Abstract

Three regimes of condensation have been observed between 74 and 80 K in the adsorption and desorption of a submonolayer film of xenon. The first one corresponds to thej condensation or evaporation of a two-dimensional (2D) ‘gas’, the second one to the growth of 2D crystal in the presence of the 2D gas, and the third one to the completion of the 2D crystal on the (0001) graphite face. Zero order kinetics for both adsorption and desorption is found in the large range of coverage (0.3 < θ <0.9) where the two phases coexist on the surface. The activation energy of desorption of the 2D crystal is measured; its value (∼6 kcal mole −1) is in fair agreement with the value of the latent heat of evaporation of this phase (5.5 or 5.7 kcal mole −1) determined previously. No activation energy of nucleation has been observed during the adsorption process. The growth rate is controlled by the incident flux only.

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