Stranski-Krastanov

Figure 10.5. The three modes of growth of films (a) Frank and van der Merwe s monolayer (two-dimensional) mode (b) the Volmer-Weber three-dimensional mode (c) the Stranski-Krastanov mode involving two-dimensional growth followed by three-dimensional growth.

In practice, uniform films are obtained for only a limited number of film-substrate material combinations (17). The more common experience is that the deposited material forms 3D clusters. The clusters may form directly on the bare substrate, in the Volmer-Weber growth mode, or on top of a very thin but uniform film of the deposit, the Stranski-Krastanov growth mode. We now discuss a method for determining the equilibrium configuration of the deposited material. 

Therefore, we predict that for a system with any finite misfit, a uniform film with a thickness greater than several monolayers is not the equilibrium state the system can lower the chemical potential by the formation of clusters. Clusters will form on either the bare substrate (Volmer-Weber mode any finite misfit with WKl and large misfits if W >1) or on a few layers of uniform film (Stranski-Krastanov mode up to moderate misfits with W>1). This will be true for any system without long-range (e.g. electrostatic) forces. 

NbOx Pt(lll) Stranski-Krastanov growth (distorted Nb06 octahedral) (2)... 

Stranski-Krastanov growth has been documented for copper on Au(lll) [101, 102], Pt(100) and Pt(lll) [103], for silver on Au(lll) [104, 105], for cadmium on Cu(lll) [106] and for lead on Ag(100) and Ag(lll) [107-109]. In all of these examples, an active metal is deposited onto a low-index plane of a more noble metal. Since the substrate does not undergo electrochemical transformations at the deposition potential, a reproducible surface can be presented to the solution. At the same time, the substrate metal must be carefully prepared and characterized so that the nucleation and growth mechanisms can be clearly identified, and information can be obtained by variation of the density of surface features, including steps, defects and dislocations. 

If fls Am, misfit is present, positive or negative, and growth proceeds by the Stranski-Krastanov mechanism, which is composed of two steps. In the first step a 2D overlayer of M ij on S is formed, and in the second step 3D crystallites grow on top of this predeposited overlayer (Fig. 7.20). 

Figure 5.1. Scheme of the different mechanisms of growth (a) Frank-van der Merwe, (b) Voimer-Weber and (c) Stranski-Krastanov. The substrate and overlayers are represented by dark grey and light grey shading, respectively. 

On the other hand, n-alkanes (n = 4, 6, 7) adsorbed from the vapour phase on Ag(lll) surfaces also grow following the Stranski-Krastanov mechanism (Wu et al, 2001). 

Cadmium bulk deposition was found to occur according to Stranski-Krastanov mechanism, with the Cd(OOOl) plane parallel to Au(lOO) [241, 266]. 

On Cu(lll) different structures were proposed. The bulk deposited cadmium forms a close-packed hexagonal lattice in perchlorate solutions, growing according to modified Stranski-Krastanov mechanism [292]. 

Ikemiya et al. [445] have investigated both the atomic structure and growth of electrodeposited Te films on Au(lOO) and Au(lll) with large lattice misfits. Deposition was performed in sulfuric acid solutions using in situ AFM. On both substrates, bulk-deposited Te films were formed according to the Stranski-Krastanov mechanism. Their atomic structures changed with the increasing film thickness. 

Intermediate mechanism between (1) and (2). At first, an epitaxial monolayer is formed, followed by three-dimensional nucleation. This is called the Stranski-Krastanov mechanism. 

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