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.

Our ability to pattern nanostructures offers a unique path to discovery and innovation in science and technology. When nanostructures are smaller than a fundamental physical length scale, conventional theory may no longer apply, and new phenomena emerge.

The demand for precise micro-optical elements and subsystems is increasing drastically, influenced mainly by the exploding information and communications markets. For many applications, technologies capable of high-volume production of these elements are needed. Favored methods are replication technologies such as injection molding, hot embossing, or UV molding. The challenge for materials scientists is to synthesize materials that can be formed into micro-optical structures and that can resist extreme environmental conditions during operation and stocking (e.g., temperature changes from −45°C to +125°C).

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.

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.

As physical processes for generating miniaturized structures increase in resolution, the types of scientific questions one can ask and answer become increasingly refined. Indeed, if one had the capability to control surface architecture on the 1–100-nm length scale with reasonable speed and accuracy, one could ask and answer some of the most important questions in science and, in the process, develop technologies that could allow for major advances in surface science, chemistry, biology, and human health. This length scale, which is exceedingly difficult to control, comprises the length scale of much of chemistry and most of biology. Indeed, chemical and biochemical recognition events are essentially sophisticated examples of pattern-recognition processes. Therefore, if one could pattern on this length scale with control over feature size, shape, registration, and composition, one could systematically uncover the secrets of recognition processes involving extraordinarily complex molecules. Arecent invention, dip-pen nanolithography (DPN), may provide access to this type of control over surface architecture and entry into a new realm of structure-versus-function studies for chemists, biologists, physicists, and materials scientists.

Impressive advances in vapor-phase deposition and photolithographic patterning techniques have been fueling the silicon microelectronics revolution over the last 40 years. However, for many interesting classes of materials, including biological materials or functional synthetic polymers, vacuum deposition and photolithography are not the techniques of choice for producing ordered structures and devices. Many of these materials selfassemble into well-ordered microstructures when deposited from solution, and patterning may be more readily achieved by solution-based selective deposition and direct-printing techniques. It is appealing to consider novel ways of manufacturing functional circuits and devices based on techniques that are similar to printing visual information onto paper.

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.