Granular electrodeposits

As already stated, the nuclei behave as microelectrodes in the initial stage of electrodeposition of metals onto inert substrates.33 If nucleation exclusion zones around nuclei are formed,35,36 an inert substrate can be partially covered even at long deposition times, due to the nucleation exclusion zones overlapping, which results in the formation of granular electrodeposits.37,38 In this way, a granular... 

Radmilovic V, Popov KI, Pavlovic MG, Dimitrov AT, Hada-Jordanov S (1998) The mechanism of silver granular electrodeposits formation. J Solid State Electrochem 2 162-169... 

On the other hand, Xiao et al. [215] reported that smooth, dense, and erystalline PbTe films with nearly stoichiometric composition could be obtained by an optimized electrodeposition process from highly acidic (pH 0) tellurite solutions of uncomplexed Pb(II), on Au-coated silicon wafers. The results from electroanalyti-cal studies on Te, Pb, and PbTe deposition with a Pt rde at various temperatures and solution compositions supported the induced co-deposition scheme. The microstructure and preferred orientation of PbTe films was found to change significantly with the deposition potential and electrolyte concentration. At -0.12 V vs. Ag/AgCl(sat. KCl), the film was granular and oriented preferentially in the [100] direction. At potentials more negative than -0.15 V, the film was dendritic and oriented preferentially in the [211] direction (Pig. 3.13). 

Fig. 8 (A) Mechanism of formation of electrodeposits on the surface of an electrolyte and (B) an atomic force microscope (AFM) image reveals the granular nature of a Co deposit. (From Ref. l)...

The morphology of in situ deposited PAn s using chemical oxidants is very similar to that of thin electrodeposited films. For thin films (60 nm thick), AFM studies reveal granular features of 50-100 nm in diameter that are densely packed giving smooth films.209 Thicker films are much rougher with granular features up to 200 nm in diameter. 

Figure 2 shows a SEM micrograph of a layer, electrodeposited at -0.42V for 300 seconds. This compact and granular structure is a representative result for films electrodeposited from both electrolytes. Analysis of the current transients, related to the initial stages of the deposition, indicate an instantaneous nucleation process (7). 

It was shown that thin films of Cu, Co and Ni could be successfully deposited onto Si substrates, without the need of a seed layer. For all three metals, uniform layers with a compact and granular morphology could be obtained. From RBS data the deposition rates as well as the current efficiencies could be determined. For Co films it was shown that addition of boric acid caused the evolution of hydrogen. On the other hand, it was possible to improve the current efficiency of electrolytes containing boric acid by increasing the concentration of cobalt sulfate in the bath. For Ni films electrodeposited from a highly concentrated sulfate electrolyte, it was observed the formation of texture in the (220)-direction. Electric measurements performed on Ni/n-Si structures yielded values for Schottky barriers which are comparable to the ones obtained for junctions fabricated by vapor deposition. 

The electrodeposition process investigated for the deposition of PMT occurs in several steps [623-626] (1) nucleation, (2) first monolayer, (3) fibrous film (layer by layer), (4) granular structure. 

Electrodeposition at —3.40 V produced blackish electrodeposits on the Cu substrate. The total transported charge was 178.4 C. The SEM image of the electrodeposits obtained by electrodeposition at —3.40 V was shown in Fig. 6.23. The morphology of both electrodeposits was granular with a nonuniform size... 

Miyazaki, K., Kainuma, S., Flisatake, K., Watanabe, T. and Fukumoro, N. (1999), Giant magnetoresistance in Co-Cu granular alloy films and nanowires prepared by pulsed-electrodeposition , Electrochim. Acta, 44,3713-19. 

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