Cobalt, electroless deposition

It is interesting to note that Brenner and Riddell (2-4) accidentally encountered electroless deposition of nickel and cobalt during electrodeposition of nickel-tungsten and cobalt-tungsten alloys (in the presence of sodium hypophosphite) on steel tubes in order to produce material with better hardness than that of steel. They found deposition efficiency higher than 100%, which was explained by an electroless deposition contribution to the electrodeposition process. 

Although the concept of phase is well defined thermodynamically, here phase refers to a mechanically separable homogeneous part of an otherwise heterogeneous system. The concept of phase change refers here to a change in the number present or in the nature of a phase or phases as a result of an imposed condition such as temperature or pressure. To clarify and illustrate the topic at hand, we use the specific cases of electrolessly deposited nickel and electrodeposited cobalt. 

Electroless plating — An autocatalytic process of metal deposition on a substrate by reduction of metal ions from solution without using an external source of electrons. It is promoted by specific reductants, namely formaldehyde, sodium hypophosphide, sodium boro-hydride, dialkylamine borane, and hydrazine. Electroless deposition has been used to produce different metal (e.g., nickel, cobalt, copper, gold, platinum, palladium, silver) and alloy coatings. It can be applied to any type of substrate including non-conductors. Some substrates are intrinsic catalytic for the electroless deposition other can be catalyzed usually by sensibilization followed by Pd nucleation also, in some non-catalytic metallic substrates the electroless process can be induced by an initial application of an appropriate potential pulse. In practical terms, the evaluation of the catalytic activity of a substrate for the electroless deposition of a given metal is... 

As it is already established in the published literature, both of the above categories have their advantages and disadvantages.1,3 Furthermore, as it was suggested by Djokic6 in the example of electroless deposition of cobalt with hydrazine, the contribution from both electrochemical and metal hydroxide mechanisms is quite possible. 

An adequate mechanism, however, must describe all the steps occurring during the deposition process, as listed below for the example of electroless deposition of nickel or cobalt with appropriate... 

Many electroless deposition processes are very useful for the fabrication of various devices in the electronics industry. Significant importance for the electronics applications have metals such as silver, gold, nickel, copper, cobalt, palladium, and related alloys. All of these mentioned metals can quite simply and successfully be deposited via electroless deposition. 

Selective electroless deposition of cobalt alloys offers a novel approach for forming self-aligned metallic cap layers. Such films have better adhesion to copper than dielectric films. 

Nanostructured and planar films of poly(p-xylylene) have been fabricated by an oblique angle polymerization method. Subsequently, these films were coated with cobalt by an electroless deposition method [104],... 

Djokic SS (1997) Electroless deposition of cobalt using hydrazine as a reducing agent. J Electrochem Soc 144(7) 2358-2363... 

Kem and coworkers have also explored controllable, uniform metal deposition by employing TMV as a biotemplate. In their studies, the addressable amino acid side chains that function as metal nncleation sites are first activated with a metal complex, followed by incubation with the desired metal for metallization and its subsequent chemical reduction to form metal nanoparticles. By employing this approach of electroless deposition, discrete nickel, silver, and cobalt nanoclusters were selectively formed on the interior or exterior of the virus by controlling the pH and the activation complex used in the reaction. In addition... 

Fig. 7.5 Powders of (a) nickel produced by electroless deposition with hydrazine, (b) silver produced with formaldehyde, (c) cobalt produced with hypophosphite, and (d) cobalt produced with hydrazine [21] (Reprinted with permission from ECS—The Electrochemical Society.)...

The Fe, Co, and Ni deposits are extremely fine grained at high current density and pH. Electroless nickel, cobalt, and nickel—cobalt alloy plating from fluoroborate-containing baths yields a deposit of superior corrosion resistance, low stress, and excellent hardenabiUty (114). Lead is plated alone or ia combination with tin, iadium, and antimony (115). Sound iasulators are made as lead—plastic laminates by electrolyticaHy coating Pb from a fluoroborate bath to 0.5 mm on a copper-coated nylon or polypropylene film (116) (see Insulation, acoustic). Steel plates can be simultaneously electrocoated with lead and poly(tetrafluoroethylene) (117). Solder is plated ia solutioas containing Pb(Bp4)2 and Sn(Bp4)2 thus the lustrous solder-plated object is coated with a Pb—Sn alloy (118). 

Electroless nickel deposition may then be carried out directly onto steel, aluminium, nickel or cobalt surfaces. Surfaces of copper, brass, bronze, chromium or titanium are not catalytic for deposition of nickel-phosphorus and the reaction must be initiated by one of the following operations ... 

Figure 8.14. Rate of electroless cobalt deposition as a function of pH at 30 and 100 g/L citrate one-factor experiments. (From Ref. 65, with permission from the Electrochemical Society.)...

Electrochemical deposition All the early thin-film recording media were electroless or electrodeposited cobalt or cobalt alloys. Electroless Co(P) deposits contain 2-4% P. The coercivity (Hc) of these deposits is a function of the deposit thickness d according to one of the two functions, depending on deposition conditions [147-149]... 

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