Finite-size effects at first-order phase transitions observed in adsorbed oxygen films

Abstract

At a first-order phase transition the specific-heat signal is of δ-like shape. However, this is true rigorously only for systems with infinite dimensions. For finite systems the specific heat is rounded, the degree of rounding depending on the size of the system. Model systems to investigate such rounding effects are physisorbed layers. Such layers are always finite, since substrate properties make adsorption sites of only finite size available. Recent theoretical investigations study the finite-size effects of temperature-driven first-order phase transitions by analyzing various moments of the energy distribution. The theoretical results describe the rounding of the singularities and the shifts in the location of the specific-heat maxima in a manner which is suitable for immediate comparison with experimental results. The only unknown fit parameter is the system size. The present paper describes fit results for physisorbed layers. The presently determined experimental system size is found to be in good agreement with that size known from neutron diffraction studies.