One of the goals of contemporary science is the atomic or molecular design of materials in order to achieve specific properties. There is special interest in imitating with these designed materials the remarkable integrated functionality we see in biology. Soft matter offers a particularly good opportunity to realize these goals because of the vast structural space offered by organic systems.

The microstructure and properties of thermally sprayed deposits depend critically on the thermal- and kinetic-energy histories of the particles entrained in the hot-gas jet. At impact, the particle temperature, molten fraction, size, velocity, and chemistry, along with substrate temperature and surface characteristics, control the morphology of individual particle splats. These factors control the adhesion, strength, microstructure, and porosity of a coating and influence the residual-stress state. In order to produce higher-quality coatings and expand the use of this versatile family of technologies, the ability to model and measure particle behavior is essential.

Our understanding of materials phenomena is based on a hierarchy of physical descriptions spanning the space-time regimes of electrons, atoms, and matter and given by the theories of quantum mechanics, statistical mechanics, and continuum mechanics. The pioneering work of Clementi and co-workers provides a lucid example of the traditional approach to incorporating multiscale phenomena associated with these three mechanics. Using quantum mechanics, they evaluated the interactions of several water molecules. From this data base, they created an empirical potential for use in atomistic mechanics and evaluated the viscosity of water. From this computed viscosity, they performed a fluid-dynamics simulation to predict the tidal circulation in Buzzard's Bay. This is a powerful example of the sequential coupling of length and time scales: a series of calculations is used as input to the next rung up the length/time-scale ladder.

Most research to develop highly transparent and conductive thin films has focused on n-type semiconductors consisting of metal oxides. Historically, transparent conducting oxide (TCO) thin films composed of binary compounds such as SnO2 and In2O3 were developed by means of chemical- and physical-deposition methods. Impurity-doped SnO2 (Sb- or F-doped SnO2, e.g., SnO2:Sb or SnO2: F) and In2O3: Sn (indium tin oxide, ITO) films are in practical use. In addition to binary compounds, ternary compounds such as Cd2SnO4, CdSnO3, and CdIn2O4 were developed prior to 1980, but their TCO films have not yet been used widely.

Many food-processing operations are designed to create the microstructure that gives the food product its characteristic properties. From milk we can produce different cheeses, yogurts, spreads, or whipped products where the properties are determined by the structure. Other examples of fabricated foods are cereal products such as pasta, meat products such as sausages, and so on. All of these products are based on colloidal structures such as gels, emulsions, foams, or combinations thereof. Microscopy provides the tools for describing how a particular structure is engineered, and, therefore, how it relates to the properties of the product.

The technology underlying the ability to focus MeV ion beams to spot sizes ranging from 100 nm to 1 μm using nuclear microprobes has continually evolved over the last 30 years to a high state of sophistication. However, it is only in the last few years that powerful analytical techniques have been developed that fully exploit its capabilities for materials analysis. This has opened up new and exciting applications for the characterization of crystallograph-ic and electronic properties of materials and increased our basic understanding of ion-solid interactions.

The operation of a nuclear microprobe is analogous to that of a scanning electron microscope, in which a focused beam of charged particles is swept over the sample surface to produce spatially resolved images using an analytical signal produced by the ion-solid interactions. Nuclear microprobes were originally developed to image variations in sample composition by measuring x-rays emitted from the sample, backscattered ions, or nuclear-reaction products, as are widely used with unfocused beams. Accounts of these analytical techniques using focused ion beams for applications in biomedicine, geology, and archaeology, and the micro-probe hardware required to accomplish them, are given in References 2–4.

Their high magnetic rigidity means that MeV ions require much stronger magnetic fields to focus them than those required for keV electrons in a scanning electron microscope.

Injection, transport, and recombination of charge in semiconductors are important phenomena for governing the operation of microelectronic devices, the function of radiation detectors, and for fundamental studies of the properties of advanced materials. A new technique for the study of these important phenomena is ion-beam induced charge (IBIC) microscopy, which uses a focused, scanned beam of MeV ions. The information provided by this technique is used to study single-event effects in operating integrated circuits (ICs), charge-collection efficiency in radiation detectors that contain defects or other nonuniformities, and radiation damage in semiconductor materials. Detailed information can also be provided for physics-based simulation codes.

As with the related and more widely known technique of electron-beam induced current (EBIC) microscopy, an energetic ion slowing in a sample creates charge in the form of electron-hole pairs. These may drift from their origin under the influence of an internal electric field or diffuse through field-free regions of the sample. In the case of IBIC microscopy, however, a single MeV ion creates a dense path of electron-hole pairs, displaces sample atoms, and may induce sample-atom spallation or fission. In addition to these atomic effects, the other major differences between IBIC and EBIC are that an MeV ion will typically reach depths an order of magnitude deeper in the sample than the electrons used in EBIC and will also undergo relatively minimal sideways scattering. Thus deeply buried structures can be probed with relatively little loss of spatial resolution. The collection of the charge primarily depends on the electric-field distribution from, for example, p-n junctions in an irradiated device and the material properties in the immediate vicinity of the induced charge. The ability to scan a focused MeV ion beam over the area of an integrated circuit, for example, enables the mapping of the combined effect of material properties and field distribution through the measurement of charge-collection efficiencies.

Synthetic biomaterials can be divided into metals, polymers, ceramics, and composites. Polymeric biomaterials and composites can be classified as biostable, partially biodegradable, or totally biodegradable. Biostable polymers are inert, cause minimal tissue response, and retain their properties for years. Because only a temporary supporting biomaterial is required in many clinical applications, totally or partially biodegradable polymeric materials are often better than biologically biostable materials.

Biodegradation implies the degradation of a material induced by the activities of an organism, but it is also influenced by pure physicochemical reactions. Degradable polymeric or composite materials retain their support from days to months, depending on their properties. They are biologically degraded, gradually, into tissue-compatible components that are absorbed, used in the organism, and finally secreted by the normal ways.

Biodegradable materials are the best choice for internal fixation of fractures because the biodegradable implant provides and maintains the required fixation during the healing process. It decomposes gradually and transfers the stresses increasingly to the healing bone, thus avoiding stress-shielding. Micromovement at the fracture and correction of the bone-mass decrease are possible, too. After healing, when absorbed, the device can be utilized in energy and protein metabolism. Implanted biodegradable devices do not require a removal operation, which is a financial and psychological benefit to the patient.

Semiconductor-grade silicon is one of the most perfect crystalline materials that can be fabricated. It contains less than 1 ppb of unintended impurities and negligible twins or dislocations. Dopants can diffuse in this near-ideal crystal only by interacting with atomic-scale point defects: interstitial atoms or vacancies. These defects migrate through the silicon lattice, occasionally binding with a dopant atom and displacing it by one or more lattice positions.

What started as a scientific challenge roughly 10 years ago has become a technological reality today, as materials from supramolecular polymers and their many applications as smart materials have emerged. Synthetic polymeric materials are among the most important classes of new materials introduced in the 20th century. They are primarily used for construction, but electronic and biomedical applications are also at the forefront of science and technology.

In thermal spraying, coatings are formed by particles flattening and piling up on the substrate. At impact, the sudden deceleration of the particle causes a pressure buildup at the particle-surface interface; the high pressure inside the particle forces melted material to flow laterally and ductile material to deform. The particle spreads outward from the point of impact and forms a “splat.” The arresting of spreading results from the conversion of particle kinetic energy into work of viscous deformation and surface energy. Solidification constraint (when the solidification front is advancing from the substrate surface fast enough to interact with the liquid during spreading) and mechanical constraint (due to the roughness of the substrate surface) can interfere with the flattening process.

One of the most interesting unsolved problems in fracture mechanics is the precise understanding of the energy-dissipation mechanisms that occur as a crack advances. In most cases, this energy-release rate is many times the surface energy created. One of the main reasons for this difference is the fact that plastic deformation can occur in the crack-tip region as dislocations nucleate and are emitted from the crack tip. Experimental studies provide little insight into the precise mechanisms for this process because they cannot reach the atomistic scale. For example, a crack that may seem experimentally sharp, and therefore indicative of brittle fracture, may not be sharp at the atomic level. Continuum mechanics has a similar limitation, since the assumptions of elasticity theory usually break down in the crack-tip region. Atomistic simulation studies provide researchers an opportunity to obtain precise atomic configurations in the crack-tip region under various loading conditions and to observe the basic energy-dissipation mechanisms.

Magnets based on metal oxides have been important for hundreds of years. Magnetite, Fe3O4, Co-doped γ-Fe2O3, and CrO2 are important examples. The oxide (O2-) bridge between the magnetic metal ions has filled p orbitals (Figure 1a) that provide the pathway for strong spin coupling. Albeit with twice as many atoms, cyanide (C≡N−) can bridge between two metal ions via its pair of empty antibonding orbitals (Figure 1b) and filled nonbonding orbitals. Even prior to a detailed understanding of either their composition or structure, magnetic ordering of several cyanide complexes, although at low temperature, was noted. The differing atoms at each end of the cyanide ion have different binding affinities to metal ions, and simple coordination compounds, for example, [FeII(CN)6]2− (ferrocyanide), with alkali cations can easily be made. Replacement of the alkali cations with transition-metal cations affords insoluble materials, for example FeIII4[FeII(CN)6]3 (Prussian blue). Prussian blue has been used as a pigment and as an electrochromic and electrocatalyst material. The structure of Prussian blue was elucidated to be cubic (isotropic) with ⟶FeII⟵C≡N⟶FeIII⟵N≡C⟶FeII⟵ linkages along all three crystallographic directions (Figure 2). The FeII … FeIII separation is ∼5 Å. However, based on the composition, this is an idealized structure, as one FeII site per unit cell is missing. Water fills the vacant sites as well as the channels present in the structure. Due to the structural defects, it has been a challenge to grow single crystals.

“Soft solution processing” is rapidly becoming a viable approach for the fabrication of advanced nanostructured materials. It involves the use of environmentally friendly chemicals and preparation methods with minimum energy input. Construction of ultrathin films by the room-temperature, layer-by-layer self-assembly of dilute aqueous solutions (or dispersions) of polyelectrolytes (or polymers), nanoparticles, and nanoplatelets is clearly soft solution processing (see the articles by Yoshimura et al. in this issue).

Most of the process of eating is a learned skill. While an infant readily puts most things in its mouth, the ability to distinguish food from any other material has to be taught, and even then it is several years before the whole range of foods can be consumed efficiently. Yet by the time we are 5–10 years old, our mastery of the complex set of mechanical actions involving tongue, teeth, and swallowing is so complete that we do not consciously note what we are doing or how we do it.

Transparent conducting oxides (TCOs) have been known and employed technologically for more than 50 years, primarily in the form of doped single-cation oxides such as In2O3 and SnO2. Beginning in the 1990s, however, multi-cation oxide TCOs began to be developed in Japan (see the article by Minami in this issue and the references therein) and at the former Bell Laboratories. Since then, new TCO phases are being reported with increasing frequency as technological interest in this area heightens. At the same time, our fundamental understanding of the chemical and structural origins of transparent conductivity continues to expand and promises a pathway to dramatically improved materials for a host of applications. This article describes a collaborative, multi-investigator bulk an d thin-film research effort at Northwestern University aimed at the synthesis, characterization, and enhanced understanding of multi-cation (compound and solidsolution) TCOs, and provides a brief account of what we are discovering about this important class of materials.

Polymer electrolytes have been a focus of the scientific community for a quarter century. They extend the realm of traditional solid-state ionics from hard materials to include soft materials and, in doing so, pose issues both fundamental (e.g., how are structure and transport defined in a concentrated electrolyte with an immobile solvent?) and technological (e.g., how can polymer ionics be used to construct electrochemical devices such as sensors, batteries, and fuel cells?)