#### 6.3.3 Freund-Chason Model

Freund and Chason took a completely different approach for the islands’ encounter [107].
They treated the problem using the Hertzian contact theory with cohesive attraction [108],
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

| (6.7) |

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.