Nucleation-coalescence growth mechanism

the sequence of growth of electrodeposited gold by nucleation-coalescence mechanism has four stages (1) formation of isolated nuclei and their growth to TDC, (2) coalescence of TDC, 

It is interesting to note that it was concluded in this work that the first few angstroms of deposit form an alloy layer. Another interesting and important conclusion in this work is that the sequence of growth of electrodeposits (at 20 °C) is very similar to that of the evaporated deposits (at 250-300 °C). 

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The mechanisms of the crystal-building process of Cu on Fe and A1 substrates were studied employing transmission and scanning electron microscopy (1). These studies showed that a nucleation-coalescence growth mechanism (Section 7.10) holds for the Cu/Fe system and that a displacement deposition of Cu on Fe results in a continuous deposit. A different nucleation-growth model was observed for the Cu/Al system. Displacement deposition of Cu on A1 substrate starts with formation of isolated nuclei and clusters of Cu. This mechanism results in the development of dendritic structures. 

In Chapter 7 various growth models were described layer growth (Section 7.9), nucleation-coalescence growth (Section 7.10), development of texture (Section 7.11), columnar microstructure (Section 7.12), and other structural forms (Section 7.13). In this section we discuss the effects of additives on these growth mechanisms. 

There are two basic mechanisms for formation of a coherent deposit layer growth and 3D crystallites growth (or nucleation-coalescence growth). A schematic presentation of these two mechanisms is shown in Figure 7.11. 

This creates nucleation sites randomly distributed on the electrode surface (Pt, ITO, Au, etc.). Then, the nucleus size increases and the nuclei coalesce. In the first stage of the nucleation process, the contribution of a two-dimensional nucleation is important, indicating that the polymeric deposit initiates by the formation of a two-dimensional film. At longer times, upper structures appear which corroborates a three-dimensional growth. This 2D and 3D nucleation and growth mechanism (NGM) of PTh and PPy has been extensively studied by different techniques [22-24] and presents similarities with the electrodeposition of metals [25, 26]. As a result, thin films (<1 pm) are compact and smooth in morphology (due to a two-... 

Figure 7.11. Schematic representation of layer growth (a,b) and the nucleation-coalescence mechanism (c).

Thus, the sequence of growth of electrodeposited gold by the nucleation-coales-cence mechanism has four stages (1) formation of isolated nuclei and their growth to TDC, (2) coalescence of TDC, (3) formation of linked network, and (4) formation of a continuous deposit. This sequence of growth stages is schematically shown in Figure 7.14. 

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