A wide variety of microorganisms accumulate an optically active polymer of D(−)-3-hydroxybutyric acid, P(3HB), as an intracellular storage material of carbon and energy. The P(3HB) was first isolated from Bacillus megaterium in 1925 by Lemoigne. Many prokaryotic organisms, such as bacteria and cyanobacteria, have been found to accumulate P(3HB) up to 80% of their cellular dry weight when growth is limited by the depletion of an essential nutrient such as nitrogen, oxygen, phosphorus, or magnesium. Recently, many bacteria have been found to accumulate copolymers of D(−)3-hydroxy-alkanoic acids with a chain length ranging from three to 14 carbon atoms. In addition, 4-hydroxybutyric acid was found as a constituent of bacterial polyhy-droxyalkanoates (PHA).

Bacterial PHA polymers have attracted much attention as environmentally degradable thermoplastics for a wide range of agricultural, marine, and medical applications. PHA is degraded in soil, sludge, or sea water. Some microorganisms such as bacteria and fungi secrete extracellular PHA depolymerases to degrade environmental PHA and utilize the decomposed compounds as nutrients. In this article, I report the metabolism, production, and properties of bacterial PHA.

Evaluating the mechanical properties of thin films on thick substrates is tricky. Some useful techniques for mechanical property measurements on macroscopic film specimens exist, e.g., internal stress measurements by x-ray diffraction or by wafer buckling. Many conventional techniques, however, such as indentation for hardness measurement or scratch testing for evaluation of adhesion or wear resistance, yield results that are difficult or impossible to evaluate in terms of more fundamental film properties. In fact, these techniques are more practical engineering tools than tools for scientific study.

One solution is to miniaturize the test probe to dimensions approaching the film thickness. The nanoindentation technique for submicrohardness measurement described elsewhere in this issue by Pharr and Oliver is a recent example of such an approach. Still, for very thin films it is difficult to separate the influence of the substrate properties from the film properties, and the indentation process is inherently too complex to be well suited for determining fundamental materials parameters.

The rapidly evolving field of micromechanics offers some new possibilities in thin film characterization. Important film properties such as internal stress, elastic moduli, plastic yield limit, and fracture data can be extracted from experiments with micromachined test structures in the 10–1,000 μm size range.

Thin-film materials are playing an ever-increasing role in basic and applied research and are the basis for a large number of devices. In many cases, thin films are used in multilayered configurations so that the interfaces between different materials play a key role in their properties. The thicknesses of thin films being investigated approach interatomic spacing, so interfacial structure and chemistry become dominant. The field is now at a stage where it is no longer sufficient to only obtain qualitative information; it is also necessary to understand the structure and chemistry quantitatively and to determine limits on the accuracy of the various characterization tools. The present and next issues of the MRS Bulletin bring together a number of experts in the most commonly used characterization tools. To highlight and encourage international collaboration, the articles presented here are jointly written by scientific groups in the United States and Europe.

The first issue of this series is dedicated to the most commonly used techniques: electron microscopy, x-ray diffraction, and surface analysis. The article on electron diffraction by Ourmazd, Scheffler, Heinemann, and Rouviere presents studies of atomic resolution microscopy and their limitations. Aspects highlighted are the importance of comparing simulations to the images obtained in the electron microscope, and the importance of theoretical studies to obtain quantitative information. The article by Fullerton, Bruynseraede, and Schuller describes recent developments in the field of x-ray diffraction. This article focuses on a refinement technique capable of quantitative determination of interfacial roughness, interdiffusion, and crystal structure changes in a variety of novel multilayer configurations.

The realization of a revolutionary generation of electronics based on high-temperature superconductors (HTS) crucially depends on the ability to make high-quality thin film microstructures. These will incorporate materials such as YBa2Cu3O7-δ (YBCO), TlBaCaCuO, or BiSrCaCuO in a fashion similar to the circuits and devices made of their low Tc counterparts Nb or NbN. Without exception, the most valuable structures will be composed of multiple layers of superconducting films and dielectrics, in some cases combined with normal metals, low-temperature superconductors, or a variety of semiconductors. Generically, these can be combined in two ways: in a hybrid design where specialized packages and bonding are used to attach dissimilar materials, or in a monolithic thin film structure such as the one seen in Figure 1.

The division between hybrid and monolithic multilayers results from the historical development of electronic circuits. Hybrid designs typically require linewidths and alignment accuracy somewhat less demanding than those used in fully integrated circuits. The advantage of hybrid construction is the separation of incompatible processing steps onto different substrates or die. The monolithic integrated circuit, whether microelectronic, millimeter wave, or radio frequency, can be made in large batches with concomitant economy of scale and can be fabricated with fewer parasitic constraints. Superconducting integrated circuits have followed the semiconductor pattern of being developed in a hybrid fashion, then transferred to a fully integrated process.

As early as 1893, mineralogist W.C. Broegger recognized the first example of the transition from the crystalline to aperiodic (amorphous) state in minerals and defined the term “metamikte.” Metamict minerals were considered to be one of three classes of amorphous materials (porodine and hyaline being the other two), but distinguishable as phases that were originally crystalline, as evidenced by well-developed crystal faces. The amorphous state was determined on the basis of a characteristic conchoidal fracture and optical isotropy. There was no mention of radiation damage as a potential cause. In 1914, Hamberg first suggested that metamictization is a radiation-induced, periodic-to-aperiodic phase transition caused by alpha-decay of the constituent radioactive uranium and thorium. In the late 1930s, Stackelberg and Rottenbach tried to test this hypothesis directly by bombarding a thin slab of zircon with alpha particles. Although unsuccessful, the experiment must have been one of the first in which an “ion beam” was used to “modify” a material. After this early effort, there was little research on metamict minerals, and they remained a mineralogical curiosity.

R.C. Ewing's interest in this topic began in the early 1970s. Since then, there has been a continuing research program using modern analytical techniques on minerals that have received α-decay doses up to 1026 α-decay events/m3 over geologic time periods up to 109 years. As an example, electron diffraction patterns have shown that naturally occurring zirconolites (CaZrTi2O7) containing varying concentrations of thorium oxide (up to 19 wt% ThO2) are amorphized to different degrees depending on their age and the resulting α-decay event dose (Figure 1).

Those in charge of creating and endorsing curricula for engineering colleges appear to generally agree that materials science should be included. More than jus an acceptance of ABET (Accreditation Board for Engineering and Technology) certification requirements, the consensus view is that engineers really need to know about the materials they will someday use Unfortunately, there appears to be some disagreement about where this exposure to materials science fits into the overal scheme of things (scheduling or course sequence, so to speak). There is also dis agreement as to what engineering students should know about materials and by inference, as to who is most knowledge able and best qualified to teach this information. As a result of these disagreements students at some engineering departments have had to take, during the final semester, an introductory materials course taugh by instructors whose professional experience lies outside materials science and engineering.

Product Concept: Fluid packaging device.

Description: A package is required to contain approximately 50 ml (55–60 grams) of a viscous, 2-phase, thermally labile, aqueous medium containing proteins, carbohydrates, salts, nucleic acids and fats. A seamless ellipsoidal container is anticipated having a maximum radial dimension of 45 mm and a maximum axial dimension of 60 mm. The container wall must be permeable to respiratory gases and water vapor. External surface texture must be minimal. White coloration is acceptable, but the ability to incorporate solid or patterned surface coloration is desirable. The package wall must weigh approximately 5 g, the material must contain at least 0.3 g of bioavailable calcium, and it must be recyclable and biodegradable. The container must withstand 400-g drop test impacts.

Processing: All materials must be maintained and the container fabricated by aseptic processing in neutral-pH, aqueous medium at less than 40°C and with a unit production time of less than 24 hours.

Unit cost: Filled unit containers must be produced for approximately $4.00/100 units, with approximately $1.00/100 units allocated to container components and assembly.

Laboratory Solution: Not achievable in the laboratory.

Biological Solution: The eggshell.

In its composition, architecture, and function, the eggshell is an elegant solution to the design problem posed above—a multilayered bioceramic composite, consisting of a mineral phase (primarily calcite, CaCO3) deposited on and within a complex organic phase (the matrix). The eggshell provides a unique microenvironment for housing embryonic development. It protects the embryo, regulates respiratory gases, water and ions, and provides calcium for embryonic skeletal development.

Plants and animals have been exploited as sources of materials for centuries but, as our ability to analyze and fractionate them has progressed, the extraordinary range of properties available from materials produced by living systems has continued to grow. Doi, in another article in this issue of the MRS Bulletin, presents a discussion of a group of naturally occurring polyesters related to poly(beta-hydroxybutyrate). These polyesters are formed in vivo by several microorganisms as part of an energy storage scheme. Research on these systems has allowed growth conditions to be found that can lead, in a controlled fashion, to a number of copolymers. Useful materials based on these bacterial polyesters appear to be at hand.

The in-vivo formation of polyesters in microorganisms also illustrates several of the important reasons for examining biocatalytic polymer synthesis. First, unlike most industrial syntheses of polyesters, the poly(beta-hydroxybutyrate) biosynthesis occurs at a near-ambient temperature using a carbohydrate feedstock. Second, and perhaps most importantly, the stored polyesters are readily biodegraded by the bacteria that manufacture them, so materials based on these polyesters should also be biodegradable. Third, although there are side chains along the polymer backbone, they are introduced in a highly stereo-specific fashion during in-vivo synthesis, leading to an entirely stereoregular polyester. However, along with these advantages, there are also significant limitations to bacterial polyester synthesis. First, there are some substrates that are not incorporated into the polyester by the bacteria. Second, normal metabolism leads to the polyester, always incorporating a fraction of hydroxybutyrate monomers. Third, the backbone is always comprised of four-atom, A-B type 3-hydroxy acid repeat units with variations appearing in the side chain at carbon-3.

Electronic packaging involves using an appropriate combination of conductive and dielectric materials to electrically interconnect and mechanically support electronic components in a reliable and cost-effective manner. Since the invention of the integrated circuit in 1959 and mass wave-soldering in 1958, the vast majority of electronic packaging has involved a planar substrate to which semiconductor devices in protective packages are attached by melting eutectic solder. The planar substrates or printed circuit boards (PCBs) were invented in 1940, but their widespread implementation was limited until the invention of mass soldering. PCBs use conventional epoxy-glass dielectric material with mass patterned conductive traces of copper, but alternative materials have been used for either enhanced electrical performance or lower product cost.

Charles-Augustin Coulomb published data on the size, strength, and stiffness of harpsichord wire available in Paris in the late 18th century which has not been cited in the literature on musical instruments despite this century's revival of baroque music and the instruments upon which it was played. During an investigation of the internal friction of several antique music wires by means of a torsion pendulum similar to the one invented by Coulomb and first described in the 1784 mémoire (Figure 1), it occurred to us to ask what Coulomb had used as the suspensions in his pendulum. His biographer, C.S. Gillmor, mentioned “harpsichord strings”, and in Coulomb's 1784 Torsion mémoire we found: J'ai pris trois fils de clavcin, tels qu'on les trouve répandus dans le commerce, roulés sur des bobines, et numerotés (“I used three harpsicord wires, such as one finds distributed in commerce, wound up on spools, and numbered”).

The spools of wire recently discovered in the stand drawer of a harpsichord in France fit Coulomb's description. The instrument was built in Paris in 1732 by Antoine Vater, and the wire found with it was wound up on small wooden spools similar to spools for thread. The spool of red brass wire had a mark punched in one end and the spool of iron wire had the gauge size (No 5) written on it in ink, while the spool of yellow brass wire had neither mark nor number. Samples of the wires from these three spools, generally agreed to be of 18th century manufacture, were collected by J. Scott Odell of the Smithsonian Institution as part of a research project which he initiated into the physical properties of antique wire. With these samples in hand it was possible to measure certain of their properties and to compare these properties with those reported in Coulomb's Torsion mémoire in 1784. Since Coulomb's wire was undoubtedly of 18th century manufacture (a degree of confidence that we do not always have with collected samples), and the data were taken not long after the wire was drawn, comparison with the Vater wire allows us to detect if, during two centuries, significant changes occur in highly drawn wire.

Thin film stresses are important in many areas of technology. In the semiconductor industry, metal interconnects are prone to stress voiding and hillock formation. Stresses in passivation layers can lead to excessive substrate curvature which can cause alignment difficulty in subsequent lithographic processing. In other thin film applications, stresses can cause peeling from mechanical failure at the film-substrate interface. Beyond these issues of reliability, stress and the resulting strain can be used to tune the properties of thin film materials. For instance, strain, coupled with the magnetostrictive effect, can be utilized to induce the preferred magnetization direction. Also, epitaxial strains can be used to adjust the bandgap of semiconductors. Finally, the anomalous mechanical properties of multilayered materials are thought to be partially due to the extreme strain states in the constituents of these materials. To fully optimize thin film performance, a fundamental understanding of the causes and effects of thin film stress is needed. These studies in turn rely on detailed characterization of the stress and strain state of thin films.

X-ray diffraction and the elastic response of materials provide a powerful method for determining stresses. Stresses alter the spacing of crystallographic planes in crystals by amounts easily measured by x-ray diffraction. Each set of crystal planes can act as an in-situ strain gauge, which can be probed by x-ray diffraction in the appropriate geometry. Hence it is not surprising that x-ray diffraction is one of the most widely used techniques for determining stress and strain in materials. (For reviews of this topic, see References 5–7.) This article is a tutorial on the use of x-ray diffraction to extract the stress state and the unstrained lattice parameter from thin films. We present a handbook of useful results that can be widely applied and should be mastered by anyone seriously interested in stresses in crystalline thin films with a crystallographic growth texture.

We co-organized the first MRS technical symposium dealing with the environment at the 1991 Spring Meeting in Anaheim, California. Entitled “Environmentally Conscious Materials Processing,” the symposium dealt with waste minimization, pollution prevention, alternative materials and processes, recovery and recycling, and chemical sensors for process stream monitoring. This symposium captured much interest among the press and the materials community. Because of the growing interest in the environment, the MRS Bulletin asked us to guest edit this special issue that deals with the interrelated areas of materials science and the environment.

In recent years, environmental concern has heightened in the United States and around the world. Public concern was greatly raised by increased environmental awareness incidents such as the accident in Bhopal, India, and the oil spill in Alaska by the Exxon Valdez. As a result, U.S. companies are more concerned with public acceptance of their operations. In addition, manufacturers have been subject to increasingly stringent environmental legislation. Federal, state, and local legislation currently regulate air emissions, water discharges, occupational exposure, and treatment and disposal of various hazardous chemicals. In addition, the Montreal Protocol, an international agreement signed by the United States, regulates the production and use of halogenated organic compounds now known to deplete the Earth's ozone layer. Associated with these stringent environmental regulations are increasing waste-associated costs. Waste disposal costs are increasing at an annual rate of about 10%.

The laser, as a source of “pure” energy in the form of monochromatic and coherent photons, is enjoying ever increasing popularity in diverse and broad applications from drilling micron-sized holes on semiconductor devices to guidance systems used in drilling a mammoth tunnel under the English Channel. In many areas such as metallurgy, medical technology, and the electronics industry, it has become an irreplaceable tool.

Like many other discoveries, the various applications of the laser were not initially defined but were consequences of natural evolution led by theoretical studies. Shortly after the demonstration of the first laser, the most intensely studied theoretical topics dealt with laser beam-solid interactions. Experiments were undertaken to verify different theoretical models for this process. Later, these experiments became the pillars of many applications. Figure 1 illustrates the history of laser development from its initial discovery to practical applications. In this tree of evolution, Pulsed Laser Deposition (PLD) is only a small branch. It remained relatively obscure for a long time. Only in the last few years has his branch started to blossom and bear fruits in thin film deposition.

Conceptually and experimentally, PLD is extremely simple, probably the simplest among all thin film growth techniques. Figure 2 shows a schematic diagram of this technique. It uses pulsed laser radiation to vaporize materials and to deposit thin films in a vacuum chamber. However, the beam-solid interaction that leads to evaporation/ablation is a very complex physical phenomenon. The theoretical description of the mechanism is multidisciplinary and combines equilibrium and nonequilibrium processes. The impact of a laser beam on the surface of a solid material, electromagnetic energy is converted first into electronic excitation and then into thermal, chemical, and even mechanical energy to cause evaporation, ablation, excitation, and plasma formation.

Microscopic properties of thin films are often strongly influenced by departures from “perfection.” These can take the form of extended defects such as dislocations, interfacial roughness, or point defects. Direct imaging of extended defects was one of the early contributions of electron microscopy to solid-state science. Since then, the role of extended defects in controlling the fabrication and properties of thin films has been extensively studied and reviewed. Recently, in-situ observation of strain relaxation in thin-film structures has increased our understanding of dislocation kinetics and its effect on properties of thin films.

In this article, we focus on electron microscopic studies of interfacial roughness, the effect of processing on thin films, and the role and properties of intrinsic point defects in solids. Concurrent development of sophisticated theoretical and experimental approaches has substantially facilitated the investigation of point-defect properties. Here, we illustrate how results from theory and experiment can be combined to form a detailed picture of point-defect diffusion in solids, and highlight areas needing increased attention. Microscopic properties of thin films cannot be covered in a single review. For this reason, and because fabrication of semiconducting thin films has reached unprecedented levels of sophistication, we illustrate this article with references to semiconducting materials.

Our main conclusions can be summarized as follows, (a) Thin films of the highest quality are bounded by interfaces that are microscopically rough. Moreover, thin-film interfaces contain roughness on many length scales, each affecting a subset of the physical properties of interest.

The preceding article by Davies treated the behavior of single ions as they slow down in a solid, colliding with atoms of the solid and often transferring enough energy to initiate atomic displacement cascades. For a 200 keV As ion with a speed ~108 cm/s and a range in Si of ~ 2 × 10−5 cm, the cascade is completed in less than 10−12 s. The small volume excited in the cascade relaxes over 15 decades or more in time in a series of increasingly deliberate steps. The experimental evidence for most of these decades is indirect. No probes with sufficient spatial and time resolution exist to examine the spatial and temporal evolution of collision cascades created by individual incident ions. The first few decades in time have been followed in metals by molecular dynamics (MD) calculations and also approximated by continuum theory. The results of MD calculations for 5 keV cascades in Ni are shown in Figure 1. The behavior is in-terpreted as indicative of local “melting,” consistent with the concept of a “thermal spike” in the material. Extension of MD calculations to times of nanoseconds and longer is still prohibitively expensive in computer time, and application to covalently bonded systems, where the interatomic forces are much more complex than in metals, has not yet been reported.

As Davies has noted, the atoms of the cascade rapidly lose their high vibrational excitation to atoms in the surrounding material, and in only a few picoseconds the system cools. This constitutes a very rapid thermal quench—slower only than the quench associated with deposition of individual atoms (or small atomic clusters) on a cold substrate. The quench may produce a small volume of material with a different phase than its surrounding. For example, a small volume of “hot” Si atoms may be highly disordered and may quench to produce a small amorphous Si region in a crystalline Si matrix.

The discovery of high transition temperature, Tc, superconductivity in copperoxide-based ceramics by Bednörz and Miiller, and the subsequent increase in Tc above the boiling point of liquid nitrogen (77 K), renewed interest in employing superconducting thin films in high-speed, low-power electronic device applications (e.g., compact high-quality factor filters, delay lines, and Josephson elements for high-speed, low-power switching). However, realization of these benefits requires well-controlled, reliable superconducting thin film technology which addresses not only the growth of superconducting thin films, but also the development of a multilayer device technology encompassing materials with metallic, semiconducting, and insulating properties.

From the earliest days of extractive metallurgy, materials scientists and geoscientists have shared common ground. Experimental approaches, such as phase equilibrium and structural studies, are often similar, as are the questions asked in attempts to connect microscopic fundamentals to technologically desired or naturally observed bulk properties. The actual materials studied by both groups are often similar or even identical, such as silicate ceramics and glasses, magnetic oxides, and crystals based on the perovskite structure.

Nuclear magnetic resonance (NMR) was applied to solid-state physics shortly after the technique was invented in 1946. Even at the start, many of the samples placed in magnets in physics laboratories were large single crystals of naturally occurring minerals such as gypsum (CaSO4 · 2H2O) and fluorite (CaF2), perhaps borrowed from mineralogist colleagues. In the last 10 years, however, applications to both the earth and materials science have rapidly expanded because of improvements in both technological capabilities and basic theory. Only work on inorganic materials will be discussed here, although 13C NMR studies have proved very useful in characterizing the complex, often inseparable mixtures of large organic molecules found in soils, kerogen, and coal. I will not attempt to thoroughly review the broad and fast growing literature in inorganic applications. Instead, I have chosen examples, primarily from our recent studies, to illustrate the scope of what is and will become possible.

Several recent books clearly introduced the basic concepts of solid-state NMR, and applications to crystalline and glassy silicates as well as NMR at high temperature have been reviewed recently.

The impetus for a biomimetic approach to mineralization stems from the need for increasingly sophisticated materials showing greater efficiency, specialization, and optimization—properties that ultimately depend on the control of molecular and supramolecular structure, and hence on methods of predictive chemical fabrication. Biomineralization is of central importance to the development of new approaches in materials science because, as discussed in the preceding article by Fink, the formation of bioinorganic materials, such as bones, shells, and teeth is highly regulated and responsive to the surrounding environment in a manner not achieved by conventional synthetic routes. Some possible areas of overlap are shown in Figure 1. As in the other areas of biomaterials discussed in this and next month's issue of the MRS Bulletin, there are two potential connections between the natural processes of biomineralization and the synthetic demands of materials science; first, the commercial exploitation of biologically derived, tailored materials, and second, the assimilation and adaptation of biological concepts and mechanisms into “artificial” materials design and synthesis. The former is an extension of biotechnology, by which microbial systems could be utilized to produce mineral powders. Some of the possible processes have been discussed elsewhere. In general, the use of biological sources is only applicable where the high production costs are offset by a marketable specialty product. While this is feasible for organic-based products such as polyhydroxybutyrate (see next month's MRS Bulletin) it imposes a severe limitation when we transfer the approach to biomineralization.

More than 12 billion tons of industrial waste are generated annually in the United States. This is equivalent to more than 40 tons of waste for every man, woman and child in the country. The sheer magnitude of these numbers is cause for concern and drives us to identify the characteristics of the wastes, the industrial operations that are generating the waste, the manner in which the wastes are being managed and the potential for reducing wastes. This article will provide a brief overview of the information available on waste generation and management. A more comprehensive examination of this topic is provided in a recent issue of the journal Hazardous Waste and Hazardous Materials devoted entirely to inventories of waste generation and management. This article will begin by examining the sources of industrial waste. From an analysis of the sources of industrial waste, we will move to an examination of management methods. Finally, we will note changes in rates of waste generation over the past decade and close by highlighting critical gaps in existing data.