bluuebunny/crossref_metadata_2025_split huggingface dataset:
Crack formation due to annealing of Al2O3 films grown on Si(100) by MOCVD
Authors: Singh M. P. , Shivashankar S.A. 
Published: April 2011

ABSTRACTWe report crack formation in alumina films grown on Si(100), caused by annealing in a controlled oxidizing ambient. The films were grown in a low-pressure CVD reactor, using aluminium acetylacetonate as precursor. High purity argon and nitrous oxide were employed as carrier and oxidizing gas, respectively. The films were characterized by optical microscopy and SEM/EDAX. The proportion and chemical nature of the heteroatoms, namely C and H, incorporated into the films from the precursor, were characterized by XPS, and FTIR. As-deposited films do not exhibit any cracks, while post-deposition annealing results in cracks. Apart from the delamination of the films, annealing in nitrous oxide ambient leads to an unusual crack geometry, which we term the “railway-track”. These twin cracks are very straight and run parallel to each other for as much as several millimeters. Often, two such linear tracks meet at exactly 90°. Between some of these tracks lie bullet-like structures with very sharp tips, oriented in a specific direction. As cracks are generally activated by residual stress, both thermal and intrinsic, the origins of the stresses that generate these linear cracks are discussed. The redistribution of stress, arising from the removal of C and H during annealing, will also be discussed. An attempt has been made to correlate the formation of cracks with the crystal structure of the film.
Initial Stages of InAs Quantum Dots Evolution in GaAs/AlAs Matrixes
Authors: Yakimov Michael , Tokranov Vadim , Katnelson Alex , Oktyabrsky Serge 
Published: April 2011

ABSTRACTWe have studied the first phases of post-growth evolution of InAs quantum dots (QDs) using in-situ Auger electron spectroscopy in conjunction with Reflection High Energy Electron Diffraction (RHEED). Direct evidence for InAs intermixing with about 6ML (monolayers) of the matrix material is found from Auger signal behavior during MBE overgrowth of InAs nanostructures. Re-establishment of 2D growth mode by overgrowth with GaAs or AlAs was monitored in single-layer and multi-layer QD structures using RHEED. Decay process of InAs QDs on the surface is found to have activation energy of about 1.1 eV that corresponds to In intermixing with the matrix rather than evaporation from the surface.
Morphological Evolution of Ag/Mica Films Grown by Pulsed Laser Deposition
Authors: Warrender Jeffrey M. , Aziz Michael J. 
Published: April 2011

ABSTRACTMany vapor-deposited metal-on-insulator films exhibit a morphological progression with increasing thickness consisting of several distinct stages: (1) nucleation of 3-dimensional na-nocrystalline islands; (2) elongation of the islands; (3) film percolation. Here we report a study of this progression during Pulsed Laser Deposition (PLD), a technique for film deposition that differs from thermal deposition in that the depositing species arrive in short energetic bursts, leading to instantaneous deposition fluxes orders of magnitude higher than can be achieved in thermal growth. Atomic Force Microscopy reveals that advancement through this same morphological progression occurs at lower thickness in PLD films relative to films grown under comparable conditions by thermal deposition, with PLD films having lower RMS roughness at a given thickness. We also observe that for a constant amount deposited per pulse, films deposited at higher laser pulse frequency are further advanced in morphological state. Kinetic Monte Carlo simulations reveal that PLD nucleation behavior differs from that of thermally deposited films, and this can account for the observed differences. Simulations also reveal a scaling of the percolation thickness with pulse frequency that is consistent with experiment.
Morphology Control of Pulsed-Laser Deposited Ag Quantum Dots
Authors: Machi Kinuyo , Nagare Sanshiro , Hamada Kenji , Senna Mamoru 
Published: April 2011

ABSTRACTSelf-organized Ag nanodots were deposited on Si(100) by a pulsed laser deposition method. A compact apparatus was specially developed for this purpose with Nd:YAG-laser. Factors dominating size and morphology of the nanodots were examined by systematically varying species and pressure of the gas in the deposition chamber, deposition time, and the target –substrate distance (TSD). Pulse frequency (10Hz), pulse width (8ns) and laser wavelength (266nm) were kept constant. The dot size increased with pressure in the range between 0.005Pa to 1Pa, in Ar gas. At pressures as high as 100Pa, dot size decreased again with slightly different morphology. Increasing deposition time from 3, 5, to 10min brought about an increase in the average dot size from 5±2.1nm, 9±2.4nm, 10±3.0nm, respectively, under the constant Ar pressure, 100Pa. It is particularly to be noted that decreasing TSD from 100mm to 50mm brought about an increase in the dot size from 5±2.1nm to 9±3.3nm at Ar pressure, 100Pa, and deposition time, 3min. We discuss factors making self-organized Ag nanodots, and proposed key values to evaluate homogenize of dots assembly.
Bismuth-Induced Layer-by-Layer Growth in the Homoepitaxial Growth of Fe(100)
Authors: Kamiko Masao , Chihaya Hiroaki , Mizuno Hiroyuki , Xu Junhua , Kojima Isao , Yamamoto Ryoichi 
Published: April 2011

ABSTRACTWe have investigated the effect of Bi on the homoepitaxial growth of Fe(100) by means of reflection high-energy electron diffraction (RHEED). It was clearly found that Bi induces layer-by-layer growth of Fe on Fe(100)-c(2×2)O reconstruction surface. The result of the dependence of the growth behavior as a function of Bi layer thickness suggests that there is optimum amount of Bi surfactant layer that induces the smoother layer-by-layer growth. A strong surface segregation of Bi was found at the top of surface and acts as a surfactant by promoting the interlayer transport.
Simulating Oxide Interfaces and Heterointerfaces
Authors: Harding John H. , Duffy Dorothy M. , Harris Duncan J. 
Published: April 2011

ABSTRACTInterfaces can be considered at a variety of length scales. All interfaces except grain boundaries are dielectric interfaces. In many cases, the geometric constraints of matching two lattices must be considered, together with the misfit strains that are often present. Continuum mechanics is useful for tackling such problems. In many cases, however, the local ordering of ions must also be considered. Atomistic simulation is therefore necessary, together with the problems associated with large length scales and long time scales. We discuss a number of examples to illustrate the issues involved and the compromises between different approaches that must be made.
The Effect of Y on the Strength of FeCrAl Alloy/Sapphire Interfaces
Authors: Basu Soumendra N. , Gupta Vijay K. 
Published: April 2011

ABSTRACTThe effect of Y on the interfacial strength of the FeCrAl/sapphire system has been quantitatively measured by the laser-spallation technique in order to understand the ‘reactive element effect’. The presence of Y improved the interfacial strength of the FeCrAl/sapphire interface in the as-deposited state from 330±31 MPa to 686±36 MPa. However, after a high temperature anneal of 16 hours at 850°C, the interfacial strength of the Y-free samples increased to 545±68 MPa, while the interfacial strength of Y-containing sample decreased to 599±22 MPa. The increase in the interfacial strength of the Y-free films was attributed to an improvement in the crystalline quality of the interface. The decrease in interfacial strength of the annealed Y-containing film in spite of the improvement in the crystalline quality of the interface was attributed to the depletion of Y at the interface due to formation of Y2O3 precipitates, again consistent with the view that Y improves the strength of FeCrAl/sapphire interfaces significantly.
Stabilization of Indium Tin Oxide Films to Very High Temperatures
Authors: Gregory Otto J. , You Tao , Platek Michael , Crisman Everett 
Published: April 2011

SummaryThin film strain gages based on indium-tin-oxide (ITO) are being developed to measure to static and dynamic strain at temperatures approaching 1500°C. These ceramic strain gages exhibit excellent oxidation resistance and high temperature stability, surviving more than 25 hours of testing in air at 1470°C. Electron spectroscopy for chemical analysis (ESCA) studies indicated that interfacial reactions between ITO and alumina can increase the stability of ITO at elevated temperature. Solid state diffusion of aluminum into the ITO at these temperatures can produce a very stable ITO/Al2O3 solid solution [1, 2]. To determine the nature of the interfacial reaction product, ITO films were deposited onto both Al2O3 and AlN surfaces and thermally cycled to 1500°C. AlN films were used to reduce/eliminate oxygen transport to the interface, so that aluminum-indium interactions alone could be studied. ITO films were deposited onto Al2O3 and AlN films, which were rf sputtered on platinum-coated alumina substrates. The resulting ESCA depth files showed that an interfacial reaction had occurred between the ITO and the Al2O3 and AlN. The presence of two new indium-indium peaks at 448.85 and 456.40eV, corresponding to the indium 3d5 and 3d3 binding energies were observed in both cases; i.e. the AlN and the Al2O3. These binding energies are significantly higher than those associated with stoichiometric indium oxide. In addition, aluminum doped ITO films were formed by co-sputtering from multiple targets and electrical stability of these films was compared to undoped ITO films over the same temperature range (25–1500°C) [1–4].
Chemical Structure of N Atoms Incorporated Into 1 nm-thick SiO2/Si as Revealed with the Dissolution and Hydrogenation in Hydrofluoric Acid
Authors: Mizuta Naomi , Watanabe Satoru 
Published: April 2011

ABSTRACTBy detecting vibrational frequencies for N–H structures, the chemical states of N atoms at silicon nitride on silicon, SiN/Si, and silicon oxide with nitrogen on silicon, SiO(N)/Si, systems were deduced after being chemically decollated with H atoms in dilute HF solution. Using the fact that the decollation was associated with the dissolution of these films, we obtained their depth profile. The frequency was increased to an extent of 10 cm-1 by the existence of a thin oxide layer between the SiN layer and the Si substrate. The N–H structure bound to the Si substrate was observed at 3390 cm-1 just before the completely removal of the surface layer. We also observed the NH structure of crystal SiN form, whose frequency was unchanged to be 3325 cm-1. The same technique was applied to detect the chemical structure of the N atoms in an ultra-thin SiO(N) with 5% of the N atoms. The frequency peak of the bulk N structure was observed with that of OH structures. The peak was shifted from 3375 cm-1 to 3405 cm-1 at the interface region, suggesting densification of the film in the interface region. Prior to complete removal, we observed the surface state of the N atoms and the H atoms. Then the frequency of the NH was unaffected by the film formed with the various methods. No SiH structure was observed on the resultant film surface during etching.
Direct Determination of the Stacking Order in Gd2O3 Epi-Layers on GaAs
Authors: Yacoby Yizhak , Sowwan Mukhles , Pindak Ron , Cross Julie , Walko Don , Stern Ed , Pitney John , MacHarrie Robert , Hong Minghwei , Clarke Roy 
Published: April 2011

ABSTRACTWe have used Coherent Bragg Rod Analysis (COBRA) to investigate the atomic structure of a 5.6 nm thick Gd2O3 film epitaxially grown on a (100) GaAs substrate. COBRA is a method to directly obtain the structure of systems periodic in two-dimensions by determining the complex scattering factors along the substrate Bragg rods. The system electron density and atomic structure are obtained by Fourier transforming the complex scattering factors into real space. The results show that the stacking order of the first seven Gd2O3 film layers resembles the stacking order of Ga and As layers in GaAs then changes to the stacking order of cubic bulk Gd2O3. This behavior is distinctly different from the measured stacking order in a 2.7 nm thick Gd2O3 in which the GaAs stacking order persists throughout the entire film.
Melt Infiltration Processing of Foams Using Glass-Forming Alloys
Authors: San Marchi C. , Brothers A. , Dunand D. C. 
Published: April 2011

ABSTRACTProcessing of foams from bulk metallic glass (BMG) alloys, using melt infiltration techniques, is reported for the first time. Foaming methods based on infiltration of two types of pattern materials are described: investment of a continuous refractory yielding very low relative density structures (5% dense relative to the BMG), and investment of a discontinuous refractory pellet bed yielding higher relative density (50–60% dense relative to the BMG). Both methods are capable of producing foam structures; however high surface area and diminished thermal conductivity, especially in lower density structures, make vitrification of the alloy difficult.
On Relaxation Kinetics in Liquid and Glassy Ag-Cu Metallic Alloy
Authors: Bakai Alexander S. , Lazarev Nikolai P. , Ngai Kia L. 
Published: April 2011

ABSTRACTMolecular dynamics simulations of structure, thermodynamic and kinetic properties of model metallic AgCu alloy are performed to elucidate its behavior at glass transition. In spite of small variations of inherent structure of the alloy the relaxation kinetics undergo dramatic changes at the glass transition. The time dependences of the mean square displacements and the non-Gaussianity parameter show the signatures of anomalous diffusion in an intermediate time region. Analysis of time evolution of van Hove correlation function indicates the existence both jump displacements and short-range cooperative atomic rearrangements. Below Tg these cooperative rearrangements do not contribute to long-range diffusion but they still dominate the relaxation at short time.
Assessment of Geochemical Containment Properties in the Near-field of a Deep Underground Repository
Authors: Pellegrini Delphine , De Windt Laurent 
Published: April 2011

ABSTRACTFor safety evaluation of deep repositories, the evolution of chemical containment properties of clayey barriers in spent fuel disposal tunnels are assessed using reactive transport modelling. The disturbances related to cement components are more particularly studied for relevant time scales (100,000 years) and dimensions. Theoretical distribution coefficients (Kd) and maximum concentrations are derived for Cs, Tc and U and their sensitivity to the system evolution estimated. Mineralogical transformations and ion sorption are shown to be interdependent mechanisms controlling the intensity and spatial expansion of the alkaline plume. Simulations for a normal diffusive scenario and an altered one involving an advective flow lead to limited perturbations of the mineralogy and containment properties of the multi-barriers system, but emphasize the possibility of a migration pathway through the excavation damaged zone.
Polymer Pendant Crown Thioethers for Removal of Mercury from Acidic Waste Streams-Characterization and Extraction Performance
Authors: Baumann Theodore F. , Fox Glenn A. , Nelson Art J. , Andrews Joy C. , Bishop Darrell B. , Reynolds John G. 
Published: April 2011

ABSTRACTThe removal and immobilization of mercury(II) ions from industrial waste streams is a difficult and expensive problem requiring a robust extractant that is resistant to corrosive conditions. We have now developed an acid-resistant thiacrown polymer that has potential utility as a selective and cost-effective Hg2+ extractant. A new crown thioether, 2-hydroxymethyl-1,4,8,11,14-pentathiacycloheptadecane ([17] aneS5-OH), was synthesized through reaction of 2,3-dimercapto-1-propanol with 4,7,10-trithiatridecane-1,13-di-p-toluenesulfonate; then treated with thionyl chloride to form 2-chloromethyl-1,4,8,11,14-pentathiacycloheptadecane ([17] aneS5-Cl); followed by conversion to 2-(N-methyl)aminomethyl-1,4,8,11,14-pentathiacycloheptadecane ([17] aneS5-NHMe), through reaction with methylamine. The synthesis of the 4-vinylbenzyl-substituted thiacrown was readily accomplished by treating with 4-vinylbenzyl chloride. Co-polymerization of the 4-vinylbenzyl-substituted thiacrown with DVB (80% divinylbenzene) using AIBN as the radical initiator generated the highly cross-linked crown thioether polymer. The polymer based material was tested for Hg(II) extraction activity from acidic solutions. The material was found to extract 95+% of the Hg in a pH range of around 1.5 to over 6.0, with contact times of less than 30 min and in the presence of high concentration of competing ions such as Pb, Cd, Al, and Fe. The spent polymer could also be stripped of the Hg2+ and reused without sufficient loss of loading capacity. Characterization of the binding sites by XPS and XAS show only some of the S atoms in the thiacrown participate in the binding of Hg. Our results indicate this polymer has the potential to treat highly acidic wastes efficiently. This thiacrown polymer is far more effective in extracting Hg2+ from aqueous solution than previously reported Hg2+ extrac-tants, not only being very fast and efficient and selective, but also independent of pH.
Investigation of reactor graphite processing with the carbon-14 retention.
Authors: Ojovan M. I. , Karlina O. K. , Klimov V. L. , Bergman G. A. , Pavlova G. Yu. , Yurchenko A. Yu. , Dmitriev S. A. 
Published: April 2011

ABSTRACTThe system C – Al – TiO2 has been demonstrated to be a strong candidate for the processing of irradiated reactor graphite waste with the retention of biologic hazardous carbon-14 in chemically and thermal stable corundum-carbide ceramics. The corundum-carbide ceramics is obtained from the powdered precursors blend through self-sustaining thermochemical reactions. Investigations of the system C – Al – TiO2 were carried out both theoretically and experimentally. The refining thermodynamic calculations of the phase composition of resulting end product were performed for a wide variety of components content in the system being investigated. Aluminium oxycarbides production was taken into account in the calculations. Thermodynamic functions of aluminium oxycarbides Al4O4C and Al2OC have been calculated for this purpose using currently available literature evidences and own assessments of missing data. On the basis of thermodynamic simulation the proportions of the source substances were determined, which result in the aluminium oxycarbides production. These simulation results have been supported by XRD-analysis of produced specimens. The experimental processing of reactor graphite was conducted by the use of self-sustaining reactions in C – Al – TiO2 powder blends. Test specimens were produced by mass ranging from 0.1 to 3 kg in the argon atmosphere. Various techniques were used to characterize the produced specimens. The compressive strength of specimens of corundum-carbide matrices produced ranges from 7 to 13 MPa. The leaching rates of Cs-137 and Sr-90 from specimens ranged between 10-4 and 10-5 g/(cm2.day) respectively. The carry-over of the carbon combined in carbon monoxide from the reacting mixtures during exothermic process may run up to 1% wt. that appropriates roughly to less than 0.01% wt. of the carbon-14 in the irradiated reactor graphite.
Characterization of Uranium Speciation in a Metallic Matrix
Authors: Curran Gini , Allen Patrick G. , Caputo Daniel F. , Czerwinski Ken R. 
Published: April 2011

ABSTRACTThree metallic slag samples recovered from the site of their inadvertent creation several decades after the fact were sectioned and analyzed to determine uranium speciation to evaluate environmental behavior as well as assess proliferation resistance of the waste form. Uranium concentration in the highly inhomogeneous samples was up to 5% by weight as determined by gamma spectroscopy. Sample sections were milled in a hardened steel ball mill for x-ray absorption spectroscopy analysis (XAS). Powders were digested in a mixture of heated concentrated nitric acid and peroxide and analyzed for elemental content using ICP-AES and ICP-MS. Though elemental content of the samples varied widely, high concentrations of Al were consistently found. Other metals of significance were Ti, Fe, Ni, Cu, Zn, and Sn. High Pb concentrations were occasionally found. XAS analysis revealed the samples contained primarily uranyl and another phase identified as a uranium-aluminum melt.
A Study on the Chemical Forms and Migration Behavior of Carbon-14 Leached from the Simulated Hull Waste in the Underground condition
Authors: Kaneko Satoru , Tanabe Hiromi , Sasoh Michitaka , Takahashi Ryota , Shibano Takayuki , Tateyama Shinji 
Published: April 2011

ABSTRACTThe chemical forms of carbon leaching from carbon-containing Zr and Fe-based metallic materials have been investigated to improve the estimation of the contribution of C-14 in the performance assessment of TRU waste disposal. Both organic and inorganic carbons were identified in the leached solution with carbon containing zirconium and steel, and the concentrations of total carbon (organic plus inorganic) in the leached solutions increased with time. The carbon concentrations in the leached solution for both metallic samples were higher at higher pH. With High Performance Liquid Chromatography (HPLC), organic carbons were identified to be low-molecular weight alcohols, carboxylic acids and aldehydes.To explore the chemical state of carbon in the matrix materials, the leaching experiments were carried out also for ZrC, Fe3C, the powder mixtures of carbon and zirconium, and of carbon and iron. The low-molecular weight organic carbons were detected only in the case of carbides (ZrC and Fe3C). The chemical forms of carbon in the zirconium alloy were suggested to be carbide or carbon by H.D. Smith[1]. The present result suggests that the chemical forms of carbon in zirconium or iron are mainly in the form of carbide.In the interest of performance assessment, the distribution coefficients of the organic carbon species identified in the leached solution for cement were obtained. As expected, some of them were shown to be larger than the values assumed in the performance assessment of Progress Report on Disposal Concept for TRU Waste in Japan[2].
Review of Corrosion Modes For Alloy 22 Regarding Lifetime Expectancy of Nuclear Waste Containers
Authors: Rebak Raúl B. , Estill John C. 
Published: April 2011

ABSTRACTAlloy 22 (UNS N06022) was selected to fabricate the corrosion resistant outer barrier of a two-layer nuclear waste package container. This paper reviews the main corrosion degradation modes that are predicted for the outer layer of the container. Current results show that the containers would perform well under general corrosion, localized corrosion and environmentally assisted cracking (EAC). For example, the general corrosion rate is expected to be below 100 nm/year and the container is predicted to be outside the range of potential for localized corrosion and environmentally assisted cracking.