Index of refraction, a fundamental optical constant that enters in the descriptions of almost all optical phenomena, has long been considered an intrinsic property of a material. However, the recent progress in negative-index material (NIM) research has shown that the utilization of deep-subwavelength-scale features can provide a means to engineer fundamental optical constants such as permittivity, permeability, impedance, and index of refraction. Armed with new nanofabrication techniques, researchers worldwide have developed and demonstrated a variety of NIMs. One implementation uses a combination of electric and magnetic resonators that simultaneously produce negative permittivity and permeability, and consequently negative refractive index. Others involve chirality, anisotropy, or Bragg resonance in periodic structures. NIM research is the beginning of new optical materials research in which the desired optical properties and functionalities are artificially generated. Clearly, creating negative index materials is not the only possibility, and the most recent developments explore new realms of materials with near-zero indexes and inhomogeneous index profiles that can produce novel phenomena such as invisibility. Furthermore, the concept of controlling macroscopic material properties with a composite structure containing subwavelength-scale features extends to the development of acoustic metamaterials. By providing a review of recent progress in NIM research, we hope to share the excitement of the field with the broader materials research community and also to spur new ideas and research directions.

Worldwide, 1.2 billion people lack access to sufficient amounts of clean water, and 2.6 billion lack adequate sanitation. Also, industry relies on large quantities of water during manufacturing, which is then returned to the environment. Having adequate water supplies, and removing pathogens, chemicals, and other contaminants with high throughput at a low cost is a growing challenge around the world. This issue of MRS Bulletin examines how materials research, through the development of membranes, catalysts, nanoparticles, and other materials, is addressing these needs.

Polymers are highly attractive for their inherent properties of mechanical flexibility, light weight, and easy processing. In addition, some polymers exhibit large property changes in response to electrical stimulation, much beyond what is achievable by inorganic materials. This adds significant benefit to their potential applications.

The focus of this issue of MRS Bulletin is on polymers that are electromechanically responsive, which are also known as electroactive polymers (EAPs). These polymers respond to electric field or current with strain and stress, and some of them also exhibit the reverse effect of converting mechanical motion to an electrical signal.

There are many types of known polymers that respond electromechanically, and they can be divided according to their activation mechanism into field-activated and ionic EAPs. The articles in this issue cover the key material types used in these two groups, review the mechanisms that drive them, and provide examples of applications and current challenges. Recent advances in the development of these materials have led to improvement in the induced strain and force and the further application of EAPs as actuators for mimicking biologic systems and sensors. As described in this issue, the use of these actuators is enabling exciting applications that would be considered impossible otherwise.

Biological systems have the ability to sense, react, regulate, grow, regenerate, and heal. Recent advances in materials chemistry and micro- and nanoscale fabrication techniques have enabled biologically inspired materials systems that mimic many of these remarkable functions. This issue of MRS Bulletin highlights two promising classes of bioinspired materials systems: surfaces that can self-clean and polymers that can self-heal. Self-cleaning surfaces are based on the superhydrophobic effect, which causes water droplets to roll off with ease, carrying away dirt and debris. Design of these surfaces is inspired by the hydrophobic micro- and nanostructures of a lotus leaf. Self-healing materials are motivated by biological systems in which damage triggers a site-specific, autonomic healing response. Self-healing has been achieved using several different approaches for storing and triggering healing functionality in the polymer. In this issue, we examine the most successful strategies for self-cleaning and self-healing materials and discuss future research directions and opportunities for commercial applications.

In nature, the molecular-recognition ability of peptides and, consequently, their functions are evolved through successive cycles of mutation and selection. Using biology as a guide, it is now possible to select, tailor, and control peptide–solid interactions and exploit them in novel ways. Combinatorial mutagenesis provides a protocol to genetically select short peptides with specific affinity to the surfaces of a variety of materials including metals, ceramics, and semiconductors. In the articles of this issue, we describe molecular characterization of inorganic-binding peptides; explain their further tailoring using post-selection genetic engineering and bioinformatics; and finally demonstrate their utility as molecular synthesizers, erectors, and assemblers. The peptides become fundamental building blocks of functional materials, each uniquely designed for an application in areas ranging from practical engineering to medicine.

Availability of affordable energy has enabled spectacular growth of industrialization and human development in all parts of the world. With growth now accelerating in developing countries, demands on energy sources and infrastructure are being stretched to new limits. Additional energy issues include the push for renewable resources with reduced greenhouse gas emissions and energy security affected by the uneven distribution of energy resources around the globe. Together, these issues present a field of opportunity for innovations to address energy challenges throughout the world and all along the energy flow. These energy challenges form the backdrop for this special expanded issue of MRS Bulletin on Harnessing Materials for Energy. This article introduces the global landscape of materials issues associated with energy. It examines the complex web of energy availability, production, storage, transmission, distribution, use, and efficiency. It focuses on the materials challenges that lie at the core of these areas and discusses how revolutionary concepts can address them. Cross-cutting topics are introduced and interrelationships between topics explored. Article topics are set in the context of the grand energy challenges that face the world into the middle of this century.

The ever-increasing demand for information storage has pushed research and development of nonvolatile memories, particularly magnetic disk drives and silicon-based memories, to areal densities where bit sizes are approaching nanometer dimensions. At this level, material and device phenomena make further scaling increasingly difficult. The difficulties are illustrated in the examples of magnetic media and flash memory, such as thermal instability of sub-100-nm bits in magnetic memory and charge retention in flash memory, and solutions are discussed in the form of patterned media and crosspoint memories. The materials-based difficulties are replaced by nanofabrication challenges, requiring the introduction of new techniques such as nanoimprinting lithography for cost-effective manufacturing and self-assembly for fabrication on the sub-25-nm scale. Articles in this issue describe block-copolymer lithographic fabrication of patterned media, materials studies on the scaling limits of phase-change-based crosspoint memories, nanoscale fabrication using imprint lithography, and biologically inspired protein-based memory.

The articles in this issue of MRS Bulletin provide a sample of what is novel and unique in the field of in situ transmission electron microscopy (TEM). The advent of improved cameras and continued developments in electron optics and stage designs have enabled scientists and engineers to enhance the capabilities of previous TEM analyses. Currently, novel in situ experiments observe and record the behavior of materials in various heating, cooling, straining, or growth environments. In situ TEM techniques are invaluable for understanding and characterizing dynamic microstructural changes. They can validate static TEM experiments and inspire new experimental approaches and new theories.

In this issue we have endeavored to answer the question, “Whither oxide electronics?” This issue provides a framework and perspective on the progress in the field of oxide electronics over the past several decades, as well as the challenges and opportunities in the years to come. Building on the foundations laid by the pioneers in the materials community and spurred by the discovery of high-temperature superconductivity, there has been both tremendous progress in understanding the complex science of oxide electronic materials and the discovery of other fascinating new phenomena, including colossal magnetoresistance, multiferrocity, and two-dimensional electron gases in correlated oxide systems. Thin-film heterostructures provide a pathway to create novel devices and combinations of physical phenomena. Indeed, the ability to synthesize and control oxide heterostructures using sophisticated deposition techniques has become a key enabler of the recent advances in this field. These oxides are beginning to enter mainstream products because of their higher performance, for example, ferroelectric memories and oxides with high dielectric constant for computers that run at higher speed and use less power.

The field of organic electronics is entering its commercial phase. The recent market introduction of the first prototypes based on organic transistors fabricated from solution is set to augment the existing market presence of organic light-emitting diode applications. Organic photovoltaic products are not far behind. In this article, we provide a brief overview of these devices, with our main focus being organic transistor applications. In particular, we examine some of the key performance requirements for working devices. We also review some of the important advances in semiconductor design and device fabrication techniques and discuss some of the technical challenges that remain in the optimization of next-generation products.

The field of materials tribology has entered a phase of instrumentation and measurement that involves accessing and following the detailed chemical, structural, and physical interactions that govern friction and wear. Fundamental tribological research involves the development of new experimental methods capable of monitoring phenomena that occur within the life of a sliding contact. Measuring friction phenomena while the process is ongoing is a major improvement over earlier techniques that required the surfaces to be separated and analyzed, thereby interrupting the friction-causing event and modifying surface conditions. In the past, MRS Bulletin has highlighted how in situ approaches can greatly enhance our understanding of materials structure, processing, and performance. This issue highlights in situ approaches as applied to materials tribology, namely, the study of contacting surfaces and interfaces in relative motion.

The recent development of experimental techniques that rapidly reconstruct the three-dimensional microstructures of solids has given rise to new possibilities for developing a deeper understanding of the evolution of microstructures and the effects of microstructures on materials properties. Combined with three-dimensional (3D) simulations and analyses that are capable of handling the complexity of these microstructures, 3D reconstruction, or tomography, has become a powerful tool that provides clear insights into materials processing and properties. This introductory article provides an overview of this emerging field of materials science, as well as brief descriptions of selected methods and their applicability.

This article first provides a brief review of the status of the subfield of three-dimensional (3D) materials analyses that combine serial sectioning, electron backscatter diffraction (EBSD), and finite element modeling (FEM) of materials microstructures, with emphasis on initial investigations and how they led to the current state of this research area. The discussions focus on studies of the mechanical properties of polycrystalline materials where 3D reconstructions of the microstructure—including crystallographic orientation information—are used as input into image-based 3D FEM simulations. The authors' recent work on a β-stabilized Ti alloy is utilized for specific examples to illustrate the capabilities of these experimental and modeling techniques, the challenges and the solutions associated with these methods, and the types of results and analyses that can be obtained by the close integration of experiments and simulations.

In this contribution, we briefly discuss how various physicochemical properties of surfaces affect the wettability and self-cleaning character of both naturally occurring and synthetic surfaces. Using a few selected examples from nature, we discuss the superhydrophobic effect and antifouling character of such surfaces and how these properties are associated with variations in surface chemical composition and topography. We also review a few special case studies aimed at adopting these biomimetic schemes to design and fabricate functional self-cleaning surfaces.

Patterned magnetic recording media, in which data bits are stored in discrete single-domain magnetic particles, have been proposed for the next generation of recording media. To achieve high densities, features with periodicities on the order of 25 nm and below are required over large areas, which is a challenging task for any lithography process. Block copolymers (BCPs), which phase-separate into ordered periodic nanoscale structures, might provide a path to accomplish such patterning. In this article, we describe BCP lithography and show how the self-assembled patterns can be templated to make large-area arrays of nanoscale structures with long-range order.

Organic light-emitting devices (OLEDs) have been widely developed for flat-panel displays, but only recently the efficiency of white OLEDs has risen to the point where they can be considered for solid-state lighting (SSL) applications. In this review, we discuss the requirements of solid-state lighting as they relate to OLEDs. We focus on how the color, efficiency, and cost requirements of general illumination differ from those of displays and how these differences might have an impact on the design of organic SSL. We then present some recent developments in large-area fabrication techniques that might be appropriate for solid-state lighting applications. Finally, we review recent results in the development of organic materials, device architectures, light extraction schemes, and fabrication techniques that can lead to cost-effective OLED lighting.

The primary role of a lubricant is to control the friction and wear of rubbing surfaces to optimize the operation of a component by forming an interfacial film separating the surfaces. Lubrication research seeks to develop new lubricant formulations and to optimize component life and performance. To do this, we must understand the mechanisms of film formation and film properties and the way these relate to operating conditions. In many engineering components, the lubricant film is subjected to severe mechanical and thermal stresses as it passes through the loaded zone. These severe conditions can result in molecular alignment or conformational change and the formation of new chemical species, which will impact the lubrication performance of the fluid. The lubricant response within the contact is often transient and thus has proved difficult to study by conventional surface analytical methods. One alternative is to replace one of the surfaces by a transparent window and use molecular microspectroscopy (infrared or Raman) to analyze the film within the contact zone formed during rubbing. This article reviews the development and application of in-contact molecular spectroscopy for the study of lubricant properties within the rubbing interface for both conventional and biolubrication systems. This technique has been used to study molecular conformation, chemical composition, and pressure distribution in the high-pressure region of the contact zone. However, challenges remain, including detecting very thin films, obtaining depth profile information, and applying these methods more generally to biotribology.

Field-activated electroactive polymers (FEAPs) are a class of electroactive polymers that are insulating and exhibit coulombic interaction with and dipole formation in response to external electric signals. There are many polarization mechanisms in insulating polymers, from the molecular to the mesoscopic and even the macroscopic level, which couple strongly with mechanical deformation and can be used to create polymer actuators and sensors. FEAPs feature fast response speed limited by the polymer dielectric and elastic relaxation time, a very large strain level (to more than 100% strain), high electromechanical efficiency, the ability to operate down to micro/nanoelectromechanical devices, and a highly reproducible strain response under electric fields. One challenge in FEAP actuators and electromechanical devices is reducing the operation voltage to below 100 V or even 10 V while achieving an electromechanical conversion efficiency comparable with that of inorganic electroactive materials.

Artificially engineered metamaterials have emerged with properties and functionalities previously unattainable in natural materials. The scientific breakthroughs made in this new class of electromagnetic materials are closely linked with progress in developing physics-driven design and novel parallel fabrication methods. For example, a smooth superlens has been demonstrated with 30-nm imaging resolution, or 1/12 of the corresponding wavelength, far below the diffraction limit. Similarly, a photoswitchable optical negative-index material has been printed, showing a remarkable tuning range of refractive index in the communication wavelength. New frontiers are being explored as intrinsic limitations challenge the scaling of microwave metamaterial designs to optical frequencies. These novel metamaterials promise an entire new generation of passive and active optical elements, such as paper-thin superlenses and modulators.

Membrane techniques for water treatment have been growing significantly for the last decade. Reverse osmosis, for example, is the leading seawater desalination technique. Nanofiltration membranes are used more and more for hardness removal and even to desalinate slightly polluted waters. Ultrafiltration and microfiltration membranes are used extensively mainly as membrane bioreactors in wastewater recovery. While this trend is growing, the membranes still may be improved significantly, based on new materials designed to increase the flux of water through the membranes at reduced pressures while maintaining or even improving the rejection of dissolved matter or suspended matter. Better membranes will reduce energy consumption while maintaining affordable separation properties.