Freund and Chason took a completely different approach for the islands’ encounter . They treated the problem using the Hertzian contact theory with cohesive attraction , in an attempt to overcome the deficiencies in the description of the zipping process by Nix and Clemens. The geometry of the problem was also changed; in fact, they claim that the conditions in the Nix-Clemens model are suitable in the case of a fully covered substrate while the depositing material is only filling gaps. Therefore, Freund and Chason proposed a change in the perspective of the problem. Instead of using a transversal cross section, they decided to analyze the process using a top view of the structure, as shown in Fig. 6.7.
In fact, the Freund-Chason model expands the dimensionality of the problem and a 3D description of the geometry is also possible. The stress estimation using the Freund-Chason model is given by
where is the problem dimensionality. and are parameters which depend on the stated problem dimension with values , , , and , , . The Freund-Chason model is more in line with experimental measurements, especially for materials with high adatom mobility.