Over a decade ago, theorists predicted that photonic crystals active at visible and near-infrared wavelengths would possess a variety of exciting optical properties. Only in the last several years, however, have experimentalists begun to build materials that realize this potential in the laboratory. This lag between experiment and theory is primarily due to the to the challenges associated with fabricating these unique materials. As the term “crystal” suggests, these samples must consist of highly perfect ordered arrays of solids. However, unlike conventional crystals, which exhibit order on the angstrom length scale, photonic crystals must have order on the submicrometer length scale. In addition, many of the most valuable properties of photonic crystals are only realized when samples possess a “full” photonic bandgap. For such systems, large dielectric contrasts and particular crystal symmetries create a range of frequencies over which light cannot propagate. Realizing the nanoscopic architectures required to form such systems is a challenge for experimentalists. As a result, fabrication schemes that rely on lithographic techniques or spontaneous assembly have been a focus in the development of the field.

This nursery rhyme is one of the oldest, most familiar, and shortest treatises on fracture mechanics in the literature. Nevertheless, it makes several important points: (1) fracture occurs in response to some driving force (for Humpty, a “great fall”), (2) fracture involves material separation, and (3) fracture is irreversible.

Some of the most important cultural icons in the world are oil paintings. Preserving them for future generations requires a fundamental understanding of the long-term chemical, mechanical, and physical behavior of their components. If the properties are understood, modeling and even predicting the effects of exposure to changes in temperature, relative humidity, shock, and vibration are possible.

The articles thus far in this MRS Bulletin issue on Emerging Methods for Micro- and Nanofabrication have addressed the creation of structures or devices on a small scale. What is implicit in some of these articles is that a substrate of sufficient flatness is available upon which to build these structures in a controlled way. A related area, therefore, is the formation of these flat surfaces, as well as the development of the tools to make them.

Many microelectromechanical systems (MEMS) use the changing capacitance of movable parallel plates to drive and sense motion. An increase in this capacitance improves the performance of these micromechanical structures by means of increased electromechanical coupling for lower driving voltages and increased sensitivity of the micromechanical motion.

Willem de Kooning (1904–1997) and Jackson Pollock (1912–1956) are perhaps the best-known members of the abstract expressionist movement, a group of diverse artists from disparate backgrounds who radically transformed American art during the 1940s and into the 1950s. While the development and legacy of abstract expressionism remains a subject of considerable debate, what this diverse group of artists had in common was the belief that the materials, and the ways the artists applied them, are crucial to the expression of their art.

The recent development of microscopes that allow for the examination of defects at the atomic scale has made possible a more direct connection between the defects and the macroscopic response they engender (see, e.g., the December 1999 issue of MRS Bulletin).

The spontaneous emission of an atom is not a property of the atom only; it also depends on the local optical surroundings. The simplest demonstration of this effect was provided by the early experiments of Drexhage, who studied the emission rate of luminescent europium ions close to a mirror. It was found that while the spectral distribution of the emission remained constant, the emission rate was dependent on the position of the Eu3+ ions relative to the mirror. This effect is due to interference of the optical modes incident to and reflected at the mirror. Since then, the modified spontaneous emission of atoms in cavities has been studied extensively. More recently, the control of spontaneous emission in solid-state systems has become of great interest because it enables the tailoring of the emission properties of optical materials. It was shown how the spontaneous-emission rate of optical probe ions or dyes inside dielectric films is modified by the presence of a dielectric interface, in a dielectric multilayer, or a microcavity. The dependence of the decay rate on the optical surroundings in these one-dimensional systems can be described in terms of Fermi's “golden rule,” which states that the decay rate is proportional to the local optical density of states (DOS). The spatial variation in the DOS is due to the interference of optical modes reflected and refracted at the dielectric interface(s).