Microelectromechanical systems (MEMS) devices are being manufactured in the hundreds of millions and are widely deployed for pressure sensor, accelerometer, display, and printing applications. This suggests customer confidence in the longterm reliability of MEMS (also known as microsystems or micromachines) under diverse stringent conditions.

Nano-ordered composite materials consisting of organic polymers and inorganic compounds have been attracting attention for their use in creating high-performance or high-functionality polymeric materials. The term “polymer hybrid” describes blends of organic and inorganic components with molecular-level dispersions.

Chemical vapor deposition (CVD) is an attractive method for producing bulk and thin-film materials for a variety of applications. In this method, gaseous reagents condense onto a substrate and then react to produce solid materials. The materials produced by CVD are theoretically dense, highly pure, and have other superior properties.

In the last few years, photonic crystals have gained considerable interest due to their ability to “mold the flow of light.” Photonic crystals are physically based on Bragg reflections of electromagnetic waves. In simple terms, a one-dimensional (1D) photonic crystal is a periodic stack of thin dielectric films with two different refractive indices, n1 and n2. The two important geometrical parameters determining the wavelength of the photonic bandgap are the lattice constant, a = d1(n1) + d2(n2), and the ratio of d1 to a (where d1 is the thickness of the layer with refractive index n1, and d2 is the thickness of layer n2). For a simple quarter-wavelength stack, the center wavelength λ of the 1D photonic crystal would be simply λ = 2n1d1 + 2n2d2. In the case of 2D photonic crystals, the concept is extended to either airholes in a dielectric medium or dielectric rods in air. Therefore, ordered porous dielectric materials like porous silicon or porous alumina are intrinsically 2D photonic crystals.

Studies of the actinide elements and compounds were (and are) motivated by the need to characterize their structural and thermodynamic properties for the development of nuclear fuels and the treatment of waste, whether it be for long-term storage or ideas involving transmutation in high-powered accelerators. For the most part, tables giving these data exist, although the data for transuranium compounds are rather sparse. A much more difficult task is to understand the data and develop theories that have predictive power in this part of the periodic table. In doing this, however, we are confronted with the extremely complicated electronic structure of the 5f shell and the great paucity of high-quality data on materials containing transuranium isotopes.

Two-dimensional (2D) methods for transferring patterns to planar substrates have enabled the technological revolution in microfabrication that has marked the last 40 years. The overall trend toward increased miniaturization has led to the development of new types of devices in areas unrelated to conventional microelectronics: analytical tools, chemical reactors, microelectromechanical systems (MEMS), optical systems, and sensors. The widespread use and high level of technological development associated with photolithography has also made the methodologies for microelectronics—patterning photosensitive polymers, etching and deposition of thin films, and liftoff—ubiquitous in the fabrication of these new classes of microsystems. These new systems have specialized requirements, however, and are not simple extensions of microelectronics technologies. They often require materials—especially organic polymers—that are not commonly used in microelectronic systems, they must have low cost, and they may need 3D structures in order to implement complex designs. These requirements have stimulated the development of new methods for microfabrication.

Semiconductor materials are widely used in both optically and electrically pumped lasers. The use of semiconductor quantum wells (QWs) as optical-gain media has resulted in important advances in laser technology. QWs have a two-dimensional, step-like density of electronic states that is nonzero at the band edge, enabling a higher concentration of carriers to contribute to the band-edge emission and leading to a reduced lasing threshold, improved temperature stability, and a narrower emission line. A further enhancement in the density of the band-edge states and an associated reduction in the lasing threshold are in principle possible using quantum wires and quantum dots (QDs), in which the confinement is in two and three dimensions, respectively. In very small dots, the spacing of the electronic states is much greater than the available thermal energy (strong confinement), inhibiting thermal depopulation of the lowest electronic states. This effect should result in a lasing threshold that is temperatureinsensitive at an excitation level of only 1 electron-hole (e-h) pair per dot on average. Additionally, QDs in the strongconfinement regime have an emission wavelength that is a pronounced function of size, adding the advantage of continuous spectral tunability over a wide energy range simply by changing the size of the dots.

Scientific consideration of how to scale electronics down to the molecular level started in the mid-1970s. Unfortunately, at the time, researchers did not have the adequate analytical tools to perform the experiments. That has changed drastically, and therefore interest in this field has been renewed, especially over the last few years.

Modern semiconductor technology has been enabled by the ability to control the number of carriers (electrons and holes) that are available in the semiconductor crystal. This control has been achieved primarily with two methods: doping, which entails the introduction of impurity atoms that contribute additional carriers into the crystal lattice; and charging, which involves the use of applied electric fields to manipulate carrier densities near an interface or junction. By controlling the carriers with these methods, the electrical properties of the semiconductor can be precisely tailored for a particular application. Accordingly, doping and charging play a major role in most modern semiconductor devices.

The three most important components of tissue engineering are biomaterials, cellular biology, and vascular supply. Biomaterials are needed to control the delivery of new cells into the body. In the absence of biomaterials, cells that are injected into a vein, a cavity, or tissue tend to disperse, so a sufficiently high density of cells to perform the intended function—replacement or repair of a damaged structure—is never achieved.1 A porous delivery system is needed that confines the cells to the desired location and promotes their nourishment until blood vessels grow in and new tissue is formed. Biomaterials such as plastics can provide such a porous delivery system.

In recent years, high thermal conductivity has been found in materials with heterogeneous microstructures, that is, ceramics and films with granular microstructures having different phases. Understanding the thermal conductivities and microstructures of these materials is more difficult, however, than in the case of single-crystal materials because they consist of grains and grain boundaries.

Elemental plutonium is considered to be one of the most complex elements in the periodic table and, by some, one of the more toxic, given its moderate radioactivity and that it is a heavy metal. Essentially a manuf actured element (only traces are found in nature), it was first discovered and produced some six decades ago. Amazingly, hundreds of tons of plutonium are pre sently in existence. Crystalline solids formed by plutonium and nonmetallic elements (e.g., hydrogen, oxygen, halides, etc.) were some of the first compounds investigated, and oxides and oxide-related materials have always been important compounds.

The drive toward miniature photonic devices has been hindered by our inability to tightly control and manipulate light. Moreover, photonics technologies are typically not based on silicon and, until recently, only indirectly benefited from the rapid advances being made in silicon processing technology. In the first part of this article, the successful fabrication of three-dimensional (3D) photonic crystals using silicon processing will be discussed. This advance has been made possible through the use of integrated-circuit (IC) fabrication technologies (e.g., very largescale integration, VLSI) and may enable the penetration of Si processing into photonics. In the second part, we describe the creation of 2D photonic-crystal slabs operating at the λ = 1.55 μm communications wavelength. This class of 2D photonic crystals is particularly promising for planar on-chip guiding, trapping, and switching of light.

Studying the raw materials used by ancient glassmakers provides information about ancient glassmaking practices, the relationship between glassmaking and other craft technologies (silicate-based or non-silicate-based), and the trading patterns of specific cultures. Colored opaque glasses are of particular interest because they were among the first mass-produced and mass-distributed glasses.

Reinforcement of polymers with a second phase, whether inorganic or organic, to produce a polymer composite is common in the production of modern plastics. Polymer nanocomposites (PNCs) represent a radical alternative to these conventional polymer composites.

The field of microelectromechanical systems (MEMS) involves the interaction of the physical environment with electrical signals through the use of microbatchfabricated devices. MEMS is a growing technology, and commercial MEMS products are becoming commonplace.

Since the discovery of high-Tc superconductors (HTSs), especially the Bi-based oxide superconductors (Bi-HTSs) in 1989, much effort has been concentrated on the fabrication of Bi-HTS wires and tapes. Bi-HTSs are interesting materials from the viewpoint of practical applications. One of the interesting applications of Bi-HTSs is the cryogen-free conduction-cooled magnet. Besides having a high transition tem- perature (Tc), Bi-HTSs have high upper critical fields (Bc2) or high irreversibility fields (Birr) at temperatures below ∼30 K. Because ∼30 K can be efficiently main- tained by a cryocooler, a Bi-HTS magnet cooled with a cryocooler has great potential in many technological applications. Another promising application of Bi-HTSs is the high-field magnet. When the temperature is reduced to ∼5 K, Bi-HTSs show a much higher Bc2 or Birr than do conventional metallic superconductors (low-temperature superconductors, LTSs) such as Nb3Sn. This indicates that Bi-HTSs also have great potential for use in a high- field superconducting magnet if the magnet is operated at low temperature.

Microcontact printing (μCP) is a low-cost technique for rubber stamping that combines the high spatial resolution of sophisticated forms of photolithography with capabilities (e.g., single-step patterning of large areas and nonplanar surfaces) that are not present in other approaches. μCP will be useful for applications where established methods are ineffective. Two areas are particularly promising: (1) plastic electronics, where the chemical incompatibility of the constituent materials with common photoresists and developers can preclude the use of photolithography, and where μCP with rotating cylindrical stamps forms an excellent match with the type of reel-to-reel processing that is envisioned for these systems; and (2) new classes of optical-fiber and microcapillarybased devices, where μCP allows highresolution (∼0.2 μm) circuits, photomasks, and actuators to be printed directly on the highly curved surfaces of cylinders with submillimeter diameters. This article describes some highlights of our work in these and related areas.

Activated carbons are the most important carbon materials used in water treatment. Their known world production is around 500,000 tons per year, of which about 80% is used for liquid-phase applications. These solids are manufactured in powder or granular form from a large variety of raw materials and are unique and versatile adsorbents due to their highly developed porosity, their large surface area (which in some cases can be up to 3000 m2/g), and their variable surface chemistry.