Effects of energy heterogeneity on phase transitions in a model monolayer system

Abstract

The effects of substrate binding-energy variation on the first-order phase transitions of monolayer films are studied. The analysis relates these effects to a binding-energy distribution characteristic of the substrate. A model two-dimensional system is constructed which has a phase diagram similar to that of xenon on graphite. The ideal uniform system undergoes transitions between gas, liquid, and solid phases, displaying distinctive signatures in vapor-pressure isotherms and heat capacities. Our calculations show how the introduction of energy heterogeneity causes the transition signatures to broaden and shift in ways which depend on both the intrinsic nature of the transition and the substrate binding-energy distribution. Comparisons with experiments lead to estimates of the distributions on different types of graphite.