Studies of Physical Adsorption

Physical adsorption refers to the state when molecules are weakly bound to surfaces (binding energies less then one-tenth of an electron volt). The many phenomena observed in physisorbed films have attracted the attention of a diverse group of scientists because they reveal fundamental behavior of matter in a different way from bulk systems. This program presents a multi-facetted attack on a set of problems of current interest. One broad area of focus is film structure; interesting questions include the nature of two dimensional phases (commensurate, incommensurate, orientationally ordered) and transitions between such phases, the growth of films as they become three dimensional and wetting transitions. A closely related problem involves the dynamical properties of these films. Both of these will be addressed by thermodynamic and scattering techniques, traditional probes used in bulk systems. Another fundamental area of investigation is the binding of gas molecules to surfaces; this also is to be studied by scattering. Accompanying these experiments will be theoretical studies concerned with the same issues. Included are the application of statistical mechanics to describe the collective phenomena associated with film ordering. Computer simulation is a particularly powerful tool to explain and predict these properties, as well as test theoretical hypotheses about the force laws. The systems to be considered include both monatomic and polyatomic adsorbate species. While the popular graphite substrate will receive some attention, magnesium oxide and other substrates will get somewhat greater emphasis. The "compound" system of solid and monolayer film will be studied by both elastic and inelastic scattering probes.