Multilayer Materials
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Y1990
important hâve shown new and intriguing structures and properties. Studies of this new class of materials include ail those characteristic of materials science and engineering and solid state physics research and development, and also extend into an increasing number of scientific disciplines and technological arenas. This breadth of investigation results from the ability to synthesize materials having microstructures not found in nature — new dimensional régimes in solids are accessible and hence new science and technology are created. Additionally, multilayer structures can be synthesized using elemental, alloy, or compound layers to form both microstructures and combinations of elements/materials that cannot be produced using traditional processing approaches, again creating new opportunities. The growth of multilayer materials into a significant area of activity is based on efforts in synthesis or fabrication, in characterization of structure and composition, and in property measurement. Inhérent to the interplay of thèse areas of investigation is a primary materials research activity—the development of an understanding of the relationships between synthesis, resulting structure/ microstructure, and properties. The dynamics of such interdisciplinary and intradisciplinary processes are clearly seen in the articles p r e s e n t e d h è r e , which explore three différent areas that multilayer structures hâve impacted: • "Metastable Phase Formation in Thin Films a n d M u l t i l a y e r s , " by B.M. Clemens and R. Sinclair; • "Artificially Layered Superconductors," by I.K. Schuller, J. Guimpel, and Y. Bruynseraede; and • "Multilayer Optics for the Soft X-Ray and Extrême Ultraviolet," by T.W. Barbée Jr. If a multilayer material is composed of individual layers four atomic planes thick, half the atoms in one layer are in contact with atoms of the other layer— half the atoms in this structure are interfacial atoms. Hence, thèse materials may dif-
fer significantly from bulk materials of the same composition and may exhibit new and useful characteristics as well as forming new and unexpected phases. This is the emphasis of the contribution by professors B.M. Clemens and R. Sinclair of Stanford University, who examine the effects of the large interfacial areas in multilayers and describe many of the new and interesting materials aspects of multilayer structures. The dimensional control available with multilayer structures facilitâtes the fabrication of samples in which the characteristic multilayer structural length, the multilayer period, may be made of the same order as lengths characteristic of nonlocal physical phenomena in solids. Samples having such correlated physical structure/physical phenomena scales allow unique studies of the basic physical mechanisms of nonlocal phenomena and strikingly powerful tests of theory. The article by I.K. Schuller, J. Guimpel, and Y. Bruynseraede reviews how this approach has been applied to the study of superconductivity and shows that unexpected physics should be expec
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