The martensitic (also called displacive or diffusionless) transformation is a classical cooperative phenomenon in solids similar to ferromagnetism. Although the displacement of each atom is not large, the transformation results in a macroscopic change in shape, since all of the atoms move in the same direction in a domain or variant. As a result, unique properties arise, such as the shape-memory effect and superelasticity, whose characteristics are quite distinct from those of normal metals and alloys. Because of these unique properties, shape-memory alloys (SMAs) have been used as new functional materials for applications such as couplings, sensors, actuators, and antennas for cellular phones. In this issue of MRS Bulletin, we present an overview of recent progress in this field. In this introductory article, we discuss fundamental notions, such as the mechanism of the shape-memory effect, the martensitic transformation, and superelasticity, along with examples of applications and other important recent topics not treated in the following articles. It will be shown that progress in the science and technology of shape-memory alloys has been achieved by the side-by-side development of fundamentals and applications.

This article focuses on self-assembled photovoltaic materials based on a new class of semiconducting block copolymers for application in photovoltaic devices. Topics discussed include the materials concept for efficient photovoltaic-device structures, their macromolecular design and synthesis, and their performance in relation to their molecular, mesoscopic, and interfacial structures. An ideal organic material for this application would have to compete with amorphous silicon in regard to energy-conversion efficiency and fabrication costs. The potential of the semiconducting block copolymers presented in this review lies in the promise of large-area, mechanically flexible, self-structured photovoltaic devices fabricated by inexpensive processing techniques.

Compared with LiCoO2, the dominant cathode material in today's lithium batteries, lithium nickel oxide derivatives [Li(Ni, M)O2, where M – Co, Fe, Al, Mg] offer a higher specific energy at a lower cost. The synthesis and structure of these materials are described. The electrochemical performances of the pure nickel compound and a number of multicomponent systems are assessed. The goals of these fundamental studies are to optimize the synthesis conditions and material composition to achieve good electrochemical reversibility, decrease capacity loss upon cycling, and enhance thermal stability in the deintercalated state in order to improve cell safety.

This article describes the current level of understanding of dislocation plasticity in thin films and small structures in which the film or structure dimension plays an important role. Experimental observations of the deformation behavior of thin films, including mechanical testing as well as electron microscopy studies, will be discussed in light of theoretical models and dislocation simulations. In particular, the potential of applying strain-gradient plasticity theory to thin-film deformation is discussed. Although the results of all studies presented follow a “smaller is stronger” trend, a clear functional dependence has not yet been established.

High-throughput and systematic studies of complex materials systems using the approach of “continuous phase diagramming” (CPD) are described in this article. The discussions focus on the techniques of epitaxial film synthesis of CPD and mapping physical and structural properties, using two different material systems as examples: doped perovskite manganese oxides and magnetic alloys. In doped perovskite manganese oxides, a highly correlated system, mapping the optical, electrical, and magnetic properties, reveals surprising evidence of electronic phase transitions that correlate with the low-temperature magnetic order. In magnetic alloys, application of CPD, particularly using real-time characterization during epitaxial growth, makes it possible to examine structure–property relations systematically.

Optical components based on vertical-cavity surface-emitting lasers (VCSELs) are moving from 850-nm wavelengths to 1.31-μm and 1.55-μm wavelengths. These long-wavelength devices, enabled by new developments in materials technology, will compete directly with distributed-feedback (DFB) and Fabry-Pérot (FP) laser technologies in fiber-optic markets. In addition, the unique properties of VCSELs are opening up a new category of optically integrated components that are not possible with traditional edge-emitting laser source technologies. These VCSEL structures, such as linear and two-dimensional arrays, have the potential to dramatically reduce the cost structure of traditional optical networking equipment and provide a path for rapid growth in optical bandwidth.

Proteins are nature's workhorses. They enable living systems to use available energy sources and convert energy from one form into another. Understanding the underlying design principles of how proteins have evolved to fulfill the necessary functions of life can provide researchers with new insights into how to enhance the performance of synthetic nanosystems with far greater sophistication. This review summarizes the relationship between various protein functions and the underlying engineering principles of their overall structures. For example, proteins can specifically recognize other biomolecules with a selectivity and affinity several orders of magnitude superior to their synthetic counterparts. Mimicking a protein binding site with a structurally fixed synthetic analogue is insufficient, since structural changes in the active sites enhance molecular recognition and the catalytic activity of proteins. Recent data also show that protein function can be switched by stretching proteins into nonequilibrium states under physiological conditions. Schemes by which the exposure and structure of recognition sites are switched can be implemented in the design of mechanically responsive synthetic and hybrid systems. Motor proteins, finally, are the jewel in nature's crown, as they can convert one free-energy form into another to generate mechanical force. It is thus of considerable interest to integrate the chemically powered engines into synthetic materials and devices. Finally, we have to advance our ability to assemble nanocomponents into functional systems. Again, lessons can be learned from how biology solves the challenge of systems integration.

Reflective full-color liquid-crystal displays (LCDs) are attracting a great deal of interest as portable information systems because of their extremely low power consumption and light weight; also, the color does not wash out in outdoor use. In this article, reflective LCDs are classified into three types. Among them, the diffusing-reflector type and the front-diffusing film type are suitable for high-quality active-matrix displays. Diffusing-reflector LCDs have the advantage of uniform reflectance at the desired viewing angle due to the design of the surface microstructure of the reflector. Front-diffusing film LCDs using metallic mirrors and an optimally designed light-controlling film enable high contrast in a wide viewing-angle range and uniform reflectance with no blurring. Thus, both types have a high potential for achieving excellent color quality comparable to printed paper. In the near future, these reflective LCDs will likely be applied not only to portable systems, but also to high-performance wireless monitor displays and various other information systems.

For a century, nickel-cadmium (Ni-Cd) batteries have been widely used as electrochemical energy-storage cells. However, due to the rapid development of portable electronic devices and the increasing search for cleaner electric vehicles, new generations of batteries have been investigated during the last few decades. Among them, nickel metal hydride (Ni-MH) batteries, with their larger capacities and improved environmental compatibility, have shown their ability to replace Ni-Cd cells. The negative electrodes of Ni-MH batteries are made of reversibly hydride-forming intermetallic compounds. In this article, the crystallographic and thermodynamic properties of these compounds will be reviewed. Their hydrogen-absorption properties, their electrochemical performance, and the solutions that have been found to achieve reliable cycle life will be presented. The industrial market for Ni-MH batteries will also be discussed in comparison with other battery systems.

An abrasive-free polishing (AFP) solution for chemical–mechanical planarization (CMP) of copper films on semiconductor wafers has been developed to overcome such disadvantages of conventional CMP as dishing, erosion, Cu and oxide loss, and microscratching. Electrochemical methods are an effective way of understanding the role of each chemical component in the AFP solution in order to optimize its performance. Analysis of the reaction layer of Cu elucidates the reasons for the excellent results that have been obtained. By applying the AFP solution for Cu CMP in combination with a slurry for CMP of the metal barrier layer, seven-level multilayer Cu interconnections can be successfully fabricated.

In this article, we discuss creep deformation as it relates to thin films and multilayer foils. We begin by reviewing experimental techniques for studying creep deformation in thin-film geometries, listing the pros and cons of each; then we discuss the use of deformation-mechanism maps for recording and understanding observed creep behavior. We include a number of cautionary remarks regarding the impact of microstructural stability, zero-creep stresses, and transient-creep strains on stress–strain rate relationships, and we finish by reviewing the current state of knowledge for creep deformation in thin films. This includes both thin films that are heated on substrates as well as multilayer films that are tested as freestanding foils.

A class of steels (ultrahigh-carbon steels, or UHCSs) containing high levels of carbon (i.e., ∼1–2 wt%) were originally developed for their superplastic characteristics. In combination with excellent room-temperature properties, the steels were developed for their commercial potential starting in the mid-1970s and continuing to the present time. The compositional similarities between these modern steels and ancient Damascus steels led to a revisiting of the history and metallurgy of Damascus and related steels. Also, as part of the development of UHCSs, modern laminated composites containing them have been designed and manufactured that have unique toughness characteristics. These laminated composites also have similarities to a range of laminated materials of historical interest. Finally, some comments are made on the utility of radiocarbon dating to determine the age of ancient irons and steels. Ten sidebars supplement this article as Web Extras on the MRS Bulletin Web site at www.mrs.org/publications/bulletin/2002/dec/.

Distributed Bragg reflectors (DBRs) not only serve as high-reflectance mirrors to define the laser cavity of a vertical-cavity surface-emitting laser (VCSEL), but they also must conduct electricity, confine currents, and provide a single-crystal template for the gain region of the laser. Basic optical and electrical properties of DBRs are presented in this article. Three examples of DBR structures used in VCSEL applications from the ultraviolet to the infrared are given to illustrate the complexity and range of materials science issues that are encountered in DBR growth. Fabrication issues are also discussed.

A diffusion multiple is an assembly of three or more different metal blocks, in intimate interfacial contact, that is subjected to a high temperature to allow thermal interdiffusion. The power of using a diffusion multiple approach in the efficient mapping of phase diagrams and materials properties for multicomponent alloy systems is illustrated in this article using several examples. It is now possible to map phase diagrams and materials properties at an efficiency some 3 orders of magnitude higher than the conventional one-alloy-at-a-time approach. With this high efficiency, many critical materials data that otherwise would be too time-consuming and expensive to acquire can be obtained and employed to accelerate our understanding of a system's materials physics and chemistry. It is postulated that coupling the diffusion multiple approach with the CALPHAD (calculation of phase diagrams) method will have a significant impact on the computational design of materials.

The elimination of conventional peripheral LSI (large-scale integration) drivers is considered essential to the development of future low-cost, energy-efficient, lightweight, and thin displays. System-on-glass (SOG) displays are a type of display with various functional circuits integrated on a glass substrate. Low-temperature polycrystalline silicon (LTPS) thin-film transistors (TFTs) make the integration of circuits possible because they can be assembled into complex, high-current driver circuits. Furthermore, LTPS TFTs are attracting attention for driving organic light-emitting devices (OLEDs). This article introduces present and future LTPS TFT technologies for SOG displays.

Solid-state nuclear magnetic resonance (NMR) spectroscopy has been employed to characterize a variety of phenomena that are central to the functioning of lithium and lithium-ion batteries. These include Li insertion and de-insertion mechanisms in carbonaceous and other anode materials and in transition-metal oxide cathodes, and ion-transport mechanisms in polymer and gel electrolytes. Investigations carried out over the last several years by the authors and other groups are reviewed in this article. Results for lithium manganese oxide spinel cathodes, carbon-based and SnO anodes, and polymer and gel electrolytes are discussed.

The value of Nitinol (Ni-Ti) in the field of medicine has proven to be far greater than just as the simple “springy metal” it was once considered to be. In particular, its use in vascular implants highlights many valuable yet subtle behaviors, including a “biased stiffness,” enhanced fatigue resistance, low magnetic susceptibility, and good biocompatibility. Nitinol today is nearly as well known to medical-device designers and physicians as are stainless steel and titanium, and it is the enabling ingredient in a growing number of successful and profitable life-saving devices.

The development of new conjugated-polymer tools for the study of the biological realm, and for use in a clinical setting, is reviewed in this article. Conjugated-polymer actuators, based on the changes of volume of the active conjugated polymer during redox transformation, can be used in electrolytes employed in cell-culture media and in biological fluids such as blood, plasma, and urine. Actuators ranging in size from 10 μm to 100 μm suitable for building structures to manipulate single cells are produced with photolithographic techniques. Larger actuators may be used for the manipulation of blood vessels and biological tissue.

This article gives a brief review of advances in optical-fiber temperature and pressure sensors. Developments over the last two decades have seen enhancements in utility and performance, as more advanced techniques are applied. Applications to industrial problems are highlighted.

Identifying candidate materials to replace SiO2 as the gate dielectric for complementary metal oxide semiconductor (CMOS) applications is a difficult task. Proper assessment of the critical materials requirements is essential, and it is important to devise an approach to predict materials properties without having to make many unnecessary measurements on high-ĸ materials. Such an approach helps to eliminate unlikely candidates and focus on the most promising ones. Clearly, this type of modeling approach requires an understanding of several physical and chemical characteristics, including the bonding and electronic structure, band alignment with Si, and the nature of the dielectric constant and interface properties. We present a critical assessment of some existing methods and models of materials properties, as well as a comparison of the present modeling approach with some experimentally determined values.