bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of Microbiological Activity on the Mobility of Redoxsensitive Radionuclides in Sediments
Authors: Stroetmann Irmgard , Kämpfer P. , Dott W. , Schüle J. , Sokotnejat R. , Winkler A. , Pekdeger A.
Published: March 2011

The influence of microbial activity on the transport and migration behaviour of redox-sensitive radionuclides (e.g. Technetium (Tc) and Selenium (Se)) in groundwater environment were investigated within an interdisciplinarary research program. Soil material and sediments were investigated with batch- and recircu-lation column experiments. The number of microorganisms in the water was determined by counting the colony forming units (CFU) on R2A agar at regular periods.

The results of sterile and non sterile recirculation column experiments showed within 80 days a high fixation of the radionuclides in the unsterile samples (80% of Tc, 50% of Se compared with the initial concentration Ao), and no fixation in the sterile samples. There was no difference in the redox values.

It could be shown that the immobilisation of the redox-sensitive elements Tc and Se are strongly determined by microbial activity, depending on the different sediments and their microbial live stock. There are indications that the microorganisms found in the non sterile columns are allochthonous bacteria which were dragged into the experimental systems and samples during laboratory work and sampling. The composition of the microbial flora was shown to be very heterogenous and different in each individual column and within the same column at different times. Thus these columns might have been contaminated with microorganisms during sampling and handling of the experimental systems under non sterile conditions, as done generally in most laboratories.
Comparison of International Source-Term Codes
Authors: Zhou W. , Apted M. J. , Robinson P.
Published: March 2011

Source-term codes to predict the release of radionuclides from nuclear waste packages have been developed and implemented worldwide. A survey and initial comparison of the attributes and capabilities of 13 international source-term codes was recently completed. This preliminary analysis focused on comparison of transport factors/processes and solution methods. This initial comparison is a necessary first step in a properly-conceived, systematic benchmarking of source-term codes. Advantages of such a comparison include assurance of the mathematical correctness of implemented models, comparison and quantification of variances introduced by different types of simplifications, and identification and quantification of the impact of near-field processes.
Three-Diiensional Coupled Ground Water Flow. Thermal Transport and/or Migration of Nuclides Analysis by Boundary Element Method
Authors: Kawamura Ryuji
Published: March 2011

In the safety analyses of radioactive waste disposal, it is important and indispensable to analyze coupled problems of ground water flow, thermal transport and/or migration of nuclides. The three-Dimensional coupled problems is solved by boundary element method in this paper. The results of this method are compared with those experiments of JAERI and STRIPA SWEDEN on the thermal problem, and with those analyses of analytical and FEM results on the migration problem. In this formulation, natural convection is considered by Boussinesq approximation. An example of coupled ground water flow and migration of nuclides with decay chain U2 3 4 → Th2 3 0→ Ra2 2 6 is also tried.
Diffusive Transport of Carbon Dioxide through USW-G4 Topopah Spring Tuffs
Authors: Sarwar Ali M. , King Franklin G. , Ilias Shamsuddin
Published: March 2011

The estimation of diffusive transport of gases through tuffs is important in order to assess whether Yucca Mountain is an environmentally safe and acceptable repository for high-level radioactive waste. The purpose of this study is to provide effective diffusivity data which may be used to calculate the amount of diffusion of carbon dioxide through Yucca Mountain tuff layers to the environment. The effective diffusivity of carbon dioxide was measured for tuff samples from five different layers of the USW-G4 drillhole, which is located in the central part of the proposed repository horizon. The tuff samples studied are from the following layers and depths: Vapor Phase (83.6 m), Upper Lithophysal (130.1 m), Middle Nonlithophysal (224.5 m), Lower Lithophysal (243.9 m, 266.9 m, 297.3 m and 335.2 m), and Lower Nonlithophysal (356.3 m and 371.0 m). A steady-state, counter-diffusion method, using gas chromatographic analysis, was used to determine the effective diffusivity of carbon dioxide through tuff samples. Effective diffusivity increased with temperature between 25°C and 125°C for all layers. The effect of temperature on diffusivity correlated well using second-order polynomials. The porosity, specific surface area and mean pore radius were also determined. In general, diffusivity increased with porosity, specific surface area and mean pore radius, but did not correlate well. From the measured data , it appears that the diffusion takes place primarily in the combined Knudsen and bulk diffusion regimes.
Chemical Implications for the Presence of Introduced Materials in the Post-Emplacement Environment
Authors: Meike Annemarie
Published: March 2011

This paper addresses our ability to predict the chemical consequences of the presence of introduced materials, many of them man-made, in a radioactive waste repository. The chemical modeling ability required to describe this environment over a 10,000 year period is unique and unprecedented. It requires knowledge of parameters that have never been measured, many of them with respect to introduced materials. This paper discusses considerations that are required to establish the potential significance of introduced materials, especially those that could compromise the lifetime of the waste packages or affect the transport of radionuclides from breached containers. The paper presents issues related to the stability of individual compounds, the potential alteration of predicted natural chemical reactions, the potential moderation of those effects by natural zeolites, and the potential for interactions at elevated temperatures between rock, water, water vapor, radiation, waste package, and introduced materials.
Probabilistic Calculations of Groundwater Travel Time in Heterogeneous Three-Dimensional Porous Media
Authors: Bagtzoglou Amvrossios C. , Baca Robert G.
Published: March 2011

Groundwater travel time (GWTT) estimation at a potential high-level waste (HLW) repository is subject to various technical uncertainties. These uncertainties stem from model and data uncertainties and cannot be resolved with field tests because of the long time (> 1,000 yr) and large space (> 5,000 m) scales involved. Therefore, computational methods for demonstrating and determining compliance with the GWTT rule will be used. Stochastic theory based approaches constitute a natural framework for performing GWTT estimations under conditions of uncertain and/or limited data.

This study employs the generation of spatially correlated hydraulic conductivity fields by the Nearest Neighbor Model (NNM). Repeated (Monte Carlo) realizations of the statistically equivalent random fields are obtained, and the saturated steady-state groundwater flow equation is solved. These results are then used to estimate GWTT along particular paths by releasing a large number of water particles at various starting points. By doing so, path variability is sampled through the realization ensemble space and also through the independent particle “flights” within a specific flow field realization. The uncertainty in predicted GWTT due to parameter variability is assessed for a data set characteristic of the saturated zone at Yucca Mountain at three levels of parameter heterogeneity. However, since several parameters and the boundary conditions of the problem have been arbitrarily assumed, direct conclusions regarding the proposed Yucca Mountain site cannot be drawn from this study.
Water - Compacted Na-Bentonite Interaction in Simulated Nuclear Fuel Disposal Conditions: the Role of Accessory Minerals
Authors: Melamed A. , Pitkänen P.
Published: March 2011

In an earlier laboratory study1, ion exchange processes and smectite alteration were investigated through the interaction between compacted Na-bentonite (Volclay MX-80) and simulated granitic groundwater solutions. The change of montmorillonite from Na- to Ca-rich was found to be the major alteration process in the bentonite. In the water, a concentration decrease in Ca, Mg and K, and an increase in Na, HCO3 and SO4 were recorded. The total amount of Ca available in the water, however, was found insufficient to account for the recorded formation of Ca-smectite, and it is therefore assumed that the accessory Ca-bearing minerals in the bentonite provide the fundamental source of these cations.

X-ray powder diffraction analyses and microscope observations of the bentonite samples were re-conducted. Quartz, feldspars, pyrite, calcite and traces of gypsum were revealed as the primary accessories. In reacted samples, goethite and siderite are found as the secondary mineral products in association with corroded pyrite grains, while calcite and gypsum tend to disappear. From these results it is assumed that the oxygen present in the water and bentonite pore space promotes the oxidation of pyrite (dissolved) and the precipitation of goethite. The pore water pH decreases and calcite is partly dissolved. Through the dissolution, the bulk amount of Ca ions in addition to those arising by diffusion from the water is provided. Some of the reaction-released bicarbonate and Fe2+ re-precipitate in the bentonite as siderite, while the rest (as also SO4 ions) diffuse into the water.

Though the relative oxygen content in the experiment may be considered higher than that of the repository concept for nuclear fuel disposal (interaction in a semi-closed system with high water/bentonite ratio), the near field geochemistry predictions imply limited oxidizing conditions, which will be characterized by the above-described processes in sulphide-bearing bentonite and occur for some time after the sealing of the repository.
Moisture Movement in a Clay based Buffer Material under Isothermal Conditions
Authors: Mohamed A.M.O. , Shooshpasha I. , Yong R.N. , Onofrei C.
Published: March 2011

Several series of one dimensional tests were performed to examine the moisture and soil water potential distributions in the buffer material compacted to a dry density of 1.67 Mg/m3 and volumetric water content of 0.28. Diffusivity parameters were calculated using the measured moisture profiles combined with the finite difference method. Powell’s optimization was used to determine the material parameters.

It is experimentally demonstrated that the moisture distribution is highly dependent on the test boundary conditions. When volume change was allowed to take place during infiltration process, the buffer material adsorbs more water than in the case of no volume change. This is attributed to an increase in hydraulic conductivity by one order of magnitude. As the volumetric water content increases soil water diffusivity increases and soil water potential decreases.
Reactions of High-Feo Olivine Rock with Groundwater and Redox-Sensitive Elements Studied by Surface-Analytical Methods and Autoradiography
Authors: Hellmuth K-H. , Siitari-Kauppi M. , Rauhala E. , Johanson B. , Zilliacus R. , Gijbels R. , Adriaens A.
Published: March 2011

The reaction of unaltered olivine rock with groundwater and redox-sensitive elements (Tc, Re, and U) was investigated at elevated temperatures in the laboratory. Olivine was found to react easily with water taking up trace elements in alteration products. The alteration products were characterized using Rutherford backscattering, secondary ion mass spectrometry and electron microprobe analysis. The sample surfaces were studied by autoradiography and digital image processing techniques.
Equilibria in Saturated Bentonite
Authors: Arthur R. C.
Published: March 2011

It has been proposed that smectite clays, the predominant minerals in bentonite, are metastable solid solutions whose compositional heterogeneity prevents strict adherence to fixed ion activities and activity ratios characterizing invariant equilibria among stoichiometric phases [1,2]. This is qualitatively confirmed in the present analysis of exceptionally well-constrained experimental data [3] using a solid-solution model defined by the phase rule and estimated ideal site-mixing parameters. The results suggest that equilibria are approached among smectite solid solutions and kaolinite or halloysite, and that these minerals coexist metastably with respect to asiO2(aq)· Irreducible uncertainties are generated in the model by analytical and conceptual deficiencies in understanding compositional variability in smectite. However, their estimated effects on smectite’s stability are relatively small, and are comparable to the effects of experimental uncertainty in standard Gibbs energies on the stabilities of stoichiometric minerals.

An alternate analysis of the data further confirms that smectite does not behave like a stoichiometric phase [3]. Ion-exchange models for this clay mineral may therefore be thermodynamically ill defined because stoichiometric behavior is assumed implicitly under limiting conditions of fixed proportions of cations on exchange sites. Ion exchange is a pragmatic simplification enabling empirical analysis of some experimental data. However, its empirical, rather than thermodynamic, basis should not be overextended to conditions that are beyond an experimentally calibrated range.
Characterization of a Lignite Ash from the Metc Gasifier II. Scanning Electron Microscopy
Authors: Stevenson R. J. , Larsen R. A.
Published: March 2011

Lignite coal ash produced in a stirred, fixed-bed gasifier at the Morgantown Energy Technology Center (METC) has been studied by scanning electron microscopy using both morphologic and chemical analyses. Detailed chemical analyses of phases, grains, and traverses across grains illustrate the heterogeneous nature of the ash. These data support the concept that most of the ash was formed by partial melting and subsequent crystallization and agglomeration.
Disposal of Western Fly Ash in the Northern Great Plains
Authors: Groenewold Gerald F. , Hassett David J. , Koor Robert D. , Manz Oscar E.
Published: March 2011

Leachates from western fly ashes are typirally alkaline. Our studies indicate a strong correlation between alkalinity of western fly ash leachate and trace element concentrations. Elements of particular concern include As, Se, and Mo. A base neutralization mechanism is operative in all of the overburden types found at mine disposal sites in western North Dakota. Regional geological similarity suggests that this mechanism is operative throughout the Northern Great Plains. Although the mechanisms of neutralizatioti are speculative, laboratory experiments indicate significant neutralization at all levels of base above background levels. Long-term monitoring of fly ash disposal-sites indicates that alkaline neutralization of fly ash leachate is occurring. Further, field data indicate that toxic trace elements (particularly As and Se) in disposal site leachates decrease in concentration as the pH of the learhate is neutralized. Thus, the intrinsic corditions at Northern Great Plains fly ash disposal sites appear to promote significant attenuation of critical toxic elements found in fly ash leachates. Regardless of the pH, leachates in those settings have high concentrations of sodium and sulfate. Western fly ashes are commonly cementitious. Our studies indicate that fly ashes comnoniy develop significant strength after several months of burial, particularly if emplaced in an unsaturated disposal setting. Once cementitious reactions have occurred, the fly ashes show little potential for leaching. Thus, a combination of intrinsic disposal-site conditions and the cementitious behavior of the fly ashes suggests that surface-mine disposal of western fly ashes in the Northern Great Plains, assuming proper disposal-site selection, may not cause long-term environmental problems associated with toxic trace elements.
The Characterization of Alloyed NiGeAuAgAu Ohmic Contacts to AlInAs/GaInAs Heterostructure by Auger Electron Spectroscopy and Wavelength Dispersive X-Ray Analysis
Authors: Capani P. M. , Mukerjee S. D. , Rathbun L. , Griem H. T. , Wicks G. W. , Eastman L. F. , Hunt J.
Published: March 2011

In a lattice-matched <100> InP/Ga0.47In0.53As/Al0.48In0.52As system used for modulation-doped field effect transistors (MODFETs), low resistance ohmic contacts to the two-dimensional electron gas have been fabricated using alloyed NiGeAuAgAu metallization. In this work we examine the use of Auger electron spectroscopy (AES) and wavelength dispersive x-ray spectroscopy (WDX) analyses for studying the metal-semiconductor interactions and their correlation with measured ohmic contact resistance.
The Use of Leed for the Characterization of Surface Damage from Pulsed Laser Irradiation
Authors: Helms Aubrey L. , Cho Chin-Chen , Bernasek Steven L. , Draper Clifton W.
Published: March 2011

Low Energy Electron Diffraction (LEED)-Spot Profile Analysis and Auger Electron Spectroscopy (AES) have been used to study the response of Mo(100) single crystal surfaces to Q-switched, frequency doubled Nd:YAG laser pulses. The experiments were conducted in a special ultra-high vacuum (UHV) system which allowed the surfaces to be irradiated under controlled conditions. Laser fluences both above and below the melt threshold were employed. For the melted surfaces, good epitaxial regrowth was observed. The spot profile analysis indicates the formation of random islands on the surfaces. Surfaces which had been previously disordered by 3 KeV Ar+ implantation were laser surface melted and observed to regrow epitaxially as has been observed in the case of ion implanted silicon. The formation of the islands and stepped structures is explained by considering the activation of dislocation sources by the induced thermal stresses resulting in slip.
Ultrasensitive Elemental Analysis of Materials Using Sputter Initiated Resonance Ionization Spectroscopy
Authors: Parks J. E. , Beekman D. W. , Schmitt H. W. , Spaar M. T.
Published: March 2011

Sputter Initiated Resonance Ionization Spectroscopy (SIRIS) is a technique being developed by Atom Sciences, Inc. to perform ultrasensitive elemental analysis of materials. SIRIS uses sputtering to atomize a solid sample and resonance ionization (RIS) to selectively ionize an element of interest. The SIRIS technique is capable of detecting impurities at the 0.1 ppb level (5 × 1012/cm 3) in a routine analysis time of 5 minutes. RIS and the SIRIS technique are briefly reviewed. We report a detection efficiency for SIRIS of 2 ppb sensitivity and recent results are given for standard well-characterized samples of boron-doped silicon. Current progress is described for the development of depth profiling and the analysis of silicon in gallium arsenide. The SIRIS detection of silicon in standard reference materials certified by NBS is presented.
Characterization of Thin Metal Films by SIMS, AUGER, and TEM
Authors: Furman B. K. , Benedict J. P. , Granato K. L. , Prestipino R. M. , Shih D. Y.
Published: March 2011

Secondary ion mass spectrometry (SIMS), Auger spectroscopy, and transmission electron microscopy (TEM) were applied to study Au, Cu, Ti, Ti-W, Cr, Al-Cu, and Al metal films deposited on both Si and ceramic substrates.

SIMS analysis of as-deposited metal films was used to characterize impurity levels, both metallic and gaseous, incorporated during deposition. The results revealed that the levels varied under generally accepted deposition conditions. As-deposited and annealed films were examined with SIMS, Auger, and TEM to study interdiffusion, grain growth, and impurity segregation as a function of processing conditions. Metallic impurities were observed to modify Au/Ti interdiffusion. Large variations in residual H, C, O, and N were observed in as-deposited Al and Al-Cu films.

Hydrogen, incorporated during deposition of Ti films, was observed to redistribute after thermal annealing in N2 or thermal cycling in forming gas (N2-10% H2). Samples thermally cycled in forming gas absorbed additional H into the Ti layer. SIMS/ion imaging was used to study the incorporation and segregation of H. Differences in H behavior were observed to be dependent upon metal structure, composition, and substrate material.
The Characterization of Intentional Dopants in HgCdTe using Sims, Hall-Effect, and C-V Measurements
Authors: Lapides L. E. , Whitney R. L. , Crosson C. A.
Published: March 2011

The properties of selected dopants in liquid-phase epitaxial (LPE) layers of HgCdTe have been studied using secondary ion mass spectrometry (SIMS), Hall-effect, and capacitance-voltage (C-V) measurements. The layers were grown from Hg-rich melts on {111}-oriented CdTe and CdZnTe single-crystal substrates. Diodes, for the C-V measurements, were homojunctions formed by ion implantation or heterojunctions formed by the growth of a second layer on the base layer. Dopant concentration distributions in both single- and double-layer structures were characterized by SIMS and C-V measurements. The dopant profiles measured by SIMS were quantified using relative sensitivity factors calculated from ion implanted impurity profiles measured on standard reference samples. Using specialized SIMS techniques, such as molecular ion spectrometry, As concentrations as low as 2 × 1015 cm−3 have been measured. In the HgCdTe:In/HgCdTe:As system minimal dopant interdiffusion is observed in SIMS profiles. The growth of the second layer has insignificant effect on the As distribution in the base layer, and C-V data indicate that the electrical properties change only slightly. Carrier types and concentrations were determined by Hall effect and C-V measurements. Good agreement between dopant concentrations and carrier concentrations was observed, indicating 100% activation of the dopant atoms, for all dopants studied. Examples of implant calibration profiles, dopant concentration distributions, carrier concentration vs temperature measurements, and 1/C2 vs V data are presented, along with graphs and tables comparing dopant profiles with electrical properties.
Hydrogen Measurement of Thin Film Silicon: Hydrogen Alloy Films Technique Comparison
Authors: Pollock Gary A.
Published: March 2011

The hydrogen content in thin film silicon:hydrogen alloy material has been measured by five techniques: 15N nuclear resonance reaction analysis, secondary ion mass spectrometry, infrared spectroscopy, nuclear elastic scattering spectroscopy, and Rutherford backscattering spectroscopy. NRA and SIMS data agree most closely in this study, although SIMS data from three of four laboratories are considerably scattered. The hydrogen content of TFS ranges from 18% at a deposition temperature of 150°C to 10% at 250°C. It varies little, if any, with thickness. Some advantages and disadvantages of the five techniques are discussed.
MeV Helium Microbeam Analysis: Applications to Semiconductor Structures
Authors: Brown R. A. , McCallum J. C. , McKenzie C. D. , Williams J. S.
Published: March 2011

We have employed an MeV He+ microbeam for the analysis of micron-scale semiconductor structures. The analysis combines a unique beam scanning and mapping capability with powerful ion beam techniques such as particleinduced x-ray emission, Rutherford backscattering and ion channeling. These analysis capabilities are applied to the measurement of dopant profiles in polycrystalline resistors, identification of micro-alloying in metal-GaAs contacts and damage/atom location in individual polycrystalline silicon grains. The latter application utilises the newly-developed technique of channeling contrast microscopy.
Elastic Recoil Analysis of Hydrogen in Ion-Implanted Magnetic Bubble Garnets Using 44 MeV Chlorine Ions
Authors: Leiberich A. , Flaugher B. , Wolfe R.
Published: March 2011

Elastic recoil analysis using 44 MeV chlorine ions is a precise and timesaving method of measuring hydrogen profiles of ion implanted magnetic bubble garnets. Neon, nitrogen and hydrogen ion-implanted modified yttrium iron garnets, which are used for magnetic bubble devices based on ion implanted propagation patterns, (12P2), were studied with respect to their hydrogen concentration-depth distributions. A description and calibration of the elestic recoil analysis setup are presented along with the necessary simple algorithms to obtain the final hydrogen concentration-depth profiles from the measured energy spectra generated by recoiled protons. The garnet samples were annealed with or without a surface coating of SiO2. At 250°C, the hydrogen was found to diffuse throughout the aamaged surface layer but not into the underlying undamaged material. At 350°C, the hydrogen diffused out of the uncoated garnet, but was sealed into the implant damaged garnet layer by the thin oxide coating. Such hydrogen retention correlates with previously reported beneficial effects of an oxide layer deposited at a low temperature after implantation but before processing on ion implanted bubble devices.
Surface Composition of Carburized Tungsten Trioxide and its Catalytic Activity
Authors: Nakazawa Masatoshi , Okamoto H.
Published: March 2011

Abtract

The surface composition and electronic structure of carburized tungsten trioxide are investigated using X-ray photoelectron spectroscopy (XPS). The relationship between the surface composition and the catdlytic activity for methanol electro-oxidation is clarified. The tungsten carbide concentration in the surface layer increases with the carburization time. The formation of tungsten carbide enhances the catalytic activity. On the other hand, the presence of free carbon or tungsten trioxide in the surface layer reduces the activity remarkably. It is also shown that, the higher the electronic density of states near the Fermi level, the higher the catalytic activity.
Instantaneous Impedance of Aluminium in Anodic Polarization Status
Authors: Yingyang Zhu , Kuang Wang , Rizhang Zhu , Wenqi Zhang
Published: March 2011

The instantaneous impedance of AL in 1N NaCl at various polarization tines has been measured using LapLace transformation method. In an instant of beginning polarization, the dependance of interfacial resistance, Rf, on polarization current, ip, follows:

Interfacial capacitance, Cf, however, indepenrs of ip, only depends on film's thickness. In the course of polarization, Rf changed hardly with time, Cfchanged greatly. This is due to little difference between the resistance on corroded region and the resistance on the region with film, and great difference capacitance on both regions. A reasonable model has beon pronosed to explain the experimental results.
Characterization of Precipitates Decorating Stacking Faults in Single Crystal Silicon
Authors: Ryoo K. , Drosd R. , Wood W. E.
Published: March 2011

Oxidation of silicon wafers containing lattice damage at the surface normally results in the formation of extrinsic stacking faults. Optical microscope investigation following decorative etching shows that on certain samples the faults have a straight line appearance while on others the ends of the defect are much enlarged giving a “dog-bone” shape. TEM investigation confirmed that the dog-bone shaped faults were decorated with colonies of precipitates near their edges. These colonies resided on the (111) fault planes and extended over several thousand angstroms. Precipitate spots were not found in the diffraction pattern due to the small volume fraction, but translational Moire fringes were observed for certain matrix g-vectors, thus aiding in the crystallographic analysis. EDX analysis was also performed and revealed that precipitates were due to Cu and Ni contamination. The electrical impact of the defects on P-N junction was measured, showing a strong influence on both reverse and forward bias current/ voltage characteristics.
An In-Situ Study of Velocity/Driving Force Relations for Interfacial Migration
Authors: park Woonsup , Allen Samuel M.
Published: March 2011

The migration kinetics of antiphase boundaries (APBs) in long-range ordered Fe-Al alloys are analyzed using in-situ hot-stage transmission electron microscopy, making it possible to observe the interfacial migration directly as it occurs. The observed domain structures are essentially two dimensional due to the thin foil configuration of the specimen, facilitating analytical interpretation of the data. By measuring the local curvatures and migration distances from a series of micrographs taken at a constant temperature, the proportionality constant relating velocity to curvature can be determined. This proportionality constant, called the mobility for APB migration, is found to be independent of the curvature for <100> APBs in Fe-27 atomic percent Al at 745K, having the value of 4.8×10−19 m2/s.
Electron Microscopy Study of Structural Changes During Isothermal Annealing of a Ni4Mo-Based Alloy Containing Chromium
Authors: Vasudevan K. , Stansbury E. E.
Published: March 2011

Transmission electron microscopy has been used to study phase transformations in a Ni4Mo alloy containing 2.08 wt pct chromium following isothermal annealing at 850, 800 and 700°C. At these temperatgres, the DO22 phase forms initially, which then transforms to Ni3Mo. At 700°C, the DO22 phase forms from bands composed of Ni4Mo and Ni2Mo aligned parallel to {111} fcc planes, and is relatively stable. A second mechanism for the formation of Ni3Mo occurs at 700°C. Large Ni4Mo domains form at grain boundaries. These su~sequently transform to Ni3Mo, with the simultaneous presence of stacking faults on (010) Ni3Mo planes.

These observations are correlated to the optical microstructure. Grain size influences the type, volume, and distribution of second phases. Sequences and mechanisms of transformations are related to the experimental observations.
Detection and Imaging of Supported Catalyst Particles
Authors: Treacy Michael M. J.
Published: March 2011

In this short review we contrast and compare the relative merits of three imaging techniques in the CTEM and STEM, for detecting subnanometer size catalyst clusters. It is shown that incoherent dark field signals, such as those obtained by hollow-cone illumination in the CTEM, and the annular detector in the STEM, are significantly more sensitive to subnanometer size clusters than the bright field signal. Sensitivity to clusters of high atomic number increases as the illumination (or detector) semi-angle increases, although at the expense of decreased signal-to-noise. The STEM annular detector signal offers advantages over the CTEM hollow-cone signal in this respect since it has a higher electron collection efficiency. A further advantage of the STEM is that image contrasts may be enhanced by electronically combining the annular detector signal with the axial energy loss signal. This ratio method, or Z contrast technique, has been used with success to detect single Pt atoms on thin low atomic number supports.
Characterization of Reactively Sputtered Titanium Carbide Films by Analytical Electron Microscopy
Authors: Tafto J. , Rajeswaran G. , Saulys T.
Published: March 2011

TICx films prepared by reactive sputtering using a Ti target and different methane partial pressures were characterized by analytical transmission electron microscopy. The films are polycrystalline, and the plasmon energy increases considerably with increasing carbon content. Combination of the information obtained from electron energy loss plasmon and core loss spectra, and electron diffraction indicates that x in TiCx increases linearly with methane partial pressure. We find that the face centered cubic TIC phase spans the composition from TiC0.2 to TiC1.0 and when x<l we have a mixture of TiC1.0 and amorphous C.
Origin of Grown-in Dislocations in III-V Compound Semiconductor Epitaxial Layers
Authors: Nakahara S. , Chu S. N. G.
Published: March 2011

A transmission electron microscope was used to study the origin of grown-in dislocations observed in quaternary InGaAsP layers grown by vapor phase epitaxy on (001) InP substrates. Many of the grown-in dislocations were found to exist as dislocation dipoles and were connected to particles formed at the lnGaAsP/lnP interface. X-ray micro-analysis has indicated that the particles are quaternary alloys having chemical compositions slightly richer in both Ga and P than that of the lattice-matched InGaAsP layer. In some cases, this compositional deviation led to a significant lattice mismatch. As the particle grows larger, a strain relaxation occurs by generating misfit dislocations around the particle in the form of a dislocation half loop. If these dislocation half loops do not develop into a complete loop by totally surrounding the particle, they leave two unclosed dislocation segments (a dislocation dipole), which are replicated by the quaternary overlayer along the substrate normal direction, i.e., [001]. These dislocations eventually become a source for grown-in dislocations.
TEM Studies of Low Energy Argon and Iodine Ion Milling Phenomena in Compound Semiconductors
Authors: Cullis A. G. , Chew N. G. , Hutchison J. L.
Published: March 2011

The nature of disorder produced by low energy Ar+ and I+ ions (and atoms) in the III–V compound semiconductors InP and InSb, and in the II–VI semiconductors CdTe, ZnS and ZnSe has been studied in detail by conventional and high resolution transmission electron microscopy. It is demonstrated that for Ar+ ion bombardment the disorder in the III–V compounds comprises segregated indium islands which accumulate on the machined surfaces, while for the II–VI compounds the disorder consists of dense arrays (∼1011 cm−2) of small dislocation loops near to each bombarded surface. When Ar+ ions or Ar atoms are used for thin specimen preparation by milling prior to electron microscopy, the disorder produced gives contrast which seriously obscures images and so complicates their interpretation. This problem concerning the presence of artifactual defects can be greatly reduced or even eliminated by the use of reactive I+ ion milling for the final thinning of specimens.
The Growth of Interdisciplinary Materials Research at Suny-Buffalo
Authors: Anderson Wayne A.
Published: March 2011

Materials Science and Materials Engineering are recognized as essential areas of growth for advancement in applications of new devices and materials. The educational program at the university level must be dynamic in nature to keep pace with advances in science and instrumentation. State University of New York at Buffalo has sponsored an interdisciplinary proposal solicitation to promote efforts in the forefront of science. Materials-related efforts are described herein which will lead to improved external funding of research, improved educational programs, more sophisticated instrumentation, high quality graduate students, and high quality faculty.
Plasma Emission Spectroscopy and Chemical Analysis of Amorphous Hydrogenated Carbon
Authors: Park Chang Soo , Bodart Jeffrey R. , Han He-Xiang , Feldman Bernard J.
Published: March 2011

The emission spectra of various hydrocarbon plasmas used in the growth of amorphous hydrogenated carbon (α-C:H) thin films have been measured.The presence of CH, H, H2, and C2 species in the plasma have been observed.The chemical composition of the α-C:H films was determined by combustion analysis and shows roughly equal atomic concentrations of H and C and a surprising large concentration of 0.The plasma emission spectra and chemical composition results can be partially understood in terms of relative bond strengths of the different molecules involved, and these results give some insights into the growth kinetics of α-C:H thin films.
Reactive Ion Etchtng Model for Silicon Dioxide Guadalupe Fortuno
Authors: Fortuño Guadalupe
Published: March 2011

The etching of SiO2 was studied during reactive ion etcing (RIE) in an SF plasma.The etch rate of SiO2, the sheath voltage and the wafer temperature were measured as a function of the percentage of SF6 in Ar and as a function of the total pressure.This was done with the purpose of better understanding the etching mechanisms involved.The results are compared with similar experiments carried out with CF4 and Ar [1].Tests to the model formulated will also be given.
Plasma Etching of Si in SF6/O2 and NF3/O2 Mixtures: Computer Simulations And Experimental Results.
Authors: Anderson Harold M. , Smith Bradley K. , Light Ron W.
Published: March 2011

Profile control in polysilicon etching with SF6/O2 and NF3/O2 gas mixtures has been explored as a function of feed gas composition, power, pressure and total flow.Polysilicon appears to etch anisotropically under certain anomalous combinations of these parameters, such as high power/dilute etchant gas composition, low power/high etchant gas composition and high power/high etchant gas composition.Very rapid etch rates (3.5 μm/min) and anisotropic etching were obtained simultaneously in SF6/O2 mixtures at 250 mtorr.In order to provide a rational for explaining these anomalies, a kinetic model for these plasmas has been developed which couples electron impact events in the plasma to gas-phase chemistry and surface reactions of the etching process.Peculiarities in the electron energy distribution function (EEDF) of these gas mixtures, determined by Boltzmann calculations, appear related to the anisotropy under dilute conditions.However, anisotropic etching observed at 250 mtorr and rich SF6 gas mixtures appears more related to anomalies in power deposition to the discharge, possibly including wave interactions or resonant processes.Comparisons between computer simulations and experimental results are presented.
Considerations in Plasma Pattern Transfer Process Development
Authors: Herb G. K.
Published: March 2011

Pattern transfer by plasma etch has become an indispensable tool to fabricate semiconductor devices whose critical feature dimensions are less than 3.0 μm.Traditional wet chemistry techniques do not maintain linewidth fidelity (isotropic profile) and lose applicability for features whose aspect ratio (width:thickness) is below 3:1.Plasma processes must keep pace with the rapid introduction of innovative device designs whose packing density is continually increasing.Hence many etch process developments are based on empirical, rather than theoretical, wisdom.Often the desired etch results of anisotropy, selectivity, uniformity and cleanliness become competing requirements.

Many of today's circuit designs have structures, topography and feature dimensions so interrelated that difficulty is usually encountered during the etch process development.Many of the single layer materials that were used in yesterday's devices have become multiple material films in the current advanced designs, increasing the complexity of the etch process and confusing the interpretation of the process results.An increasingly important tool that can be used for successful etch development is the statistical fractional factorial experimental design.This paper will discuss a few examples of plasma process development that involve a rank ordering of the importance of competing etch results.
Plasma Processing in Semiconductor Manufacturing
Authors: Tracy Clarence J.
Published: March 2011

The implementation of plasma deposition and reactive ion etching into a semiconductor VLSI manufacturing process is rarely trivial.In some cases isolated process modules may appear to function well until integrated into a lengthy product flow, where interactions occur with prior or subsequent processing steps.In addition, dry processes have some unique and sometimes undesirable characteristics which need to be considered.Examples of both of these kinds of problems will be shown.Opportunities still exist for research to lead to a better understanding of mechanisms and for development work to improve the equipment and specific processes.
Anisotropic Dry Etching of S1O2 on Si and its Impact on Surface and Near-Surface Properties of the Substrate.
Authors: Oehrlein G. S. , Coyle G. J. , Tsang J. C. , Tromp R. M. , Clabes J. G. , Lee Y. H.
Published: March 2011

In the present paper structural and chemical changes which can occur in the surface and near-surface properties of the substrate during anisotropic dry etching of SiO2 on Si will be reviewed.Silicon specimens which had been etched in CF4/X%H2 (X≤40) have been characterized by X-ray photoelectron emission spectroscopy, He ion channeling, H profiling and Raman scattering techniques.Key results of our studies are summarized as follows: Plasma exposure of a Si surface leads to the deposition of a thin (≤50Å thick) C,F-film.A Si-carbide containing Si region is formed during RIE which is localized near the fluorocarbon-film/Si interface.The near-surface region (∼30–50Å) of the Si substrate is also heavily disordered as found by ion channeling and Raman scattering.A modified, less damaged Si region has been found in the case of hydrogen-based etching gases, which extends from about 30–50Å from the surface to a depth in extent of 250Å and contains a high concentration (∼ 5 at.%) of H as shown by hydrogen profiling techniques.From the observation of Si-H and Si-H2 vibrational modes by Raman scattering it has been shown that some of the H is bonded to the Si lattice.
Reactive Ion Etching Damage to Shallow Junctions
Authors: Wu I. W. , Bruce R. H. , Mikkelsen J. C. , Street R. A. , Huang T. Y. , Braun D.
Published: March 2011

The damage of reactive ion etching to shallow junctions is an important consideration in advanced technology.In this paper, the damage incurred during contact etch is studied, with emphasis on those defects responsible for junction leakage of shallow junctions.Shallow p+/n and n+/p junctions have been prepared with depths of 160 nm.Junction leakage measurements have been made for various amounts of silicon loss up to within 20 nm of the junctions by using a CHF3 + CO2 plasma.The degree of chemical and structural damage has been characterized by using photoluminescence, SIMS, and spreading carrier profiling.

The leakage current density was found to depend strongly on contact area and increase rapidly with junction etch depth after the etched surface has extended to within 80 nm of the junction boundary.The concentration and depth of damage increases with increasing plasma exposure until saturation.Etching induced defects are observed in photoluminescence, and one such defect is identified as a carbon interstitialcy.Enhanced diffusion effects were observed for both chemical contamination from the etch gas and the junction dopants.The spatial distribution of the chemical and structural damage has been found to correlate with the junction leakages.The annealing behavior of damage has also been investigated.
Modification of the Electrical Properties of a GaAs Surface by Plasma Exposure
Authors: Oren Moshe , Zemon; Stanley
Published: March 2011

Plasma processing is an essential part for the fabrication of GaAs ICs.It was found that the exposure of sulfur doped n-type GaAs layers to a plasma of helium, oxygen, or nitrogen changed their electrical characteristics without introducing crystalline damage, as observed by electron diffraction measurments or etching.Exposure to a plasma depletes the surface carrier concentration but the mobility remains unchanged.Compared to O2 and N2 the helium plasma has the largest effect on the GaAs surface.Exposure of S-doped GaAs layers to a He plasma at 350°C produces two new deep levels at 840-nm and in the region between 863 and 872-nm.These levels were not observed for a He plasma exposure at room temperature or for O2 plasma exposure at 350°C.
Reactions of Atomic and Molecular Fluorine on Silicon Surfaces
Authors: Stinespring C. D. , Freedman A. , Wormhoudt J. C. , Kolb C. E.
Published: March 2011

The reactions of atomic and molecular fluorine on silicon surfaces have been studied using x-ray photoelectron spectroscopy (XPS) and an ultrahigh vacuum (UHV) compatible microwave discharge effusive beam source of reactive species. The results indicate that molecular fluorine is dissociatively chemisorbed to form SiF2-like species on the surface. This reaction saturates at approximately monolayer surface coverage. Atomic fluorine also reacts initially to form SiF2-like surface species. Once the available surface sites are occupied, however, the fluorine atoms penetrate and react with silicon in the underlying layers. As the fluorine uptake increases, many of the subsurface silicon atoms become fully fluorinated. That is, the reaction product becomes SiF4-like. In contrast, preliminary studies indicate little difference in the behavior of atomic and molecular chlorine. These findings are compared with previous results for XeF2 adsorption, and their implications for plasma etching mechanism definition are discussed.
Indentation Load Relaxation Studies of Thin Film-Substrate Systems
Authors: Stone D. , Lafontaine W. , Ruoff S. , Hannula S.-P. , Yost B. , Li Che-Yu
Published: March 2011

Results from indentation load relaxation (ILR) tests on thin film-substrate systems are reported. In the case of a 1 pum aluminum film on silicon, the data can be interpreted as reflecting both the properties of the film and the interface between film and substrate. Data from a 37μm TiN film on 304 SS are believed to reflect the combined behavior of the film and substrate.
Device Failures in Pressure Cooker Tests at 130°C
Authors: Burgess J. F. , Yerman A. J.
Published: March 2011

The results obtained from Moisture-Temperature-Bias testing of Power- MOSFET at 130°C and 85%RH are examined. A variety of packaging techniques were tested varying from plastic encapsulation materials/methods to fully hermetic. Unprotected devices were tested as controls. The predominant failure mechanism observed was aluminum corrosion, which was manifested initially as a leakage current increase and eventually as visually observable dissolution of aluminum and eventual open circuits.

This paper examines the critical part that surface contamination plays in the corrosion process, particularly where condensed water films can form at the metal surface. The effectiveness of various plastic coating methods are viewed in the light of this concept. Aluminum lead bonds were more susceptable to corrosion than expected. A number of materials were identified that showed resistance to pressure cooker conditions.
Non-Conventional Route to Glass-Ceramics for Electronic Packaging
Authors: Gensse C. , Chowdhry U.
Published: March 2011

This paper describes a non-conventional route to formation of dense glass-ceramics at relatively low temperatures. Organometallic precursors were used to synthesize powders with controlled purity and stoichiometry in the MgO/A12O3/SiO2 system. These amorphous powders sintered by viscous flow to form a dense glass below 1000°C. Further heating resulted in the formation of very fine grained glass-ceramics. Beta-quartz, cordierite, and cordierite-mullite glass-ceramics were obtained with attractive properties for electronic packaging.
Characterization of Sol-Gel Derived Tantalum Oxide Films
Authors: Silverman L. A. , Teowee G. , Uhlmann D. R.
Published: March 2011

We have studied the densification and dielectric properties of sol-gel derived tantalum oxide thin films as the insulators in MIS capacitors. Hydrolysis of tantalum ethoxide is extremely rapid and goes to completion in ethanol. Condensation is also rapid, and goes to completion in toluene Multiple layers were applied by spin-coating up to thicknesses of 3000 Å before cracking of the coating during drying ensued. Densification occurs from room temperature to 450 C, with the original film thickness decreasing by about half in one hour at 450 C. No additional densification occurs upon heating to 750 C. The dielectric constant decreases from unfired samples to those fired at 450 C, and then increases on firing from 600 to 750 C. The value of the dielectric constant at 1 MHz for samples fired at 750 C for one hour is 20, similar to that of anodically grown Ta2O5. Leakage currents as low as 2 × 10−7 amp cm−2 have been measured for applied fields of 200,000 V cm−1.