Using both high-resolution vapor-pressure isotherm and synchrotron x-ray scattering techniques, the evolution of the film-gas interface of multilayer argon on graphite with the film thickness has been explored. It is shown that an order-disorder transition occurs at the surface layer. The disordering of the surface layer with temperature can be described by an Arrhenius law. The maximum density change associated with the order-disorder transition of the top layer increases progressively with film thickness. This behavior may reflect the fact that a liquid layer is thermodynamically unstable at the bulk solid-gas interface below the premelting temperature.

• Received 9 March 1995

DOI:https://doi.org/10.1103/PhysRevB.51.17023