rock has been analyzed, Including the effects of radioactive decay. Previous backfill analyses have neglected radioactive decay and have assumed an infinite amount of backfill. The results show that the break-through time and rate of radionuclide release depend on properties of the backfill and surrounding rock and on the waste form dimensions.Laboratory tests have been designed to validate these theoretical analyses of diffusive-convective mass transfer with solubility-limit boundary conditions. Preliminary tests are now underway at the Battelle Northwest Laboratory.Peak far-field concentrations of more soluble radionuclides such as cesium-135, with suitably long
radionuclide transport times and sufficiently large axial dispersion, are shown to he insensitive to dissolution rate. Equivalent phenomena occur in fracture-flow radionuclide transport.
Boron Redistribution During Formation of Cobalt Silicides
Authors: Zaring C. , Svensson B. G. , ÖStling M. 
Published: March 2011

ABSTRACTRedistribution of boron during the formation of the cobalt suicides Co2Si, CoSi and CoSi2 has been studied. The suicides were formed by solid state reactions of cobalt deposited on boron implanted silicon. The suicide formation was determined by Rutherford backseat tering spectrometry (RBS), and the resulting redistribution of boron was studied using secondary ion mass spectrometry (SIMS). The study shows that the atoms participating in the suicide formation diffuse in the growing suicide without any mutual interference. Boron atoms in the consumed silicon layer redistribute within the formed suicide layer and accumulate at the surface, while boron in the underlying unconsumed silicon is unaltered, and no accumulation due to snowplowing occurs at the silicide/silicon interface.
Composition Dependence of Crystallization of Co-Si Alloys
Authors: Hong Q. Z. , Barmak K. , Clevenger L. A. 
Published: March 2011

ABSTRACTThe composition dependence of crystallization of amorphous Co-Si alloys has been investigated. Crystallization temperature decreased slowly from 400°C for a Co0.42Si0.58 alloy to 300°C for a CO0.2Si0.8 alloy. However, abrupt decrease in the crystallization temperature was observed for alloys with the monosilicide and disilicide compositions. The crystallization of alloys compositionally close to the disilicide was a one-step process with an activation energy of about 1.3 eV. The heat release and the volume contraction during crystallization of the stoichiometric Co0.33Si0.67 alloy were measured to be 0.118 eV/atom and 0.6%, respectively. In the case of the CO0.2Si0.8 alloy, complete crystallization was achieved in two steps with an activation energy of 2.1 eV for the primary crystallization.
The Effect of Silicide Formation on the Electrical Properties of Gate Oxides
Authors: Gambino J. P. , Cunningham B. , Buchanan D. A. 
Published: March 2011

ABSTRACTCoSi2, or TiSi2 formation on gate polysilicon can degrade the current-voltage and capacitance-voltage characteristics of MOS capacitors. Degradation of the gate oxide breakdown field is much more severe for capacitors with TiSi2 than for those with COSi2 TEM reveals evidence for a reaction at the interface between TiSi2 and SiO2, whereas there is no observable reaction between COSi2 and SiO2- The low breakdown fields for devices with TiSi2 may be due to thinning of the gate oxide by the interfacial reaction or mechanical deformation. A high density of electron traps and a small reduction in the breakdown field is observed when COSi2 contacts the gate, possibly due to a compressive stress in the oxide exerted by the suicide. In addition, an increase in the interface state density at the Si-SiO2 interface is seen for all samples exposed to a rapid thermal anneal (RTA) at 800°C, possibly due to the release of H from dangling bonds.
Reactions at the Titanium-Silicon Interface Studied Using Hot-Stage Tem
Authors: Kirtikar Amol , Sinclair Robert 
Published: March 2011

ABSTRACTThe interaction of titanium thin films sputter-deposited onto single crystal silicon was studied by in situ heating experiments within the TEM. Reactions at the Ti-Si interface including amorphization, crystallization, allotropie phase transformations and agglomeration have been observed in real time and recorded on videotape. Interpretation of these recordings can yield a wealth of information on the silicidation process.
Determination of the Optical & Materials Properties of βFeSi2 Layers Fabricated Using Ion Beam Synthesis
Authors: Hunt T. D. , Reeson K. J. , Gwilliam R. M. , Homewood K. P. , Wilson R. J. , Spraggs R. S. , Sealy B. J. , Meekison C. D. , Booker G. R. , Oberschachtsiek P. 
Published: March 2011

ABSTRACTIBS of buried α and β iron suicide layers was achieved by the implantation of 2 MeV 56Fe+ ions into (100) single crystal silicon substrates over a dose range of 3 × 1017 to 1 × 1018 cm“-2followed by a high temperature anneal. No photoluminescence was observed from the as-implanted samples which contained a discontinuous layer of βFeSi2 precipitates approximately 1.5 μm below the silicon surface. Upon annealing at 700°C, a 200 nm polycrystalline βFeSi2 layer was formed which gave a PL signal centred at 1.55 μm. After a 900°C anneal, the layer transformed to αFeSix with a resistivity of approximately 280μΩcm.
Improved Planarization for a Sog Etchback Process by Modifying the PECVD Oxide Film
Authors: Weling Milind , Jain Vivek 
Published: March 2011

ABSTRACTIn this study we have shown, for the first time, that Inter-Metal Oxide (IMO) planarization using a spin-on-glass (SOG) etchback process can be significantly improved by changing the composition of the deposited PECVD oxide film. Earlier studies have emphasized the importance of lowering the SOG to PECVD oxide etch selectivity below unity to compensate for micro-loading effects and thereby achieve good planarization. However, we have shown that a range of selectivities could be obtained by merely changing the silicon-richness of the PECVD oxide film. It was observed that for a given etch selectivity, planarization after SOG etchback was better with a silicon-rich oxide than with a stoichiometric oxide and particularly so for tight spacings that are characteristic of sub-micron technologies. We believe that increasing the silicon-richness of the PECVD oxide suppresses the micro-loading effects and consequently enables operation at selectivities closer to unity while maintaining good planarization. This feature has an important advantage of significantly widening the process window for a SOG etchback application.
Improved Detection of Deep Voids in Al Metalization Using Phase-Optimized Thermal Wave Imaging
Authors: Welles C. G. , Bivas Albert , Smith Lee 
Published: March 2011

ABSTRACTThe importance of minimizing stress-induced voiding for reliable VLSI metalization is now well appreciated. For detection of subsurface voids in a nondestructive manner, thermal wave modulated reflectance (TW) imaging is increasingly utilized.Although the TW response is vectorial (with components that are in-phaSfi. and 90 degrees out-of-phase with the laser modulation), heretofore only the magnitude of this signal was utilized in this application. For optimum imaging of deep voids, it is desirable to selectively display a signal that responds to both phase-delay and magnitude information simultaneously. The phase delay originates from the round-trip propagation time of the thermal wave from the surface to the void.In this paper, we demonstrate the use of this technique to (a) improve the detection (i.e. signal-to-noise ratio) of subsurface voids (b) distinguish between near-surface artifacts and deep voids, and (c) demonstrate the general utility of this technique by exhibiting improved S/N in crystalline silicon defects.
Ungated Vacuum Field Emission from Ordered Arrays of Microlithographically Defined Cylinders
Authors: Hickman James J. , Georger J. H. , Anderson M. , Bergeron G. L. , Kirkpatrick D. A. 
Published: March 2011

ABSTRACTA new process has been developed which allows electroless metal deposition on ordered arrays of resist structures with high aspect ratios (10–25 μm tall x 0.5–13 μm diameter). The fabricated structures have demonstrated ungated vacuum field emission at fields of 80–300 kV/cm in background pressures of 5 × 10-6 torr. The surface composition and Interface contamination relate directly to cathode performance. Cathode performance can be optimized by controlling the chemistry at these interfaces. X-ray Photoelectron Spectroscopy depth profiles, Scanning Auger Electron Spectroscopy, and Scanning Electron Microscopy have been used to characterize this system. These structures have potential vacuum microelectronics applications such as addressable electron emitters for flat panel displays.
A Combined Thermodynamic and Kinetic Approach to the Metallization of GaAs
Authors: Austin Chang Y. 
Published: March 2011

ABSTRACTA combined thermodynamic/kinetic methodology was presented to give a rational approach to the metallization of n-GaAs when a reciprocal system of GaAs-MδsGa-MsM'-MAs exists. Fortunately, for many quaternary systems consisting of Ga-M-M'-As, such a reciprocal system does exist. This methodology may be used either for Schottky enhancement or ohmic contacts to n-GaAs. Two examples were used to illustrate the approach and preliminary results were given.
Chemical Mechanical Polishing of Interlevel Dielectrics: Models for Removal Rate and Planarity
Authors: Sivaram S. , Tolles R. , Bath H. , Lee E. , Leggett R. 
Published: March 2011

ABSTRACTThis paper reviews some of the problems limiting broad manufacturing implementation of chemical mechanical polishing (CMP) as a planarization process for interlevel dielectrics. We examine the mechanism whereby polish rates tend to decrease as the polish pad ages, and propose an explanation based on slurry transport. We review a simple theory which provides an understanding in terms of basic mechanical principles of how CMP produces its planarizing effect. Finally, we demonstrate a method capable of providing a quantitative measure of planarity.
A Comparison of AFM, SEM, and TEM Analysis of AL/SI/CU Thin Films
Authors: Westra K. L. , Thomson D. J. 
Published: March 2011

ABSTRACTAtomic Force microscopy, scanning electron microscopy, and transmission electron microscopy was used to study Al/Si/Cu films sputter deposited at 2 and 45 mTorr. AFM and SEM analysis shows the films to consist of columnar structures commonly seen in PVD deposited thin films, while the TEM analysis showed the films be polycrystalline. Comparing the columnar structures seen in the AFM and SEM study to the grains found in the TEM study, we conclude that the columns consist of single grains. Thus for these films AFM or SEM analysis can be used to determine the grain size. Finally, an AFM scan of a Al/Si/Cu deposited via was performed. The AFM image clearly shows the high resolution of the AFM, while it also illustrates the problems caused by the finite size of the AFM tip.
Study of Sitox Process and its Application to Advanced MOS Devices
Authors: Lin J. , Chen W. , Banerjee S. , Lee J. , Teng C. , Magee C. 
Published: March 2011

ABSTRACTIn this study, the application of Sllicidation Through OXide (SITOX) process to TiSi2 formation is extensively investigated. The data show that the decomposition of an interfacial SiO2 layer between Ti and the Si substrate depends not only on its thickness but also on the silicidation temperature and the type of dopants in the Si substrate. In general, high annealing temperatures and B-doped p+ Si substrates enhance the decomposition of interfacial SiO2. After the silicidation process, the O concentration at the TiSi2/Si interface is approximately two orders of magnitude higher with SITOX than with the conventional silicidation process. This high interfacial O concentration has no significant effect on the electrical properties of SITOX TiSi2 films and junction diodes. The X-ray Diffraction analysis shows that SITOX TiSi2 films have a polycrystalline structure as do conventional TiSi2 films. The average grain size in a 100 nm SITOX TiSi2 film is estimated to be about 10 μm wide, while that in a 120 nm conventional TiSi2 film is about 3 μm. Histograms of leakage current for junction diodes confirm that the SITOX process can improve the uniformity of leakage currents.
Selective Electroless Metallization of Patterned Ligand Surfaces
Authors: Dressick W. J. , Dulcey C. S. , Calvert J. M. , Georger J. H. , Calabrese G. S. , Thomas M. E. , Stever H. A. 
Published: March 2011

ABSTRACTA process for creating patterns of metal-binding ligands on a variety of substrates is described. Deep UV patterning of chemisorbed ligand-bearing organosilane films creates modified surfaces that can selectively bind species such as Pd(II) via a covalent metal ion-ligand interaction. Patterned surface-bound Pd(II) is used to initiate additive electroless metallization at the catalytic sites. Metal adhesion to the substrate is controlled by the nature of the catalyst-ligand interaction.
Eiectromigration in Cu/W Structure
Authors: Hu C. -K. , Small M. B. , Ho P. S. 
Published: March 2011

ABSTRACTMass transport by electromigration in sputtered Cu line segments on a continuous W line has been measured using the drift velocity technique at temperatures from 166 to 396 °C. The Ta/Cu/Ta line segments are patterned by dry etching techniques. Cu mass depletion (voids) at the cathode end and accumulation (hillocks) at the anode were measured as a function of time from scanning electron microscope micrographs. The edge displacement of Cu was found to increase linearly with time. The activation energy for Cu electromigration drift velocity, which relates to the product of effective charge number and diffusivity, Z*D, is found to be 0.6 eV.
Stress-Related Phenomena in Capped Aluminum-Based Metallizations
Authors: Graas Carole D. 
Published: March 2011

ABSTRACTThe effect of a TiW capping layer on the mechanical behavior of AlSi(l%)Ou(y2%) thin films was evaluated. The aluminum films studied were deposited at temperatures ranging from 150 to 450°C, on various barrier layers (Ti, TiW, and TiN). Measurement of the stacks stress during anneal up to 450°C revealed that for films deposited at 150°C, the capping layer improved yield strength regardless of the type of barrier layer used. The uncapped stacks exhibited the traditional behavior of hillock formation during heating, and hillock /grain collapse during cooling. The capped stacks, however, showed considerably reduced, or suppressed hillock formation during heating, and active tensile stress relief mechanisms during cooling included cracking, voiding, and grain boundary grooving. These observations correlated well with XRD data characterizing the extent of tensile stress buildup in the aluminum films. For films deposited at 300°C, grain deformation during cooling after deposition presumably caused hardening which prevented cracking as well as changes in texture during anneal. This was observed regardless of the presence of a capping layer. Although the stacks studied were unpassivated, this data suggests that capping. layers may enhance stress migration issues in integrated systems.