CRITICAL PHENOMENA AT SURFACES AND INTERFACES REINHARD LIPOWSKY Institut fur Festkorperforschung Forschungszentrum Jvlich Postfach 191 3 D-5170 JuJicA FRG ABSTRACT. The multitude of critical phenomena which occur at surfaces and interfaces is briefly reviewed from a theoretical point of view. Three types of critical effects are dis- tinguished related (i) to the 2-dimensional character of the interface, (ii) to its morphology, and (iii) to its structural changes at phase transitions in the bulk. Wetting phenomena in three dimensions belong to the last category (iii). Some recent theoretical results for such phenomena are also discussed: (a) Wetting of a moving interface; (b) Wetting in the 3-dimensional Ising model; and (c) Wetting of an inhomogeneous substrate. 1. Introduction During the last decade, a lot of effort has been devoted to the study of critical phenomena at surfaces and interfaces. Here and below, the term surface denotes the interface between a condensed phase and an inert vapor or 'vacuum'. Since the latter phase is transparent to most experimental probes, many experimental techniques have been used to study surface critical phenomena. However, from a theoretical point of view, there is no fundamental difference between a surface and any other interface between two thermodynamic phases. One intriguing aspect of interfaces is their reduced dimensionality. Indeed, in many cases, the interface can simply be viewed as a planar 2-dimensional system. However, it can also 'bulge' into the third dimension and then attain nonplanar morphologies. In addition, the interface itself has a third dimension which can become mesoscopic as in wetting phenomena; one then has a system which interpolates between two and three dimensions. In this paper, I will briefly review the multitude of critical phenomena which can occur at surfaces and interfaces. Three different categories of such phenomena will be distinguished: (i) Critical behavior within the 2-dimensional interface; (5) Critical effects related to the morphology of interfaces; and (iii) Changes in the interfacial C. T. Liu et al. (eds.),Ordered Intermetallics -Physical Metallurgy and Mechanical Behaviour, 107-121. @ 1992 Kluwer Academic Publishers. Printed in the Netherlands.