Phonon Modes and Heat Capacity of Monolayer Films Adsorbed in Spherical Pores

We examine the hydrodynamic phonon spectrum of a monolayer film adsorbed on the wall of a spherical pore. Due to the boundary conditions, the monolayer film exhibits a discrete phonon spectrum. The corresponding density of states per unit frequency is thus a set of delta functions and the heat capacity exhibits Arrhenius behavior at low temperatures. At high temperatures, the heat capacity approaches the C ∼ T 2 behavior of a two-dimensional monolayer film. Our results for the spherical surface film are compared to previous calculations for films confined to a cylindrical surface.