There are perhaps no more controversial materials in our society than the actinides—the elements above actinium in the periodic table that include uranium, plutonium, and many other radioactive elements. They are at the same time vilified by some for their potentially catastrophic impact on the environment and global health and praised by others for their role in ending the Cold War. And yet, at the heart of both these issues is a tremendous amount of fundamental research and technology that is essential for the actinides' rational use, safe disposition, reliable long-term storage, and the remediation of their impact on the environment.

“Environmentally conscious” materials, or “ecomaterials,” are those specifically designed to minimize adverse effects on the environment while maintaining acceptable performance and a competitive price. Related terms include “environmentally friendly” materials, or “environmentally preferable” materials, which are essentially synonymous. A notable geographic trend was observed in relation to this terminology: a recent computer search of the scientific literature under “ecomaterials” produced eight hits, all from authors in Asia, while “environmentally friendly materials” produced six hits, primarily from authors in North America and Europe.

Until the beginning of the 19th century, flame produced by combustion was the only source of artificial light. Since then, physical phenomena other than pyroluminescence have been used to produce light. Limelight (incandescence of calcium oxide heated by the flame from an oxyhydrogen blowpipe), gas mantles (candoluminescence of gas-flame-heated rare-earth oxides), and the electrical Jablochkoff candle (an early type of carbon-arc lamp) were among the important milestones that led to modern lighting technology. In the 21st century, most of the residential lighting worldwide is provided by tungsten incandescent lamps. Compact fluorescent lamps are also actively promoted because of their higher performance—a broader spectrum for higher-quality white light and elimination of 100–120-Hz flickering, for example. Most work environments employ fluorescent tubes for general lighting, and street lighting is dominated by sodium lamps. Lighting consumes ∼2000 TWh of energy annually, about 21% of the global consumption of electricity. However, during the past 20 years, none of the conventional lighting technologies has exhibited a significant improvement in efficiency. The drive to save lighting energy and reduce its negative environmental impact (i.e., carbon emissions and the disposal of mercury contained in discharge lamps) stimulates the search for new, efficient sources of light.

During a lecture on the optical properties of gold in 1857, Michael Faraday remarked that “a mere variation in the size of its particles gave rise to a variety of resultant colors.” Since Faraday was referring to his studies of nanometer-scale gold particles (now commonly referred to as nanocrystals), it is clear that the topic of this issue of MRS Bulletin is an old field with an important history. Indeed, the study of Faraday's gold sols was critical for the development of several aspects of modern materials science, including how light interacts with matter and how colloids can be formed, manipulated, and controlled.

The electronics revolution of the past 50 years has its roots in two scientific and technological areas. On the one hand, there have been tremendous advancements in our understanding of the physics of metals, dielectrics, and semiconductors, leading to the development of devices such as the transistor. On the other hand, a variety of processing techniques such as thin-film growth and deposition, ion implantation, and photolithography have allowed the massive integration of electronic functionality within a very small area, leading to microprocessors and high-density memory, among other innovations.

New methods for micro- and nanofabrication will be essential to scientific progress in many areas of biology, physics, chemistry, and materials science. They will also form enabling technologies for applications ranging from microfluidic devices to micro-optical components to molecular diagnostics to plastic electronics to nanoelectromechanical systems. In many cases, advances will be aided by the highly engineered and spectacularly successful lithographic techniques that are used for microelectronics. These methods have certain drawbacks, however, that will limit their applicability to new devices and fields of study. For example, photolithographies cannot be used with many organic and biological materials due to their chemical incompatibility with typical photoresists and developers; they cannot easily pattern features with dimensions of less than ∼100 nm; they require expensive capital equipment and facilities; they have difficulty forming features on curved, uneven, or rough objects; they can only directly pattern a small set of specialized, photosensitive materials; they cannot reproduce features with complex, three-dimensional (3D) shapes; and they can only pattern small areas in a single step. This situation creates a need for research into alternative patterning methods with capabilities that can complement those of photolithography and other established approaches.

This issue of MRS Bulletin focuses on the preparation and application of hybrid organic–inorganic materials, which are broadly defined as synthetic materials with organic and inorganic components. Hybrid organic–inorganic materials are of two kinds: homogeneous systems derived from monomers or miscible organic and inorganic components, and heterogeneous and phase-separated systems with domains ranging from angstroms to micrometers in size.

Every university student becomes familiar with the concept of thermal conductivity, a fundamental physical property of materials, through his or her textbooks. Initial work on high thermal conductivity was carried out in 1911 by Eucken, who discovered that diamond was a reasonably good conductor for heat at room temperature. Theoretical support for this discovery was established by Debye in 1914.

We have heard a lot about the exciting new materials being used in microelectronics, and I would like to describe some experiments making use of in situ electron microscopy to try to understand the mechanisms of the reactions that these materials undergo during deposition and processing. I will discuss experiments in which we carry out one of these reactions within an electron microscope and record the effect on the specimen in real time. We then use measurements from the recordings to analyze the reaction mechanism in a quantitative way. In this article, I will cover two types of experiments. First, I will describe experiments in which we examine the motion of surface and interface steps during reactions, and I will discuss how that information allows us to determine reaction mechanisms. In this context, I will consider silicon oxidation and silicide formation. In the second type of experiment, we look at how surface morphology changes during reactions. In particular, we will try to understand the growth mechanism of “quantum dots,” which are becoming important for some novel microelectronic applications. After discussing these results, I will describe our attempts to extend the technique of in situ electron microscopy to look at systems other than the solid—solid or gas—solid interface.

Microelectromechanical systems, or MEMS, constitute a group of microdevices that are just beginning to affect many areas of science and technology. In diverse fields including the automotive industry, aeronautics, cellular communications, chemistry, acoustics, and display technologies and other photonic systems, these highly functional devices are making a big name for themselves, despite their diminutive size.

Preserving art through the ages is more than placing a designated object in a museum, properly storing and exhibiting it. Preservation involves more than preventing the destruction and looting of sites or the theft of and illicit trade in antiquities. It is more than conservation—that is, the assessment, documentation, and stabilization of an artifact's condition, and, if necessary, the skill and judgment to rescue an artifact, to intervene using a reversible treatment, and to follow with a program of monitoring stability.

Predicting the properties and performance of materials is central to the success of major industries producing a vast range of consumer goods and to research programs at laboratories and universities around the world. For many years, scientists have longed to have computer simulations that predict the behavior of materials and track the evolution of their microstructures from the atomic to the engineering scales. Until recently, such simulations had been little more than an elusive goal.

Diamond is one of the most intriguing and potentially useful materials known to science. It is the hardest substance that we know, and it has the highest sound velocity and the highest thermal conductivity of any material. Because diamond is so difficult to fabricate, the challenge is to take meaningful advantage of its extraordinary properties. The chemical vapor deposition (CVD) of diamond overcomes many of the fabrication problems and has become the focus of an important research and development effort worldwide. Although the General Electric Corp. succeeded about 50 years ago in the synthesis of diamond by high-pressure, high-temperature techniques, the low-pressure, or CVD, methods were developed only about 20 years ago in the former Soviet Union, Japan, and the United States. This presentation will deal with a more recent development in diamond CVD that allows one to control the crystallite size in such a way as to synthesize phase-pure nanocrystalline diamond films, which have many unique and fascinating properties not shared by other forms of diamond.

One of the fundamental physical properties of a material is its ability to conduct heat. Understanding and controlling the thermal conductivity of nonmetallic materials has been of much interest, mainly because this transport parameter is an important factor in determining the performance and reliability of various device applications.

The rapid expansion of microelectromechanical systems (MEMS) into new application areas is due in large part to the development of surface-micromachining techniques that allow the fabrication of a wide variety of MEMS devices with structural components that can execute motion in at least one direction.

The final decade of the 20th century was the most important period yet in establishing a sustainable society for the coming century. After the Earth summit held in Rio de Janeiro in 1992, the world's population was challenged to decrease its environmental impact on the Earth. Nine years after the Rio summit, we are living in a more dangerous and unsustainable world with a higher population, more resource consumption, more waste, and more poverty, but with less biodiversity, less forest area, less available fresh water, less fertile soil, and less stratospheric ozone.

Magnetic colloids, or ferrofluids, have been studied to probe the fundamental size-dependent properties of magnetic particles and have been harnessed in a variety of applications. The magnetorheological properties of magnetic colloids have been exploited in high-performance bearings and seals. The deposition of magnetic dispersions on platters and tapes marked the earliest embodiments of magnet information storage. Magnetic particles enhance contrast in magnetic resonance imaging and promise future diagnostic and drug delivery applications. The need to explore the scaling limits of magnetic storage technology has motivated the preparation of size-tunable monodisperse magnetic nanoparticles with controlled internal structures. The study of these nanoparticles is critical to efforts to separate the role of defects from intrinsic, finite size effects.

Radiation damage, and its attendant effect on a wide spectrum of materials properties, is a central issue in many advanced technologies ranging from ion-beam processing to the development of fusion power. Indeed, the various challenges presented by irradiation effects are too numerous to discuss in this brief article.

Conventional optical fibers are fabricated by creating a preform from two different glasses and drawing the preform down at an elevated temperature to form a fiber. A waveguide core is created in the preform by embedding a glass with a higher refractive index within a lower-index “cladding” material. Over the last few years, researchers at several laboratories have demonstrated very different forms of optical-fiber waveguides by using a drawing process to produce two-dimensionally microstructured materials in the form of fine “photoniccrystal fibers” (PCFs). One such waveguide is represented schematically in Figure 1. It consists of a silica fiber with a regular pattern of tiny airholes that run down the entire length. The optical properties of the microstructured silica cladding material enable the formation of guided waves in the pure silica core.

Exactly 50 years ago, E.W. Müller became the first person to observe single atoms, with the aid of the field-ion microscope (FIM). In 1967, with John Panitz and S. Brooks McLane, Müller's invention of the atom probe meant that, in his words, “We can now really deal much more intimately with the individual atoms which we encounter, since we know their names.” By combining position-sensitive detection with the time-of-flight mass spectrometry of single atoms in the atom probe, Cerezo and co-workers in the late 1980s built an instrument capable of reconstructing the three-dimensional (3D) atomic distribution of elements present in a material. The instruments that are capable of microanalysis at this level, called generically 3D atom probes (3DAPs), were the subject of two articles published in MRS Bulletin in 1994. In this article, we review some of the progress in the field since that time, in particular, the expansion of the range of materials problems that can be addressed by this powerful technique.