MULTILAYER ADSORPTION OF XENON, KRYPTON, AND ARGON ON GRAPHITE - AN ELLIPSOMETRIC STUDY

We present ellipsometric measurements of multilayer adsorption of xeno n, krypton, and argon on highly oriented pyrolytic graphite along nume rous isotherms spanning the coverage range from completion of the firs t layer to about twelve layers and the temperature range from below th e melting of the top layer to above the bulk adsorbate melting point T (m). The three adsorbates have very similar phase diagrams, and all sh ow reentrant first-order layering. The top layer of three-layer and th icker films disorders at 0.81T(m)-0.83T(m). For films thicker than thr ee layers, first-order layer condensation reappears at shifted coverag es and chemical potentials in the range 0.83T(m)-0.87T(m) to 0.92T(m)- 0.94T(m). The solid adsorbate films reach a limiting thickness of abou t 12 layers at saturation, but the limiting thickness increases rapidl y just below T(m) and reaches the equivalent of about 24 layers in the liquid region. We discuss implications of these results for roughenin g and melting of the adsorbate (111) surfaces. Chemical potentials for layer condensation are compared to a simple Frankel-Halsey-Hill theor y.