On the 2D-3D transition in epitaxial thin film growth

The theory is based on the fact that the equilibrium concentration of single atoms adsorbed on the surface of a monolayer island placed on a foreign substrate such that the substrate-deposit interaction is weaker than the deposit-deposit interaction is higher than the equilibrium concentration of atoms adsorbed on the surface of the same island now placed on a substrate of the same material. This higher adatom concentration leads to 2D nucleation on top of the monolayer island. The difference of the above equilibrium adatom concentrations appears as a driving force for the process of transformation of the initial monolayer island into a 3D island by detachment of atoms from the first monolayer island edges and their subsequent attachment to the edges of the second layer nucleus. The kinetics of this process are studied in detail, the following two cases being considered. The first case consists of breaking up and agglomeration of an initially continuous film into 3D crystals upon heating. The second case consists of change of the growth mode from layer to island mode during the vapour deposition when the substrate temperature increases. Expressions for the critical temperatures for these two phenomena to occur are derived. It is shown that they depend strongly on the substrate orientation, the critical temperature being higher for the 〈111〉 orientation in comparison with the 〈110〉 orientation, if substrate and deposit with a fcc lattice are considered. The theoretical results are compared with experimental data for deposition of Au on Mo{110}, Cu on W{110} and W{100} and Fe on Cu{111}.