Predicting the properties and performance of materials is central to the success of major industries producing a vast range of consumer goods and to research programs at laboratories and universities around the world. For many years, scientists have longed to have computer simulations that predict the behavior of materials and track the evolution of their microstructures from the atomic to the engineering scales. Until recently, such simulations had been little more than an elusive goal.

Radiation damage, and its attendant effect on a wide spectrum of materials properties, is a central issue in many advanced technologies ranging from ion-beam processing to the development of fusion power. Indeed, the various challenges presented by irradiation effects are too numerous to discuss in this brief article.

Metallization is the back end of the integrated-circuit (IC) fabrication process where the transistor interconnections are formed. Figure 1 shows the metallized part of a static random-access memory chip. Metal lines for electrical connections (Al and Cu) in Si devices are deposited as blanket films and then etched or polished away to define the conducting lines.

The strength of a material is its ability to withstand an applied load without breaking or changing its shape. The strength of an ideal, defect-free crystal can be very high, but except for rather exotic materials such as micrometer-sized whiskers, crystals will fracture and/or deform plastically under stresses that are well below their ideal strength limits.

Polymer materials range from industrial commodities, such as plastic bags, to high-tech polymers used for optical applications, and all the way to biological systems, where the most prominent example is DNA. They can be crystalline, amorphous (glasses, melts, gels, rubber), or in solution. Polymers in the glassy state are standard materials for many applications (yogurt cups, compact discs, housings for technical equipment, etc.).

This nursery rhyme is one of the oldest, most familiar, and shortest treatises on fracture mechanics in the literature. Nevertheless, it makes several important points: (1) fracture occurs in response to some driving force (for Humpty, a “great fall”), (2) fracture involves material separation, and (3) fracture is irreversible.

The recent development of microscopes that allow for the examination of defects at the atomic scale has made possible a more direct connection between the defects and the macroscopic response they engender (see, e.g., the December 1999 issue of MRS Bulletin).