Interfaces Part I: Structure, Chemistry, Electronic Properties
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TIN/SEPTEMBER1990
BULLETIN focuses on structure, chemistry and some electronic properties of crystalline interfaces, the October issue will be devoted to their mechanical and high-temperature behavior. It is widely appreciated 1 that in the quest to gain atomic-level insight into
Interfac Plane
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Figure 1. Distinction of three types of interfacial Systems. Depending on whether the System is embedded in bulk material on both sides of the interface, on only one side or not at ail, we distinguish "bulk", "epitaxial" and "thin-film" interfaces. A and B are generally différent materials.
what governs the basic physical, Chemical, electronic, and mechanical processes at solid interfaces, a highly interdisciplinary approach holds the greatest promise for long-term success. The interface community is as diverse as virtually any part of the materials research community and involves disciplines as d i s p a r a t e as solid-state, electronicstructure and thin-film physics, and solid-state and surface chemistry on the one hand, and fracture, physical metallurgy, and physical ceramics on the other. Yet, only in a few rare instances has this diverse pool of expertise been brought together in a focused attack on the various interface-related phenomena and properties. One of our goals is to draw attention to the rich and fertile common ground already existing (mostly, however, in a nucleation-like state), and to bring thèse very différent communities closer together. To facilitate this highly necessary bridge building between thèse communities, much of this introduction will emphasize what we believe are the features common to ail the différent types of interfaces. Figure 1 illustrâtes one way of classifying solid interfaces, which distinguishes three types of interfacial Systems. In this • figure the interfacial région (assumed to be infinité in the x-y plane) is embedded in the z direction between two perfect, semi-infinite bulk crystals. The lower and upper halves of this bicrystal generally consist of différent materials, A and B. (Implicitly, only flat interfaces are considered in Figure 1; however, as evidenced by much of the high-resolution électron microscopy work in récent years, macroscopically curved interfaces are usually faceted on an atomic scale.) The présence or absence of one or both of the bulk régions in Figure 1 strongly affects the lattice parameters, and hence the physical properties, in the interfacial région. By examining the différent ways the interfacial région may or may not be sandwiched between the two bulk régions, the following three types of interfacial Systems can be distinguished: 1. Bulk (orburied, internai) interfaces: Systems where the interface région is surrounded on both sides by bulk material. Examples are interphase (for A?^B) and grain boundaries (for A = B). 2. Epitaxial interfaces: Systems with bulk material on only one side of the interface and a thin film on the other. For A = B, a bulk-free surface is thus obtained. 3. Thin-film interfaces: Systems with both bulk régions remo
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