Shape-memory alloys are now widely used because they exhibit a large recoverable strain, which is caused by the conversion of variants in the martensite phase. The conversion of variants is usually promoted by the application of external stress. Recently, however, it was found that the conversion of variants can also be promoted by the application of a magnetic field to induce the martensitic state in ferromagnetic Ni2MnGa shape-memory alloys. Since then, the research in this field has focused considerable attention on applications for using the materials as actuators and sensors because their response to a magnetic field is much faster than their response to heating or cooling. Furthermore, the mechanism of the conversion of variants by the magnetic field has attracted academic interest from many researchers. In this article, we show giant magnetostrictive behavior in three ferromagnetic shape-memory alloys—Ni2MnGa, Fe-Pd, and Fe3Pt—and review the investigations performed so far by many researchers, including the present authors.

Many advanced technologies center on devices of small feature sizes made of diverse materials. Internal stresses that arise in the devices during fabrication and use can result in fracture. Fracture of an individual feature in such a device may impair the function of the device. The materials surrounding the feature have a constraining effect on the elastic energy available to drive the fracture, the plastic flow associated with the fracture, and sometimes even the atomic processes at the crack tip. This article reviews fracture behavior in small structures, several distinct roles played by plasticity, and bond-breaking kinetics. Research challenges are alsooutlined.

We review recent advances in the development of combinatorial methods for polymer characterization. Applied to materials research, combinatorial methodologies allow efficient testing of structure–property hypotheses (fundamental characterization) as well as accelerated development of new materials (materials discovery). Recent advances in library preparation and high-throughput screening have extended combinatorial methods to a wide variety of phenomena encountered in polymer processing. We first present techniques for preparing continuous-gradient polymer “libraries” with controlled variations in temperature, composition, thickness, and substrate surface energy. These libraries are then used to characterize fundamental properties such as polymer-blend phase behavior, thin-film dewetting, block-copolymer order–disorder transitions, and cell interactions with surfaces of biocompatible polymers.

The continual scaling of complementary metal oxide semiconductor (CMOS) technologies has pushed the Si-SiO2 system to its very limits and has led to the consideration of a number of alternative high-ĸ gate dielectric materials. In the end, it will be the electrical properties of the new Si/high-ĸ system that will determine its usefulness in future CMOS generations. For this reason, the study of the electrical properties of high-ĸ gate insulators is crucial. We present an overview of some of the electrical characterization techniques and reliability tests used to evaluate possible high-ĸ gate materials. Most of these techniques are well known from the characterization of SiO2 layers, but there are some additional complications, such as the presence of several different layers within one gate stack or the use of different gate electrode materials. These make the interpretation and comparison of experimental results more troublesome.

Computational modeling is playing an increasingly important role in materials research and design. At the system level, the impact of cell design, electrode thickness, electrode morphology, new packaging techniques, and numerous other factors on battery performance can be predicted with battery simulators based on complex electrochemical transport equations. Such simulation tools have allowed the battery industry to optimize the power and energy density that can be achieved with a given set of electrode and electrolyte materials. At the materials level, first-principles calculations, which can be used to predict properties of previously unknown materials ab initio, have now made it possible to design materials for higher capacity and better stability. The state of the art in computational modeling of rechargeable batteries is reviewed.

New solid-state x-ray imagers known as digital flat-panel x-ray detectors are about to be launched in the field of medical diagnostics. The combination of active-matrix technologies developed for active-matrix liquid-crystal displays and x-ray detection materials constitutes the basis of the detectors. Recently, two kinds of direct-conversion detectors have been developed in order to improve their performance. One is a detector using a thick x-ray photoconductor (∼1 mm) made of amorphous selenium, and the other is a novel hybrid panel detector using an x-ray photoconductor made of polycrystalline Cd(Zn)Te. As a result, excellent resolution and good linear sensitivity have been achieved. These detectors have great promise as next-generation digital imaging systems for fluoroscopy and radiography.

As the minimum feature size of microelectronic devices shrinks down to 130 nm, copper has been successfully adopted into logic applications.1–3 Copper requires damascene processing, which involves etching features into a dielectric substrate, filling the features with metal, and removing any excess metal. Therefore, chemical—mechanical planarization (CMP) is a key process in the final definition of the inlaid copper wires on a circuit. A second advance in the back-end processing of copper is the changing of the dielectric from SiO2 to a Low-κ material, which allows a thicker layer of dielectric to be used. Low-k dielectric films have much lower mechanical properties than SiO2; consequently, this poses new challenges in developing integration schemes.1,3–8

Acoustic emission (AE) is used as a means to anticipate the mechanical failure of critical materials and structures by detecting the release of energy caused by material rearrangement at the microlevel. Optical-fiber sensors have potential advantages over conventional tuned piezoelectric transducers and signal-processing methods for the detection of such types of ultrasonic acoustic wave events. A number of fiber Bragg grating techniques are presented, which in particular offer the potential to provide the high-speed signal processing and ability to multiplex numbers of AE sensors necessary to detect, quantify, and locate AE sources and thereby determine material properties and damage.

Hydrogen-absorbing alloys with bcc (body-centered-cubic) structures, such as Ti-V-Mn, Ti-V-Cr, Ti-V-Cr-Mn, and Ti-Cr-(Mo, Ru), have been developed since 1993. These alloys have a higher hydrogen capacity (about 3.0 mass%) than conventional intermetallic hydrogen-absorbing alloys. Generally, bcc metals and alloys exhibit two plateaus in pressure–composition isotherms, but the lower plateau is far below atmospheric pressure at room temperature. Many efforts have been made to increase hydrogen capacity and raise the equilibrium pressure of this lower plateau. The crystal structure and morphology of Laves-phase-related bcc solid-solution alloys are reviewed.

The development of vertical-cavity surface-emitting lasers (VCSELs) relies on an understanding of gain-medium physics, more so than in edge-emitting lasers. An important tool in the investigation of semiconductor gain behavior is a theory that provides a systematic account of the interaction between the laser field and the electron–hole plasma, the influence of the band structure, and the many-body effects due to Coulomb interactions among carriers. This article describes a semiclassical approach that is based on the semiconductor Bloch equations, with carrier correlation effects described at the level of quantum kinetic theory. To illustrate its application, we discuss research activities involving the development of gain media for long-wavelength VCSELs.

Chemical–mechanical polishing, or planarization (CMP), is one of several advanced microfabrication processes that provide complementary capabilities for constructing advanced electronic devices. At the current state of the art, CMP demonstrates significant advantages due to its high degree of process flexibility, particularly in the chemical formulation of polishing solutions and slurries. This article explores some possible future applications of CMP using new advanced materials other than silicon, silicon oxide, and silicon nitride. Such materials may include refractory and noble metals, high-κ insulators, and mixed metal oxide perovskites. Although no one can predict future applications with absolute certainty, it seems safe to conclude that CMP will remain a key microfabrication technology for the foreseeable future.

Microencapsulated electrophoretic (MEP) materials exhibit high optical reflectance and contrast, wide viewing angle, high resolution, and excellent image stability. MEP materials can be easily printed on large plastic sheets and laminated to a variety of electronic backplanes to construct displays. The combination of a MEP material with flexible transistor technologies enables displays that offer both the look and form of the printed page. This article reviews the basic architecture and properties of MEP materials and describes the integration of MEP materials with transistor backplanes to produce high-resolution, low-power, paperlike displays. Recent developments in ultrathin flexible displays are also reported.

Recent developments in hydrogen interaction with carbonaceous materials are reviewed in this article. The interaction is based on van der Waals attractive forces (physisorption), or the overlap of the highest occupied molecular orbitals of carbon with the hydrogen electron, overcoming the activation-energy barrier for hydrogen dissociation (chemisorption). While the physisorption of hydrogen limits the hydrogen-to-carbon ratio to less than one hydrogen atom per two carbon atoms (i.e., 4.2 mass%), in chemisorption, a ratio of two hydrogen atoms per one carbon atom is realized (e.g., in polyethylene). However, the materials with large hydrogen-to-carbon ratios only liberate the hydrogen at elevated temperature. No evidence, apart from theoretical calculations, was found for a new hydrogen-adsorption phenomenon on carbon nanotubes (CNTs), as compared with high-surface-area graphite. The curvature of CNTs and fullerenes increases the reactivity of these materials with hydrogen and leads more easily to the formation of hydrocarbons, as compared with graphite. Nanocrystalline or amorphous carbon exhibits an intermediate state for hydrogen between physisorption and chemisorption and absorbs up to one hydrogen atom per carbon atom. Nanostructured carbonaceous and metallic materials offer a large potential for hydrogen storage and must therefore be investigated in more detail.

Shape-memory alloy (SMA) thin films formed by sputter deposition have attracted considerable attention in the last decade. Current intensive research demonstrates that unique fine microstructures are responsible for the superior shape-memory characteristics observed in thin films as compared with bulk materials. Simultaneously, much effort has been undertaken to develop and fabricate micro devices actuated by SMA thin films. This article reviews the research to date on shape-memory behavior and the mechanical properties of SMA thin films in connection with their peculiar microstructures. Promising applications such as microvalves are demonstrated, along with a focused discussion on process-related problems. All of the results indicate that thin-film shape-memory actuators are ready to contribute to the development of microelectromechanical systems.

In addition to meeting the formidable challenges of replacing the nearly perfect SiO2 dielectric, a new dielectric ideally needs to replace SiO2 with minimal rearrangement of the complementary metal oxide semiconductor (CMOS) process flow. In this article, we outline the essential materials-integration issues that arise out of the technical requirements for minimizing changes to future process technologies. These include interfacial layer formation, film microstructure, deposition technologies, and electrical performance challenges such as trapped charge and the mobility degradation associated with any replacement material. Integration of the high-ĸ materials currently under consideration presents a significant challenge for materials scientists and engineers in industry and academia.

GaAs-based continuous-wave quantum-dot vertical-cavity surface-emitting lasers (VCSELs) operating at 1.3 μm at 20°C with output power of 1.2 mW have been realized. Threshold currents approach 1–1.5 mA for 8-μm oxide apertures. Operating voltages are ∼2 V. Long operation lifetimes in excess of 5000 h at 50°C without degradation have been achieved. This article describes these breakthroughs, which are based on our development of complex self-organized growth technologies for defect-free stacked quantum dots.

The following are commentaries provided by representatives from industry. These short articles lend an additional context in which to appreciate the importance of the issues and mechanisms discussed in the technical articles. The authors of the commentaries point out that the basic principles that underlie the influence of scale on material behavior are not only interesting in their own right, but also are directly applicable to issues of great significance to designers and manufacturers of small-scale devices and structures. In addition, directions for future emphasis are suggested.