Heat Capacity of Atoms Adsorbed on a Close-Packed Substrate

Abstract

The specific heat is calculated for noninteracting Fermi atoms adsorbed into deep potential wells on a close-packed substrate at low temperatures. The atoms have a small, but finite, probability of tunneling to adjacent localized sites, which creates a low-lying energy band. It is shown that in this tight-binding approximation, the band structure is identical with the two-dimensional electronic band structure in graphite, and this is used to calculate the specific heat of the adsorbed particles. For comparison, the specific heat is obtained for a constant density of states. There is a general correspondence between the two cases, with the constant density of states smoothing out the actual specific heat at the lowest temperatures. A short discussion explains how hard-core repulsion between adsorbed particles will affect the surface coverage and the mobility.