Why should we be interested in the atomic structure of interfaces?

The contributions that studies of interfaces at the atomic level have made to the classic materials paradigm, Structure-Properties-Applications, fall into the following three categories: (1) provide the basis for classifying interfaces as ''singular'', ''vicinal'' or ''general'' in the 5D boundary geometrical phase space. This leads to a general understanding of the trends by which many interface properties change when the macroscopic geometric variables change and to the further possibility of manipulating the interfacial structure (via ''interface engineering'') to optimize properties; (2) provide critical information for the continuum modeling and understanding of interfacial behavior at larger length scales. This information may involve either the values of critical parameters required for the modeling or the identification of basic mechanisms which may be relevant. A basic challenge here is to bridge the length scales so that no relevant information feeding upwards from the atomic scale is lost; (3) provide essentially complete atomistic models for small interfacial systems spanning relatively small length scales. Numerous examples are given. Future developments are considered, and it is concluded that we are in the midst of revolutionary increases in our ability to investigate interfacial materials at the atomic scale both experimentally and computationally. Also, the rapidly developing field of nanotechnology is producing useful ever smaller devices. We may therefore anticipate a continued intense interest in interfacial structure and properties at the atomic scale.