bluuebunny/crossref_metadata_2025 huggingface dataset:
Amorphous Silicon Electronics
Authors: Street R.A.
Published: August 2016

The progressive miniaturization of electronics is familiar to everyone; computing power that used to occupy a room can now be put onto a single integrated circuit. Miniaturization is admirable when size is not relevent to the electronic function, but there are plenty of devices in which a large physical size is essential. Many of these concern information technology, examples being the computer display, printer, and fax machine. Communication with the electronic world is primarily visual and operates at a large format typified by a document. In this rapidly advancing field, we are eagerly awaiting desktop interactive display surfaces that can input as well as display information, document readers, truly portable computers, electronic vision and—the oldest dream of all—the television that hangs on the wall. Realization of these hopes requires a set of technologies that permit bigger rather than smaller electronic systems, and amorphous silicon is helping to make this happen.
Microscopic Properties of Thin Films: Learning About Point Defects
Authors: Ourmazd A. , Scheffler M. , Heinemann M. , Rouviere J-L.
Published: August 2016

Microscopic properties of thin films are often strongly influenced by departures from “perfection.” These can take the form of extended defects such as dislocations, interfacial roughness, or point defects. Direct imaging of extended defects was one of the early contributions of electron microscopy to solid-state science. Since then, the role of extended defects in controlling the fabrication and properties of thin films has been extensively studied and reviewed. Recently, in-situ observation of strain relaxation in thin-film structures has increased our understanding of dislocation kinetics and its effect on properties of thin films.

In this article, we focus on electron microscopic studies of interfacial roughness, the effect of processing on thin films, and the role and properties of intrinsic point defects in solids. Concurrent development of sophisticated theoretical and experimental approaches has substantially facilitated the investigation of point-defect properties. Here, we illustrate how results from theory and experiment can be combined to form a detailed picture of point-defect diffusion in solids, and highlight areas needing increased attention. Microscopic properties of thin films cannot be covered in a single review. For this reason, and because fabrication of semiconducting thin films has reached unprecedented levels of sophistication, we illustrate this article with references to semiconducting materials.

Our main conclusions can be summarized as follows, (a) Thin films of the highest quality are bounded by interfaces that are microscopically rough. Moreover, thin-film interfaces contain roughness on many length scales, each affecting a subset of the physical properties of interest.
Nanotribology
Authors: Belak James F.
Published: August 2016

Friction, lubrication, wear, and adhesion are all phenomena familiar from everyday experience. We experience friction when we go for a walk on ordinary ground—we do not expect to fall flat on our faces, as we might when walking on ice. Wear is particularly well known because it leads to catastrophic failure and represents one of the most costly problems facing industry today. These phenomena are part of the field of tribology—the science of interacting surfaces in relative motion. A macroscopic understanding of tribology is crucial for the design and engineering of mechanical components. As dimensional tolerances of these components approach the nanometer scale and novel new materials are used in their fabrication, macroscopic understanding must give way to a microscopic atomic-scale understanding. This fundamental microscopic understanding and its practical application remain limited.

With the advent of surface proximity probes, however, those limitations are rapidly disappearing. Researchers are now able to test and develop a microscopic understanding of such tribological phenomena as boundary-layer lubrication and asperity-surface interactions—ideas that underlie our current macroscopic understanding. This emerging field is known as nanotribology or molecular tribology, the focus of this issue of the MRS Bulletin. The new experimental probes include the surface force apparatus for measuring interfacial forces as a function of surface separation and, more recently, rheological properties of molecularly thin layers; a quartz-crystal microbalance for measuring the atomic-scale friction of adsorbed monolayer films; and the atomic force microscope (AFM) for measuring nanomechanical properties of surfaces, atomicscale friction of clean surfaces, and frictional properties of surfaces coated with molecular films.
Chemical Vapor Deposition of Copper for Multilevel Metallization
Authors: Kaloyeros Alain E. , Fury Michael A.
Published: August 2016

Since the birth of integrated circuitry about thirty five years ago, microelectronics design and manufacturing technologies have evolved toward higher integration density with smaller design rules. As the semiconductor industry moves into ultra-large-scale integration (ULSI), device geometries continue to shrink into the sub-half-micron region while circuit densities increase to optimize reliability and improve performance. The resulting demands on interconnect technologies necessitate the exploitation of all development avenues: design, materials, and manufacturing.

Emerging sub-half-micron technologies require multilevel metallization (MLM) design schemes that reduce interconnection lengths and lead to lower signal transmission delays and enhanced device speeds. MLM schemes also permit increased device density, due to the ability to use the third (vertical) dimension, and easier signal routing because of higher flexibility in architectural design. These schemes, in turn, demand interconnect metals that can handle the higher current densities resulting from the decreasing size of device features, without the loss of electrical and structural integrity, and deliver the sheet resistance needed to meet performance demands. They also require reliable deposition techniques to successfully fabricate the increasingly complex architectures as lateral feature sizes are scaled down more rapidly than conductor or insulator thicknesses.
Refractory Metal Nitride Encapsulation for Copper Wiring
Authors: Li Jian , Mayer J.W.
Published: August 2016

Recent interest in copper-based metallization for ultra fast logic devices has stimulated extensive studies on thermal stability issues, as well as the search for novel deposition and etching processes. In copper wiring technology, thermal stability problems include: (1) rapid diffusion of copper into dielectric substrates, (2) low-temperature reaction with most near-noble metals and their silicides, (3) the susceptibility of copper to oxidation, (4) poor adhesion characteristics of copper on most dielectric materials, and (5) thermal-stress-induced void formation and cracking. The basic issues have been summarized in a recent review.

When copper is in contact with a silicon substrate, copper can diffuse into active regions of devices where it becomes a recombination-generation center. In addition, copper forms the silicide Cu3Si by reacting with the substrate at temperatures less than 200°C. After the formation of the Cu3Si phase, the underlying silicon in the Cu3Si/Si structure is readily oxidized even at room temperature. In the case of copper in contact with silicon dioxide under bias thermal stress (BTS), copper is found at the SiO2/Si interface under a positive electric field. Copper diffusion in doped glass, e.g., phosphosilicate glass and silicon nitride films, is a factor at temperatures below 400°C.
Planarized Copper Multilevel Interconnections for ULSI Applications
Authors: Misawa N. , Ohba T. , Yagi H.
Published: August 2016

As the degree of large-scale integration (LSI) increases, the area of a single transistor will diminish and the density of transistors will increase. Accordingly, technology for high-density wiring to interconnect the huge number of transistors is needed because transistors cannot perform any useful functions without interconnects and electrodes. For advanced microprocessor chips with a sub-half-micron design rule and at least four interconnect layers, the minimum width of the interconnects becomes less than 0.35 μm.

Aluminum or an aluminum alloy is now generally used as the interconnect material in LSI circuits because the physical and chemical properties of aluminum are compatible with current LSI processing: Aluminum forms a thin protective oxide film that withstands various thermal processes; it has relatively low electrical resistivity and halide compounds with a relatively high vapor pressure which are suitable for reactive ion etching (RIE), and it is an inexpensive material. The reliability of aluminum interconnects, however, is a major concern for maintaining the total reliability of advanced LSI. Because of its relatively low melting point, aluminum as an interconnect material is susceptible to stress- and electromigration, which leads to open failure of the interconnect. It is well-known that these failure modes are accelerated by decreasing the width and thickness of the interconnects. Hence, use of aluminum interconnects may be limited for future sub-half-micron LSIs.
Coatings for TiAl
Authors: Taniguchi Shigeji
Published: August 2016

The intermetallic compound, TiAl, and materials based on it have been receiving considerable attention because of their high specific strengths at elevated temperatures. Their mechanical properties are being extensively studied, with a view to application in aircraft or automobile engines. Before using these materials at elevated temperatures, their interactions with the environment should be investigated and suitable measures taken to overcome any degradation. It has, however, been reported that protective Al2O3 scales do not form when TiAl is exposed to an oxidizing atmosphere in spite of its high aluminum content. The formation of an A12O3 scale, or at least a scale containing a continuous A12O3 layer, is a prerequisite for providing sufficient protection. Therefore, much effort has been expended in choosing suitable alloying additions. However, relatively less effort has been devoted to surface coatings on such materials. The purpose of the alloying addition is two-fold: to improve mechanical properties, particularly ductility, and to improve oxidation resistance. However, compatible alloying elements are rare. For instance, some elements which improve the ductility, e.g., vanadium, chromium, and manganese, lower the oxidation resistance. Accordingly, a reasonable concept for the designer is to add effective alloying elements to improve the mechanical properties and to apply a coating to provide protection against the environment. For improved reliability, elements that improve the oxidation resistance can also be added to increase the protection unless they reduce the required mechanical properties.
Materials Characteristics and Dissolution Behavior of Spent Nuclear Fuel
Authors: Johnson L.H. , Werme L.O.
Published: August 2016

The geologic disposal of spent nuclear fuel is currently under consideration in many countries. Most of this fuel is in the form of assemblies of zirconium-alloy-clad rods containing enriched (1–4% 235U) or natural (0.71% 235U) uranium oxide pellets. Approximately 135,000 Mg are presently in temporary storage facilities throughout the world in nations with commercial nuclear power stations.

Safe geologic disposal of nuclear waste could be achieved using a combination of a natural barrier (the host rock of the repository) and engineered barriers, which would include a low-solubility waste form, long-lived containers, and clay- and cement-based barriers surrounding the waste containers and sealing the excavations.

A requirement in evaluating the safety of disposal of nuclear waste is a knowledge of the kinetics and mechanism of dissolution of the waste form in groundwater and the solubility of the waste form constituents. In the case of spent nuclear fuel, this means developing an understanding of fuel microstructure, its impact on release of contained fission products, and the dissolution behavior of spent fuel and of UO2, the principal constituent of the fuel.
Cements in Radioactive Waste Disposal
Authors: Glasser F.P. , Atkins M.
Published: August 2016

Depending on their radioactive content and abundance of long-lived radionuclides, radioactive wastes are often described as low, intermediate or high-level. Cements play a major role in the engineered structures, existing and planned, of most national programs for low- and intermediate-level (ILW) radioactive wastes. Final disposal of ILW is usually by burial at considerable depth (>250 meters), e.g., in planned repositories in clay at Mol (Belgium), in salt at Gorleben (Germany), and in volcanic tuffs at Sellafield (United Kingdom). A sample disposal concept is shown in Figure 1. Shallow land burial is also employed, mostly for low-level wastes (LLW) and often in concrete-lined vaults, e.g., at Drigg (UK) and Center de la Manche (France). Cements are likely to be used in a waste repository as structural elements in the engineered structure and for encapsulation of the actual waste itself (see Figure 1). In the UK, cements are also the favored material for infilling of the vault space (backfilling), and sealing.

LLW and ILW are characterized by considerable heterogeneity, and comprise liquids, solids, floes, sludges, exchange resins, and contaminated laboratory equipment. Cements are capable of converting most of these waste streams into solid and stable monoliths that can be further encapsulated in a steel or concrete container. Such a product is ideal for interim storage, transportation, and final emplacement in a repository. The technology of cementation is well-established, and suited to automation and remote handling (thereby reducing the radiation dose to workers).
What We Still Don't Know About Silicon
Authors: Eaglesham David J.
Published: August 2016

A question sometimes posed to researchers in silicon is: Why are you still working on silicon? How much more do we need to learn? Not only is Si a relatively simple element, it is one of the most common in the earth's crust. This element has been very extensively studied. One reason we keep studying silicon is because it is not just an element, it is also an industry. The microelectronics business has a massive economic impact on our lives. From cars to washing machines, almost all consumer goods contain silicon microprocessors in some form. Our daily lives depend on the stuff. Figure 1 shows the predominance of Si in a breakdown of the microelectronics industry. In 1994 microelectronics has been a $1 × 1011-per year industry worldwide, and it is still growing rapidly. CMOS, or complementary metal-oxide-semiconductor transistors, dominate this business, some being bipolar. The entire compound semiconductor industry is a small part of this picture, composing 2% of the business (although $2 billion is not bad for a “niche” market). The $100 billion business built around silicon makes it the most important element in world economics, although there is some evidence that C and O may also be important for the support of our daily lives. One thing, however, is clear-the economic need to understand silicon and everything it does is tremendous.
FGM Research Activities in Europe
Authors: Kaysser Wolfgang A. , Ilschner Bernhard
Published: August 2016

The application of functionally graded materials (FGM) principles is widespread in Europe, despite the lack of national or European programs coordinating the efforts of the individual institutions and researchers. In the following article, the status of research in Europe will be outlined by examples of research projects from various application fields. More detailed information on European FGM research is available from the proceedings of the FGM '94 symposium held in October 1994 in Lausanne, Switzerland. The symposium was organized by B. Ilschner through the Materials Department of the Swiss Federal Institute of Technology of Lausanne.
Thermal Spray Processing of FGMs
Authors: Sampath S. , Herman H. , Shimoda N. , Saito T.
Published: August 2016

Functionally gradient materials (FGMs) display continuously or discontinuously varying compositions and/or microstructures over definable geometrical distances. The gradients can be continuous on a microscopic level, or they can be laminates comprised of gradients of metals, ceramics, polymers, or variations of porosity/density. Several processing techniques have been explored for the fabrication of FGMs for structural applications, e.g., powder metallurgy, thermal spraying, in situ synthesis, self-propagating high-temperature synthesis, reactive infiltration, etc. Physical and chemical vapor deposition (CVD) techniques are also being explored to process FGM films with nanometer level gradients in composition. This article addresses the issues related to thermal-spray processing of FGMs and will only peripherally compare the advantages and limitations of thermal spray versus other processing techniques as reported in the literature.

In thermal spraying, feedstock material (in the form of powder, rod, or wire) is introduced into a combustion or plasma flame. The particles melt in transit and impinge on the substrate where they flatten, undergo rapid solidification, and form a deposit through successive impingement. Thermal spraying has been traditionally employed to produce a variety of protective coatings of ceramics, metals, and polymers on a range of substrates. More recently, the process has been used for spray-forming structural components.

Arc spray, combustion, and plasma are the major techniques comprising thermal spray. These classifications are based on the type of heat source and the method by which feedstock is injected. Arc-spray processes use electrically conductive wire as feedstock, while combustion methods use powder or wire.
Mathematical Modeling and Design
Authors: Hirano Tohru , Wakashima Kenji
Published: August 2016

For the design of functionally gradient materials (FGMs), necessary material properties, such as thermal-expansion-coefficient and Young's modulus in the specific region, are optimized by controlling the distribution profiles of composition and microstructures, as well as micropores in the materials. For this purpose, our research team employs the inverse design procedure in which both the basic material combination and the optimum profile of the composition and microstructures are determined with respect to the objective structural shape and the thermomechanical boundary conditions. Figure 1 shows the inverse design procedure for FGM, in which the final structure to be developed, as well as the boundary conditions, are specified first. After the fabrication method and an allowable material combination are selected from the FGM database, the estimation rules for the material properties of the intermediate compositions are determined based upon the micro-structure. Then, the temperature distribution and the thermal-stress distribution are calculated with the assumed profiles of the distribution functions for the constituents. Other possible combinations and different profiles are also investigated until the optimum is obtained.
CVD Processing
Authors: Hirai Toshio
Published: August 2016

Various methods are used in functionally gradient materials technology to control the composition and structure of a composite.

The chemical vapor deposition (CVD) method yields a deposit with source gases by applying variou s forms of energy (heat, light, plasma, etc.) to the gases after they are introduced into a CVD reactor. Hydride, bromide, and chloride are generally used for source materials. By continually changing the mixture ratio of source gases or by controlling the CVD conditions such as deposition temperatures, gas pressure, and gas-flow rate, CVD permits relatively easy syntheses of various FGMs (to a maximum thickness on the order of a centimeter).
Microstructural Design and Control of Silicon Nitride Ceramics
Authors: Mitomo Mamoru , Hirosaki Naoto , Hirotsuru Hideki
Published: August 2016

The improvement of mechanical properties by microstructural control has been one of the main topics of interest in the development of silicon nitride ceramics. Toughening, by developing an in situ composite or self-reinforced microstructure, has attracted particular attention.

Microstructural design is a key factor in the optimization of processing parameters. The microstructures of sintered materials are composed of silicon nitride grains and grain boundaries, which can be either crystalline, amorphous, or partially crystalline, depending on the composition, amount of sintering additives, and processing parameters. Silicon nitride ceramics have been fabricated with an addition of metal oxides and rare-earth oxides that form a liquid phase during sintering and accelerate grain boundary diffusion. The effect of composition of the glassy phase on the mechanical properties of ceramics is presented by Becher et al. and Hoffmann elsewhere in this issue. This article focuses specifically on the design and control of grain size.

As it is well recognized, many processing parameters affect grain growth behavior and the resulting microstructure. During sintering, the α- to β-phase transformation leads to a self-reinforcing microstructure on account of the anisotropic grain growth of the stable hexagonal β- Si3N4 phase. Therefore, α-rich powders are widely used for starting materials. Phase transformation accelerates anisotropic grain growth, resulting in an increase in the fracture toughness of Si3N4 ceramics. Kang and Han discuss the effect of phase transformation on nucleation and grain growth in an article in this issue. The effect of the grain-size distribution on microstructural development is described in this article, based on studies conducted mostly with β-Si3N4 powders.
Structure and Strength of Multilayers
Authors: Clemens B.M. , Kung H. , Barnett S.A.
Published: August 2016

Nanometer-scale multilayer materials exhibit a wealth of interesting structural and mechanical property behaviors. Physical-vapor-deposition technology allows almost unlimited freedom to choose among elements, alloys, and Compounds as layering constituents and to design and produce materials with compositional and structural periodicities approaching the atomic Scale. These materials have tremendous interface area density, approaching 106 mm/mm3, so that a Square centimeter area of a one-micron-thick multilayer film with a bilayer period of 2 nm has an interface area of roughly 1,000 cm2. Hence interfacial effects can dominate multilayer structure and properties leading to unusually large strains and frequently stabilization of metastable structures. The atomic-scale layering of different materials also leads to very high hardnesses and good wear resistance. These materials are a test-bed for examination of the fundamental aspects of phase stability and for exploring mechanical strengthening mechanisms. They are also becoming increasingly interesting for applications such as hard coatings, x-ray optical elements, in microelectromechanical Systems (MEMS), and in magnetic recording media and heads.

In this article, we review some of the interesting structures and mechanical properties that have been observed in nanometer-scale artificial multilayer structures.

Superlattice thin films are readily deposited by vapor-phase techniques such as sputter deposition, evaporation, and chemical vapor deposition, as well as by electrochemical deposition. Superlattice deposition Systems are similar to conventional film deposition Systems, except for the provision to modulate the fluxes and thereby produce alternating super-lattice layers.
In SituX-Ray Diffraction and XAFS Studies of Expanded Fluid Selenium Using Synchrotron Radiation
Authors: Tamura K. , Inui M.
Published: August 2016

A substantial and continuous volume expansion from liquid to rarefied vapor occurs by the change of temperature and pressure surrounding the liquid-vapor critical point without crossing the saturated vapor pressure curve. Many investigations have been carried out with molecular fluids including supercritical fluids, and several variations of the equation of state have been advanced since the famous work by van der Waals. In the expansion process the mean interatomic distance increases by up to 10 times that found under standard conditions. However reconstitution of the molecular units or other major structure changes are rare in these fluids. On the other hand, in the expansion process of metallic or semiconducting liquids, physical properties can drastically change. Liquid Hg, well-known as a prototype of liquid metals, undergoes a metal-insulator transition when the density is reduced to about 9 g/cm3near the critical point.Elemental Se, which units in its liquid form is a semiconductor with a twofold-coordinated chain structure in which atoms are covalently bonded, also experiences a semiconductor-metal-insulator transition around the critical point (critical temperature and pressure data of Se:Tc= 1615°C,Pc= 385 bar,pc = 1.85 g/cm3).

The first indication of the semiconductormetal (SC-M) transition in fluid Se was found in electrical conductivity data by Hoshino and co-workers. Figure 1 shows the contours of constant dc conductivity plotted on the pressure-temperature (P-T) plane. The high-conductivity region appears in the immediate vicinity of the critical point. Another indication of the SC-M transition was obtained from the measurement of the optical reflectivity by Seyer et al. Drude-like energy dependence of the reflectivity spectra was observed at elevated pressures and temperatures.
In SituMagnetic-Circular-X-Ray-Dichroism Measurements: An Epitaxial Fe Wedge on Cu(100)
Authors: Dávila M.E. , Arvanitis D. , Dunn J. Hunter , Mårtensson N. , Srivastava P. , Wilhelm F. , Baberschke K.
Published: August 2016

Circularly polarized x-ray radiation is attracting increasing interest as a tool for the characterization of the electronic, magnetic, and chiral properties of low-dimensional structures. Using circular light (with electric field vector parallel to the orbital plane), a dependence of the measured quantity by changing either the orientation of the light polarization or the magnetization is indicative of the existence of magnetic circular dichroism. It can be observed in x-ray absorption spectroscopy (XAS), in which the photon energy is scanned through an absorption threshold exciting a core electron into an unoccupied valence state using circularly polarized light. Synchrotron radiation sources have made this technique possible. It can also be observed in photo-emission spectroscopy from core and valence levels. Here we focus on magnetic circular x-ray dichroism (MCXD) in XAS as an element-specific tool to investigate magnetic properties of ultrathin filmsin situ. The application of magneto-optical sum rules enables the determination of the orbital and spin magnetic moments per atom from XAS spectra, as well as the easy magnetization direction.

MCXD-based magnetometry in XAS is extensively used by measuring the L absorption edges of 3d-transition metals, where large intensity changes (up to 60%) of the L-edge white lines are observed upon reversal of either the sample magnetization or the light helicity. The high magnetic contrast obtained, combined with the elemental specificity of the technique, allows for the study of very dilute samples such as ultrathin films. We first concentrate on the selection rules governing MCXD in XAS.
Synthesis of Porous Inorganic Membranes
Authors: Tsapatsis Michael , Gavalas George R.
Published: August 2016

Here we will attempt a brief overview of recent synthetic efforts for micropore and lower-end mesopore membranes. We will not address the very important classes of nonporous membranes, such as dense metals and solid electrolytes with applications in H2 and O2 separations, or meso- and macroporous membranes, which find applications in food processing and water treatment. Microporous materials provide high permselectivities for molecules encountered in the chemical-processing industry but suffer from low intrinsic permeabilities. Therefore, in order to bring microporous membrane materials to commercial applications, functional composites with small effective thicknesses (in the micron or submicron range) must be developed. For example, to achieve economical membrane-reactor sizes, fluxes as high as 0.1 mol/(m2 s) are desirable. Approaches to microporous membranes include modification of mesoporous membranes by sol-gel and chemical-vapor-deposition (CVD) techniques, carbonization of polymers to form molecular-sieve carbon, and polycrystalline-film growth of zeolites and other molecular sieves.

Microporous carbon is widely used for liquid or gas purification because of its strong adsorptive properties and high surface area. It is also used for air separation by pressure swing adsorption (PSA), relying on its adsorptive and molecular-sieving properties. From the standpoint of applications, microporous carbons are classified into activated carbons with pore size 0.8–2 nm, and ultramicroporous carbons or carbon molecular sieves with pores 0.3–0.6 nm. Activated carbons are used because of their strong adsorption properties, while carbon molecular sieves are useful on account of their molecular-sieving as well as adsorption properties.
Characterization of the Pore Structure of Membranes
Authors: Ramsay John D.F.
Published: August 2016

A better understanding of membrane microstructure and its role in the mechanisms of different separation processes is important in the development of new and more complex types of membranes. This understanding is particularly significant in the case of inorganic membranes because the permeation and separation properties are determined by the porous properties of this microstructure, which in turn is controlled by the synthesis route. This review will cover three topics: first, the origin and development of porosity in inorganic materials; second, the general definitions and terminology used to describe porous media; and third, a brief description of several techniques that can provide pore-structure characteristics of membranes.

A distinction will be made between two techniques: static and dynamic methods. Dynamic methods are based on membrane permeation characteristics and are used routinely to assess membrane performance. This review, however, will be restricted to static methods, which can provide details of porous microstructure directly. These include the following: stereology (microscopic techniques such as scanning electron microscopy [SEM]); intrusive methods (e.g., mercury porosimetry, physisorption of gases, calorimetrie methods, and nuclear magnetic resonance [NMR] analysis); and nonintrusive methods (e.g., radiation scattering with neutrons and x-rays, wave propagation, ion-beam analysis, and positron lifetime spectroscopy). Finally, the suitability of these techniques in the characterization of membrane pore structure will be discussed.

Porous materials can be formed in several ways, although the following three are most important in the synthesis of membrane structures.
The Application of CALPHAD Techniques in the Development of a New Gas-Turbine Disk Alloy
Authors: Small C.J. , Saunders N.
Published: August 2016

The development of a new nickel based superalloy for use in the high-pressure turbine disk of a modern gas turbine is one of the most expensive and protracted exercises undertaken by gasturbine manufacturers. A typical complete development cycle can take more than 10 years. This delay arises not only because of the extensive mechanical testing and Validation required to ensure the safety of the critical part, but also because of the difficulty of finding a material chemistry that provides the correct degree of balance between mechanical properties and long-term material stability. The conventional approach to this latter problem is to use a combination of experience, empirical wisdom, and a few basic calculation tools based on electron-valency theory (PHACOMP). There is thus an urgent need to develop a tool that reliably summarizes the known body of knowledge about the stability of Ni-based superalloys and provides a method that can quickly and reliably guide the alloy developer through the initial alloy-chemistry selection phase of development.

Calculation of phase equilibria using calculated phase-diagram (CALPHAD) techniques has now matured to the point where it is possible for the alloy developer to quickly and reliably calculate phase equilibrium in a matter of minutes without an in-depth knowledge of thermodynamics. There thus exists a tool that enables the definition of alloy chemistries so that specific assumptions can be tested and the final chemistry selected without having to carry out the traditional manufacturing, processing, testing, and examination of a large raft of experimental chemistries. This article aims to show how such a tool has been used and high lights the success of this approach in the field of Ni-based superalloy development.
Thermochemical Modeling of Glass: Application to High-Level Nuclear Waste Glass
Authors: Spear Karl E. , Besmann Theodore M. , Beahm Edward C.
Published: August 2016

Despite the obvious importance of understanding the chemistry of oxide glass materials, predictive thermochemical modeis of complex glasses have not yet been developed. Such modeis are important for technologies such as the disposal of high-level nuclear and transuranic waste (HLW), which are currently fore-seen as being incorporated in a host glass for permanen t Sequestration. A large number of glasses have been explored, with a borosilicate glass being the typical base composition. An example of the complexity of such a HLW glass is given in Table I. This article discusses our at-tempts to develop an accurate, easy to understand and use glass Solution model for describing the thermodynamic stability of such HLW glasses. Critical for such a model is the availability of reliable thermodynamic data that can be used in generating accurate values for thermodynamic activities of glass components as a function of temperature and glass composition. Therefore, a major part of this article focuses on developing reliable sets of thermodynamic data for complex HLW glass Systems and Subsystems. With such Information and a model, we can make predictions of the stability of these waste forms, including their volatility, leaching behavior, and corrosion reactions, and understand crystallization behavior during both the initial glass processing and long-term storage.

Using an equilibrium thermodynamic model is offen questioned, since HLW is to be stored as part of a glass phase, and glass is a nonequilibrium material. Our model uses a pseudoequilibriu map-proach in which we thermochemically treat the glass as a supercooled liquid. This is a more accurate approach than assuming a global System equilibrium, as it describes the behavior of the metas-table glass phase using thermodynamic data for the liquid phase and excludes the formation of crystalline species. As a result, developing an accurate model and data for representing the thermodynamic properties of oxide liquid phases is critical to understanding the limiting chemi-cal behavior of the nuclear waste glass.

The methodology requires that a critically assessed thermodynamic database be created for binary and ternary combinations of the major constituents in a typical waste glass. These data can then be combined to represent the thermodynamic behavior of the more complex multicomponent HLW glass Systems. If a crystalline phase is experimentally observed to precipitate from the glass under certain conditions, a thermodynamic description can be used to calculate the composition-temperature conditions under which this specific crystalline phase can exist in equilibrium with the metas-table glass phase.
Unsolved Mysteries of Water in Its Liquid and Glass States
Authors: Stanley H. Eugene
Published: August 2016

The following is an edited transcript of the presentation given by H. Eugene Stanley (Boston University), recipient of the MRS 1998 David Turnbull Lectureship, at the 1998 MRS Fall Meeting on December 2,1998, in Boston.

I would like to begin with a kind of kitchen experiment that any of you can do. Take your favorite drink. For some, this is ice water (Figure 1). Ask a simple question: “Whatshould this thermometer read?” And think for a minute of the implications of the answer to your question.

The title of this talk concerns water in two different states: the liquid State and the glass State. We'll organize this talk around three questions:

■ “What is the puzzle of liquid water?”

■ “Why do we care about this puzzle?”

■ “What do we actually do?”

The “we” in this case is a rather large number of individuals. TU focus this talk on very recent work that has been published or at least submitted this year. This work was done in collaboration with M.-C. Bellissent-Funel, S.V. Buldyrev, M. Canpolat, M. Meyer, O. Mishima, M.R. Sadr-Lahijany, A. Scala, and F.W. Starr. It's also based on earlier research a few years back with C.A. Angell, P.G. Debenedetti, A. Geiger, P.H. Poole, S. Sastry, F. Sciortino, and J. Teixeira. Any of these 15 valued collaborators could probably give this talk as well as, if not better than, I will.

We will organize the answer to our third and principal question in the following way: First, we will attempt to identify, in the spirit of Sherlock Holmes, some interesting clues.
Fluorocarbons and Fluorosurfactants for In Vivo Oxygen Transport (Blood Substitutes), Imaging, and Drug Delivery
Authors: Riess Jean G. , Krafft Marie Pierre
Published: August 2016

The development of biomaterials to treat, repair, or reconstruct the human body is an increasingly important component of materials research. Collaboration between materials researchers and their industrial and clinical partners is essential for the development of this complex field. To demonstrate the importance of these interactions, two articles in this issue focus on advances in biomaterials relating to the use of colloidal systems for transport, drug delivery, and other medical applications. These articles were coordinated by Dominique Muster (Université Louis Pasteur, Strasbourg) and Franz Burny (Hôpital Erasme, Brussels). The following is the first of these two articles.

A large variety of colloidal Systems involving highly fluorinated components have been prepared and investigated in recent years. These fluorinated Systems comprise diverse ty pes of emulsions (e.g., direct, reverse, and multiple emulsions; microemulsions; gel emulsions; waterless emulsions) with a fluorocarbon phase (and often a fluorinated Surfactant), and a ränge of self-assemblies (vesicles, tubules, helices, ribbons, etc.) made from fluorinated amphiphiles. Fluorinated Langmuir films and fluorinated black lipid membranes (BLMs) also have been investigated.

Research in this area was driven by the potential applications of such materials in medicine and biology. Fluorocarbon-based products are being developed as injectable oxygen carriers (“blood Substitutes”), media for liquid Ventilation, drug delivery Systems, and contrast agents for ultrasound imaging. One such agent has recently been approved for use in Europe and the United States. Several more products are in an advanced stage of clinical evaluation, and others are in various stages of preclinical development. From a more fundamental Standpoint, these materials are being investigated for assessing and understanding the impact that fluorinated components have on the formation, stability, structure, and properties of colloida l Systems in comparison with their hydrocarbon counterparts. The attention given to fluorinated colloids prompted the synthesis of numerous new families of fluorinated amphiphiles, which were to become components of such colloids.
Atomic-Scale Processes in Cu Corrosion and Corrosion Inhibition
Authors: Magnussen O.M. , Behm R J.
Published: August 2016

The electrochemical dissolution of clean, oxide-free metal surfaces in electrolyte solutions is a fundamental process in metal corrosion as well as in technological etching and metal-refinement processes. Due to fundamental interest and for industrial reasons, dissolution processes and the effect of organic corrosion inhibitors have been studied intensely, concentrating on the determination of macroscopic etch rates and the effect of varying chemical parameters upon the etch kinetics. In the 1920s, ideas for the microscopic mechanism of the dissolution and the reverse deposition reaction had already been put forward by Stranski, who suggested that dissolution (growth) is dominated by detachment (attachment) of atoms at low coordination sites of the crystal surface and at kink sites along monoatomically high steps (see the schematic model in Figure 1). These kink sites are preserved during the removal (or addition) of the basic building blocks of the crystal (e.g., single metal atoms for elemental metals) and hence can sustain a continuous dissolution reaction. However, the direct verification of these ideas was impossible for more than seven decades, due to the very complex (defect) structure of the surfaces of typical metal electrodes, the presumably dominating effects of these defects on the etch process, and the lack of structurally sensitive probes suitable forin situstructural characterization.
In SituX-Ray-Diffraction Studies of Passive Oxide Films
Authors: Ryan Mary P. , Toney Michael F. , Davenport Alison J. , Oblonsky Lucy J.
Published: August 2016

Most metals are thermodynamically unstable in aqueous environments. They are kinetically stabilized by the formation of very thin “passive” oxide films that provide protection from corrosion. The technological importance of passive films has led to widespread investigation of their structure and chemistry. However, despite decades of work since Michael Faraday first described the existence of the passive film on iron, the atomic structure of these films is still poorly understood. This is because the films are so thin (typically only a few nanometers thick), making measurements difficult, and because the structure can only be investigated in the (wet) electrochemical environment in which these films form.

The electrochemical nature of the formation of these oxide films is shown in Figure 1, which presents the current response of an iron electrode in an aqueous solution to an applied voltage (potential). As the potential is slowly increased from negative (cathodic) to positive (anodic), the iron first begins to dissolve. This area of dissolution is known as the active region, indicating that the iron is corroding freely as ferrous ions (Fe2+). Then, at a sufficiently anodic (oxidizing) voltage, a thin (30 Å) oxide film forms at the iron surface, preventing further dissolution. This results in a marked decrease in the measured current, a phenomenon known as passivity. Over the passive region, the current is virtually independent of applied voltage and remains extremely low, indicating that the iron is protected from additional oxidation or corrosion.
Molecular-Beam Epitaxy and Device Applications of III-V Semiconductor Nanowires
Authors: Hasegawa Hideki , Fujikura Hajime , Okada Hiroshi
Published: August 2016

A scaling-down of feature sizes into the nanometer range is a common trend in silicon and compound semiconductor advanced devices. That this trend will continue is clearly evidenced by the fact that the “roadmap” for the Si ultralarge-scale-integration circuit (USLI) industry targets production-level realization of a 70-nm minimum feature size for the year 2010. GaAs- and InP-based heterostructure devices such as high-electron-mobility transistors (HEMTs) and heterojunction bipolar transistors (HBTs) have made remarkable progress by miniaturization, realizing ultrahigh speeds approaching the THz range with ultralow power consumption. Due to progress in nanofabrication technology, feature sizes of scaled-down transistors are rapidly approaching the Fermi wavelength of electrons in semiconductors, even at the production level. This fact may raise some concerns about the operation of present-day devices based on semiclassical principles.

However, the progress of nanofabrication technology has opened up the exciting possibility of constructing novel quantum devices, based directly on quantum mechanics, by utilizing artificial structures such as quantum wells, wires, and dots. In these structures, new physical effects appear, such as the formation of new quantum states in single and coupled quantum structures, artificial miniband formation in superlattices, tunneling and resonant tunneling in single and multiple barriers, propagation of phase-coherent guided electron waves in quantum wires, conductance oscillations in small tunnel junctions due to single-electron tunneling, and so on. We expect that these effects will offer rich functionality in next-generation semiconductor quantum ULSIs based on artificial quantum structures, with feature sizes in the range of one to a few tens of nanometers. Beyond this, molecular-level ULSIs using exotic materials and various chemical and electrochemical processes other than the standard semiconductor ones may appear, butat present, they still seem to be too far in the future for realistic consideration for industrial applications.
Self-Assembled Patterning of Ultrathin Silicides by Local Oxidation
Authors: Mantl S. , Zhao Q.T. , Kabius B.
Published: August 2016

Most microfabrication techniques employ masks to transfer the desired microstructure onto a wafer using ultraviolet light, x-rays, electrons, or ions for the projection of the structures. Generally, photoresist processing and etching follow to form the final structures. In all cases, the facilities necessary to perform these processes grow increasingly more complex as the feature size of the structures diminishes, and these processes face their practical or economic limits at dimensions of about 50 nm. Thus alternative approaches are under investigation, including different self-assembly techniques. They require no costly facilities and no masks with nanometer structures, and they promise high throughput, since the patterning is directly achieved by a physical or chemical process. Self-assembled monolayers of long-chain organic molecules are the most widely studied examples, where chemisorption and spontaneous self-ordering of the molecules are observed on appropriate substrates. Another interesting example is island-ordering, laterally or in a vertical direction, during epitaxial growth. The lattice-mismatched islands tend to nucleate preferentially on top of each other when separated by a thin spacer layer, due to the associated strain field. Another approach is the use of specific stressor layers on the surface to obtain alignment of buried precipitates along the stressor lines. However, the main challenges of all self-assembly techniques are precise control of the dimensions of the structures and reproducibility.