bluuebunny/crossref_metadata_2025 huggingface dataset:
Process Considerations in Monolithic Aerogels
Authors: Hunt Arlon J. , Lofftus Kevin D.
Published: March 2011

This paper describes important process considerations in the preparation of super-critically evacuated alcogels called aerogels. Aerogels are fine grained, open pore, low density materials that possess a variety of unusual properties and have a number of diverse applications. Factors influencing the microstructure and uniformity of alcogel monoliths are discussed. The effects of hydrolysis rate, diffusion, condensation, dispersion medium, and electrostatic interactions on particle formation and gelling are outlined. These effects are illustrated with the preparation of zirconia, mullite precursors, and silica alcogels. A theoretical model of particle interaction based on the combination of van der Waals and electrostatic double layer forces is used to interpret gelation and homogeneity. Solvent substitution and supercritical drying processes are discussed.
Film Preparation by Inorganic-Organic Sol-Gel Synthesis
Authors: Schmidt H. , Rinn G. , Naβ R. , Sporn D.
Published: March 2011

Film formation by sol-gel techniques is an advantageous method to obtain inorganic coatings. The sol-gel process allows the preparation of prepolymers with suitable viscosities to use various coating techniques like dipping, spraying and spin-on coating. The main disadvantage is the shrinkage of the gel layer during drying or sintering which leads to cracks with layer thicknesses more than some micrometers.

The introduction of organics, causing a decrease of the network connectivity and increasing relaxation ability can help to overcome densification problems. Moreover, in some cases, hardness or abrasion resistance are not too much affected by organics. In these cases, the organics can be left within the inorganic network. The possibilities of inorganic-organic processing techniques will be discussed and examples for film formations will be given.
Investigation of Processing Parameters on Stability of (SOG) Files on Patterned Si Wafers
Authors: Shyu S. G. , Smith T. J. , Baskaran S. , Buchanan R. C.
Published: March 2011

Polymeric sols of SiO2 or siloxane polymers in n-propanol were investigated for use as dielectric and planarization layers on patterned silicon wafers for device application. Spin coating of the sol (SOG) resulted in rapid gelation through solvent evaporation but cracking often occurred on heating. This study examined the influence of SOG composition, deposition process and heating rate on film planarization and cracking. Planarization was found to be enhanced by layer thickness, but cracking stability was reduced. Sequential drying of the applied SOG layers and use of trlethano-lamine as a complexing base was found to significantly reduce cracking tendency in the films.
Optimization of Sol-Gel Film Properties
Authors: Melpolder Sharon M. , K. Coltrain Bradley
Published: March 2011

The preparation and characterization of organic-modified and organic/ iorganic-modified silica sol-gel spin-coated thin films is presented as a function of thermal processing. The ability to alter the film's final refractive index, thermal expansion coefficient and the polar contribution to the film's surface energetic term is reported. The stability of the coating solution at elevated temperatures was studied by analyzing changes in molecular weight, viscosity and particle size during the sol-to-gel transition. Control of the sol-gel thin film properties allows the design of a film/substrate interface where both thermal mismatches and surface energetic differences are minimized. Decreased stresses should be induced during processing, resulting in increased adhesion between the coating and the substrate.
The Instability of Polycrystalline Thin Films: Experiment and Theory
Authors: Miller K. T. , Lange F. F. , Marshall D. B.
Published: March 2011

Dense polycrystalline thin films of ZrO2 (3 and 8 mol% Y2O3) were produced by the pyrolysis of zirconium acetate precursor films, which were deposited on single crystal Al2O3 substrates by spin-coating solutions of zirconium acetate. With grain growth, these films broke into islands of ZrO2 grains. Thermodynamic calculations show that this break up lowers the free energy of the system. These calculations also predict the conditions needed for polycrystalline thin film stability.
Chemical Ways to YBa2Cu3O7−x Superconducting Materials
Authors: Bernier J. C. , Vilminot S. , El Hadigui S. , His C. , Guille J. , Dupin T. , Barral R. , Bouzat G.
Published: March 2011

YBa2Cu3O7−x has been synthesized by two chemical ways, one from oxalate coprecipitation, the other one from metalloorganic decomposition. Superconducting properties of the resulting samples have been checked by means of resistivity and magnetic measurements. Low temperature specific heat data allow to propose an explanation to the residual linear term.
The Introduction of Roman Ceramic Styles and Techniques into Roman Britain: A Case Study from the King Harry Lane Cemetery, St. Albans, Hertfordshire
Authors: Freestone Ian C. , Rigby Val
Published: March 2011

Specialised ceramics from Gaul were imported into late Iron Age Britain, and their forms copied in native techniques. Roman technology was introduced after the Conquest, and involved changes in paste preparation, surface coating and firing techniques that allowed increases in the scale, standardisation and quality of the production.
A Study of Ancient Roof Tiles Found in Pella, Greece
Authors: Kilikoglou Vassilis , Vassilaki-Grimani M. , Maniatis Y. , Grimanis A. P.
Published: March 2011

The ceramic specimens examined in this study were taken from roof tiles of the Hellenistic period found in Pella, northern Greece. They represent five chronologically successive tilings of two buildings. Neutron activation analysis results showed that a different clay was used for the construction of each roof. Results of technological analysis indicate a consistency in the manufacture of the tiles, except for the first tiling which seems to be technologically different and more advanced.
Electron-Microprobe Investigation of Early Irish Glass and Glass-making Practices
Authors: Henderson Julian
Published: March 2011

This paper discusses the largest bank of compositional data yet assembled for Early Christian (6th- 10th century AD) Irish glass. The material studied was transparent and opaque and was analysed using EPMA and SEM. The data for transparent glass offers the possibility of assessing the extent to which the glass was recycled. The crystalline inclusions in opaque glasses including those on glass-making crucibles have been studied using an SEM.
An Analytical Investigation of a Durable Second Millennium BC Glass Bead from Britain
Authors: Henderson Julian
Published: March 2011

This paper deals with a unique glass bead of probable second millennium BC date from Wilsford, Wiltshire in southern England. The date of the bead is probably Wessex II; c. 1400 – 1200 BC. It was first recognised as being glass [1] in print in 1812, but until recently [2] has been considered as being of stone rather than glass in line with its original description. Here the bead is described together with surface SEM studies, the replication work on glass of similar composition reported and its unusual chemical composition discussed in terms of its durability and comparable Bronze Age glass compositions. This paper is partly the result of a collaborative project involving the author, Margaret Guido, Michael Cable, Justine Bayley and Leo Biek.
A Role for Ceramic Materials Science in Art, History and Archaeology
Authors: Kingery W. David
Published: March 2011

One's first contact with materials occurs as infants with the swaddling cloths that warm and comfort us, but also restrain us. As life goes on material objects always surround us. They structure the way we look at the world and how we arrange our thoughts; they serve a wide range of utilitarian, aesthetic, social and symbolic functions; methods of designing, manufacturing and using materials are at the core of our technology and much of our culture. Materials technology, making and using objects, is thus in a unique position relative to history and culture. While interpretations sought by study of these objects are judgmental and humanistic, they must rest on as secure a foundation of solid materials knowledge as is possible. The central paradigm of materials technology is that the selection and processing of materials gives rise to a particular structure which is the source of useful properties (Fig. 1). This is exactly the process used by the artist who aims at aesthetic properties, and the craftsman and technologist who aim at particular properties.
A Computerized Axial Tomographic Study of Museum Objects
Authors: Cheng Yu-Tarng , Mishara Joan
Published: March 2011

Radiography is the most useful tool for the examination of objects by non-destructive means. A variety of questions can be answered by radiographic techniques. Some questions are those arising from conservation, e.g., the location, shape and size of restorations, internal flaws, hidden underpaintings and extent of deterioration such as corrosion. similarly, questions in technical and archaeometric studies include those related to methods of fabrication of objects, precise measurement of dimensions, details of internal construction and detection of different materials composing an object. However, not all of these questions can be answered equally well by conventional methods of radiography.
Bronze Age Cauldrons in Atlantic Europe: Materials Selection and Design
Authors: Northover J. Peter , Gerloff Sabine
Published: March 2011

The cauldrons and buckets of the later Bronze Age in Atlantic Europe, produced from the 12th to the 6th century BC, were some of the most complex fabrications made in that period of prehistory. They show a steadily increasing understanding of the problems posed by their design and an increasing elegance in their solution. At the same time they demonstrate considerable awareness of materials properties and provide one of the clearest instances in the Bronze Age of materials selection for specific purposes.
Changes in Waterlogged Medieval Window Glass
Authors: Alten Helen I.
Published: March 2011

Samples of wet 13th-14th c. Grisaille window glass, visually sorted according to their extent of corrosion, were examined for physical changes while air-drying and solvent-drying. Polished cross-sections of the samples were examined with a JEOL-35CF SEM with a LINK AN 10,000 dispersive x-ray analyzer. Elemental distribution maps showed distinct alterations in the positioning of elements according to the corroded nature of the glass.
A New Tool for Cellulose Degradation Studies
Authors: Arthur Jakoa E. , Jacksona J. P. , Arthurs E. , Schwalbe L. A. , Sega R. M. , Windisch D. E. , Long W. H. , Stappaerts E. A.
Published: March 2011

We describe a new technique for studying thermally-induced chemical transformations in cellulose. The apparatus consists of a carbon dioxide laser for heating, an infrared thermometer, and an optical reflectance spectrometer. To illustrate the technique, we present measurements from a single piece of sample linen along five isotherms in the range 200–290°C. The results are discussed in terms of first-order chemical rate theory and a fourstep model. From the measurements we derive the activation energies, Arrhenius constants, and reflectivities of the chromophoric states.
An Examination of Neutron Induced Autoradiography and Gamma Spectroscopy for the Study of Paintings
Authors: Olin J.S. , Endt D.W. Von , Cheng Y.T. , Ligeza M.
Published: March 2011

Neutron-induced autoradiography is a further step in the development of techniques for the examination of paintings that complements x-ray radiography and often yields unique information that cannot be obtained by other means. After exposure to a field of thermal neutrons (<0.3eV), selected elements in the painting form radioactive nuclides that in turn decay at known half-lives with the emission of gamma rays and charged particles. The charged particles, mainly electrons, expose radiographic film that is held in close contact with the painting by a very slight vacuum. Unlike x-ray radiography, which involves detecting x-rays that have passed through the painting to expose a film, autoradiography uses one activation with neutrons followed by sequential film exposures to capture the images of activated elements that have different half-lives. The autoradiographs show the distribution patterns of the pigments in which the elements occur. These pigments may be on the surface and visible in the painting or they may be beneath the surface. Often autoradiography uncovers the preliminary sketch or underpainting preceding the rough blocking in of the subject and the subsequent paint layers that create the final image. X-rays reveal almost exclusively the presence of pigments containing heavy elements such as lead and barium; autoradiography identifies the presence of activated pigments and distinguishes the fine details of paint application as well as changes in composition.
Application of Compositional Analysis to the Study of Materials and Objects of Art and Archaeology
Authors: Sayre Edward V.
Published: March 2011

Archaeologists, art historians and art conservators are almost constantly concerned with the questions of where, when and by whom the objects within their care were made. Knowledge of the conditions under which the objects were found may not answer these questions, as the objects may have traveled extensively or have existed for some time before they arrived at sites where they were discovered. Stylistic considerations often can provide answers, but not infallibly, as styles were sometimes copied at locations and at times quite different from those for which they were most characteristic. Compositional analysis can often help provide answers to these questions because traditions in the use of particular materials have often persisted in and accordingly have been characteristic of particular regions, periods and even of particular workshops. For example, the deliberate alloying of copper with tin, arsenic, antimony, lead and/or zinc has varied greatly from region to region and from time to time.
Corrosion of Silicate Glasses: An Overview
Authors: Hench Larry L.
Published: March 2011

The corrosion of silicate glasses is described in terms of four stages of surface attack which result in six types of surface conditions depending upon the glass composition and various environmental and physical factors. Type I and II surfaces correspond to durable glasses which have a very high surface SiO2 content whereas Type IV and V surfaces are unstable. Type IIIA surfaces include bioactive glasses which chemically bond to bone and Type IIIB surfaces are characteristic of the alkali borosilicate nuclear waste glasses which form multiple layers of precipitated surface films.
Developments in Quantification and Use of Environmental Cracking Mechanisms for Design and Lifetime Prediction
Authors: Andresen Peter L. , Ford F. Peter
Published: March 2011

Following a long period of qualitative assessment of environmental cracking phenomenology, there has been recent emphasis on developing quantitative, mechanistically-based predictive models. This focus is driven by scientific and engineering concerns. For example, neither pressure vessel design nor evaluation codes incorporate the contribution of environmental cracking understaticloading, nor do they differentiate between the large possible variations in both environment and material chemistry. Similarly, while numerous scientific hypotheses have been proposed to explain the crack advance process and related, contributing phenomena, ultimately their validity must withstand the scrutiny of quantification and comparison to measured cracking kinetics and observed component lifetimes.

The benefits and approaches involved in predicting environmental cracking based on mechanistic modeling of crack advance and its underlying phenomena are discussed. The benefits and approaches involved in predicting environmental cracking based on mechanistic modeling of crack advance and the underlying phenomena are discussed. The formulation of a quantitative model from fundamental mechanisms has progressed most rapidly for the film rupture / slip dissolution mechanism of environmental crack advance. Specifically, for iron and nickel base alloys in high temperature water, identification, quantification and integration of the important underlying parameters has led to algorithms which predict crack growth rates over a wide continuum in static and dynamic stressing, metallurgical microstructure and solution chemistry applicable to light water reactors. For widely studied systems, e.g., stainless and low alloy steels in 288°C water, the predictions are within a factor of 2–3 for 90% of the data which span “initiation”, the possible roles of contributing, “secondary” crack advance processes in oxidation-based mechanisms, such as environmentally enhanced cleavage, spontaneous oxidation, etc.

Similar efforts to identify and quantify the critical parameters and underlying processes in crack advance mechanisms involving hydrogen embrittlement, environmentally assisted cleavage, etc. are summarized. Conceptual approaches to and progress toward integrating these models with in-situ chemical and crack monitoring devices, with the goal of providing on-line evaluation, control and lifetime prediction of environmental cracking, are also discussed.
Quxatitative Theory of Seasitization
Authors: Devine Thomas M.
Published: March 2011

The chromium composition along the grain boundaries of sensitized austenitic stainless steel are calculated using several different quantitative theories of sensitization. The results of the calculations are compared to measured values of the chromium composition along the grain boundary in an effort to assess the validity of the various theories. The experimental results point out two facts not previously emphasized in prior studies: (1) the amount of carbide precipitation required to sensitize austenitic stainless steel is small; (2) significant de-sensitization does not occur until after large amountsof carbide precipitation have occurred.
An Empirical Model for Environmental Damage at the Crack Tip
Authors: Chang K. -M.
Published: March 2011

An experimental method that is able to verify and to characterize the damage zone developed in front of crack tip under time-dependent fatigue crack propagation has been established. The crack growth rate was found to decrease exponentially in the damaged zone. Such a crack growth behavior can be described by a mathematical model which only requires three parameters: initial crack growth rate, (da/dN)q; normal crack growth rate (da/dN)o; and damaged zone size, D. An analyticat relationship has been developed to correlate the temperature and the time of sustained loading to the size of the induced damaged zone.
Stress Corrosion Cracking of Magnesium Die Casting Alloys
Authors: Miller William K.
Published: March 2011

Contrary to limited published information on the subject, magnesium die casting alloys are shown to be susceptible to stress corrosion cracking (SCC), requiring only partial immersion in distilled water. Also described is evidence that this SCC results from a cathodic process, with perhaps hydrogen-assisted cracking and film rupture both playing roles.
Advanced Metal Matrix Composites
Authors: Crowe C. Robert
Published: March 2011

Advanced metal matrix composites are emerging as materials of construction for high performance aerospace applications. The thrust is to develop high specific strength and high specific modulus ultra-lightweight composites using Al or Mg as matrix materials for space structure applications, and for higher temperature applications, to develop materials using various aluminides as matrix materials. This paper presents an overview of the methodology used to develop advanced MMC's and discusses the problems and limitations faced in achieving the composite materials development goals.
Diffusion Cells for Integrating Temperature and Humidity Over Long Periods of Time
Authors: Trembour Fred , Smith Franklin L. , Friedman Irving
Published: March 2011

The rate of many processes, including the diffusion of water into rhyolitic volcanic glass (obsidian), as well as the racemization of amino acids is temperature dependent, and a knowledge of temperatures integrated over time periods of at least a year is necessary to quantify these processes. The construction and properties of simple devices consisting of small plastic containers that change weight at a rate that is a function of temperature and the activity of water will be described. The cells function because water diffuses through the plastic across a constant vapor-pressure gradient. This vapor-pressure gradient is maintained constant between the substances within the cell and the materials outside the cell. The plastic cells are usually filled with water and surrounded by a dehydrating agent, such as silica gel. A better arrangement is to fill the cell with a mixture of solid sodium chloride (NaCl) and a saturated solution of NaCl, and to surround the cell with pure water. A number of plastics have been investigated, including polycarbonate, polystyrene, tefzel, polyallomer, and methacrylate. The cells have been sealed by various methods including screw caps, room-temperature vulcanizing silicone rubber sealant, and rubber stoppers. The final design consists of a small cell made of a polycarbonate plastic centrifuge tube containing solid NaCl plus NaCl-saturated solution sealed with a rubber stopper and placed in a polypropylene tube containing pure water. Our aim has been to develop cells that are sufficiently sensitive to yield a precision of ±0.2°C when exposed for one year at temperatures that range from 0° to 40°, and that will fit into metal fittings that can be screwed into standard 3/4-inch plastic water pipe (approximately 1 inch outside diameter).
Technological Prospects for Germanium Silicide Epitaxy
Authors: Bean John C.
Published: March 2011

This paper describes preliminary device work on GexSi1−x, based devices and examines progress towards the realization of a silicon based heterostructure technology. Target areas for further work are identified including: An enhanced understanding of metastable-growth processes; The need for defect confinement in discommensurate epitaxy; Elimination of manufacturing barriers caused by particulate induced defects in MBE and low growth rates in low temperature CVD.

Over the last five years, studies of GexSi1−x have yielded an understanding of crystal growth mechanisms and information on electrical and optical properties such as bandstructure and heterojunction band alignment. These in turn lead to a number of preliminary device applications including optical detectors, modulation doped transistors and heterojunction bipolar transistors. In this paper, I will try to answer the question posed by the symposium organizers: In the germanium silicide system, has our understanding and experience reached the point that we have the basis for a technology, and if not, where must further work be done?
Characteristics of all-OMCVD Grown GaAs MESFETS on Si Substrates
Authors: Lee Jhang Woo , McCullough R. M. , Morrison R. H.
Published: March 2011

We present DC characteristics of all-OMCVD grown GaAs MESFET structures on Si substrates with unintentionally doped GaAs or AlGaAs buffer layers. MESFETs fabricated in two and three inch GaAs on Si wafers pinch off well and exhibit reasonably high transconductances up to 110 mS/mm for 1 μm gate devices. The reverse Schottky breakdown voltage of the MESFET gate is as high as 15 V and the forward turn on voltage is ∼0.65 V. The ohmic isolation is comparable to the typical homoepitaxial layer with a leakage current of 100 nA at a 1 V bias. The low background doping levels of unintentionally doped GaAs buffer layers is the key factor for this successful MESFET operation.
Low Pressure MOCVD Growth and Characterization of GaAs and InP on Silicon Substrates
Authors: Razeghi M. , Defour M. , Omnes F. , Nagle J. , Maurel P. , Acher O. , Huber A. , Mijuin D.
Published: March 2011

High quality GaAs and InP have been grown on silicon substrates, using low pressure metalorganic chemical vapor deposition technique. The growth temperature is 550°C and the growth rate 100 A/min.

Photoluminescence, X-ray diffraction and electrochemical profiling verified the high quality of these layers. The use of superlattices as buffer layers, (GaAs/GaInP) in the case of GaAs/Si and (GaInAsP/InP) in the case of InP/Si, decreased the amount of misfit dislocations in the epitaxial layer. Carrier concentrations as low as 5.1015 cm−3 have been measured by electrochemical profiling.
Ion Implantation and RTA in III-V Materials
Authors: Streetman B. G. , Dodabalapur A.
Published: March 2011

We review the applications of ion implantation in several III-V materials, and rapid thermal annealing techniques to activate the implant and remove the crystalline damage. Ion implantation has become the preferred technique when selective area doping is necessary. It has been used successfully to fabricate n, n+, p, p+, and semi-insulating regions in III-V binary, ternary, and quaternary compounds, and multilayer structures. Ion implantation has also been used to produce layer mixing in multilayer structures, and superlattice disordering. The annealing step necessary to activate the implant and remove the crystalline damage is complicated by several factors such as incongruent evaporation of the group V element, layer mixing, and dopant redistribution. Rapid thermal annealing techniques, which typically employ anneal times between 1 second and 100 seconds, are generally more suitable than conventional furnace annealing. The short annealing times result in much less dopant redistribution, and reduced layer mixing in multilayer structures. Even for short annealing times, it is necessary to employ a protection scheme to suppress the loss of the group V element. Several such methods are discussed, including dielectric encapsulation, proximity techniques, and controlled ambient techniques.
Activation Mechanisms in Ion-Implanted GaAs
Authors: Morris N. , Sealy B. J.
Published: March 2011

Rapid thermal annealing has been used to study the electrical activation mechanisms for magnesium and selenium implants in GaAs. By analysing the changes in electrical activity as a function of annealing time and temperature, a model has been developed which accurately predicts the electrical properties following the post-implant annealing stage. The model has been used to study the activation of other ions, particularly zinc, beryllium, tin and sulphur, the results of which will be compared with those of magnesium and selenium. The results suggest that the mechanism for electrical activation is dominated by the diffusion of gallium, arsenic or vacancies. The paper will present the model and discuss the activation mechanisms of the ions.
Ion Implantation Processing of III-V Strained-Layer Semiconductors
Authors: Myers David R.
Published: March 2011

Ion implantation has had a strong impact on the development of III-V strained-layer semiconductor (SLS) materials and device technologies. Implantation studies have helped delineate the present understanding of strained-layer stability and metastability limits. Resulting ion beam technologies have led to improvements in a variety of SLS discrete devices, including optoelectronic emitters, photodetectors, and field-effect transistors. Both SLS stability criteria and implanted SLS devices are reviewed with respect to future applications in optoelectronics.
Dry Etching and Impurity Diffusion for Integrated Optoelectronics
Authors: Coldren L. A.
Published: March 2011

In 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

Silicon 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

The 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

Selective 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

The 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

The 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

Recently, 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

The 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

The 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

Nuclear 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

The 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

The 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

Minerals 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

The 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

Due 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

It 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

The 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

In 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

Experimental 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

The 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.