At the International Summer Institute in Surface Science (ISISS), which is held bienially on the Campus of the University of Wisconsin-Milwaukee, invited speakers present tutorial review lectures during the course of one week. The majority of the presentations deal with the gas-solid interface, but now and then relevant reviews concerning liquid-solid or solid-solid interfaces are included. The goal of ISISS was outlined in the first ISISS publication: "We recognize that the International Summer Institute in Surface Science should foster mutual understanding and interaction among theorists and experimentalists in the various areas of surface science. Progress can be achieved only when we occasionally peek over the fence into neighboring areas, not so much to amuse ourselves that the grass is greener on the other side as to learn from their progress and, perhaps equally fruitfully, from their limitations and setbacks. In addition, it is an important task in any field of science to assess, take count of what is done and, what is more important, to point in future directions. " Since the foundation of ISISS in 1973, the invited speakers - internation ally recognized experts in their area of specialization - have been asked to write review articles too. We wanted in this way to ensure that the largest possible group of scientists could benefit from the special review concept."

This volume contains review articles which were written by the invited speak ers of the seventh International Summer Institute in Surface Science (ISISS), held at the University of Wisconsin - Milwaukee in July 1985. The form of ISISS is a set of tutorial review lectures presented over a one-week period by internationally recognized experts on various aspects of surface science. Each speaker is asked, in addition, to write a review article on his lecture topic. No single volume in the series Chemistry and Physics of Solid Surfaces can possibly cover the entire field of modern surface science. However, the series as a whole is intended to provide experts and students alike with a comprehensive set of reviews and literature references, particularly empha sizing the gas-solid interface. The collected articles from previous Summer Institutes have been published under the following titles: Surface Science: Recent Progress and Perspectives, Crit. Rev. Solid State Sci. 4, 125-559 (1974) Chemistry and Physics of Solid Surfaces, Vols. I, II, and III (CRC Press, Boca Raton, FL 1976, 1979 and 1982), Vols. IV and V, Springer Ser. Chern. Phys., Vols. 20 and 35, (Springer, Berlin, Heidelberg 1982 and 1984). The field of catalysis, which has provided the major impetus for the de velopment of modern surface science, lost two of its pioneers during 1984 and 1985: Professors G.-M. Schwab (1899-1984) and p.k. Emmett (1900-1985)."

This volume contains review articles written by the invited speakers at the ninth International Summer Institute in Surface Science (ISISS 1989), held at the Uni versity of Wisconsin-Milwaukee in August of 1989. During the course of ISISS, invited speakers, all internationally recognized experts in the various fields of surface science, present tutorial review lectures. In addition, these experts are asked to write review articles on their lecture topic. Former ISISS speakers serve as advisors concerning the selection of speakers and lecture topics. Emphasis is given to those areas which have not been covered in depth by recent Summer Institutes, as well as to areas which have recently gained in significance and in which important progress has been made. Because of space limitations, no individual volume of Chemistry and Physics of Solid Surfaces can possibly cover the whole area of modern surface science, or even give a complete survey of recent progress in this field. However, an attempt is made to present a balanced overview in the series as a whole. With its comprehensive literature references and extensive subject indices, this series has become a valuable resource for experts and students alike. The collected articles, which stress particularly the gas-solid interface, have been published under the following titles: Surface Science: Recent Progress and Perspectives, Crit. Rev. Solid State Sci.

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