bluuebunny/crossref_metadata_2025 huggingface dataset:
Ion-Assisted Processing of Electronic Materials
Authors: Brown Walter L. , Ourmazd Abbas
Published: August 2016

The fabrication of a state-of-the-art silicon chip consists of a carefully composed sequence of “steps.” The length, complexity, and place of each step within this process is analogous to that of a musical phrase within a long sonata. Just as a sonata consists of a series of recurring but evolving themes, a “process” utilizes a number of basic techniques that recur in a variety of contexts. A typical modern process consists of about 350 “steps.” Roughly a fifth of them belong to the class of ionassisted processing. These range from a variety of ion implantation modules, through sputter deposition and reactive ion etching of thin films, to photoresist etching and ashing. Ion-assisted processing thus has a role of major technological importance. With the range of new processes currently under active research, this trend seems likely to continue.

The technological applications of ionassisted processing rest on the basic concepts developed in research over the past 30 years. This special issue of the MRS Bulletin reviews the fundamental concepts that underpin this processing today, and highlights areas of current research which may have future technological potential. The emphasis is placed heavily on silicon, both for illustrative purposes, and because Si processing is the major customer for ion-assisted technology. The articles pinpoint areas where materials research can play a critical role in establishing the fundamental understanding needed for a realistic assessment of technological potential.
Materials Science and Engineering Education
Authors: Abbaschian R.
Published: August 2016

Materials science and engineering (MSE), as a field as well as a discipline, has expanded greatly in recent years and will continue to do so, most likely at an even faster pace. It is now well-accepted that materials are crucial to the national defense, to the quality of life, and to the economic security and competitiveness of the nation. Mankind has recognized the importance of manmade materials to the quality of life for many centuries. In many cases, the security and defense of tribes and nations have substantially depended on the availability of materials. It is not surprising that historical periods have been named after materials—the Bronze Age, the Iron Age, etc. The major requirements from materials in those days were their properties and performance. Today, in this age of advanced materials, the importance of materials to defense and quality of life has not changed. However, the critical role of materials has taken an additional dimension: it has become essential to enhancing industrial competitiveness.

The knowledge base within MSE has also expanded vastly throughout these years and continues to do so at an increasing rate. We are constantly gaining a deeper understanding of the fundamental nature of materials, developing new ways to produce and shape them for applications extending from automobiles to supersonic airplanes, optoelectronic devices to supercomputers, hip implants to intraocular lenses, or from household appliances to gigantic structures. We are also learning that, in many of these applications, we need to depend on the combinations or composites of different classes of materials (metals, ceramic, polymers, and electronic materials) to enhance their properties.
Graduate Education for Materials Scientists and Engineers: General, Special, or Fundamental?
Authors: Stiles Phillip J.
Published: August 2016

What is an appropriate educational program for preparing a PhD to enter the general work force, particularly in materials science and engineering, but also more broadly in all science and engineering fields? The question can be proposed at two different levels: What is the character of the information, knowledge, and the training a student ought to store away and be able to use after leaving the academy, and what specific information or courses does someone need to be an expert?

Since I do not have expertise in every aspect of materials science and engineering, and since the latter question can be handled through concerted effort of the appropriate experts, I will focus only on the first question.

To paraphrase the first question more starkly, how much of a generalist should a PhD be and how much of a specialist? I will try to define the generalist and specialist in polar perspective, in the sense that I use them:

1. A specialist must be grounded in that specialty, conversant with its literature and new findings, and able to converse with other specialists in the field to exchange information and perspectives.

2. A generalist must be well-grounded in the fundamentals of numerous fields. It is not necessary to be a specialist in many fields, but a generalist must have access to and be able to find and digest the happenings and literature in these other fields.
Acceptance Remarks for the Von Hippel Award of the Materials Research Society, Hyatt Regency Hotel, Boston, Massachusetts - November 27, 1979
Authors: Turnbull David
Published: August 2016

It is a high honor to receive this award; especially so, considering the distinction of the first two recipients: Professor von Hippel, who pioneered brilliantly in the development and definition of Materials Science, and Dr. Baker, under whose leadership were made the great scientific and technological discoveries at Bell Laboratories during the past decades. It is not clear to me that I belong in this progression. I feel that I am in a position rather like that of a certain Linus. I'm sure that you all know of two famous persons named Linus but you may not have heard of the Linus to whom I refer. He was identified by the ecclesiastical historian Eusebius as the first Bishop of Rome following the Apostles Peter and Paul. In any event, this award indicates that some of my colleagues, rightly or wrongly, think highly of me and that is pleasant to know.
An 8,500-Year-Old Sculpted Plaster Head from Jericho (Israel)
Authors: Kingery W. David , Vandiver Pamela B. , Noy Tamar
Published: August 2016

Jericho (Tell al-Sultan) lies in the Jordan rift valley north of the Dead Sea. Although now remembered as the city where Joshua blew his trumpet and the walls came tumbling down, it was an important settlement long before and long after this late second millennium B.C. battle. Jericho is located close to an important spring and was inhabited during the Natufian period between 11,000 and 9,300 B.C. as an encampment from which cereal grains were collected and gazelle were hunted. In the Aceramic or Pre-Pottery B Neolithic Period (7000–6200 B.C.), the site was the largest village in the area, covering three hectares. Jericho is thought to have had a population of perhaps 1,500 people who developed farming of wheat, barley, legumes, and fruit such as figs, and gradually, the herding of sheep and goats. Salt and bitumin were available to the south in sufficient abundance for trade. Although no pottery vessels were made and fired at this time, the clayey, calcareous soil, reinforced with fibrous dried vegetal material, was used as a ubiquitous building material for houses, storage pits, animal shelters and other structures. Sun-dried bricks were developed in the Pre-Pottery Neolithic A, and they became the common building element.

Variations in the color, texture, and properties of the various soils available to the Jericho villagers were well known, as exhibited by the villagers' use of different materials for specific purposes. Our studies have shown that some calcareous soils were used to make lime plaster; others, with considerable clay and sand, were used for brick and mortar; and others consisting of fine, fairly high shrinkage, montmorillonite clays were used for small objects and figurines whose manufacture required considerable plasticity and fine surface detail.
Quantitative Structural and Chemical Analysis of Thin Films: Part II
Authors: Bruynseraede Y. , Schuller Ivan
Published: August 2016

In the second of this two-part series for the MRS Bulletin, we present the most commonly used tools for the quantitative determination of structure and chemistry in thin films. The physics of thin films is at a stage during which one encounters phenomena that have a fragile dependence on the structure and chemical properties of the interface; the field, therefore, is at a stage during which quantitiative structural and chemical determination at the atomic level is a must. It is the purpose of the December and January issues of the Bulletin to provide a start for researchers interested in the field. Of course, even during the writing of these articles new techniques are being invented and it is therefore impossible to provide a comprehensive review of all techniques being used these days.
Federal Regulations Create New Challenges in Materials Science
Authors: Yost F.G.
Published: August 2016

Title 40 of the Code of Federal Regulations is a compendium of rules pertaining to environmental protection, written primarily by the Environmental Protection Agency (EPA). These environmental regulations stand some 19 inches wide on a library shelf and are enclosed by 15 volumes of everchanging information. Each of these volumes contains amendments made to the rules since the last publication of that volume, so the effective dates of new regulations can be difficult to ascertain. Interpreting certain regulations has been difficult for many, the cost of complying with them high, and the eventual impact on the national economy foreseen as gloomy. Few, however, would deny the benefits of a well-planned environmental protection plan and few would sympathize with private corporations that flagrantly ignore regulations, pollute their local environment and, when identified, sustain heavy fines from the EPA.

With problems like acid rain, air and groundwater pollution, global warming, ecological system degradation, municipal, industrial, and nuclear waste (and the federal regulations designed to control them), the need for important materials science research and development is great. These opportunities can be compared in magnitude with those provided by the Manhattan Project, during the 1940s and 1950s, and by the semiconductor revolution in later years. The difference between these past projects and the current situation is the way in which funds are appropriated for the research and how the work is performed. Rather than independently funded research performed by multiple organizations, work on environmental problems is witnessing cooperation among industry, government, academia, and the public, with a consequent savings of research monies. This cooperation is often achieved with a consortium of organizations such as SEMATECH or the National Center for Manufacturing Sciences.
Rheology of Cementitious Systems
Authors: Zukoski C.F. , Struble L.J.
Published: August 2016

Many of the useful properties of Portland cement concrete stem from chemical reactions between cement and water, which cause the slow transformation of the initial fluid suspension into a rigid solid. Because this transformation does not begin immediately, concrete may be processed—mixed, transported, consolidated into a mold, and given a smooth surface — before it becomes rigid (i.e., sets), which typically occurs a few hours after initial mixing. As a result of the need to maintain a workable suspension during processing, the flow properties of cementitious systems have seen considerable attention. However, control of workability remains poorly understood, in part because the relationships between flow and process-ability are not clear. Recent advances have been made in understanding the flow of nonreactive suspensions, and the objective of this article is to explore how these advances provide new insights concerning the behavior of cementitious materials.

There are two motivations driving investigations of cement rheology. The first is that understanding flow properties is the key to better processing. The second is that paste rheology can be used to gain a fundamental understanding of the initial cement microstructure and of the variables influencing early cement hydration reactions.
Immobilization Science of Cement Systems
Authors: Macphee D.E. , Glasser F.P.
Published: August 2016

Portland cement and Ca(OH)2, “slaked lime,” are representative of a family of materials that have conceptual and practical advantages as matrices for the immobilization of wastes. These are relatively proven construction materials with an extensive history of use in various ground-water regimes, and in various climates. The raw materials are widely available and they exhibit a reasonable amount of resistance to physical damage and attrition. They are also durable. Although modern Portland cements are only about 150 years old, numerous examples of Roman concrete made from slaked lime and volcanic pozzolanic ash survive; the Pantheon in Rome (circa A.D. 300) continues in regular use.

Satisfactory immobilization matrices can also be formed by incorporating other artificial waste materials, e.g. coal combustion fly ash, blast furnace slag, and natural materials such as calcined kaolin or siliceous volcanic ashes containing glass and zeolites. These materials react with Ca(OH)2 and cement to become an integral part of a cement matrix. Thus one waste (ash, slag) can be used to help immobilize another, and may actually improve the retentive capacity of a cementitious matrix.

Since cements require water to harden, they are tolerant of wet wastes and are especially useful for many effluents. In addition, they are low-cost, nonflammable materials with the potential to provide chemical and physical immobilization of wastes, but their set characteristics can be affected by certain material additions. Table I balances some advantages against disadvantages of the use of cement systems for waste immobilization.
The Effect of Materials on Time
Authors: Sullivan Donald B.
Published: August 2016

We all know that the properties of a material can change with time, but is the inverse possible? How can materials have an effect on time? In the strictest sense, the idea is absurd. However, our ability to keep track of time is clearly dependent on the materials we use to construct our clocks. The performance of many early mechanical clocks depended on the materials of fabrication, and today's high-technology clocks depend no less critically on materials.

My objective in this brief article is to divulge a few materials problems involved in clock technology. Since I do not attempt a comprehensive report, I will undoubtedly leave out some issues that colleagues in the field would consider important.

Navigation has been a key driving force for the development of accurate timekeeping, at least since the 17th century. While many other important applications require accurate timekeeping (e.g., synchronization for telecommunications and electrical power distribution), I focus on navigation because of its historical significance and its particularly graphic illustration of why clocks have attained such prominence.
Metallization for Integrated Circuit Manufacturing
Authors: Joshi R.V. , Blewer R.S. , Murarka S.
Published: August 2016

This issue of the MRS Bulletin focuses on current interconnect metallurgies practiced in the manufacturing of integrated circuits (ICs). The issue should serve as a reference for researchers, scientists, engineers, and those who are not familiar with the IC arena.

Al-metallization requires special attention due to its wide usage in logic and memory circuits. Logic requirements drive technology toward improved circuit performance while memory improvements require high device and wiring densities. As the dynamic random access memory (DRAM) evolves from 64 Mbits to 256 Mbits, ultralarge-scale integrated (ULSI) wiring will decrease to below sub-0.3 μm in dimensions. Such circuits require robust, reliable back end of the line (BEOL) technology that meets high-performance, low-cost, stringent electromigration requirements. We feel that several of these emerging interconnect fabrication techniques have reached a sufficient level of maturity to warrant a reasonable exposition. We will concentrate on metallization systems in this issue, leaving a discussion of dielectrics for the future, due to space limitations.

The semiconductor industry has relied on aluminum technology since the 1960s because it is a well-established, low-cost technology. Early improvements in the electromigration resistance of Al lines by the addition of Cu impurities after 1971 helped this metallurgy to endure further feature size reductions, without degradation of reliability. However, the relentless reduction in via and line size once again may bring into question the limitation of Al reliability. As a result, work on alternate low-resistivity and high-electromigration-resistant metals like Cu is continuing in parallel.
Aluminum-Based Metallurgy for Global Interconnects
Authors: Pramanik Dipankar
Published: August 2016

In an integrated circuit (IC), the global interconnects are used to run power and ground to the individual transistors as well as to send signals across the chip. The width of interconnects can vary, depending on the current that is carried by the interconnect. Figure 1 shows a cross section of a double-metal complementary metal oxide semiconductor (CMOS) circuit illustrating the major components of a multilevel metallization circuit. The global interconnect connects to the diffusion and polysilicon gates through the contacts. The intermetal dielectric electrically separates the different levels of interconnect. The connection between the global interconnects at adjacent levels is made through the vias. The choice of a global interconnect for a multilevel metallization forces one to consider how the interaction between the various components of this system can affect the performance of the interconnect. For example, the intermetal dielectric changes the mechanical stress in the interconnect; the presence of W plugs in vias can affect the electromigration resistance of interconnects. In this article, we will examine the problems that are encountered when using Al alloys as a global interconnect and illustrate how the material properties can be modified to solve these problems.
Ion Tracks in Solids: From Science to Technology to Diverse Applications
Authors: Fleischer Robert L.
Published: August 2016

Fast ions create linear trails of intense atomic disorder in many solids. Theparticle tracksare in themselves scientifically interesting because they consist of unique, localized radiation damage. They also are noteworthy for their diverse practical uses, which range from improved high field superconductors to mineral exploration and bird altimetry. The two areas—what tracks are and what they do practically—are the subjects of this introduction and the following three articles. Although the mechanism for producing tracks in insulators is semi-quantitatively well-established, there is a distinct mystery as to the formation mechanism in superconductors, inter-metallics, and metals. This mystery is the subject of the next two articles written by discoverers of tracks in these materials.

We will not discuss in detail the multitude of scientific uses for these tracks as particle-track detectors. Uses range from nuclear, elementary-particle, and cosmic-ray physics to geochronology, geochemistry, and geophysics; chemistry; and radiobiology. The interested reader can learn more on the subject through a book, part of which surveys scientific applications of particle tracks in solids. The key to these uses—and most of the practical uses—is that, in materials where tracks can be observed, either directly or by a widely applicable trick to be described, each detector sample is a nuclear particle-track chamber—the solid-state equivalent of the well-known gaseous and liquid detectors (i.e., cloud chambers and bubble chambers). The major distinction is that tracks in solids are long-lasting rather than transient features.
The Shell Model and Interatomic Potentials for Ceramics
Authors: Stoneham Marshall , Harding John , Harker Tony
Published: August 2016

In a classification of solids according to their bonding character (into metals, ceramics and glasses, polymers, and semiconductors), the ceramic class includes an enormous range of industrially important materials. From the archetypal ionic solids through oxides to silicates, and to covalently bonded materials such as SiC, they exhibit a rich variety of structures and properties. They occur as structural materials, either on their own or as composites such as SiC/Al2O3. They are important functional materials, such as fast-ion conductors as electrolytes in fuel cells (for example ZrO2/Y2O3 for hydrogen combustion) or batteries (β-alumina in the sodium-sulfur battery), ferroelectric materials such as BaTiO3 and piezoelectrics such as PZT—a solid solution of PbTiO3 and PbZrO3. The high-temperature superconductors (for example, YBa2Cu3O7) are ceramics above the superconducting transition temperature. The products of corrosion and oxidation are ionic materials, and the properties of oxide coatings are vital to the survival of high-temperature alloys in gas turbines or fuel-element claddings in nuclear reactors.

To understand the behavior of ceramic materials, and to optimize their production, processing, and application, it is often necessary to model their behavior at an atomic level. In some cases this is obvious. Ionic diffusion in a solid electrolyte is a self-evidently atomic process. In other cases the need for atomistic simulation is less clear. Oxidation, for example, is a subtle blend of atomic diffusion (often along grain boundaries), metal-ceramic bonding, stress relief, and grain growth. The course of oxidation can be spectacularly affected by impurities and alloying, and this can only be understood by considering the atomicscale processes involved.
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.
Limitations on the Use of Surface Doping for Improving High-Temperature Oxidation Resistance
Authors: Pint B.A.
Published: August 2016

For more than 50 years, scientists have studied the “magic dust” of high-temperature oxidation—certain oxygen active or “reactive” elements which, when added to alloys in small quantities, effect profound improvements in their oxidation resistance. In general, high-temperature oxidation resistance is achieved by the oxidation of one or more alloy components to form a dense, stable, slow-growing, external oxide layer, or ’scale” such as α-Cr2O3, α-Al2O3, or SiO2. When added properly, reactive elements have a beneficial effect on the formation and growth of both α-Cr2O3and α-Al2O3scales. A standard list of reactive element (RE) effects would include: (1) an improvement in scale adhesion or resistance to spallation, (2) a change in the scale growth mechanism, (3) a reduction in the oxidation rate, related to the change in mechanism, (4) a modification in the scale microstructure, and (5) in the case of alloys that form Cr2O3scales, an improvement in selective oxidation, meaning that a lower Cr concentration in the alloy is required to form and maintain an external Cr2O3scale.
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, the

molecules 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.
Beryllium, the Final Frontier: A Letter to My Grandson
Authors: Jacobson Loren A.
Published: August 2016

I realize that you have only just turned three years old, but I thought it might be interesting for you at some time in the future to read about some of the things that concern your Grandpa Jake today. In recent years, episodes of a popular television program opened with this statement, “Space, the Final Frontier!” I have worked for many years on the development of structural metals, putting most of my attention recently on the metal beryllium. And I have been feeling lately as though we need something similarly dramatic to be said about this metal, such as “Beryllium, the Final Frontier,” or perhaps more appropriately, “Beryllium, Stairway to the Final Frontier!” I want to share these thoughts with you because of two important truths about structural metals. One is that Metallurgy is like Medicine: They only call you up when something goes wrong. And the other truth is that structural materials, when they work, are invisible. So we have to work harder in order to gain the attention that structural materials deserve. Beryllium is truly the last structural metal that has outstanding properties that have not been fully exploited by society in order to meet the needs for greater structural efficiency and the savings in energy and effort that result from meeting these societal needs. So, on with “Beryllium, the Final Frontier!”
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.