bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dry Etching and Impurity Diffusion for Integrated Optoelectronics
Authors: Coldren L. A. 
Published: March 2011

ABSTRACTIn this paper the state-of-the-art in the use of dry etching for the fabrication of optoelectronic devices will be briefly reviewed, and to a lesser extent, the use of impurity-induced-disordering in these same structures will be discussed. In both instances, the author will rely heavily upon results from his own laboratory. This is being done in the interest of saving time and effort, although clearly at the risk of omitting some very important contributions from many others.
Deposition of Silicon Dioxide Layers on Inp by Flash C.V.D for Misfet Applications
Authors: Nissim Y. I. , Regolini J. L. , Bensahel D. , Post G. 
Published: March 2011

ABSTRACTSilicon dioxide films deposited on InP substrates are obtained in a reduced pressure, air and water cooled horizontal CVD reactor, with a rapid thermal heating. Deposition temperature as high as 700°C could be utilized with no degradation of the InP surface. At this temperature the resulting silicon dioxide films have excellent structural and electrical properties. MIS capacitors fabricated on InP substrates have been tested and a transistor behaviour has been observed on a first set of InP MISFETs. In situ processing for surface preparation prior to deposition can be utilized with this technique. A first attempt of in situ multiprocessing was carried on silicon substrates and is presented here.
New Al-Ni-Ge Contacts on GaAs; Their Structure and Electrical Properties
Authors: Liliental-Weber Z. , Washburn J. , Musgrave C. , Weber E. R. , Zuleeg R. , Lamper W. V. , Haas T. W. 
Published: March 2011

ABSTRACTThe structure and composition of the recently developed Al-Ni-Ge ohmic contacts to n-GaAs were investigated by transmission electron microscopy combined with secondary ion mass spectroscopy (SIMS) and Auger spectroscopy. The semiconductor/metal-alloy interface of these contacts remain very flat after annealing (500°C, for 1 min - contact resistance 1.4×10−6Ωcm2), in contrast to the widely used Au-Ni-Ge contacts. The metal sequence during deposition is found to be a critical factor in determining the electrical contact properties and the dispersion of the oxide layer on the semiconductor surface after chemical cleaning. Ge doping of the GaAs beneath the contact layer was observed by SIMS, and a tunneling mechanism through the n+GaAs:Ge layer was proposed to explain the ohmic properties of the contacts.
Impurity-Induced Layer Disordering in AlxGa1−xAs-GaAs Quantum well Heterostructures -
Authors: Deppe D. G. , Guido L. J. , Holonyak N. 
Published: March 2011

ABSTRACTSelective interdiffusion of Al and Ga at AlxGa1−x As-GaAs heterointerfaces can be carried out by conventional masking procedures and diffusion of acceptor impurities (e.g., Zn), or donor impurities (e.g., Si), or also by ion implantation. This process, impurity-induced layer disordering (IILD), makes it possible to convert quantum well heterostructures (QWHs) such as AlxGa1−xAs-GaAs superlattices (SLs) into bulk homogeneous AlyGa1−yAs where y is the average Al composition of the QWH or SL. Since th IILY process is maskable and thus selective, heterojunctions can be formed in directions perpendicular to the crystal growth direction, i.e., between as-grown “ordered” and IILD “disordered” regions. To date this process has been used most effectively in the fabrication of buriedheterostructure QW lasers, single and multiple stripe, where the disordered regions provide both optical and electrical confinement. The IILD process has also been used to advantage in the fabrication of high power laser diodes with non-absorbing “windows” at the laser facets and thus with better immunity from facet damage. In this paper we present data on the application of the IILD process to the fabrication of buried-heterostructure QW laser diodes. We also describe possible mechanisms by which the impurity-induced layer disordering proceeds based on Column III “Frenkel” defects and the influence of the crystal Fermi level on the defect solubility. These mechanisms are supported by experimental data.
Focused Ion Beam Implantation of GaAs-GaAlAs Quantum Well Structures
Authors: Petroff P. M. , Qian Xueyu , Holtz Per Olof , Simes R. J. , English J. H. , Merz J. , Kubena R. 
Published: March 2011

ABSTRACTThe effects of Implantation Enhanced Interdiffusion (IEI) in GaAs-GaAlAs quantum well structures are investigated. A Focused Ion Beam (FIB) source is used to implant narrow lines (500Å wide) with Ga+ ions. IEI in these structures is characterized by low temperature Cathodoluminescence. The dose effects and annealing kinetics dependence on IEI are presented. An unusual damage distribution which produces IEI deep below the surface is observed for the case of FIB implant. The possible origins of this effect and the limits of IEI for processing quantum wires and boxes are discussed.
Diffusion of Te or Zn into GaAs from Doped SiO2 Films by Rapid Thermal Processing
Authors: Kitagawa A. , Usami A. , Tokuda Y. , Wada T. , Kan H. , Murakami T. 
Published: March 2011

ABSTRACTThe n+ layers on semi-insulating liquid encapsulated Czochralski GaAs and p+ layers on Si-doped n-type GaAs were formed by rapid thermal diffusion (RTD) from Te- and Zn-doped oxide films, respectively. The Zn diffusion coefficient of the RTD sample at 850°C for 6s with the heating rate of 50°C/s is about two orders of magnitude higher than that of a similar furnacediffused sample at the same temperature. In addition, Zn and Te diffusion are strongly enhanced by the high heating rate of RTD. The shallow and abrupt p+n junction in GaAs is formed by RTD of Zn with the low heating rate. This shallow p+n junction is suitable for the construction of a photodiode. It is observed that the short wavelength spectral response (<800 nm) of the photodiode fabricated by RTD from Zn-doped oxide film decreases as the heating rate of RTD increases. Deep levels in these photodiodes were characterized by deep level transient spectroscopy. A electron trap EZ (Ec -0.57eV) is produced by RTD of Zn in the n-type substrate under p+n junction. The concentration of this trap is independent of the heating rate of RTD.
Laser Incorporation of Silicon into GaAs-AlGaAs Heterostructures
Authors: Epler J. E. , Ponce F. A. , Tramontana J. C. , Endicott F. J. , Paoli T. L. 
Published: March 2011

ABSTRACTRecently, a laser-scanning technique for patterning Si-induced layer disordering of GaAs-AlGaAs heterostructures has been reported. This process, called laserassisted disordering (LAD), has been successfully used to fabricate low threshold buried heterostructure lasers. In this report, the LAD process is studied in detail with scanning electron microscopy, transmission electron microscopy and secondary ion mass spectrometry. The results are discussed in the context of device fabrication.
Activation and Interdiffusion Characteristics in Implanted GaAs-AlGaAs Heterostructures on Si
Authors: Pearton S. J. , Short K. T. , Jones K. S. , Vernon S. M. 
Published: March 2011

ABSTRACTThe activation kinetics and diffusion behaviour of implanted Be and Si in two different types of MOCVD-grown GaAs-AlGaAs heterostructures on Si substrates were examined by electrochemical C-V profiling, secondary ion mass spectrometry and sheet resistivity measurements. The implanted Be displays a thermal activation energy of 0.70 eV and Si a thermal activation energy of 0.53 eV in heteroepitaxial material, similar to the comparable cases in homoepitaxial GaAs. In addition, there is no evidence for enhanced diffusivity of either species, at least for implants located away from the heterointerface. The remnant lattice disorder in the heterostructures caused by implantation and annealing is negligible compared to the as-grown disorder, as revealed by transmission electron microscopy.
Corrosion Behaviour of British Magnox Waste Glass in Pure Water
Authors: Zwicky H. U. , Grambow B. , Magrabi C. , Aerne E. T. , Bradley R. , Barnes B. , Graber Th. , Mohos M. , Werme L. C. 
Published: March 2011

ABSTRACTThe corrosion behaviour of Magnox Waste (MW) glass in deionized water has been investigated under the aegis of the Japanese-Swedish-Swiss (JSS) project. The studies carried out at PSI and BNFL included static leaching and corrosion layer characterization. The results were used by HMI to derive the modelling parameters for the MW glass with the PHREEQE/GLASSOL codes. The silica concentration was found to strongly influence the corrosion rate of the glass. The MW glass selectively retains Cs due to the formation of a Cs-Mg-Al-Si-O-rich layer on its surface.
Comparison of Glass and Crystalline Nuclear Waste Forms
Authors: Lutze W. , Ewing R. C. 
Published: March 2011

ABSTRACTNuclear waste forms may be divided into two broad categories: (1) single phase glasses with minor crystalline components (e.g., borosilicate glasses) and (2) crystalline waste forms, either single phase (e.g., monazite) or polyphase (e.g., SYNROC). This paper reviews the materials properties data that are available for each of these two types of waste forms. The prinicipal data include: (1) physical, thermal and mechanical properties, (2) chemical durability; (3) radiation damage effects. Complete data are only available for borosilicate glasses and SYNROC; therefore, this comparison focuses on the performance assessment of borosilicate glass and SYNROC.
Characterization of Waste Glasses Using Vickers Indentation, Short rod Fractometry and Drop Tests
Authors: Matzke Hj. , Scheibel H. G. , Friehmelt V. 
Published: March 2011

ABSTRACTThe German waste glasses VG 98/12.2 and GP 98/12.2, a Li-doped version GP 98/12.2 Li and a French waste glass SON 68–18–17 Li were produced as cylinders with different cooling rates and with different additions of simulated high level waste (HLW). The glass cylinders were drop-tested with speeds of up to 125 m/s. No measurable influences of glass compositions or cooling time could be identified. The dominant parameter in size distribution of fracture pieces and fines was the drop velocity (i.e. impact energy) whereas the effects of different glass temperatures during the drop tests and drop ground properties were negligible. Vickers indentation and short rod fractometry tests on pieces surviving the drop tests showed a small but scientifically interesting effect: the fracture toughness Kic increased in the order: base glass, glass containing fission products without noble metals, and glass containing all fission products, and there was a small increase in K[c for faster cooling rates. The effect of the noble metal precipitates was particularly pronounced and was due to crack branching or arrest at the metal precipitates. All these effects, however, were overcompensated by the influence of decreasing K[c in the presence of humidity and by effects of radiation damage: damaged Cm-244 doped glasses and all glasses stored and measured in a dry N2 atmosphere showed a larger increase in Kic than that due to the above differences in composition and cooling rates.
Dissolution Mechanisms of CaTiO3 - Solution Analysis, Surface Analysis and Electron Microscope Studies Implications for Synroc
Authors: Pham D. K. , Neall F. B. , Myhra S. , Smart R.ST.C , Turner P. S. 
Published: March 2011

ABSTRACTThe perovskite CaTiO3 is one of the major phases of the Synroc titanate mineral assemblage. Its chemical durability in an aqueous environment, which is relevant to the Synroc concept, has been investigated by solution analysis, surface analysis and electron microscopy. In general it has been found that dissolution due to base catalyzed hydrolysis is the most significant mechanism of attack; the results suggest that an ion exchange mechanism is confined to the first monolayer. Below 90°C the extent of attack, and release of Ca into solution, is limited by the formation of a titanaceous amorphous layer (” 100A thickness) which imposes a reaction constraint at the film-solid interface. Dissolution may also be constrained by the pH and Ca2+concentration in the bulk liquid. Above 90°C dissolution is relatively less constrained due to instability of the amorphous layer which is replaced by nucleation and epitaxial growth of TiO2 on the dissolving substrate. Thermodynamic stability of CaTiO3 for T< 90°C can easily be engineered into the waste repository, while hydrothermal stability (T > 90°C) is more difficult to achieve.
Artificial Compounds of the Crandallite Type; A new Material for Separation and Immobilization of Fission Products
Authors: Ballhorn R. , Brunner H. , Schwab R. C. 
Published: March 2011

ABSTRACTMinerals of the crandallite group (Ca, Sr. Ba, Pb, REE) H Al3((po4) 2/(OH)6) exhibit manifold possibilities for element substitutions. They occur as hydrothermal precipitates together with tin tungsten mineralization [1], as placer minerals [2], neo-formed minerals in lateritic profiles [3, 4] and lake sediments [5].An easy and cheap method of synthesizing an artificial crandallite-type material was developed. By adding 4.2 g of crandallite to an aqueous solution containing 300 g/l sodium nitrate, 0.6 g/l europium nitrate and 0.6 g/l thorium nitrate, europium and thorium were effectively separated from the solution. This was also demonstrated for Ce. La, Nd, Gd, Zr, Ba and Sr.Artificial crandallite-type material laden with strontium was subjected to a Soxlet test. A dissolution of strontium of 0.06 to 0.08 wt.% with reference to the total strontium content resulted. As shown by Herold [6] the substitution of Ca by larger bivalent or higher charged ions results in an increase in the thermodynamic and thermal stability of artificial crandallites.
Hydration Mechanisms of Silicate Glasses: Discussion of the Respective Role of ion Exchange and Water Permeation
Authors: Dran J.-C. , Petit J.-C. , Trotignon L. , Paccagnella A. , Delia Mea G. 
Published: March 2011

ABSTRACTThe comparative leaching behavior of a soda-lime glass and of a simulated nuclear glass has been investigated through H and Na depth profiles obtained with resonant nuclear reaction analysis. It is shown that glass surface hydration involves both H+/Na+ ion exchange and permeation of molecular water, the first process being dominant at low temperature and solution ionic strength and the second for high values of these two parameters. The shape of the H profile as well as the response of H retention to thermal treatment indicate that on the nuclear glass, most of the molecular water is more weakly bonded than on the soda-lime glass.
The Development of a Mechanistic Basis for Modelling Fuel Dissolution and Container Failures Under Waste Vault Conditions
Authors: Shoesmith D. W. , Sunder S. , Ikeda B. M. , King F. 
Published: March 2011

ABSTRACTDue to the long containment periods required for radionuclides in a nuclear waste disposal vault, the justification that a particular containment system is acceptable will be based on relatively short-term experimental data used to support predictive models. To justify this approach, we must possess a sound mechanistic understanding of processes such as fuel dissolution, radionuclide release and container corrosion. Since these processes are driven by oxidants in the vault, it is natural to study them by electrochemical techniques. In this paper, we have reviewed a number of electrochemical methods used in the study of waste vault reactions. More detailed descriptions are given of the development of predictive models for the dissolution of UO2, the crevice corrosion of titanium alloys and the uniform dissolution of copper.
Research Priorities: Are we Tackling the Host Important Problems in Waste Management?
Authors: McCombie C. 
Published: March 2011

ABSTRACTIt is for me an honour and a privilege to have been asked to open the technical programme of the 1988 MRS conference with a talk on the important topic of research priorities in radioactive waste management. It is essential in this field that we continually review the relevance and applicability of our work; this is clearly recognized by the organisers of the MRS conferences, as witnessed also by the 1985 meeting where an entire session was devoted to overviews of research priorities, and by the 1982 meeting, where a very interesting panel discussion on the topic was led by Professor Tom Pigford.
Electrochemical and X-Ray Photoelectron Spectroscopic Studies of UO2 Fuel Oxidation by Specific Radicals Formed During Radiolysis of Groundwater
Authors: Sunder S. , Shoesmith D. W. , Christensen H. , Bailey M. G. , Miller N. H. 
Published: March 2011

ABSTRACTThe effects of groundwater radiolysis on the oxidation and dissolution of UO2 has been studied. The production of a specific radical was maximized by using suitable solution chemistry, and the effect of a particular radical was investigated. Experiments were performed to study the effects of OH, O2, and CO, radicals. An electrochemical cell and a UO2 electrode were designed to do ijri situ electrochemical measurements in gamma fields, 300 -20 Gy/h. During radiolysis, the oxidation of UO2 was monitored by recording the corrosion potential of the UO2 electrode as a function of time. The fastest increase and highest corrosion potentials were observed in solutions favoring the formation of O2 radicals. XPS analysis of the UO2 surface showed that oxidation has proceeded beyond the UO2.33 stage. Computer calculations of water radiolysis showed that steady-state concentrations of the radicals are very low, about 10−9 mol-dm−3, in most cases, and even lower if the reactions with the UO2 surface are included. The radicals are produced at a much faster rate than the observed changes in the corrosion potential, suggesting thereby that another slower reaction is corrosion rate controlling.
Corrosion Resistance of Candidate Overpack Materials in Deep Argillaceous Disposal Environments
Authors: Debruyn W. , Tas H. , Dresselaers J. 
Published: March 2011

ABSTRACTIn situ corrosion testing and in situ monitoring of the near field chemistry are performed as part of the Belgian experimental program for the qualification of an overpack material for long term HLW containment in deep clay formations. Several test facilities are now in operation and some of the first experimental data are presented and discussed in terms of the program objectives.
A New Insight into the Nature of the Leached Layers Formed on Basaltic Glasses in Relation to the Choice of Constraints for Long Term Modelling
Authors: Crovisier J. L. , Atassi H. , Daux V. , Honnorez J. , Petit J. C. , Eberhart J. P. 
Published: March 2011

ABSTRACTExperimental basaltic glass dissolution in fresh water is compared with analyses made on subglacial hyaloclastites from Iceland. The dissolution is initially selective and remains selective if the solution is renewed, whereas it becomes apparently congruent in non-renewed conditions. The congruent dissolution is ascribed to a pH increase (up to 7.0–7.5) which is hampered in the former conditions. The palagonite hydrated layer on the Icelandic basaltic glasses is made up of amorphous to crystallized clay-like materials. The chemical composition of palagonite is close to that of the intergranular clayey material, thus, it is inferred that in most cases no significant chemical gradient exists in the solution between the reaction zone, namely the glass/palagonite interface, and the intergranular solution. We conclude that the dissolution of basaltic glass under subglacial conditions is controlled by thermodynamics and that kinetic constraints, such as the diffusion of species through the altered layers, do not play a major role.
Time Depndence of pH in a Cementitious Repository
Authors: Atkinson Alan , Everitt Nicoia M. , Guppy Richard M. 
Published: March 2011

ABSTRACTThe pH of a cementitious radioactive waste repository is expected to decrease with time as water leaches out soluble ions or as a result of reactions between repository constituents. These processes have been simulated in the laboratory and the results compared with behaviour anticipated from the known chemistry of cement compounds.The studies indicate that the pH in Portland cements and Blast Furnace Slag cements (BFS) is likely to remain above 10.5 for very long periods of time, of the order of several hundred thousand years for a typical repository. They also show that extensive use of Pulverized Fuel Ash (PFA) leads to uncertainty in long term pH which could be as low as 9 to 10 in some cases.
Condiment: Source Code for Risk Assessment of French Nuclear Waste Repository
Authors: Mangin J. P. , Mouche E. , Lovera P. , Nguyen Ngoc H. 
Published: March 2011

ABSTRACTCONDIMENT is the source code used in MELODIE, the overall French computer code for risk assessment of nuclear waste repositories in geological formations. This code models the diffusion-convection of elements released by a waste package, up to a distance of a few meters from the package. Two versions have been developed simultaneously:- CONDIMENT2 deals with the case of a single element. This version is more specifically designed for vitrified high-level wastes. The boundary conditions are furnished by studies on aqueous corrosion of French nuclear glass R7T7.- CONDIMENT3, deals with two ions that are liable to precipitate. This version is more specifically designed for wastes immobilized in cement.CONDIMENT3 is verified in a configuration for which an analytical solution exists.
Mechanism of Ionic Diffusion in Dense Bentonite
Authors: Cheung S.C.H. , Gray M. N. 
Published: March 2011

ABSTRACTA new model based on ionic diffusion in surface (bound) and interstitial (free) water in compacted bentonite systems has been developed. The model is supported by data obtained from flow-through diffusion experiments using Cs+, I- and Cl-. The results show that diffusion depends on the charge of the diffusing species: cations are attracted to the clay particle surface, but are not immobilized, whereas anions are repelled from the clay particle surface. Cations diffuse through both surface and interstitial water, and anions diffuse mainly through interstitial water. The clay structure has been found to affect the diffusion of cations and anions.
Equilibrium Leach Testing of Intermediate Level Waste
Authors: Heafield W , Barlow P , Hunt A 
Published: March 2011

ABSTRACTExperiments examining the leach characteristics of encapsulated Intermediate Level Wastes in repository near-field conditions have been undertaken in the UK since 1982. The Equilibrium Leach Test was developed in order to provide a realistic static leach test for the measurement of equilibrium concentrations and chemical states of individual nuclides within a particular waste, or combination of wastes, and the components of the near-field barriers of a repository, after water has ingressed into the system. The significant components of the near-field ie waste material, waste matrix and repository backfill are equilibrated with water under static conditions.Results illustrate the high degree of protection afforded by the near-field, which under repository conditions will be complemented by the additional protection of the far-field and the biosphere. Analytical results show that a cement based matrix and cementitious backfill provide the lowest radionuclide concentrations, for long lived radionuclides.
Laboratory Experiments of Mass Transfer in the London Clay
Authors: Bourke P. J. , Gilling D. , Jefferies N. L. , Lever D. A. , Lineham T. R. 
Published: March 2011

ABSTRACTAqueous phase mass transfer through the rocks surrounding a radioactive waste repository will take place by diffusion and convection. This paper presents a comprehensive set of measurements of the mass transfer characteristics for a single, naturally occurring, clay. These data have been compared with the results predicted by mathematical models of mass transport in porous media, in order to build confidence in these models.