Magnetic recording and optical recording are the major technologies used to provide long-term storage of information in today's computer systems. Magnetic recording has been used for data storage in computer systems for over 40 years, and the advances in technology that have occurred in that time frame are nothing short of phenomenal. One might expect that after 40 years of dominance, the rate of progress in magnetic recording would be slowing down and that other technologies would be moving in to replace it. However rather than slowing down its rate of progress, magnetic recording is now advancing at a faster rate than at any time in the past. Magnetic hard-disk drives represent the largest segment of the data-storage business, and the number of hard-disk drives sold is increasing at about 20% per year. Tape drives continue to enjoy a very substantial market and are also advancing at a rapid pace while flexible disk drives continue to appear in every personal computer sold and have recently increased capacity by nearly two orders of magnitude.

Optical recording was introduced into the marketplace in 1989 and has secured a significant market. However thus far, optical recording has primarily found new market niches, rather than being directly competitive with magnetic recording. CD-ROMs are widely used for the distribution of prerecorded information—a business that is now comparable in size to the magnetic-tape-drive business. On the other hand, erasable, optical drives, which were first introduced in 1989, have not had nearly as much success and have much smaller markets than either magnetic hard drives or tape drives.

The transmission electron microscope (TEM) is one of the most useful tools available to the materials scientist. Yet both the complexity and expense of the equipment, and the huge investment in time necessary to become proficient in specimen preparation and image acquisition and analysis, mean that it is difficult for most industrial institutions to maintain a state-of-the-art TEM facility. How can industry overcome this problem? One solution is to set up a collaboration with a university, an industrial partner, or a government research laboratory. Such collaborations can be extremely valuable to the company, which gains access to microscopes, specimen-preparation equipment and the expertise of professional microscopists, and to the research laboratory, which benefits from the industrial perspective and the private sector's proficiency in materials preparation and processing.

Such collaborations exist, and they can produce excellent results. In this article, we present three case studies in which successful collaboration has occurred between industry and one of the Department of Energy's scientific user facilities, the National Center for Electron Microscopy (NCEM-see sidebar). Our aim is not only to describe results that we hope will be of scientific interest but also to encourage industrial researchers to consider collaborations with institutes such as NCEM.

Heteroepitaxy is an important area of materials research because of its applicability to a variety of technological applications. One area presently attracting a great deal of research is heteroepitaxy of electronic and optoelectronic materials. Here the word heteroepitaxy is emphasized to distinguish it from the much more common epitaxial growth of essentially the same material where only variations in the concentration of dopants is allowed. When materials scientists and engineers from the electronics industry refer to heteroepitaxy, they mean the oriented-crystal growth of some interesting (at least, to them!) material on a single-crystal substrate of some other material. By using heteroepitaxy, it is possible to tailor the electronic or optical properties in a way that is just not possible with doped, epitaxial growth of the same material. There are some rare examples of pairs of materials that have the same crystal structure, are very closely lattice-matched, and are dissimilar enough in their optical and/or electronic properties to make heteroepitaxy interesting. One such couple, AlxGa1−xAs/GaAs (lattice mismatch of 0.1% when x = 1), has been extensively exploited over the last 30 years.

Computer-aided design of alloys is becoming increasingly useful, replacing the completely experimental approach. The computer-aided approach significantly reduces the cost of alloy design and more easily leads to optimum properties by reducing the amount of experimentation. Design of high-strength, high-conductivity alloys is a good example of the efficacy of using the computer to design experimental alloys.

Alloys that have both high strength and high electrical conductivity are needed for many applications such as lead frames, connectors, conducting springs, and sliding contacts. Figure 1 shows the strength and conductivity of some commercially available copper-based alloys. Since dissolved solutes in an otherwise pure metal rapidly reduce the electrical conductivity (as well as the thermal conductivity), solid solution strengthening is not suitable for designing this class of alloys. Such alloys must be designed on the basis of precipitation or dispersion hardening. The theory of the yield stress of alloys with precipitates or dispersed phases has been well-formulated and may be used for alloy design. The solubility of the hardening phase in the matrix must be very small. Otherwise the conductivity will be degraded too much. Nordheim's rule relates conductivity to dissolved solute in alloys and is also available for alloy design. Decreasing the dissolved solute increases the conductivity and strength due to an increase in the volume fraction of the precipitate.

Since its development over 150 years ago, silver-halide imaging has retained a central role in the imaging world, despite advances in electronic imaging over the last five to 10 years. At present the high cost of electronic cameras and printing systems prohibits their widespread general use. Nevertheless digital electronic features are now being incorporated into silver-halide-based imaging systems. Development of new films that incorporate magnetic-storage capability into conventional silver-halide film, as well as smaller cameras and tighter winding radii, put more stringent requirements on the physical performance of the final silver-halide-based product.

For many years, advances in silver-halide imaging focused on improved photographic emulsions, providing improvements in resolution, color balance, and latitude. Advances in the photographic emulsions resulted from particle shape and morphology control of the silver-halide crystal, as well as new sensitizing dyes, couplers, and other image-modifying addenda that provided increases in speed and quality. Literature on the “science of photography” and “photographic materials and processes” emphasizes silver-halide chemistry and the function of sensitizing dyes and couplers in color photography as they impact film latitude, resolution, color balance, etc., with minor mention of the support materials and properties. Literature on support characteristics and physical properties is limited.

Since their commercialization in the late 1940s, applications for synthetic polymers have grown at an extraordinary rate, to the point where polymers are now ubiquitous in our society. The demands placed upon polymer performance have paralleled the growth in applications and has driven the development of sophisticated multiconstituent polymer formulations with many outstanding physical and mechanical properties. Many applications require that a polymeric material be attached to or in contact with another material. In some cases, such as the classic nonstick fry pan, as well as lubrication and release paper, it is desirable to create surfaces that do not interact with the material in contact. On the other hand, in applications such as rubber toughening of blends, filled or fiber-reinforced polymers, and coatings, dissimilar materials must adhere to each other if high performance is to be obtained. While the majority of the research and development efforts to date have centered on optimizing bulk properties, the focus is now shifting toward the development of polymer systems with controlled surface and interfacial properties.

The recent flurry of activity in polymer interfacial science can be traced to the simultaneous emergence of three factors: a strong commercial need to control the surface properties of advanced multicomponent polymer systems, the availability of sophisticated theoretical methods for studying polymer surface and interphase problems, and the devel opment of new characterization techniques capable of investigating molecular level structure at polymer interphases. The seven articles that comprise this issue provide an overview of basic polymer interface science by discussing some of the current advances in polymer interface theory, by presenting many of the new techniques available for polymer interphase characterization, and by illustrating some of the interesting and challenging problems associated with their applications.

Flat-panel displays (FPDs) will soon become ubiquitous products in our homes, workplaces, and a number of places in between. Familiar display applications pioneered by the venerable cathode-ray tube (CRT) will progressively utilize a number of different FPDs. Flat-panel displays will also initiate and pioneer new applications, as was the case with notebook computers and personal digital assistants.

The future proliferation of FPDs can no longer be doubted for two simple reasons. First, such devices help us cope with this already information-saturated society. Second, the technological momentum and financial commitment needed for FPDs to take hold are already irreversibly set in place. It is the insatiable current and near-future demand that are pulling the field, and that are fueling a flurry of research and development activities. The display market has grown in size from tens of millions of dollars only a decade ago to a nearly ten-billion-dollar industry. This market growth is expected to continue at a brisk pace during the next decade.

This of course is in no way bad news for materials scientists and engineers. We nearly always benefit from development of new and complex products. It is in regard to these rather incipient but advanced manufacturing technologies where we often encounter challenging, relevant, and interesting materials problems. The better we address these obstacles during these early and therefore critical times, the more successful the FPD technology will be in fulfilling the potential opportunities that lie ahead.

When trying to identify the beginnings of “tissue engineering” as a defined scientific field, the first major scientific meeting devoted to “tissue engineering” comes to mind. This meeting took place in 1988 at Granlibakken, Lake Tahoe, California. When looking through the proceedings of this meeting, one can see that many of the fundamental challenges of tissue engineering, still unresolved today, were articulated back at that time. As practiced today, the field of tissue engineering is based on a blending of engineering principles in the materials sciences with the principles of cell and tissue biology to create functional replacements for aged, traumadamaged, or diseased human tissues and organs.

The driving force behind the field of “tissue engineering” is the desire to replace defective human tissue with artificial substitutes to improve the quality of human life. This desire is not unique to our times but can be traced back several thousand years. The earliest reports of the use of artificial materials in wound healing are contained in the Edgar Smith papyrus. This historic document mentions the use of sutures and woundclosure devices around 4000 B.C. and the use of metals in bone repair around 2000 B.C. In ancient times, Native Americans apparently used silk and hair as suture materials.

In 1900 natural tissues like amnion and placenta were suggested as skin replacements, an approach that was obviously doomed to fail due to immunological reactions. The general lack of understanding of the immune response at the beginning of this century forced researchers and clinicians to abandon attempts to use natural tissues as medical implants and contributed to a focus on synthetic materials. Advances in metallurgy facilitated the introduction of metals for bone reconstruction and dental prosthesis, and the large number of casualties during World War I resulted in the establishment of stainless steel and other metals as the preferred orthopedic implant materials.

The growth of semiconductor heteroepitaxial layers is assuming ever greater importance due to the demands of modern electronic-device fabrication. Furthermore although low-strain heterosystems such as AlGaAs/GaAs remain the basis of many device structures, there is an increasing trend also to use more highly strained combinations such as InGaAs/GaAs and SiGe/Si. However the growth of the latter epitaxial systems must be approached with great care in order to achieve the optimum layer structural quality. Of course for any given alloy-layer composition, interfacial misfit defects in general will be introduced when the layer thickness exceeds a critical value, as originally described by Frank and van der Merwe, and Jesser and Matthews. (See the article by F.K. LeGoues in this issue for more general considerations of misfit-defect introduction.) In addition the morphology of such strained layers must be given very careful attention. It is the purpose of this article to examine our current understanding in this latter area.

When any epitaxial layer is grown, initially it might be expected that a flat surface would result under ideal growth conditions when internal defects have been eliminated. This would be expected to minimize the surface step density and hence the surface energy. However nature has a way of confounding our simplest expectations and while for homoepitaxial layers in the absence of kinetic effects this expectation virtually can be realized, the presence of strain in a heteroepitaxial system can severely affect the observed layer morphology.

The beauty of art is the result of complex intuitive and cognitive choices made by the artist. Understanding the genesis of these choices can be as illusive as the resulting imagery, but great art seems to initiate in us a curiosity about the ideas, methods, and materials used by the creators. Connoisseurship in this century has been enriched by the application of scientific-analysis methods. The results of these investigations into the physical properties of art have shed new light on their authenticity and individual histories as well as on the craft in general. Developments in the fields of physics and chemistry have allowed us to understand more about how we perceive and interact with works of art. The articles in this issue of MRS Bulletin describe the choices made by the artist and the techniques used to analyze works of art ranging from cave paintings to pastels on paper.

This issue of the Bulletin had its genesis in an interdisciplinary course at Cornell University, “Art, Isotopes, and Analysis.” Stan Taft and James Mayer taught the course with guest lectures by Maryan Ainsworth, Richard Newman, and Dusan Stulik. Michel Menu, Debora Mayer, Dusan Stulik, Richard Newman, and Arleyn Simon have carried on the guest-lecture tradition at Arizona State University (ASU). They also participated in a symposium, “Revelations Beneath the Surface: The Science of Art,” held June 14, 1996 at ASU. The photograph (Figure 1) shows the symposium speakers.

The properties of polymeric surfaces and interfaces are ubiquitous in their myriad commercial applications: paints and coatings, adhesives, lubrication, biocompatible materials, flocculation and steric stabilization of colloids, membranes and separation media, immiscible polymer blends, and filled composites. Some of these applications require low-energy surfaces that are chemically inert and are not easily wet with other materials. Other applications require high adhesion and strong interactions between the polymer and substrate. This article discusses fundamental principles governing the behavior of polymer surfaces and interfaces, then illustrates various means available for polymer-interface modification.

Atomistic simulations are playing an increasingly prominent role in materials science. From relatively conventional studies of point and planar defects to large-scale simulations of fracture and machining, atomistic simulations offer a microscopic view of the physics that cannot be obtained from experiment. Predictions resulting from this atomic-level understanding are proving increasingly accurate and useful. Consequently, the field of atomistic simulation is gaining ground as an indispensable partner in materials research, a trend that can only continue. Each year, computers gain roughly a factor of two in speed. With the same effort one can then simulate a system with twice as many atoms or integrate a molecular-dynamics trajectory for twice as long. Perhaps even more important, however, are the theoretical advances occurring in the description of the atomic interactions, the so-called “interatomic potential” function.

The interatomic potential underpins any atomistic simulation. The accuracy of the potential dictates the quality of the simulation results, and its functional complexity determines the amount of computer time required. Recent developments that fit more physics into a compact potential form are increasing the accuracy available per simulation dollar.

This issue of MRS Bulletin offers an introductory survey of interatomic potentials in use today, as well as the types of problems to which they can be applied. This is by no means a comprehensive review. It would be impractical here to attempt to present all the potentials that have been developed in recent years. Rather, this collection of articles focuses on a few important forms of potential spanning the major classes of materials bonding: covalent, metallic, and ionic.

Characterization of materials properties is critical for the understanding of materials behavior and performance under operating conditions. Tailoring materials properties, which are functions of the materials states, is essential for advanced product design. The need to characterize materials for a myriad of applications has spurred the development of many new methods and instruments. Unfortunately many of these characterization tools require destructive sectioning. Also many characterization techniques do not provide key information about material parameters in their operating environments. An ideal characterization tool would provide data about the material properties that are related to micro-and macrostructure without destructive sectioning. Such data can only be obtained using nondestructive-evaluation (NDE) methodologies. Therefore NDE is essential for almost any industrial product. Nondestructive evaluation has become an integral part of materials research because it enables the determination of material parameters (such as micro- and macrostructure, stress, physical properties, and defects) at nearly any point, line, surface, or volume element of interest and at nearly any state during the life of the material. Nondestructive evaluation is based on many different methods that rely on elastic waves, penetrating radiation, light, electric and magnetic fields, chemical sensing, etc. The large number of potential methods makes NDE not a single field but a synergism of many scientific and engineering disciplines. Since it would be impractical here to present all the new NDE methodologies with application to materials research, this issue of MRS Bulletin focuses exclusively on those ultrasonic techniques that are increasingly important in materials characterization.

The following is an edited version of the Von Hippel Award address, given by recipient W.W. Mullins at the 1995 MRS Fall Meeting. Mullins received the Materials Research Society's highest honor “for pioneering and profound contributions to the understanding of grain boundary motion, morphological stability, the structure of surfaces and interfaces, and flow and diffusion as stochastic phenomena.” Mullins is University Professor Emeritus of Materials Science and Engineering at Carnegie-Mellon University.