Multilayer adsorption of oxygen on graphite near the triple point

Abstract

Using an ellipsometric technique, we have observed layer-by-layer adsorption isotherms of oxygen on a small patch of a single cleaved surface of highly oriented pyrolitic graphite. As many as nine steps are seen. The overall features are characteristic of wetting at the triple point ($T_3$=54.35 K): Below $T_3$, bulk crystallite formation preempts film growth after a limited number of layers. Above $T_3$, the film grows to a thickness equivalent to about 40 layers. However, indications of bulk droplets appear above about 12 layers. Our results suggest not quite complete wetting even by the liquid phase.