Taking a look at the thermodynamics at the surface of the film, it is seen that bonds are broken, releasing energy, and bonds are formed, confining energy. The thermodynamics involved were modeled by the two Germans W.Kossel and N.Stranski in 1920. This model is called Terrace ledge kink model (TLK).
The adatom can create more than one bond with the crystal, depending on the structure of the crystal. If it is a simple cubic lattice, the adatom can have up to 6 bonds, whereas in a face-centered cubic lattice, it can have up to 12 nearest neighbors. The more bonds created, the more energy is confined, making it harder to desorb the adatom.
A special site for an adatom is a kink, where exactly half of the bonds with the surface can be created, also called the "half-crystal position".