Carbon in the form of diamond is the stuff of dreams, and the image of the diamond evokes deep and powerful emotions in humans. Following the successful synthesis of diamond by high-pressure methods in the 1950s, the startling development of the low-pressure synthesis of diamond films in the 1970s and 1980s almost immediately engendered great expectations of utility. The many remarkable properties of diamond due in part to its being the most atomically dense material in the universe (hardness, thermal conductivity, friction coefficient, transparency, etc.) could at last be put to use in a multitude of practical applications. “The holy grail”—it was realized early on—would be the development of large-area, doped, single-crystal diamond wafers for the fabrication of high-temperature, extremely fast integrated circuits leading to a revolution in computer technology.

Excitement in the community of chemical-vapor-deposition (CVD) diamond researchers, funding agencies, and industrial companies ran high in expectation of early realization for many of the commercial goals that had been envisioned: tool, optical, and corrosion-resistant coatings; flat-panel displays; thermomanagement for electronic components, etc. Market projection predicting diamond-film sales in the billions of dollars by the year 2000 was commonplace. Hopes were dashed when these optimistic predictions ran up against the enormous scientific and technical problems that had to be overcome in order for those involved to fully exploit the potential of diamond. This experience is not new to the scientific community. One need only remind oneself of the hopes for cheap nuclear power or for high-temperature superconducting wires available at hardware stores to realize that the lag between scientific discoveries and their large-scale applications can be very long. Diamond films are in fact being used today in commercial applications.

In materials that conduct both electricity and heat, the thermal and electrical currents are coupled. This thermoelectric coupling can be used to construct devices that act as temperature sensors, heat pumps, refrigerators, or power generators. A temperature difference ΔT across any electrical conductor will generate a corresponding voltage difference ΔV The ratio ΔV/ΔT is defined as the Seebeck coefficient S after Thomas See-beck who first discovered the effect in 1823. Probably the most familiar use of this effect is the thermocouple in which the union of two dissimilar metals generates a voltage in response to an imposed temperature difference. Interestingly an electrical current I passing through the junction of two dissimilar conductors results in the absorption or release of heat in the vicinity of the junction depending on the direction of the current. The ability to heat or cool in this manner was first discovered by Peltier and explained by Lord Kelvin. The latter showed that the amount of heat produced (or absorbed) near the junction is given by ΠI = STI where Π is called the Peltier coefficient and T is the temperature. It is primarily this effect that makes thermoelectric (Peltier) refrigeration possible. Thermoelectric refrigerators and power generators are attractive for many applications as they have no moving parts (except electrons and holes), use no liquid refrigerant, and last indefinitely.

Glass serves a critical function in diverse technologies ranging from medicine to telecommunications. Fax machines and text scanners use micro-optic lens arrays made from ion-exchanged, gradedindex glass to image original documents. Data for long-distance communication by telephone or computer are transmitted in the form of modulated laser light through highly transparent glass fibers. These signals are boosted for long-haul transmission by stimulated emission in erbium-doped glass optical amplifiers. Lap-top computers use flat-panel-display glass in their liquid-crystal screens (see “Materials for Flat-Panel Displays,” MRS Bulletin, March 1996). Gall-bladder and hysterectomy surgeries have been made minimally invasive in part because of slender glass imaging endoscopes.

Functionality in glass is expanding rapidly. New properties are often attributable to new defect species created by strong optical or electrical fields. For example rare-earth-doped ZBLAN glass (a commercial fluoride glass), when exposed to high peak-intensity femtosecond laser pulses, becomes phosphorescent. (See the cover of this issue.) The phosphorescence is visible to the naked eye up to 12 hours after illumination. Other compositions show similar effects. Phosphorescent glasses are transparent and may be more easily formed into contiguous films and fibers than powder or microcrystalline phosphors.

The following article is an edited version of the Von Hippel Award address, given by recipient Gabor A. Somorjaiat the 1997 MRS Fall Meeting. Somorjai received the Materials Research Society's highest honor for “his extraordinary multidisciplinary contributions to the atomic-level understanding of materials surfaces and surface processes with technological importance in hetergeneous catalysis, corrosion, and tribology.”

Chalcopyrite nonlinear optical (NLO) semiconductors are presently enjoying a major renaissance. This rebirth of interest is due primarily to the success of recent materials research-and-development (R&D) programs that have dramatically improved the availability of large crackfree high-quality crystals. This overview provides a general review of chalcopyrites, of their application in laser systems that exploit second-harmonic generation (SHG) or optical parametric oscillation (OPO), and of the materials-selection criteria for laser crystals to assist in focusing R&D efforts. It also suggests broader application areas. The overview concludes with a number of specific recommendations for further R&D efforts to advance this materials technology.

The archetype infrared NLO chalcopyrites are AgGaSe2 (a I-III-VI2 semiconductor) and ZnGeP2 (a II-IV-V2 semiconductor). Using samples of naturally occurring pyrites, Pauling correctly established the chalcopyrite's crystal structure (diamondlike where Zn and Ge cations are ordered) in 1932 after two previous false starts by others. Levine, who has extensively studied the nonlinear susceptibilities of a number of bond types, stated in 1973 that the chalcopyrite structure is so favorable for NLO properties that it will be difficult to ever find materials with larger nonlinearities in the infrared spectral region. That statement has proved to be prophetic.

Goodman of Great Britain first reported that chalcopyrites were semiconductors. However the first observation that these materials were semiconductors is generally attributed to A.F. Ioffe and N. A. Goryunova of the A.F. Ioffe Physico-Technical Institute (IPT) in St Petersburg, Russia.

By most recent estimates, improved attention to friction and wear would save developed countries up to 1.6% of their gross national product—over $100 billion annually in the United States alone. It is thus not surprising that tribomaterials, materials designed for use in moving contact (sliding, rolling, abrasive, etc.) have for decades attracted the interests of materials scientists and mechanical and chemical engineers. However the field of tribology is hardly a recent one. Such tribological advances as Leonardo da Vinci's design of intricate gears and bearings (some of which were not built until the Industrial Revolution provided sufficiently strong materials) and the landmark 18th century development of a timepiece allowing accurate longitudinal positioning of ships at sea (accomplished via a self-lubricating wooden gear) could easily be termed “modern,” given the overall longevity of the field.

As important as tribomaterials are to technology, their discovery has usually been serendipitous. Materials scientists have frequently been able to provide explanations for why tribomaterials perform as well as they do. They have also been able to substantially improve the performance of tribomaterials through the development of new alloys, composites, and/or improved surface-engineering methods. They have however been far less successful at a priori design of tribomaterials with improved performance, largely because friction and wear processes have not been understood at the fundamental level.

The late 1980s marked the advent of renewed interest in fundamental areas of tribology, sparked by a number of new experimental and theoretical techniques that made it possible to study the force of friction in geometries that are well-defined at the nanometer scale.

The following is an edited transcript from the 1997 David Turnbull Lectureship presentation given by Merton C. Flemings at the 1997 Materials Research Society Fall Meeting. Flemings was cited for “his contributions to the foundations and technology of solidification processing and for educating a generation of materials engineers.”

The interplay between materials science and sports equipment takes many forms. Certainly a broad cross section of materials is used in sporting equipment to improve performance and safety, and to reduce cost. The new materials used in sports equipment originate from a long history of innovation, drawing from and contributing to other technologies. Amateurs and professionals play sports, so rules on the use of new technology vary immensely. This allows for a short circuit of new technology into the market-place in some cases and restriction or prohibition of opportunities in others. Also materials selection and development for sports equipment must stretch beyond consideration of the object itself to include the human interface and design of a system that best makes use of the materials. Sports after all are about human capability and interaction. The equipment is just a facilitator. Certainly more efficient ways exist of placing a ball into a hole than hitting it with a long metal stick from hundreds of yards away. This is perhaps the most unique element of materials development for sports. The rules governing materials development are not just laws of science and of government but rules put into place just for “sport.” Because of the connection of sports to the lives of so many people, either as participants or spectators, materials science of sporting equipment is also a great platform for educating students about materials selection and behavior.

The last decade and a half has seen an explosive growth in the synthesis of diamond materials by a variety of chemicalvapor-deposition (CVD) processes driven by both scientific curiosity and technological exploitation for diverse applications in the fields of hard coatings, tools, optics, passive and active electronics, thermal management, corrosion protection, and radiation detection. Beginning in the 1980s, micron-sized diamond particles were reported by a few groups using hot filaments and a seemingly magical (alchemical) recipe of hydrocarbons and hydrogen. Now near the end of the 1990s, the basic science of diamond growth by CVD is well-understood. Diverse plasma- and thermal-based techniques have been developed for deposition of diamond. Polycrystalline films several mm thick and over 12 in. (30 cm) in diameter are a reality. Many companies are commercializing a wide range of products, and the cost of deposition has dropped by over three orders of magnitude. This article reviews these developments and highlights challenges for the future. It is organized along two themes: scientific advances and technological progress.

ZnGeP2 and CdGeAs2 have long been recognized as promising crystals for infrared frequency generation. They exhibit the highest nonlinear optical coefficients (d36 equals 75 pm/V and 236 pm/V for ZnGeP2 and CdGeAs2, respectively) among all known compounds that possess adequate birefringence for phase matching. ZnGeP2's transparency range (0.62−13 μm) makes it the optimum material for shifting the wavelength of 2-μm pump lasers into the 3–5-μm range via optical parametric oscillation (OPO), whereas that of CdGeAs2 (2.3–18 μm) is better suited for doubling the frequency of CO2 lasers (9–11 μm) into the same range via second-harmonic generation. In both cases however, the application of these materials has been hindered by great difficulty in achieving crack-free single crystals, and by large defect-related absorption losses.

The horizontal-gradient-freeze (HGF) growth technique has been instrumental in overcoming these difficulties. “Ultralow” axial gradients (1–3°C/cm) have been used to control stoichiometry by minimizing vapor transport as well as to eliminate cracking due to anisotropic thermal expansion. (The a-axis and c-axis thermal-expansion coefficients of ZnGeP2 differ by a factor of two, whereas those of CdGeAs2 differ by a factor of 15.) In addition, oriented seeds were used to ensure monocrystalline nucleation (because even a small degree of polycrystallinity can lead to cracking even in low gradients) and growth along preferred directions to facilitate fabrication of device crystals. Finally growth was performed in a two-zone, transparent furnace in order to monitor and control the seeding-and-growth process.