bluuebunny/crossref_metadata_2025_split huggingface dataset:
Characteristics and Recovery of SI Surfaces Plasma Etching in CHF3 / C2F6
Authors: Park H.-H. , Kwon K.-H. , Koak B.-H. , Lee S.-M. , Kwon O.-J. , Kim B.-W. , Lee J.-W. , Yoo J.-B. , Sung Y.-K. 
Published: March 2011

ABSTRACTThe effects of SiO2 reactive ion etching (RIE) in CHF3 / C2F6 on the surface properties of the underlying Si substrate have been studied by X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS) techniques. The observed two major modifications are (i) a ∼50nm thick silicon layer which contains carbon and fluorine and (ii) 2∼3nm thick residue layer composed entirely of carbon, fluorine, oxygen and hydrogen on the silicon surface. The thermal behaviors of attributed peaks for C 1s, Si 2p, O 1s and F 1s of residue film have been analyzed after in-situ resistive anneal under ultra high vacuum (UHV) condition. C-F1, C-F2 and C-F3 bonds decompose and form C-CFx (x≤3) bonds above 200°C. Above 400°C, C-CFx bonds also decompose to C-C/H bonds. For recovery of the modified silicon surface, reactive ion etched specimens have been exposed to an oxygen plasma. By XPS analysis, the effect of an O2 plasma treatment has been revealed to be completed within 20min. With an O2 plasma pre-treated, a rapid thermal anneal (RTA) treatment as low as 500°2 is found to be effective for removal of impurities in the silicon.
Single Step Low Temperature In-Situ Substrate Cleaning for Silicon Processing
Authors: Ramm Juergen , Beck Eugen , Steiner Franz-Peter , Pixley Ralph E. , Eisele Ignaz 
Published: March 2011

ABSTRACTSilicon wafers as obtained from the manufacturer are immersed in a large area argon/hydrogen plasma for surface cleaning. The plasma discharge is maintained between a heated cathode and the grounded process chamber at discharge voltages of about 30 V for which discharge currents up to 100 A can be chosen. In this regime, neither the chamber walls nor the substrates are sputtered. Chemical reactions at the wafer surface are assumed to be mainly stimulated by low energy electron bombardment. The etch rates for diamond-like carbon (DLC) on silicon wafers were determined for selected discharge parameters and compared with the previously obtained results for SiO2. It was found that 5 minutes in-situ cleaning prepares the silicon wafers for homoepitaxy at 500 °C and higher substrate temperatures, whereas a short anneal at 500 °C was necessary to obtain low temperature homoepitaxy at 300 °C on (100) and 400 °C on (111) silicon. This seems to be due to hydrogen passivation of silicon during the cleaning procedure.
Comparison between Air and UV/Ozone Surfaces Passivation Methods of GaAs (100) Substrates
Authors: Ingo G.M. , Padeletti G. , Mattogno G. , Scandurra A. 
Published: March 2011

ABSTRACTAir and UV/ozone exposure have been used for growing sacrificial thin oxide layers on HCl etched GaAs (100) surfaces. Passive films have been then desorbed by vacuum thermal cleaning in order to prepare suitable surfaces for molecular beam epitaxy (MBE) growth. Structure, thickness and chemical composition of passive films and desorbed surfaces have been studied by ellipsometry and angle dependent X-ray photoelectron spectroscopy (ADXPS). The results have indicated an increased chemical reactivity of both arsenic and gallium during UV/ozone exposure, compared to that of air exposure, that produces Ga (III) oxide enriched films. Furthermore, XPS results have also shown that the thermal desorption behavior are different. In particular, GaAs (100) after short term UV/ozone exposure and oxide film desorption, has an As/Ga surface atomic ratio close to unity and a level of carbon contamination below the XPS detectability. On the contrary, air exposed surfaces never have a stoichiometric composition and carbon is not completely removed by a vacuum heating.
Structure of Sulphur-Passivated InP(100)-(1×1) Surface
Authors: Lu Z.H. , Tao Y. , Yang B.X. , Feng X.H. , Mitchell D.F. , Yelon A. , Graham M.J. , Sacher E. 
Published: March 2011

ABSTRACTX-ray photoelectron spectroscopy, X-ray photoelectron diffraction, and S K edge X-ray absorption near-edge structure were used to characterize the air-stable S-passivated InP(100)-(lxl) surface prepared in (NH4)2S solution. The results show that one monolayer of sulphur which is bonded only to In is adsorbed on the surface. The S is found to occupy bridge-bonded sites, and the orientation of the In-S bond is determined to be in the [011] azimuth, with an In-S-In bridge-bond angle of about 100°.
tudy of the Surface Cleaning Effects to the InGaAs Quantum Well Wires by Atomic Force Microscopy and Photoluminescence Spectroscopy
Authors: Tan I-Hsing , Stone Song Shi , Prater Craig , Mirin Richard , Hu Evelyn , Bowers John , Merz James , Hansma Paul 
Published: March 2011

ABSTRACTThe efficacy of residual photoresist removal on the top surface of the InGaAs QWW grating and the effects of surface oxides on the optical property of quantum well wires (QWWs) were examined through atomic force microscopy (AFM) and photoluminescence (PL) spectroscopy. Different resist removal treatments, including acetone, ozone and diluted HC1 were evaluated. Both AFM and PL measurements reveal that with the surface cleaning processing we have developed, high luminescence efficiency from the QWWs is conserved after removal of the residual photoresist.
Cleaning and Oxidation of Heavily Doped Si Surfaces
Authors: Yasaka T. , Uenaga S. , Yasutake H. , Takakura M. , Miyazaki S. , Hirose M. 
Published: March 2011

ABSTRACTHF-treated Si surfaces and the oxidation kinetics in pure water or in clean room air have systematically been studied by x-ray photoelectron spectroscopy (XPS). The oxidation of heavily-doped n-type Si appears to proceed parallel to the surface, resulting in the layer-by-layer oxidation. The oxide growth rate in pure water for heavily-doped n-type Si is significantly higher than that of heavily-doped ptype Si. This is explained by the electron tunneling from the Si conduction band to adsorbed O2 molecules to form the O2 state. O2 ions easily decompose and induce a surface electric field, enhancing the oxidation rate. The growth rate of native oxide on heavily-doped n-type Si is less sensitive to the crystallographic orientations than the case of lightly doped Si where the steric hindrance against oxygen molecules significantly lowers the oxidation rate of the (110) and (111) surfaces. We suggest that the decomposed oxygen can penetrate into Si without steric hindrance. It is also found that the oxidation of heavily-doped n-type Si in pure water is effectively suppressed by adding a small amount (10 ∼ 3600 ppm) of HCI.
Low Temperature Epitaxy on H-Passivated Si(100) by Sputter Deposition
Authors: Chen Chau-Chen , Smith Donald L. , Anderson Greg , Hagstrom Stig B. 
Published: March 2011

ABSTRACTConventional preparation of Si for epitaxy involves high-temperature heating to remove surface oxide or to remove H passivation left by HF cleaning. Attempted MBE on H-passivated Si(100) has resulted in amorphous films below 640 K. We show that the use of ion beam sputtered Si allows the growth of thick (300 nm) epitaxial layers on H-passivated Si(100) at high rate (0.65 nm/s) and at 483 K, well below the H desorption temperature. This is because the sputtered Si has translational kinetic energy of tens of eV, well above the Si-H bond strength of a few eV, so that the passivating H does not block the epitaxial bonding sites as it does in MBE. The ability to grow epitaxially on H-passivated Si not only reduces the maximum Si processing temperature required, but also keeps the substrate passivated against contamination until the onset of deposition.During deposition, the LEED pattern changes gradually from the 1 × 1 of the H-passivated Si to the 2 × 1 reconstruction of bare or partially hydrogenated Si(1 00), yet SIMS shows that little of the disappearing H accumulates at the substrate interface or in the bulk of the film. Thermal desorption spectra show that its bonding remains similar to that on the substrate surface. Thus, it appears to float to the surface of the depositing film and become gradually knocked off of the surface over the course of a few hundred nm of deposition. Cross-sectional TEM lattice imaging shows near-perfect ordering of the epilayer and a barely distinguishable substrate interface.
In Situ Analysis of Surface Contaminant Desorption during Low-Temperature Silicon Substrate Cleaning using Reflection Electron Energy Loss Spectrometry
Authors: Wong Selmer S. , Nikzad Shouleh , Ahn Channing C. , Smith Aimee L. , Atwater Harry A. 
Published: March 2011

ABSTRACTWe have employed reflection electron energy loss spectrometry (REELS), a surface chemical analysis technique, in order to analyze contaminant coverages at the submonolayer level during low-temperature in situ cleaning of hydrogen-terminated Si(100). The chemical composition of the surface was analyzed by measurements of the C K, O K and Si L2,3 core loss intensities at various stages of the cleaning. These results were quantified using SiC(100) and SiO2 as reference standards for C and O coverage. Room temperature REELS core loss intensity analysis after sample insertion reveals carbon at fractional monolayer coverage. We have established the REELS detection limit for carbon coverage to be 5±2% of a monolayer. A study of temperature-dependent hydrocarbon desorption from hydrogen-terminated Si(100) reveals the absence of carbon on the surface at temperatures greater than 200°C. This indicates the feasibility of epitaxial growth following an in situ low-temperature cleaning and also indicates the power of REELS as an in situ technique for assessment of surface cleanliness.
NH4F Pre-Cleaning of Silicon (100) for UHV-CVD Epitaxy
Authors: Cohen Susan L. , Blum Joseph , D'Emic Christopher , Gilbert Monica , Cardone Frank , Stanis Carol , Liehr Michael 
Published: March 2011

ABSTRACTNH4F etching of Si(100) surfaces has been evaluated as a pre-clean for UHV-CVD low temperature epitaxy of silicon. A combination of surface science and epitaxial growth experiments have found that while the NH4F treatment provides surfaces which have less carbon, oxygen and fluorine impurities than a standard dilute HF pre-clean, there is a significant density of crystallographic defects in the epitaxial films which limits the usefulness of this approach.
The Impact of Alpha-Radiolysis on the Release of Radionuclides from Spent Fuel in a Geologic Repository
Authors: Neretnieks Ivars 
Published: March 2011

ABSTRACTSpent nuclear fuel buried in deep geologic repositories may eventually be wetted by water. The alfa-radiation will radiolyse the water and produce hydrogen and oxidizing agents, mainly hydrogen peroxide and oxygen. The hydrogen will escape by diffusion and the oxidizing agents may attack the canister materials, oxidize the uranium oxide matrix or diffuse out and oxidize reducing agents in the surrounding rock.The rate of radiolysis has been computed recently within the Swedish nuclear fuel safety projects KBS. It is strongly influenced by the amount of available water and by the presence of dissolved iron. The movement of the oxidizing agents out from the canister and their reaction with the reducing agents (mainly ferrous iron) in the Swedish crystalline rock has been modelled as well as the movement of the radionuclides within and past the redox front. Some substances such as uranium, neptunium and technetium will precipitate at the redox front and will be withdrawn from the water to a considerable extent.
Thermodynamic Coupling of Heat and Matter Flows in Near-Field Regions of Nuclear Waste Repositories
Authors: Carnahan C. L. 
Published: March 2011

ABSTRACTIn near-field regions of nuclear waste repositories, thermodynamically coupled flows of heat and matter can occur in addition to the independent flows in the presence of gradients of temperature, hydraulic potential, and composition. The following coupled effects can occur: thermal osmosis, thermal diffusion, chemical osmosis, thermal filtration, diffusion thermal effect, ultrafiltration, and coupled diffusion. Flows of heat and matter associated with these effects can modify the flows predictable from the direct effects, which are expressed by Fourier's law, Darcy's law, and Fick's law. The coupled effects can be treated quantitatively together with the direct effects by the methods of the thermodynamics of irreversible processes. The extent of departure of fully coupled flows from predictions based only on consideration of direct effects depends on the strengths of the gradients driving flows, and may be significant at early times in backfills and in near-field geologic environments of repositories. Approximate calculations using data from the literature and reasonable assumptions of repository conditions indicate that thermal-osmotic and chemical-osmotic flows of water in semipermeable backfills may exceed Darcian flows by two to three orders of magnitude, while flows of solutes may be reduced greatly by ultrafiltration and chemical osmosis, relative to the flows predicted by advection and diffusion alone. In permeable materials, thermal diffusion may contribute to solute flows to a smaller, but still significant, extent.
Experimental Studies of Packing Material Stability
Authors: Allen C.C. , Lane D.L. , Palmer R.A. , Johnston R.G. 
Published: March 2011

ABSTRACTThe Basalt Waste Isolation Project is conducting experiments to assess the stability of bentonite (sodium montmorillonite)and crushed basalt as waste package packing materials in a nuclear waste repository in basalt. The experiments are designed to identify changes in physical, chemical, and mineralogical properties that these materials could undergo in the repository environment. A series of bentonite dehy-dration experiments showed that after 1 year at 370°C the clay's structural and swelling properties were preserved and only reversible dehydration occurred. At 440°C, however, irreversible dehydration, collapse of the clay structure, and loss of swelling ability took place. Hydrothermal tests using bentonite, or an equal mixture of bentonite and basalt, along with synthetic groundwater, were also conducted. Abentonite + water experiment showed negligible structural alteration at 200°C, although some iron enrichment of the clay occurred. At 300°C, partial conversion of the mont-morillonite to an iron- and potassium-rich smectite occurred, along with the formation of secondary quartz and albite. An experiment in the basalt + bentonite + water system at 150°C resulted in partial etching of the basalt grains, but no detectable change in rock or clay mineralogy. At 300°C, the basalt was strongly etched. Furthermore, iron- and potassium-rich smectite apparently replaced montmorillonite as the dominant clay, and secondary silica, zeolites, and minor feldspar were formed. These mineral assemblages are thought to be metastable at 300°C, based on natural analogs. The kinetics and reaction paths of further transformations of packing materials are important areas for continued study.
Irradiation-Corrosion Evaluation of Metals For Nuclear Waste Package Applications in Grande Ronde Basalt Groundwater
Authors: Nelson J.L. , Westerman R.E. , Gerber F.S. 
Published: March 2011

ABSTRACTThe corrosion behavior of several iron-base and titanium-base alloys was studied in synthetic Grande Ronde Basalt groundwater at temperatures of 150°C to 2500°C and under irradiation dose rates to 2 × 106 rad/hr. The objective of these ongoing studies is to help select one or more materials for waste-package canisters that will maintain their integrity for time periods up to 1,000 yr in a nuclear waste repository constructed in basalt. The corrosion rates of iron-base alloys under irradiated conditions were generally 2 to 3 times as high as those obtained on similar materials under nonirradiated conditions. The titanium alloys exhibited low corrosion rates but absorbed significant amounts of hydrogen under irradiated conditions.
Stochastic Analysis of Groundwater Traveltime for Long-Term Repository Performance Assessment
Authors: Clifton P.M. , Baca R.G. , Arnett R.C. 
Published: March 2011

ABSTRACTThis paper describes a method of stochastically analyzing groundwater traveltime. The method uses a Monte Carlo technique to generate a suite of random spatial fields that are subsequently input to the groundwater flow and groundwater traveltime equations. Stochastic inputs to these equations can be (1) transmissivity (or hydraulic conductivity), (2) effective thickness (or effective porosity), or (3) boundary conditions. In a transient problem, storage coefficient (or specific storage) could also be stochastically treated. Spatial correlation in the random input fields is accounted for by means of a multivariate random-number generator, which requires the first two statistical moments of these fields to be specified. The output from the Monte Carlo analysis is a suite of groundwater traveltime realizations that can be used to derive exceedance probabilities. These probabilities provide a measure of the degree of confidence in meeting set criteria.A preliminary application of this method using data from the deep basalts beneath the Hanford Site is also presented. The results illustrate how this method can be used to evaluate compliance with a technical criterion relating to groundwater traveltime.
The Corrosion of Spent Uo2-Fuel in Synthetic Groundwater
Authors: Forsyth P S , Svanberg K , Werme L 
Published: March 2011

ABSTRACTSegments of fuel and clad have been leached in deionized water and in groundwater. The leachants were centrifuged through membrane filters. Both centrifugate and the filters were analysed for U, Sr-90, α- and γ-emitters. The results are discussed in terms of preferential leaching, solubility limitations and adsorption effects. For U an apparent saturation at about 800 ppb was observed. Pu also appeared to attain saturation at a few ppb. For Sr the leach rate was 3·10-7/d after ca 400 days. Attempts to impose reducing conditions showed decreased leach rates.
Multicomponent Leach Tests in Standard Canadian Shield Saline Solution on Glasses Containing Simulated Nuclear Waste
Authors: Heimann Robert B. , Wood Donald D. , Hamon Richard F. 
Published: March 2011

ABSTRACTLeaching experiments on borosilicate glass frit and simulated nuclear waste glasses were performed as a preliminary to leaching experiments on glasses incorporating radioactive waste. The experimental design included (i) simulated waste glass, (ii) ASTM Grade-2 titanium container material, (iii) clay buffer material, (iv) Standard Canadian Shield Saline Solution, and (v) granitic rock.Cumulative fractions of release for boron were determined, as well as the solution concentrations of silicon, iron, strontium and cesium. The leach rates for boron after 28 d were approximately 5x10-6 kg.m-2 .8-1 for experiments in stainless steel vessels, and 2xl0-7 kg.m-2 .s-1 in Hastelloy* vessels. There is an apparently strong relationship between the clay/groundwater ratio, the concentration of iron in the solution, and the concentrations of silicon, strontium, and cesium.
An Integrated Approach to the Description of Radionuclide Release and Transport in the Geosphere
Authors: Neretnieks Ivars , Rasmuson Anders 
Published: March 2011

ABSTRACTThe basic models for predicting the transport of radionuclides in the near field and in the geosphere (far field), used in the Swedish KBS-3 work, are presented. The transport of corrosive substances to the canister is also accounted for.
Geohydrology Surrounding a Potential High-Level Waste Repository in Richton Salt Dome, Mississippi
Authors: Teubner Michael D. , Murphy Peter J. , Swanson Owen E. 
Published: March 2011

ABSTRACTA site investigation study is currently being performed in the vicinity of Richton Salt Dome, Mississippi. Description of the geohydrology setting of the area is integral to assessment of the site's ability to isolate nuclear waste, and to the design and construction of repository shafts and seals. Two ground-water models are being developed to assist the evaluations and design efforts: a regional model to better define the regional groundwater flow system; and a near-dome model to refine the flow system around the dome. Initial results suggest that present conditions of ground-water flow away from the dome will meet the hydrologic requirements for a suitable repository site.
Far Field Flow Uncertainty Analysis for the Palo Duro Basin
Authors: Devary Joseph L. , Battelle Battelle , HARPER William V. , ONWI Onwi , SYKES Jon F. , WILSON John L. 
Published: March 2011

ABSTRACTIn order to license an underground nuclear waste repository DOE must demonstrate its safety. Sensitivity and uncertainty analyses play a critical role in both performance assessment and licensing. This paper focuses on the application of a variety of techniques to arrive at a comprehensive sensitivity and uncertainty analysis for performance measures relating to ground-water travel in the Wolfcamp aquifer of the Palo Duro Basin (see Figure 1). Scenario analysis is not examined; rather, analysis is based on well understood models for flow in porous media. Both Monte Carlo and first order second moment techniques are utilized to obtain output uncertainties. The approach results in a logical, comprehensive analysis that blends both deterministic and statistical methods. It provides for an extensive screening of the parameters, accounts for parameter and spatial correlations, and quantifies uncertainties for the major performance measures in ground-water travel. The results are useful for both licensing and the identification of additional data needs.
The Composition and Stratigraphic Distribution of Materials in the Lower San Andres Salt Unit 4
Authors: Hubbard N. , Livingston D. , Fukui L. 
Published: March 2011

ABSTRACTThe salt bed in depositional cycle 4 of the Permian Lower San Andres Formation, Palo Duro Basin, Deaf Smith County, Texas consists of massive salt interlayered with discrete bands and beds of anhydrite and claystone. The massive salt consists of about 90% halite, with 7% anhydrite and 3% clays disseminated in and among the halite crystals.The halite in this salt bed contains fluid inclusions filled with a (Na, K, Mg)Cl brine, with an average Mg concentration of about 50,000 mg/liter. The anhydrite in the salt will saturate the brines in CaSO4, which in turn may coat the waste package with anhydrite because of the retrograde solubility of CaSO4. This may increase waste package lifetime to failure by corrosion.
The Geomicrobiology of Nuclear Waste Disposal
Authors: West Julia M. , McKinley Ian G. 
Published: March 2011

ABSTRACTThe geomicrobiology of high-level nuclear waste disposal is a new field in the area of nuclear waste management. Until recently the likelihood of microbial contamination in a deep repository had not been considered, but possible biogeochemical effects of repository materials, radionuclide transport and groundwater chemistry must now be realistically assessed.This work was funded by the UK Department of the Environment and the Commission of the European Communities.
The Role of Colloids in Nuclear Waste Disposal
Authors: Avogadro A. , Marsily G.De 
Published: March 2011

ABSTRACTAspects of formation and characterization of a radioactive colloidal fraction released by the waste form or produced by association with microcolloids naturally existing in ground water or produced either by corrosion of container material or by degradation of backfill material are discussed. A filtration model has been developed in order to describe colloidal transport under field conditions. Comparison between data obtained with laboratory column experiments and theoretical evaluations is presented.