X-ray scattering study of the structure and freezing transition of monolayer xenon on graphite

We have performed an extensive x-ray scattering study of the freezing transition of incommensurate xenon physisorbed on graphite as a function of temperature and chemical potential. At a coverage of 1.1 monolayers the transition is continuous to within the substrate-determined resolution, with correlation lengths in the fluid phase exceeding 50 atomic spacings. At coverages less than one monolayer the transition is first order. A comparison is made with current theories of two-dimensional melting. © 1983 The American Physical Society.