PHASE TRANSITIONS IN SURFACE FILMS 2
by Professor H. Taub, University of Missouri, Columbia/MO (U.S.A.)
From its inception this NATO Advanced Study Institute in June 1990 was envisioned as a sequel to one with the same title organized eleven years earlier and also held at the Ettore Majorana Centre in Erice, Sicily. Both ASI's reviewed the current understanding (experimental and theoretical) of phase transitions of surfaces, interfaces, and thin films as well as the related structural and dynamical properties of these systems. In the years following the first ASI, continued rapid progress in this field has been as impressive as that which occurred earlier. In this volume (NATO ASI SERIES B267), new developments have been grouped under the following topics: 1) monolayers; 2) surface reconstruction, roughening, and melting; and 3) wetting phenomena, multilayer structures, and film growth.
Among examples of phenomena which have now been extensively investigated and were barely touched upon at the previous ASI are the surface roughening transition and surface melting of bulk solids. The structure and phase transitions of multilayer films and of monolayer-adsorbed-on-fluid substrates are now being pursued experimentally with the same rigor as were the monolayer-on-solid systems previously. In addition, considerable progress has been made by several diffraction techniques in structure determinations of monolayer phases modulated by a crystalline substrate. The study of surface dynamics has greatly benefitted from the results obtained by high-resolution neutron scattering which has revealed new features in the excitation spectra of helium films on graphite, has allowed the corrugat in the adatom-substrate potential of various monolayers on graphite to be probed quantitatively, and has elucidated surface melting by measurements of molecular diffusion in multilayer films.
Some of the most exciting results have been achieved not so much by using new samples but with familiar systems - single-crystal surfaces, films adsorbed on single-crystals, and monolayers adsorbed on water - which are now accessible to newly developed or improved experimental techniques. These techniques include synchrotron x-ray diffraction, helium atom scattering, ellipsometry, and high-resolution electron diffraction.
The experimental advances have spurred intense theoretical activity in several new areas: phase transitions involving modulated structures, surface roughening and reconstruction, wetting and film growth, and the statistical mechanics of membranes. Also, computer simulation of surface phenomena has developed greatly in the last ten years and played an increasingly important role in the interpretation of experiments.
The volume concludes with a valuable conference summary by M. Wortis who addresses the question: `where are we headed next?' Likely directions include disordered systems, surfaces of biological interest, solid-liquid and solid-solid interfaces, and a new concern with dynamical properties.
Reference books: B51, B148, B211, B229, B231, B239, B248, B253, B257, B259, B263, B267