“Superhard” coating materials are defined by hardness values that exceed 40 GPa. In this issue of MRS Bulletin, we focus on noncarbon-based superhard coatings, with the exception of a review of carbon nitride (CN) materials. Nanometer-scale multilayered nitride coatings were the first to show the superhard property, and these coatings have quickly made their way into industry as protective coatings for cutting-tool operations. Nanocomposite thin films also exhibit superhardness, and some of these materials have hardnesses approaching that of diamond. Cubic boron nitride (c-BN), which is naturally superhard, has proven very difficult to deposit at thicknesses exceeding 0.1 μm, but it is now reported that chemical vapor deposition techniques based on fluorine chemistries can produce c-BN films up to 20 μm thick. The search to produce cubic β-CN has led to the development of noncubic, fullerene-like forms of CN that are both hard and elastic, a very interesting combination of properties that has already been put to use in the hard-disk industry. Overall, the development of hard and superhard coatings during the past 20 years has been remarkable. We have progressed from trying (and often failing) to deposit hard coatings to now designing new nanometer-scale multilayered and nanocomposite coatings that exhibit excellent hardness properties and other high-performancecharacteristics.

The following article is an edited transcript based on the Von Hippel Award presentation given by Howard K. Birnbaum of the University of Illinois at Urbana-Champaign on December 4, 2002, at the Materials Research Society Fall Meeting in Boston. The award citation states, “Through innovative use of a wide range of novel experimental tools, Howard K. Birnbaum has made seminal contributions to our understanding of intrinsic point defects, hydrogen in metals, and grain-boundary segregation, especially as these effects relate to mechanical properties. He has also stimulated, directed, and influenced interdisciplinary research throughout the materials community.” This presentation summarizes the major phenomenological observations associated with hydrogen effects on fracture and the viable mechanisms that can account for these observations. It is shown that there are three fracture mechanisms that are consistent with the experimental observations and that the operative fracture mechanism depends on the type of system and the conditions under which it is exposed to hydrogen in aggressive environments.

This introductory article provides the background for the September 2003 issue of MRS Bulletin on Ultrahigh-Temperature Materials for Jet Engines. It covers the need for these materials, the history of their development, and current challenges driving continued research and development. The individual articles that follow review achievements in four different material classes (three in situ composites—based on molybdenum silicide, niobium silicide, and silicon carbide, respectively—and high-melting-point platinum-group-metal alloys), as well as advances in coating systems developed both for oxidation protection and as thermal barriers. The articles serve as a benchmark to illustrate the progress made to date and the challenges ahead for ultrahigh-temperature jet-engine materials.

An overview of key materials for optical communications, including semiconductors, dielectrics, glasses, and organics, is presented in this issue of MRS Bulletin. Materials quality is in all cases crucial for advanced device and system performance. Materials properties and important problems are reviewed, and their impact on the performance of state-of-the-art optical devices is assessed and demonstrated by means of selected examples.

This brief article describes the content of the December 2003 issue of MRS Bulletin on New Frontiers in the Application of Neutron Scattering to Materials Science. New techniques, new instrumentation, and new sources are providing exciting opportunities for the use of neutron scattering in materials research at a time when the pace of research and development is accelerating while the complexity of the issues governing materials use is increasing. At a time such as this, it is critical to use the best tool for the job, and neutron scattering is evolving into a tool that can be used with many others, rather than a technique only for the specialist. It is also providing unprecedented resolution in energy to allow the study of the slow dynamics characteristic of many problems in soft matter and to probe surfaces and interfaces in a unique way. In this issue, we have chosen three areas to emphasize these trends: neutron reflectivity as a probe of surfaces and interfaces, the use of neutrons to study complex fluids, and high-resolution neutron scattering studies of dynamics. We also give a view of the future of neutron sources, with an article outlining the opportunities to be provided by sources proposed or under construction in Europe, Japan, and the United States. It is our hope that this sampling of new opportunities in neutron scattering will encourage wider use of these techniques to help solve the challenging materials research problems of today and tomorrow.

This article introduces the October 2003 issue of MRS Bulletin on “New Materials for Spintronics.” As a result of quantum mechanics, the carriers in ferromagnetic metals such as Fe, Co, and Ni are spin-polarized due to an imbalance at the Fermi level in the number of spin-up and spin-down electrons. A carrier maintains its spin polarization as long as it does not encounter a magnetic impurity or interact with the host lattice by means of spin-orbit coupling. The discovery of optically induced, long-lived quantum coherent spin states in semiconductors has created a range of possibilities for a new class of devices that utilize spin. This discovery also points to the need for a wider range of spin-polarized materials that will be required for different device configurations. In this issue of MRS Bulletin, we focus on three classes of candidate spintronic materials and review the current state of our understanding of them: III–V and II–VI semiconductors, oxides, and Heusler alloys. The field of spin-polarized materials is growing very rapidly, and the search for new magnetic semiconductors and other suitable spin-injection materials with higher Curie temperatures is bringing spintronics closer to the realm of being practical.

The focus of this issue of MRS Bulletin is to explore the impact of materials science and technology on microelectronics packaging and integration. Progress in microelectronics packaging has been intimately tied to the continuous advances made in the associated materials, process technologies, and design tools. This is especially true now, as packaging moves into an era driven by the need for complex system-level solutions. This issue is our attempt to present the current status of microelectronics packaging technology and integration and to highlight various perspectives on the future evolution of the field.

This brief article describes the content of the August 2003 issue of MRS Bulletin focusing on Advanced Fabrics. The six articles will feature reviews of advanced fibers, new fabric constructions and design considerations, materials for novel fabric properties, and the incorporation of new elements within fabric structures to add multifunctional, wearable features to clothing.

This article introduces the February 2003 issue of MRS Bulletin on “Single-Event Upsets (SEUs) in Microelectronics.” These radiation effects in devices and circuits have been recognized in recent years as a key reliability concern for many current and future silicon-based technologies. This introduction sets the scope for critical discussions on this subject. The articles in the issue reflect the interdisciplinary nature of SEU research. The contributing authors include experts from several specializations: technology reliability, materials science, device physics, circuit designs, and theoretical and experimental nuclear physics. We review the current understanding of SEU problems from the perspectives of radiation physics, circuit design issues, and global technology developments. The discussions cover the key areas of modeling, circuit analyses, accelerator tests and experiments, basic nuclear data, and environmental neutron measurements.

This article introduces the November 2003 issue of MRS Bulletin on Inkjet Printing of Functional Materials. The issue is devoted to the emerging non-graphic-arts uses of inkjet printing as a technique for depositing and patterning functional materials in the liquid phase onto a substrate. The articles provide an overview of a selected range of representative applications in the field of structural ceramics, polymer electronics, and protein chips, and address some of the key challenges that face the broad scientific and industrial community as it attempts to apply a mature and well-developed graphic arts printing technique to the deposition of functional materials.

This brief article describes the content of this issue of MRS Bulletin on Cellular Solids. Cork, wood, sponge, and bone are all examples of cellular solids in nature. Engineered honeycombs and foams are now made from polymers, metals, ceramics, and glasses, and their structure gives them unique properties that can be exploited in a variety of applications. The articles in this issue provide an overview of the fabrication, structure, properties, and applications of such porous solids as cellular ceramics, aluminum and other metallic foams, and scaffolds for tissue engineering, as well as discussions of techniques for understanding, modeling, and measuring their behavior and properties.

This issue of MRS Bulletin provides an overview of the state of the art and emerging trends in the area of adhesives. An adhesive is basically defined by its function, which is to assemble two surfaces together. In order to fulfill this function, the properties of an adhesive must include easy positioning at the interface, rapid and complete bond formation and subsequent hardening, and a bond strength adapted to the specific application (structural, permanent, removable, rigid, or soft). A variety of solutions exist in practice, and their application requires an understanding both of polymer chemistry and materials science. The main families of adhesives, their properties, and their basic design principles will be discussed in the articles in this issue, while this introductory article presents an overview of the functions required of adhesives and future trends.

Inkjet print heads have become the dominant printing element for home and office printers; they have been a key driver forthe digitization of wide-format graphic arts printing and other printing areas as diverse as addressing and carton coding. In the past few years, inkjet print heads have begun to have an impact in areas outside the graphics arts. In these applications, the inkjet print head may be considered a manufacturing tool; this implies that it will differ in design depending on the application. Also, standards forreliability, consistency, and dependability will differ from those in graphic arts areas. Even though non-graphic-arts applications differ widely in their details, there are general considerations in terms of the systems that are required. Each nontraditional application has specific goals for manufacturing, and a unique inkjet print head designed to meet these goals may be required. This article focuses on a specific piezo-based inkjet print head that has been engineered to meet the manufacturing requirements for flat-panel displays basedon light-emitting polymeric materials.

We describe how the material properties of III–V semiconductors, including bandgap, band structure, band offset, refractive index, absorption, and ionization coefficient, are exploited for lasers and photodetectors for fiber-optic communications. The material systems discussed for 1.3 μm and 1.55 μm light emission include the more traditional GaInAsP and AlGaInAs on InP, the more recently investigated GaInAs quantum dots and low-bandgap GaInNAs on GaAs as well as GaAsSb/GaAs Type II structures, and the potentially viable GaN/AlGaN from intersubband transitions (i.e., between quantized conduction-band energy levels). As an example of photodetector applications, GaInAsP/InP and wafer-fused GaInAs/Si are discussed in terms of gain and noise factor for use in avalanche photodiodes with separate absorption and multiplication regions.

The properties of solid foams depend on their structure, which usually evolves in the fluid state as gas bubbles expand to form polyhedral cells. The characteristic feature of foam structure—randomly packed cells of different sizes and shapes—is examined in this article by considering soap froth. This material can be modeled as a network of minimal surfaces that divide space into polyhedral cells. The cell-level geometry of random soap froth is calculated with Brakke's Surface Evolver software. The distribution of cell volumes ranges from monodisperse to highly polydisperse. Topological and geometric properties, such as surface area and edge length, of the entire foam and individual cells, are discussed. The shape of struts in solid foams is related to Plateau borders in liquid foams and calculated for different volume fractions of material. The models of soap froth are used as templates to produce finite element models of open-cell foams. Three-dimensional images of open-cell foams obtained with x-ray microtomography allow virtual reconstruction of skeletal structures that compare well with the Surface Evolver simulations of soap-froth geometry.

Recent years have witnessed extensive research aimed at developing functional, tetrahedrally coordinated ferromagnetic semiconductors that could combine the resources of semiconductor quantum structures and ferromagnetic materials systems and thus lay the foundation for semiconductor spintronics. Spin-injection capabilities and tunability of magnetization by light and electric field in Mn-based III–V and II–VI diluted magnetic semiconductors are examples of noteworthy accomplishments. This article reviews the present understanding of carrier-controlled ferromagnetism in these compounds with a focus on mechanisms determining Curie temperatures and accounting for magnetic anisotropy and spin stiffness as a function of carrier density, strain, and confinement. Materials issues encountered in the search for semiconductors with a Curie point above room temperature are addressed, emphasizing the question of solubility limits and self-compensation that can lead to precipitates and point defects. Prospects associated with compounds containing magnetic ions other than Mn are presented.

Fibers and coatings with unique optical, magnetic, and electrical properties are being widely studied for use in both military and commercial applications. New materials are being developed in this research effort, with unique tunable coloration properties across the visible spectrum as well as spanning the infrared and ultraviolet region of the electromagnetic spectrum. These dynamic color-responsive “chameleon” fiber systems will have wide application to a variety of new textile products. These new materials will also allow penetration into markets normally not dependent on textile materials. New markets, such as the optical communication and electronics market areas, will include bio-sensors, detector applications for textile materials, and “smart materials” that can change their color, hue, or depth of shade by application of a static or dynamic electric field for applications such as smart uniforms.

Historically, the primary function of microprocessor packaging has been to facilitate electrical connectivity of the complex and intricate silicon microprocessor chips to the printed circuit board while providing protection to the chips from the external environment. However, as microprocessor performance continues to follow Moore's law, the package has evolved from a simple protective enclosure to a key enabler of performance. The art and science of semiconductor packaging has advanced radically over the past few decades as faster and more powerful microprocessors with tens of millions of transistors continue to be available, which require more signal and power input/output connections as well as greater power-dissipation capabilities. Key drivers for the development of packaging technologies include power delivery, thermal management, and interconnect scaling, in which the space transformation from fine-featured silicon interconnects to the relatively coarse features seen on motherboards has to be enabled by the package. These drivers, under constant market-driven cost pressure, have led to increased demands on new materials and new package architectures to enable silicon performance. Significant advances have already been made in the areas of heat dissipation, power delivery, high-speed signaling, and high-density interconnects. It is expected that the future evolution of microprocessors will be increasingly challenging in these areas. This article focuses on providing a broad perspective view of the evolution of microprocessor packaging and discusses future challenges.

Among the experimental techniques used to characterize complex fluids, neutron scattering has played a unique and successful role, primarily for two reasons: (1) neutrons access the proper length and time scales, especially small-angle neutron scattering and reflectometry for structural and kinetic studies and neutron spin echo for dynamic investigations; and (2) for hydrogen-containing substances, the exchange of hydrogen by deuterium facilitates labeling on a molecular scale, an extremely important method for deciphering complex structures in multicomponent materials. In this short review, we give a number of examples for successful neutron studies of dense particle suspensions, including aggregation phenomena, in situ kinetic studies on shape transformations, shear-induced surfactant self-assembly phenomena near surfaces, and dynamics of complex fluids. Finally, we give an outlook on future developments.