Observation of a first-order triple-point dewetting transition in methane adsorbed on graphite

We report the results of high-resolution heat capacity measurements of multilayer methane adsorbed on graphite near the bulk triple point. These measurements indicate that the films studied, from 5 to 18 layers thick, undergo two wetting transitions in the process of melting. The first is a first-order dewetting transition at T_w ∼ 90.5 K, and the second is a continuous wetting transition at the triple point, T_t = 90.66 K. The melting transition in the film begins at T_w, and moves to lower temperatu for thinner films