Nuclei density

FIGURE 6.13. The nucleus density as a function of the pulse length for deposition at -1.30V from 2naM KAu(CN)2 +0.2M KCN (pH 14), determined using SEM. The nuclei were grown at -1.10 V after the nucleation pulse so that the deposition charge was -3.0mC/cm. After Oskam and Searson." (Reproduced by permission of The Electrochemical Society, Inc.)... 

In this potential regime, the nucleus density increases exponentially with applied potential. 

Equations (5) and (6) can be combined to give the following expression for the nucleus density ... 

Figure 5 shows the potential dependence of the nucleus density obtained from analysis of the current transients according to equation (7). The exponential dependence of the nucleus density on potential suggests thermal activation of nucleation sites, consistent with classical nucleation models [5,8] where N0 °= exp(-eAU/kT). 

Analysis of deposition transients shows that deposition of copper on TiN from 50 mM copper (II) pyrophosphate solution proceeds through instantaneous nucleation of three dimensional hemispherical clusters and diffusion limited growth. Determination of the diffusion coefficient from the current maximum and analysis of the current decay using the Cotrell equation yielded values of 1 x 10 6 to 2 x 10 6 cm2 s, slightly lower than the value for Cu2t ions due to the presence of the pyrophosphate ligand. The potential dependence of inux and t,n suggest that the nucleus density is the only potential dependent parameter. 

Figure 5. Nucleus density determined from deposition transients plotted versus the deposition potential.

The growth of nuclei can be either kinetically or diffusion limited or under mixed control. In many cases, it is observed that diffusion of metal ions to the surface is rate limiting. As the growth becomes diffusion limited, the diffusion zones around individual nuclei will start to overlap, and linear diffusion to the planar surface may occur before nuclei impinge on each other. If nucleation is progressive, the development of diffusion fields may block active sites for nucleation, leading to the situation where the final nucleus density is smaller than Nq (18-20). 

From analysis of the nucleation and growth mechanism, conditions for the deposition of adherent, continuous gold films can be determined. First, a nucleus density on the... 

Figure 8 The nucleus density versus the applied potential for a 2 mM KAu(CN)2 + 0.2 M KCN (pH 14) solution, determined from AFM. Also shown is the nucleus density obtained from SEM using a 50 mM KAu(CN)2 +1 M KCN (pH 14) solution.

It is obvious that the larger nucleus density, the thinner is the thickness of the metal film required to isolate the substrate from the solution. At the same time, a thinner surface film will be less coarse than a thicker one. This means that a smoother and thiimer surface film will be obtained at larger deposition overpotentials and nucleation rates, i.e., by electrodeposition processes characterized by high cathodic Tafel slopes and low exchange current densities. 

Markov I (1976) Saturation nucleus density in the electrodeposition of metal onto inert electrodes. I. Theory. Thin Solid Films 35 11-20 Markov I, Stoycheva E (1976) Saturation nucleus density in the electrodeposition of metal onto inert electrodes. II. Experimental. Thin Solid Films 35 21-35... 

In order to determine nucleus density, growth rate must be estimated from the Lau-ritzen-Hoffmarm model, as follows ... 

Figure 6.1. Effect of temperature on the nucleus den- Figure 6.2. Effect of nucleus density on the haze of 2 sity of iPP containing 200 ppm poly(vinylcyclo- mm injection molded iPP plates containing the three...

Nucleus density can be determined from DSC measurements carried out under isothermal conditions at various temperatures. Figure 6.1 shows the relationship between nucleus density and temperature obtained by the above described method. The nucleus density decreases drastically with increasing temperature. Figure 6.2 shows that high nucleus density is important requirement for high quality clarifier. With increasing nucleus density optical properties improve considerably. ... 

Menyhard A, Gahleitner M, Varga J, Bernreeitner K, Jaaskelainen P, 0ysaed H, Pukanszky B (2009) The influence of nucleus density on optical properties in nucleated isotactie polypropylene. Eur Polym J 45 3138-3148... 

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