Effects of Atomic-Level Disorder at Solid Interfaces

Extract

The importance of interface materials is based largely on their inherent inhomogeneity, i.e., that the chemical composition and physical properties at or near an interface can differ dramatically from those of the nearby bulk material. For example, the propagation of a crack along an interface — rather than through the surrounding bulk material — indicates a different mechanical strength near the interface. Also, the elastic response and thermal behavior near an interface can be highly anisotropic in an otherwise isotropic material, and can differ by orders of magnitude from those of the adjacent bulk regions. Typically, these gradients extend over only a few atomic distances.

Because relatively few atoms control the properties in the interfacial region, the inherent difficulty in the experimental investigation of buried interfaces is actually an advantage in the atomic-level study of solid interfaces by means of computer-simulation techniques. While the limitations of such simulations are well known, this article will attempt to demonstrate the unique insights they can provide on some aspects of the mechanical behavior of both buried and thin-film interfaces. While to date, relatively little simulation work has focused directly on the observation of crack extension, we will discuss two types of phenomena with particular relevance in the fracture behavior of interface materials, namely their elastic and high-temperature properties. We will conclude with an outlook, too optimistic perhaps, on how the complementary capabilities of continuum-elastic theory, atomic-level computer simulation, and experiment could (and probably should) be combined in a new strategy for tackling the difficult problem of interface fracture to elucidate the underlying complex interplay between elasticity, plasticity, and temperature.