Nucleation and Growth of Surface Nuclei

Theoretical and experimental studies of the initial stages of building of a metal crystal lattice introduced a major advancement in the interpretation of the deposition processes and resulted in a series of new models [1, 16]. Experimental studies include applications of in situ surface analytical methods [17-21], including scanning tunneling microscopy (STM) and atomic force microscopy (AFM). 

Initial stages of electrocrystallization are discussed in Sect. 3.2.2, growth mechanisms are discussed in Sects 3.2.3 and 3.2.4, and the effect of additives on these processes are discussed in Sect. 3.2.5. 

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 A ions, AG(N), has two components (terms) 

Both the terms in Eq. (30) are functions of the size of the cluster A. The first term increases linearly with A and the second increases as A2/3. The dependence of the energy of formation of a cluster A G(N) on the number of adions A in a 2D cluster is shown in Fig. 13. It can be seen that AG increases initially, reaches a maximum, and then decreases with increasing A. At the maximum the cluster size is Ac. The size of the critical nucleus Ac (the number of atoms in the cluster) in two-dimensional (2D) nudeation is given by 

The spontaneous growth of clusters is possible after the maximum AG is reached. This critical cluster is the nucleus of the new phase and it is characterized by equal probability for growth and dissolution. The growth of clusters before a maximum is reached, and when average AG is increasing, is due to statistical energy fluctuations, which allow local higher values of AG, beyond the maximum [22], 

---

Nucleation and growth processes of the metal lattice. Understanding of the nucleation and growth of surface nuclei, formation of monolayers and multilayers, and growth of coherent bulk deposit is based on knowledge of condensed-matter physics and physical chemistry of surfaces. 

---