© Copyright, Department of Physics, University of Illinois at Urbana-Champaign

Atoms on Surfaces

Many practical devices, such as compact disks, magnetic memories, semiconductor chips, and optical coatings, utilize thin films of atoms deposited on solid surfaces. Atoms bind to sites on the surface; the binding energy depends on the kind of site. The equilibrium number of atoms on the various sites is determined by minimizing the free energy.

Consider a solid surface with two kinds of binding sites for a particular type of atom. There are M1 = 60000 sites with binding energy Δ1 = 0.1 eV and M2 = 20000 sites with binding energy Δ2 = 0.15 eV. A total of N = 900 atoms occupy these sites: N1 are on sites of type 1 and N2 are on sites of type 2.

Calculate the values of N1 and N2, and from these, their ratio for the equilibrium state at 300 K.

N1 / N2 =