bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cathodoluminescence, Electroluminescence, and Degradation of ZnCdSe Quantum Well Light Emitting Diodes
Authors: Nikiforov A. Yu. , Cargill G. S. , Guo S. P. , Tamargo M. C. , Chen Y.-C. 
Published: June 2019

AbstractWe have studied luminescence and degradation of a ZnCdMgSe/ZnCdSe/ZnCdMgSe QW LED grown by MBE and lattice matched to its InP substrate. Results have been obtained from time-resolved and bias-dependent cathodoluminescence spectroscopy and from electroluminescence spectroscopy. Reversible and irreversible variations in luminescence intensity were observed during bias cycling and electron bombardment. Cathodoluminescence from the QW LED was modeled by calculating current generation and transport, bias-dependent energy levels, envelope wave functions, overlap integrals, and carrier escape rates. Results of these calculations agree qualitatively, but not quantitatively, with bias-dependent intensity and wavelength changes observed in the experiments.
High-Performance AlGaN-Based Visible-Blind Resonant Cavity Enhanced Schottky Photodiodes
Authors: Kimukin Ibrahim , Biyikli Necmi , Kartaloglu Tolga , Aytür Orhan , Ozbay Ekmel 
Published: June 2019

AbstractWe have designed, fabricated and tested resonant cavity enhanced visible-blind AlGaN-based Schottky photodiodes. The bottom mirror of the resonant cavity was formed with a 20 pair AlN/AlGaN Bragg mirror. The devices were fabricated using a microwave compatible fabrication process. Au and indium-tin-oxide (ITO) thin films were used for Schottky contact formation. ITO and Au-Schottky devices exhibited resonant peaks with 0.153 A/W and 0.046 A/W responsivity values at 337 nm and 350 nm respectively. Temporal high-speed measurements at 357 nm resulted in fast pulse responses with pulse widths as short as 77 ps. The fastest UV detector had a 3-dB bandwidth of 780 MHz.
Investigation of Thin Film Growth of B12As2 by Chemical Vapor Deposition
Authors: Nagarajan R. , Edgar J.H. , Pomeroy J. , Kuball M. , Aselage T. 
Published: June 2019

AbstractThe chemical vapor deposition of icosahedral boron arsenide, B12As2, on 6H-SiC (0001) (on and off-axis) substrates was studied using hydrides as the reactants. The effects of temperature and reactant flow rates on the phases deposited and the crystal quality were determined. The growth rate increased with temperature from 1.5μm/h at 1100°C to 5 μm/h at 1400°C and decreased thereafter. X-ray diffraction revealed that the deposits were amorphous when the deposition temperature is below 1150° C. Above 1150°C, smooth B12As2 films were formed on 6H-SiC substrates with an orientation of (0001) B12As2 parallel to 6H-SiC (0001). Raman spectroscopy confirmed the strongly c-axis oriented nature of B12As2 film on 6H-SiC.
Solar Blind (Al,Ga)N Metal-Semiconductor-Metal Devices for High Performance Flame Detection
Authors: Mosca Mauro , Reverchon Jean-Luc , Grandjean Nicolas , Omnès Franck , Duboz Jean-Yves , Ribet Isabelle , Tauvy Michel 
Published: June 2019

AbstractIn this work we report on solar blind (Al,Ga)N photovoltaic metal-semiconductor-metal (MSM) detectors with a cutoff wavelength as short as ∼270 nm. (Al,Ga)N heterostructures, that allow backside illumination, were grown on sapphire substrates by both metalorganic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE). We observed that both the interdigitated electrodes and the contact areas contribute to the overall photocurrent. In order to avoid the parasitic current due to the contact pads, we developed a new process where the electrodes are deposited on the (Al,Ga)N surface whereas the contact pads are deposited on an insulator (dielectric) layer besides the electrodes. Some layers develop microcracks related to excess stress. In that case, we showed that both the dark current and the responsivity strongly depend on the crack density. By using our two-level process, we could reduce the parasitic effects of cracks on the dark current. Several dielectrics were tested and our results are reported; values of dark current < 10 fA have been measured at 10 V bias voltage. An extremely high performance can then be reached in these ultraviolet solar blind detectors.
High-Speed Solar-Blind AlGaN Schottky Photodiodes
Authors: Biyikli Necmi , Kimukin Ibrahim , Kartaloglu Tolga , Aytür Orhan , Ozbay Ekmel 
Published: June 2019

AbstractWe report high-speed solar-blind AlGaN-based Schottky photodiodes. AlGaN/GaN heterostructure device layers were grown on sapphire substrate. The devices were fabricated on AlGaN/GaN heterostructuresusing a microwave compatible fabrication process. Schottky photodiodes with Au and indium-tin-oxide (ITO) Schottky contacts were fabricated. Current-voltage, spectral responsivity, and high-speed measurements were performed. Both Schottky samples exhibited very low sub-pA dark currents at high reverse bias. A bias dependent spectral responsivity was observed with a peak responsivity of 89 mA/W at 267 nm, and 44 mA/W at 263 nm for Au and ITO-Schottky devices respectively. Time-based high-frequency measurements at 267 nm resulted in pulse responses with rise times and pulse-widths as short as 13 ps and 74 ps respectively. The fastest solar-blind detector had a record 3-dB bandwidth of 1.10 GHz.
GaN Epitaxial Growth by Molecular Beam Epitaxy utilizing AlGaN Buffer Layer with Nanopipes
Authors: Yun F. , He L. , Reshchikov M. A. , Morkoç H. , Jasinski J. , Liliental-Weber Z. 
Published: June 2019

AbstractGaN layers were grown on AlGaN with nanopipes by molecular beam epitaxy (MBE) and analyzed. AlGaN films were grown by MBE using rf-plasma nitrogen source under metal-rich condition. Within the Al composition range of 0.5-0.6, open-end nanopipes were formed at the surface of AlGaN films with a density of ∼6×109 cm-2 and a size ranging from 10 to 20 nm. These nanopipes, observed within ∼300 nm of the surface, served as a nanoporous AlGaN template for re-growth of GaN epilayers. GaN epilayers grown to different thickness by MBE were studied for their microstructural and optical properties. For an AlGaN buffer layer with dislocation density of 3×1010 cm-2 near its surface, the overlaying GaN layers with thickness ranging from 0.1 μm to ∼2μm were grown and analyzed by transmission electron microscopy for dislocation density. The GaN layer started with hexagonal islands on the nanopiped AlGaN and began to coalesce at about 0.1μm thickness. At a thickness of 2.0 μm, the dislocation density reduced to ∼1×109 cm-2. Low temperature photoluminescence data demonstrate the improved optical quality of GaN epilayer grown on the porous AlGaN buffer layer.
Pulsed Laser Deposition in a Zinc Alloy Corrosion Study
Authors: Guerrero-Penalva R. , Farías M.H. , Cota-Araiza L. 
Published: June 2019

AbstractA significant improvement in corrosion resistance of the protecting oxide of alloys has been observed when adding small amounts of reactive elements, such as yttrium, this effect has been called reactive element effect (REE). The general mechanism of the REE has not been determined yet. In this work, we study a growing of a yttrium oxide film and its interaction with the phases η and α that constitutes the alloy Zn-22Al-2Cu named ZinalcoTM The alloy's surface was coated by a pulsed laser deposition technique. The deposit is controlled and characterized by x-ray photoelectron spectroscopy. The mechanism by which the reactive element produce its effects in this alloy is explained by the preferential interaction among the active sites related to the zinc rich phase and enhancing aluminum movement toward the surface where it is oxidized and the protection film formed.
Studies on Ultra-short Laser Micro Structuring
Authors: Zergioti I. , Papazoglou D. G. , Gamaly E. , Rode A. , Fotakis C. 
Published: June 2019

AbstractA comparative study of the effect of ultrashort (0.5 ps) and short (30 ns) pulses on Laser transfer of Cr is presented in this paper. The dynamics of the process was investigated by stroboscopic schlieren imaging for time delays up to 3 νsec following the laser irradiation pulse. In contrast to the ns laser the directionality of the ejected material is very high in the case of the sub-ps laser process. The narrow angular divergence (3°) of the sub-ps pulses permits the direct dynamic transfer of the material and opens up new application possibilities for the fabrication of high spatial resolution microstructures.
Novel Growth of Biodegradable Thin Films via Matrix Assisted Laser Processing
Authors: Mercado A.L. , Fitz-Gerald J.M. , Johnson R. , Talton J.D. 
Published: June 2019

AbstractThe ability to controllably deposit polymers onto flat or curved surfaces in a quasi-dry environment while retaining native-like structure is of extreme importance to the medical and microelectronics communities. Current applications range from protective and conformal coatings for microelectronics to sustained drug delivery platforms in the pharmaceutical industry. In this research, biodegradable thin films of poly(DL-lactide-co-glycolide) (PLGA), were deposited onto flat substrates of Si and NaCl using a pulsed excimer laser, (λ= 248 nm) with fluences ranging from 0.1 – 1.0 J/cm2 via matrix assisted pulsed laser evaporation (MAPLE). Results are shown from scanning electron microscopy (SEM) to study morphological features and Fourier Transform Infrared Spectroscopy (FTIR), and Nuclear Magnetic Resonance (NMR) to measure chemical structure compared to original PLGA.
Direct Photo-Imprinting in High Photosensitive Organically Modified Germanosilicate (ORMOGSIL) Glasses
Authors: Jang Jae Hyeok , Kang Dong Jun , Bae Byeong-Soo 
Published: June 2019

AbstractDirect photo-imprinting of both surface relief pattern and refractive index modulation upon the organically modified germanosilicate (ORMOGSIL) glass using its large volume change was performed by ultraviolet exposure. A large refractive index increase up to 10-2 is induced by ultraviolet-induced densification in the ORMOGSIL glasses. The photosensitivity in the ORMOGSIL glass was enhanced by introducing a photo-polymerizable methcrylate group in the glass structure. Also, a surface AFM scans and optical microscope images of unetched sample show that the volume compaction in the ultraviolet illuminated region is associated with periodic pattern inscription.
Development, Application and Validation Of Models for Waste Package Long-Term Performance; Current Trends
Authors: Werme Lars O. , Grambow Bernd 
Published: June 2019

AbstractCurrent trends in modelling waste package performance are reviewed mainly from the perspective of the Swedish SKB studies. Examples are given, which illustrate the approaches for modelling different waste forms, i.e. HLW glass and spent nuclear fuel, and candidate canister materials, such as copper and steel. The relative importance of thermodynamics, reaction kinetics and near-field transport are discussed.
Corrosion Behavior of Container Materials in Grande Ronde Basalt Groundwater
Authors: Anantatmula R. P. , Fish R. L. 
Published: June 2019

AbstractThree candidate waste package container materials were tested for 5 mo at 200 °C in Hanford Site Grande Ronde Basalt groundwater (9.75 pH) under anoxic conditions (<0.1 mg/L dissolved oxygen in water). The materials were cast carbon steel (American Society for Testing and Materials (ASTM) A27), wrought carbon steel (American Iron and Steel Institute (AISI) 1020), cupro- nickel 90-10, and Fe9CrlMo steel. Testing was performed in 1-L titanium autoclaves at a pressure of 6.9 MPa and a flow rate of ∼O.02 mL/min. Anoxic conditions were achieved by constantly sparging the synthetic groundwater in the reservoir with argon. In addition, the groundwater was conditioned by placing a 2.54-cm layer of crushed basalt (∼O.635 cm average size) at the bottom of each autoclave. The average corrosion rates at 200 °C were 0.9 μm/yr for cupronickel 90-10 and Fe9CrlMo steel, 1.1 μm/yr for cast carbon steel, and 1.4 μm/yr for wrought carbon steel. Pitting was not detected in any of the specimens. Posttest analysis of the corrosion speci- mens indicated the formation of a thin film of iron smectite clay on the surface of all specimens. In addition, magnetite formation immediately adjacent to the specimen surface was observed in the iron-base alloys, consistent with previous investigations. Based on the present investiga- tions, all the materials exhibited significantly lower corrosion rates than were used in the Environmental Assessment (∼5 μm/yr) [1] for calculating acceptable container lifetimes. However, longer term general corrosion tests and tests to study the container materials susceptibility to other degradation modes are necessary prior to making a final evaluation of the suitability of these materials for use in fabricating high-level nuclear waste containers.
Leaching Studies of Cement-Glass Package Containing Sodium Borate
Authors: Okamoto Masahiro , Chino Koichi , Baba Tsutomu , Izumida Tatsuo , Kawamura Fumio , Kikuchi Makoto 
Published: June 2019

AbstractA new solidification technique using cement-glass, which is a mixture of sodium silicate, cement, additives, and initiator of the solidification reaction, was developed for sodium borate liquid waste generated from pressurized water reactor (PWR) plants. The cement-glass could solidify eight times as much sodium borate as cement could, because the solidifying reaction of the cement-glass is not hindered by borate ions.The reaction mechanism of sodium silicate and phosphoric silicate (initiator), the main components of cement-glass, was studied through X-ray diffraction and compressive strength measurements. It was found that three- dimensionally bonded silicon dioxide was produced by polymerization of the two silicates. The leaching ratio of cesium from the cement-glass package was one-tenth that of the cement one. This low value was attributed to a high cesium adsorption ability of the cement-glass and it could be theoretically predicted accordingly.
Integrated Testing of the Srl-165 Glass Waste Form
Authors: Phinney D.L. , Ryerson F.J. , Oversby V.M. , Lanford W.A. , Aines R.D. , Bates J.K. 
Published: June 2019

AbstractIntegrated testing of the important components of a glass waste form waste package has been performed in order to gain a better understanding of the processes of radionuclide release and transport in the near field environment. Based upon an interpretation of the depth of penetration of hydrogen in reacted SRL-165 glass we have modeled the radionuclide release from the glass as a combined process of (1) the diffusive exchange of alkalis and boron in the glass for hydrogen species in the solution (D=10−16 cm2/s) and (2) surface dissolution. Surface dissolution controls the release of components not exchanged by diffusion and takes place at a rate of 1.5-3.0 μm/yr. Subsequent to release the radionuclides may remain in the leach solution, diffuse into the tuff, or precipitate as secondary phases. Precipitation is particularly important for plutonium and americium. Diffusive transport of radionuclides through the tuff takes place at an extremely slow rate, D=10−16 cm2/s. As such, the mass of radionuclides incorporated in the tuff by diffusion during the tests is inconsequential relative to that in the leach solution (with the exception of plutonium) and can be ignored in mass balance calculations. Mass balance calculations based upon the release of radionuclides by surface dissolution of the glass waste form are in good agreement with observed solution chemistry when allowances are made for a pulse of dissolution early in the tests. This pulse may be due to either the rapid dissolution of high-energy surface features early in the inLegrated tests, or an initially high surface dissolution rate that decreases with time as silica saturation is approached [1], or a combination of the two.
On a Global Database Strategy for Public Engineering Decision Making
Authors: Fong Jeffrey T. , P.E.  
Published: June 2019

AbstractA historical review of how engineers contributed to the solution of societal (public) and individual (private) problems is presented, with emphasis on the last thirty years when computers began to alter drastically the practice of engineering.The concept of a 3-prong representation of the engineering decision making process, i.e., database, analysis, and judgment, is introduced. The importance of generating a suitable body of experimental and actual performance data and of coupling the database with a state-of-the-art analysis and extrapolation methodology for “public engineering” is illustrated in three case studies involving (a) the nuclear reactor safety study of 1975, (b) the Alaska pipeline weld defect assessment study of 1976, and (c) the Welding Research Council-Pressure Vessel Research Committee (PVRC) Round Robin Flaw Detection Program (1966-86) for thick-section steel welds.For most of the public engineering projects involving long-term prediction of performance from short-term test data, the time-honored approach of supplementing experimental or service data with engineering judgment is frequently open to a public challenge. To remedy the situation, a new approach of using both the personal computers (PC) and the mainframes to (a) accelerate the peer review of existing data, (b) design a strategy for acquiring new data, and (c) facilitate a regional or global exchange of field data with standardized format, is outlined.Application of the above approach to strengthen the judgment component of public engineering projects such as the management of high-level nuclear wastes is discussed through an example on the fatigue life prediction of stainless steel 304 piping and components.
Modeling of the Effect of Iron Corrosion Products on Nuclear Waste Glass Performance
Authors: Grambow B. , Zwicky H. U. , Bart G. , Bjorner I. K. , Werme L. O. 
Published: June 2019

AbstractExperiments [1], performed in the frame of the JSS-project (joint Japanese [CRIEPI], Swiss [NAGRA], Swedish [SKB] project), demonstrated that the effect of iron corrosion products on the long-term stability of HLW-glass depends on the effective surface area of the corrosion products. The experimental results were described quantitatively by thermodynamic and kinetic modeling with the computer codes GLASSOL and PHREEQE. The model interprets the effect in terms of surface sorption of a monolayer of silica molecules from solution. Silica saturation occurs in solution only, when all surface sites are occupied. The effect of bentonite is also considered. The agreement between calculations and experiment is about as good as in the case of modeling the glass-water reaction only.
Modelling of the Dissolution of Silicate Glasses by a Monte-Carlo Code (ETCH)
Authors: Dran J-C. , Langevin Y. , Doorhyee E. , Petit J-C. 
Published: June 2019

AbstractA Monte-Carlo code has been developed to infer dissolution rates of silicate glasses from their chemical composition. The glasses are considered as solid solutions of oxides and silicates, being divided into elementary cells of network formers, in which network modifiers can be incorporated. The different types of cells are randomly distributed and a resistance capacity to dissolution is assigned to each cell. We have tested the case where each cell is removed in a constant time as soon as it is in contact with the solution and a second one where each cell is dissolved in a time depending on the number of already dissolved neighbor cells. The first hypothesis leads to a percolation threshold when the proportion of fast etching cells reaches 25 %. Above, the dissolution front progresses via contiguous channels of fast etching cells. In the second hypothesis the variations of the etch rate with the proportions of each component are much closer to a linear combination of individual etch rates. These predictions have been successfully compared to experimental data on different series of silicate glasses of increasing complexity. Such a treatment could be straightforwardly extended to nuclear glasses.
Long-Term Corrosion Behavior of Copper-Base Materials in a Gamma-Irradiated Environment
Authors: Yunker Wlyne H. , Glass Robert S. 
Published: June 2019

AbstractThe U. S. Department of Energy is currently evaluating the feasibility of using copper-base materials for the manufacture of nuclear waste con- tainers. One site under consideration for geologic disposal of nuclear waste is at Yucca Mountain, Nevada. One feature of this waste repository will be the initial presence of ionizing gamma radiation at high dose rates, which may alter the corrosive medium. To evaluate such effects, three copper-base materials (pure copper, 7% aluminum-copper and 30% nickel-copper) have been exposed (presgntly up to 14 months) to a gamma radiation field of approxi- mately 1 × 104 roentgens/hr. The exposure environments have been: 1) both groundwater (regional to the repository site, although taken from a lower elevation) at 95°C; 2) the water-vapor saturated air phase above it; and 3) air/water vapor at 150°C. In addition to uniform corrosion, both pitting and crevice corrosion have been observed. Characterization of the corrosion layers by X-ray diffraction has shown the presence of mixed copper(I) and copper(II) oxides. Studies by Auger Electron Spectroscopy (AES) have also been conducted in order to further characterize the compositions and structures of these corrosion products.
An X-ray Absorption Spectroscopy Investigation of the Ta Site in Alpha-Recoil Damaged Natural Pyrochlores
Authors: Greegor R.B. , Lytle F.W. , Chakoumakos B.C. , Lumpkin G.R. , Ewing R.C. , Spiro C.L. , Wong J. 
Published: June 2019

AbstractX-ray absorption spectroscopy has been used to investigate the Ta LIII and LI absorption edges of metamict and annealed pyrochlore minerals A1-2B2O6Y0-1. The LIII edge absorption spectra exhibit a pronounced doublet in primary absorption resonance for the annealed samples which have the pyrochlore structure. The doublet in the LIII edge resonance becomes less pronounced and for some samples even merges Into a singlet for the samples in the unannealed, fully damaged (metamict) state. The LIII edge resonance of the damaged samples closely resembles Ta205 or disordered manganotantalite (MnTaNbO6 ), while the LIII edge resonance for the annealed samples most closely resembles the synthetic pyrochlore KTaWO6·H20. These results are supported by the Ta LIIIedge x-ray absorption data. Fourier transforms of the Ta LIII edge x-ray absorption fine structure (EXAFS) show first neighbor Ta-0 bond lengths of 1.96 ± 0.05 A for the samples in the annealed and metamict state.The complex structure of Ta205 is used as a model for the Ta-containing oxygen polyhedra in metamict pyrochlores, as it embodies some of the topologic features consistent with the reduction of long-range periodicity with increasing alpha-decay dose: 1) greater distortion of the primary coordination shell around Ta, 2) slightly increased mean second nearest-neighbor <Ta…X> distances, and 3) a wider distribution of second nearest-neighbor distances. These modifications are incorporated in a large unit cell with a b translation of 40 A.
Choice of French Clays as Engineered Barrier Cokponents for Waste Disposal
Authors: Coulon H. , Lajudie A. , Debrabant P. , Atabek R. , Jorda M. , Andre-Jehan R. 
Published: June 2019

AbstractResults are presented of physical measurements on candidate buffer materials for use in nuclear fuel waste disposal. The materials being considered as constituent elements of engineered barriers are essentially calcium smectite clays, in other terms swelling clays, coming from fourteen french deposits. The criteria for good candidates are mainly: smectite content in the clay materials, carbonate and organic material content and bulk density of the material, compacted under a pressure of 100 MPa.