bluuebunny/crossref_metadata_2025_split huggingface dataset:
Biology and Materials? Part II
Authors: Alper Mark 
Published: August 2016

The October issue of the MRS Bulletin focused on two areas of research in biomolecular materials; biomineralization and protein fibers. In addition, the development of a new carbohydrate-based material with a variety of novel properties was discussed.In this issue, we turn to two other types of materials based on biological systems: (1) polymers and other materials produced through enzyme-catalyzed biosynthetic reactions and (2) protein and lipid complexes based on biological membrane structures. In each case, as in the October issue, a discussion of how Nature produces and uses these materials is followed by reports describing manipulations of these systems to enhance their properties for nonbiological applications.In the October issue, Kaplan and Cappello discussed in detail the synthesis of proteins. They described how living organisms expend a very large fraction of their energy producing these polymers to grow and repair damage to their bodies. (The other major fraction of their energy is dedicated to maintenance of brain function). Synthesis of carbohydrates, lipids, and other materials, however, is achieved through a somewhat more complex process. The organism outlines a pathway that consists of a sequence of reactions; each reaction converts a substrate-the product of the preceding reaction-to a product which is the substrate for the next reaction. The net result of the action of the pathway is the conversion of a nutrient to a useful material, often of far different chemical structure.
Copper-Based Metallization for ULSI Applications
Authors: Li Jian , Blewer Robert , Mayer J.W. 
Published: August 2016

Multilevel metallization of very large-scale integrated (VLSI) circuits has become an area of intense research interest as devices are scaled down in order to increase circuit density. As device dimensions approach the submicron regime, reliability becomes more of an issue. Metallization generally requires good conductivity, electromigration resistance, controllable contact performance, corrosion resistance, adherence, thermal stability, bondability, ability to be patterned into a desirable geometry, and economic feasibility.Aluminum and its alloys have been commonly used as the main metallization materials because they meet most of the metallization requirements for microelectronic devices. Aluminum, however, suffers from major limitations, such as elec-tromigration and stress-voiding induced open-circuit failure. For the development of ultralarge-scale integration (ULSI) for fast-switching-speed devices, the electrical resistivities of aluminum and its alloys are not low enough. As the minimum geometry is scaled down to one-quarter micron, aluminum and its alloys potentially will be replaced by other materials such as Cu, Au, or superconductors for on-chip interconnection.
Crystal Interface Engineering in High Tc Oxides
Authors: Char K. 
Published: August 2016

Interfaces between metal oxides have not been studied as extensively as metal or semiconductor interfaces. Even in magnetic metallic systems, new phenomena are still being discovered, such as giant magnetoresistance, which has been attributed to an interface phenomenon. As general interest in metal oxides increases, researchers are studying a large variety of heterostructures consisting of superconducting oxides, conducting oxides, ferroelectric oxides, magnetic oxides, and optical oxides. As the complexity and level of integration increase, scientists need a better understanding of the interfaces in metal oxide systems. For example, interface issues in grain boundaries in high Tc oxides and in Josephson junctions of the superconductor/normal material/superconductor (SNS) type have been identified as important technological barriers. In heterostructures based on ferroelectric materials, fatigue problems are believed to be associated with the interface between the conducting electrodes and the ferroelectric metal oxides, and with grain boundaries in the ferroelectric materials.In this article we will focus on the interface issues related to YBCO superconductors. We will describe interface phenomena observed in several systems, such as YBCO/metal contacts, YBCO/YBCO grain boundaries, and YBCO/epitaxial metal oxides. From their seemingly universal behavior, we will try to identify the origin of the interface phenomena and will describe some recent efforts to control such phenomena.
Refractory Oxide Coatings on SiC Ceramics
Authors: Lee Kang N. , Jacobson Nathan S. , Miller Robert A. 
Published: August 2016

Silicon-based ceramics are leading candidate materials for high-temperature structural applications such as heat exchangers, advanced gas turbine engines, and advanced internal combustion engines. They have excellent oxidation resistance in clean oxidizing environments due to the formation of a slow-growing silica scale (SiO2). However, durability in high-temperature environments containing molten salts, water vapor, or a reducing atmosphere can limit their applications. Molten salts react with silica scale to form liquid silicates. Oxygen readily diffuses through liquid silicates and rapidly oxidizes the substrate. High water vapor levels lead to hydrated silica species, such as Si(OH)4(g) and subsequent evaporation of protective scale. Complex combustion atmospheres containing oxidizing (CO2, H2O) and reducing (CO, H2) gases form SiO2 and then reduce it to SiO(g). In situations with extremely low partial pressures of oxidant, direct formation of SiO(g) occurs. All these reactions can potentially limit the formation of a protective silica scale and thus lead to an accelerated or a catastrophic degradation.One approach overcoming these potential environmental limitations is to apply a barrier coating which is environmentally stable in molten salts, water vapor, and/or reducing atmospheres. Refractory oxides such as mullite (3Al2O3 · 2SiO2), yttria-stabilized zirconia (ZrO2-Y2O3), or alumina (Al2O3) are promising candidate coating materials because of their excellent environmental stability in these severe conditions. Refractory oxide coatings can also serve as thermal barrier coatings because of their low thermal conductivity. Key requirements for an adherent and durable barrier coating include coefficient of thermal expansion (CTE) match and chemical compatibility with the substrate. Mullite in general meets all the requirements and thus appears most promising.
Degradation of Thermal-Barrier Coatings at Very High Temperatures
Authors: Stott F.H. , de Wet D.J. , Taylor R. 
Published: August 2016

Thermal-barrier coatings are finding increasing use in engineering applications, particularly in gas turbines. Such coatings, consisting of ceramic insulating layers bonded to the superalloy substrate by oxidation-resistant alloy coatings, are deposited onto components to reduce heat flow through the cooled substrate and to limit operating temperature. They have been used effectively on static components such as combustor cans, flare heads, hot gas seal segments, fuel evaporators, and deflector plates, giving considerable improvements in component life. They have been used successfully on vane platforms. In recent years, the emphasis has shifted toward the development of coatings for high-risk areas, such as turbine blades.A ceramic thermal-barrier coating needs to be refractory and chemically inert, and to have low thermal conductivity. However, it also needs to possess a high thermal expansion coefficient of ~11 × 10−6 K−1, to match the nickel-base superalloy substrate. The latter specification has focused attention on ZrO2. However, ZrO2 is polymorphic and undergoes two phase changes, cubic to tetragonal at 2350°C and tetragonal to monoclinic at 1170°C. The latter transformation is accompanied by a 5% volume increase which means that ZrO2 has to be alloyed to stabilize one of the high-temperature phases. Early systems in the 1970s consisted of ZrO2 stabilized with MgO, but this has been shown to be a metastable system. Present-day commercial thermal-barrier coatings consist of a plasma-sprayed yttria- or magnesiastabilized zirconia layer on top of an M-Cr-Al-Y bond coat. The latter plays a very important role by helping to key the ceramic to the alloy substrate and to accommodate the mechanical strains arising because of differences in thermal expansion coefficients and elastic moduli between the ceramic and the substrate.
Fullerenes
Authors: Rao C.N.R. , Ōsawa Eiji 
Published: August 2016

Although C60 and other such molecules had been predicted earlier on the basis of theoretical considerations, the identification of these molecules by mass spectrometry in the year 1985 is an important landmark. The discovery of a ready method of preparation by arc evaporation of graphite in 1990 gave a big boost to this area of research. Today, research on carbon has undergone a renaissance and the new carbon molecules and structures probably constitute the second greatest sensation in physical science since the 1986 discovery of high-temperature super-conductivity in cuprates.These fascinating cage molecules of carbon, containing 6- and 5-membered rings, with considerable pi electron density, exhibit interesting chemical as well as materials properties. The phase transitionh of fullerenes and the electronic properties of the derivatives of C60 are indeed interesting. And, as if this were not enough, many other novel carbon structures have recently been discovered. Nanotubes are a major discovery. Closed on either end, nanotubes can be opened by mild oxidation at the reactive site at the closed end and can be filled with metals. Carbon onions made of concentric giant fullerenes constitute another interesting form of carbon. The onions have also been stuffed with metals and metal carbides. Clearly, carbon research has many surprises in store, with promising applications. It is only appropriate that the MRS Bulletin has dedicated a special issue to the new carbon structures and we are happy to serve as guest editors, presenting a wide variety of topics that convey the flavor of this fascinating field. We begin with a personal account of Buckminsterfullerene by co-guest editor Harry Kroto.
Phase Transitions, Superconductivity, and Ferromagnetism in Fullerene Systems
Authors: Rao C.N.R. , Seshadri Ram 
Published: August 2016

By virtue of their unique structures, fullerenes exhibit novel chemical transformations. Particularly pertinent to this article are the interesting properties exhibited by fullerenes in the solid state. These molecules are spherical or near-spherical in shape. Molecules with high point-group symmetry, which are not bound strongly in the solid state, tend to crystallize into structures with long-range periodicity of the molecular centers of mass, but the molecular orientations are random or even dynamically disordered. When dynamically disordered, themolecules rotate about some preferred axis. C60 and C70 satisfy the criteria for such orientationally disordered solids and exhibit rich phase behavior in the solid state. Since C60 has high electron affinity, it forms anion salts with alkali and alkaline-earth metals as well as with strong organic donor molecules. With tetrakis dimethylaminoethylene (TDAE), which is a very powerful electron donor, C60 forms a 1:1 solid that is ferromagnetic. C60-TDAE is the molecular organic ferromagnet with the highest Tc (of 16 K) known to date. Some of the alkali and alkaline-earth fullerides, on the other hand, show superconductivity, with transition temperatures going up to 33K. We shall briefly examine some of these solid-state properties.
Overview of FGM Research in Japan
Authors: Koizumi M. , Niino M. 
Published: August 2016

Space planes require high-performance heat-resistant materials which can withstand ultrahigh temperatures and extremely large temperature gradients. To meet these needs, functionally gradient materials (FGMs) were proposed about 10 years ago in Japan.Figure 1 shows a conceptual diagram of functionally gradient materials, taking into account the relaxation of thermal stress. For the surface that contacts high-temperature gases at thousands of degrees, ceramics are used to provide adequate heat resistance. For the surface that provides cooling, metallic materials are used to furnish the necessary thermal conductivity and mechanical strength. In addition, the composition of these materials is formulated to provide optimum distribution of composition, structure, and porosity to effectively relax thermal stress.Since fiscal 1987, an R&D project entitled “Research on Fundamental Techniques to Develop Functionally Gradient Materials for Relaxation of Thermal Stress,” which aimed to develop ultra heat-resistant materials, had been carried out with special coordination funds from the Science and Technology Agency. The five-year project had two phases; Phase I was carried out from 1987 to 1989, and Phase II from 1990 to 1991.
Powder Processing of Functionally Gradient Materials
Authors: Watanabe R. 
Published: August 2016

Powder metallurgical (P/M) processing of FGMs provides a wide range of compositional and microstructural control, along with shape-forming capability. Oxide/metal systems are desirable because this materials combination can be used to easily tailor materials properties. However, there are many problems to be investigated which pertain to each of the processing steps; process innovations will often be required to realize the versatility of this route. In this article, I briefly review the present status of the powder-processing method.Powder metallurgical fabrication of FGMs involves the following sequential steps with a selected material combination of metals and ceramics: determination of the optimum composition profile for an effective thermal-stress reduction; stepwise or continuous stacking of powder premixes according to the predesigned composition profile; compaction of the stacked powder heap and sintering with or without pressurizing. Besides the conventional powder metallurgical routes, a spray deposition method, using mixed powder suspensions and a slurry stacking method, have been developed to form continuously graded stacking. A powder spray stacking apparatus has been devised, which is fully automatic with computer control. Deposited compacts were cold isostatically pressed (CIP) and consolidated by hot isostatic pressing. Their microstructures show that this process provides fine compositional control with desired profiles.Differential temperature sintering by laser-beam heating has been studied to add versatility to the P/M process. The surface of the green compacts is scanned with a laser beam using a predesigned scanning pattern to ensure homogeneous heating over the entire surface.
Recent Progress in Silicon Nitride and Silicon Carbide Ceramics
Authors: Mitomo Mamoru , Petzow Günter 
Published: August 2016

We know from experience that ceramic materials are brittle and easily broken. This is one reason why ceramics have not been used as engineering materials. Fracture is the result of crack growth through the microstructure. It was Griffith who proposed that ceramics have intrinsic cracks which grow under applied stress. The concentration of the applied stress at the crack tip decreases the strength to a level of about 1% or less of the theoretical strength. If the crack starts to grow, strength decreases so sharply that a catastrophic fracture occurs.In spite of the brittle nature of ceramics, their application as engineering materials was proposed in the 1960s because ceramic materials made of silicon nitride or carbide have higher strength at high temperatures than metals and oxide ceramics. Non-oxide ceramics have lower thermal-expansion-coefficients than oxides, resulting in better thermal shock resistance, which is one of the most important requirements for engineering ceramics.
In Situ Synchrotron Radiation Research in Materials Science
Authors: Montano Pedro A. , Oyanagi Hiroyuki 
Published: August 2016

X-rays have found a wide range of applications in chemistry, physics, and materials engineering since their discovery in 1895 by W. Roentgen. The materials science community uses x-ray-based techniques extensively for characterization of materials. In the 1970s a new tunable source of x-rays from the radiation produced by synchrotron accelerators emerged. Synchrotron radiation (SR) is an intense and forward-focused beam of radiation that is emitted when the path of an electron traveling at almost the speed of light is bent by a magnetic field. Figure 1 illustrates the evolution of radiation intensity provided by various x-ray sources. In situ SR techniques provide real-time observation of atomic arrangements with high spatial sensitivity and precision, which are important features not only in fundamental materials research, but also in the development of novel processing techniques and in the search for new exotic materials. A major advantage of SR is that it covers a wide range of wavelengths continuously from infrared to gamma rays. This feature is attractive since a wealth of detailed information on the electronic and structural properties of materials can be obtained by optimizing the wavelength of the radiation.Since the establishment of “first generation” facilities in the early 1970s, the x-ray emittance from synchrotron storage rings, where electrons traveling at almost relativistic speed s are constrained by magnetic fields to follow curved trajectories, has shown dramatic improvements. See Table I for an extensive list of SR facilities presentiy in use throughout the world.
Infrared Reflection Absorption Spectroscopy of Selective Etching and Decomposition Stimulated by Synchrotron Radiation
Authors: Urisu Tsuneo 
Published: August 2016

The study of processing stimulated by synchrotron radiation (SR) started about 13 years ago. Unfortunately, for semiconductor processing, the reaction rate of this technique was considered to be too slow for practical applications. However the situation is rapidly changing as device dimensions shrink to the nanometer range, which requires high controllability and low defect densities, but is not so reliant on quick processing since much less material is involved. SR etching—which has a typical etching rate of 1–10 nm/min, capability of high-resolution etching due to the short wavelength of SR photons, high controllability, low damage production, and a clean reaction system—is considered to be extremely suitable for nanometer processing.The benefit of SR etching is that it has unique material selectivities. However the mechanisms for the selectivity are not yet clarified. Consideration of the future application of the SR process to nanometer structure fabrication is dependent upon the development of in situ observation techniques that can evaluate the reaction surface at an atomic or molecular level. Recently we have developed an in situ observation technique: infrared reflection absorption spectroscopy using buried metal layer substrates (BML-IRRAS), which is especially suitable for in situ monitoring of beam-induced reactions on the semiconductor surface in high vacuum.
Microporous Inorganic Membranes for Gas Separation
Authors: Morooka Shigeharu , Kusakabe Katsuki 
Published: August 2016

Microporous inorganic membranes are potentially useful in gas separation in emerging areas such as catalytic reactors, gasification of coal, molten-carbonate and solid-electrolyte fuel cells, and water decomposition by thermochemical reactions. If the feed or product gases can be separated at elevated temperatures specific to each process, the energy required for purification could be greatly reduced. Advances in the development of inorganic membranes have been quite rapid in recent years. For example, in 1991 the reported CO2/N2 selectivity at ambient temperature was less than 10, but by 1997 it had improved to approximately 100.The permeation rate and permselectivity of porous inorganic membranes are dependent on the microstructures of membrane/support composites such as pore size and distribution, porosity, tortuosity, and the affinity between permeating species and pore walls. Figure 1 shows the relationship between molecular weight and kinetic diameter (calculated from minimum equilibrium cross-sectional diameter) for a selected series of molecules. Hydrogen and helium are smaller and lighter than the others. Structural isomers such as n-C4H10 and i-C4H10 have the same mass but quite different sizes. Therefore, the control of micropores is of critical importance in these cases. However, the molecular masses and sizes of CO2 and N2 are not greatly different; thus the difference in affinity is important for separation of these molecules.In order to achieve effective separation of small-molecule gases, the membrane pores should be smaller than 2 nm. In the case of mesopores or macropores, gases permeate with low selectivities through these pores. In this article, preparation processes and permeation properties of porous inorganic membranes are reviewed, and permeation mechanisms are discussed.
Computer Simulations from Thermodynamic Data: Materials Protection and Development
Authors: Spencer P.J. 
Published: August 2016

The development and optimization of materials and processes are generally extremely time-consuming and costly Operations. As a result, significant delays are frequently encountered before important materials advances can be introduced in technological applications. For these reasons, thermodynamic calculations and simulations based on critically evaluated data are now finding wide and increasing use as basic tools in materials and process design. Commercial Software packages incorporating thermodynamic databases are already available for this purpose. Their use enables the number of direct measurements to be minimized, as Information on necessary process conditions can be obtained very rapidly and inexpensively to achieve a product of the required purity with the minimum waste of energy and materials.Typical examples of materials development now being assisted and improved with the help of thermodynamic calculations are■ selection of optimum melting and casting conditions for complex alloys,■ optimization of deposition conditions in chemical-vapor-deposition and physical-vapor-deposition production of metal and oxide coatings,■ definition of suitable compositions and heat-treatment conditions in the production of application-specific materials, and■ prediction of energy requirements and environmental emissions associated with specific materials-processing Operations.Equilibrium thermodynamic calculations alone can sometimes prove satisfac-tory for Simulation of high-temperature technological processes. However, for reliability of simulations at lower temperatures, kinetic factors cannot be neglected. For this reason, recent Software developments include descriptions of diffusion phenomena, or rates of reaction. Significant here is the more fundamental Information provided for nonequilibrium conditions.This often gives new insight into the basis of compositional and phase changes in complex Systems under different process conditions. The reliability of thermodynamic simulations clearly depends upon the reliability of the data used. A significant drawback here is that many classic thermodynamic data compilations contain values for pure inorganic substances only (e.g., References 4–6). There are very few processes, however, for which the reactants and products can be regarded as simple stoichiometric Compounds. Even very small amounts of dissolved gases or other impurities in a product material can seriously impair its properties.