Cluster adions

In the formation and growth of adion clusters, two processes are of fundamental importance (1) the arrival and adsorption of ions (atoms) at the surface, and (2) the motion of these adsorbed ions (adions, adatoms) on the surface. An adion deposited on the surface of a perfect crystal stays on the surface as an adion only temporarily since its binding energy to the crystal is small. It is not a stable entity on the surface, but it can increase its stability by the formation of clusters. The free energy of formation of a cluster of N ions, AG(N), has two components (terms) ... 

Both terms in Eq. (7.1) are functions of the size of the cluster N. The first term increases linearly with N, and the second increases as Dependence of the energy of formation of a cluster AG(A0 on the number of adions A/ in a two-dimensional (2D) cluster is shown in Figure 7.1. It is seen from the figure that AG initially increases, reaches a maximum, and then decreases with increasing N. At the maximum, the cluster size is N. The size of the critical nucleus (the number of atoms in the cluster) in 2D nucleation is given by... 

In some theoretical treatments of the growth-decay process of clusters, growth is considered to proceed by the gain or loss of single adions, Aj. Thus, allowed reactions for the model system are... 

---