Kossel site

When the crystal surface is in contact with a supersaturated solution, the rate of deposition of molecules or ions exceeds the rate of dissolution. The Kossel sites are filled progressively until the started surface layer is completed. In order for growth to continue, a new layer must then be... 

The half-crystal position is the same as the position called a kink site, and is shown in Fig. 7.134. This term is due to Kossel (1927) and Stranski (1928). The half-crystal position occurs in the way shown in Fig. 7.134. The energy of binding of an atom in the kink position is just half of the total energy of an atom in the bulk of the ciystal. 

The discovery of the heterogeneity of surfaces, and in particular of dislocations (see Section 7.12.12), was made in the 1930s (Taylor, 1936), but there had been theoretical work on metal deposition at an earlier time. The model of the surface employed by these earlier workers (Kossel, 1927 Stranski, 1928 Erdey-Gruz, and Volmer, 193 l)was a flat plane without steps and edges to which the adions produced by ion transfer from the double layer could surface diffuse. The only way a metal could grow on a perfect planar surface without growth sites was by nucleation of the deposited atoms, rather than diffusion to the growth sites shown in Fig. 7.134. 

It is possible that in the future we may recognize Kossel s idea of the anlage, a basic protein determiner found in all cells, to be the modern-day equivalent of the coat or masking protein which actually determines the particular areas of the DNA (deoxyribonucleic acid) molecule which are to function in RNA (ribonucleic acid) formation in a given cell—that is, Kossel s anlage may be the intellectual antecedent of the principle of cellular differentiation as viewed by many today. On the other hand, if such kindness to our predecessors is to be extended to the ideas of Richard Block, who transformed KossePs anlage first to the basic amino acids (7) and then to common peptides, it can easily be said that the concept of the common active site sequence of many enzymes (20) is what Block meant when he inferred that a peptide anlage determined the function of many proteins. 

Among the different surface atom positions illustrated on Fig. 2.8, the kink site position, or the half crystal position, as introduced independently by Kossel [2.12] and Stranski [2.13], has a special significance for the definition of the equilibrium conditions (vapor pressure, equilibrium concentration, equilibrium electrode potential, etc.) of the infinitely large (bulk) crystal. 

Kossel hypothesized that kink sites present the most probable position for solute integration due to the higher bonding energy... 

Figure 6.26. Sites for impurity adsorption on a growing crystal, based on the Kossel model a) kink (b) step (c) ledge face). After Davey and Mullin, 1974)...

Fig. 9.7 — The cubic coordination sites considered in the Kossel-Stranski theory of phase growth. The different sites are conveniently distinguished by their cubic coordination number, m, as shown in the figure.

Fig. 3. Kossel s model of molecular attachment kinetics (layer-by-layer growth). Building blocks from a liquid nutrient phase are attached (adsorbed) by a growing crystal surface at a site (A) and migrate on it to join the most beneficial attachment places with the largest number of free bonds to be saturated by such a linking (kink sites K). (S) and (F) correspond to the stepped and closely packed (flat) faces, respectively.

Figure 1-35. Metal dissolution according to the model of Kossel and Stranski (Kossel, 1927 Stran-ski, 1928), from (a) kink, (b) step, or (c) adsorption sites to the electrolyte (d). b) Metal dissolution energy diagram with superimposed potential drop A

Model of metal surface with step, kink, and terrace sites after Stranski and Kossel. (From Stranski, I.N., Z. Physik. Chem., 136, 259, 1928 Kossel, W., Nachr. Ges. Wiss. GSttingen. Math. Physik. K.L, 135,1927.)... 

Fig. 5.24 The Kossel model of a surface lower dimensional defects within the surface as a two dimensional imperfection. The differing energies of the structural elements with varying numbers of contacts (see numbering) are of particular importance for reactivity and growth [104], The triple contact corresponds to the so-called half-crystal site.

Undoubtedly, the most important contribution of Kossel and Stranski to the theory of nucleation and crystal growth is the definition of the concept half-crystal position. In an infinitely large crystal, the atom in this, often called kink site position, (Figure 1.19b), is bonded with a semi-infinite crystal block, with a semi-infinite crystal lattice plane and with a semiinfinite crystal row. Attaching or detaching one atom to and from the halfcrystal position a new half-crystal posihon is created and this is what makes... 

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