A dissertation presented to the graduate faculty of the university of virginia in candidacy for the degree of doctor of philosophy

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In this work we report adsorption measurements on a single cleaved surface of highly oriented pyrolitic graphite (HOPG). This eliminates the possibility of capillary conden- sation, while providing a surface with larger facet size and better energy uniformity than exfoliated graphite. We have measured adsorbate coverage by a phase-modulation ellipsometric technique, using laser light reflected from a 0.1 x 0.2 mm spot on the graphite surface. We have studied various gases (Kr, O2, C2H4 and CF4) in the vicinity of their respective bulk triple point Te (except for the case of Kr where all the data were recorded below T.). We have observed layer-by- layer adsorption where as many as nine steps could be seen. The overall features were characteristic of wetting at the triple point: below Te, bulk crystallite formation preempts film growth after a limited number of layers. Above Tt, the film grows to a thickness equivalent to about 40-50 layers. However, indications of bulk droplets appear above about 10-12 layers. Our results suggest not quite complete wetting by the liquid phase of the various gases studied.