Gold, electrodeposition

Fig. 12.14 Spread of silver sulphide from discontinuities in gold electrodeposits on silver substrates. The gold was deliberately scratched and the specimen exposed for 24 h to an atmosphere containing 10< o SO2. Immediately after this the sulphide stain extended 0-2 mm. Five years later, the stain extends to about 13 mm, after storage in a normal indoors atmosphere...

The principal use of gold is as a very thin coating about 0-05 /xm thick for electrical and electronic applications. Because of the thinness of gold electrodeposits, porosity must be very carefully controlled since seepage of corrosion products from substrate or undercoat exposed at these pores can have serious adverse effects on both appearance and electrical properties of the composite. The porosity can vary with the thickness of the deposit (Fig. 13.1), and with the type of plating bath and with its method of operation (Fig. 13.2), and the phenomenon has been extensively studied by Clarke and many other workers. 

Saliba, R., Mingotaud, C., Argoul, F. and Ravaine, S. (2002) Spontaneous oscillations in gold electrodeposition. Electrochem. Commun., 4, 629-632. 

Gold, and more recently iridium, has been considered ideal biomaterials for stents. It is liiglily radio-opaque (it shows clearly in X-ray type analysis) and it is considered inert (corrosion should not be expected of the surface due to its noble characteristics.) Indeed, a gold electrodeposited stainless steel stent made it through clinical trials and it was actually approved for clinical use. " It was, nonetheless, a failure because its rate of restenosis was higher than stents already on tlie market When the production process for the stent was reviewed, it turned out that proper heat treating of the plated surface was not performed. Early animal da-... 

Gold electrodeposition has been reported from chloroaluminate-based liquids and from a liquid made of an organic salt and AuQs [55,56]. Although gold can be electrodeposited in high quality from aqueous solutions the latter result is interesting, especially with respect to the deposition of unusual alloys of gold with less noble elements. 

As illustrated in Fig. 3, a single-polystyrene sphere was first deposited on a microelectrode and then gold was electrodeposited around the sphere. A blocking layer was then adsorbed at the upper planar gold surface before sphere removal. This blocking layer confines the electrochemical reactions to the inside of the nanocavity. After sphere removal, a spherical cap recess is obtained, the dimensions of which are controlled by the templating sphere size and the thickness of gold electrodeposited. 

Molcadskyte, O.A. (1979) Kinetics of gold electrodeposition from acid solutions. Institute of Chemistry, PhD thesis. Vilnius. 

Cheh, FLY. and Sard, R. (1971) Electrochemical and structural aspects of gold electrodeposition from dilute solutions by direct current /. Electrochem. Soc., 118 (11), 1737-1747. 

Survila, A., Mockevicius, V., and Visomirskis, R. (1987) Chronopotentio-metric study of gold electrodeposition from cyanide solutions. Sov. Electrochem., 23 (6), 769—774. 

The amine moieties, which were oriented toward the gold surface, could not get protonated and thus the capped nanoparticles were more negatively charged as compared to the aminosilane moieties that enhanced their electrophoresis. Another important mechanism that facilitated gold electrodeposition was anodic oxidation of the gold nanoparticle surface, which ranoved the gold capping and thus increased its tendency to participate in film formation. 

Hemispheres of gold electrodeposited onto microelectrodes provide a quick and easy way of fabricating nano-gap junction electrodes in the laboratory without the need for microfabrication facilities. Two methods have been proposed to fabricate dual-hemisphere junctions via electrodeposition (i) the connection method and (ii) the disconnection method. For the connection method gold is electro-deposited onto two adjacent... 

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