Surface Melting and Roughening of Adsorbed Argon Films

Argon multilayers adsorbed on graphite display heat-capacity anomalies attributed to surface roughening and surface melting. Melting begins 3° or 4° below the triple point, producing strong peaks with power-law risers $\sim {(T_t-T)}^{-r}$, $r=1.35\mathrm{}\pm 0.03$. The exponent and the thickness dependence of peak temperature agree with the theory of surface melting under long-range forces. Rounded anomalies at $\sim 0.8T_t$ are identified with roughening transitions. The two types of anomalies are well separated, indicating that melting and roughening are distinct forms of surface disorder.