Electrodeposited nanomaterials

1 Metals such as nickel, cobalt, iron, copper, zinc and chromium 

Nanociystalline deposits of Ni (Natter eta/., 1998), Co (Pizenioslo etal, 2001a), Fe (Natter et al, 2000), Cu (Natter and Hempelmann, 1996) and Cr (Przenioslo et al, 2001b) with crystallite sizes between 10 and 100 nm prepared by pulse electrodeposition are reported. The grain size distribution in NC copper deposited by pulse deposition from an acid copper bath containing citric acid studied by TEM and scanning electron micrography (SEM) are shown in Fig. 5.6 and 5.7 (Natter and Hempelmarm, 1996). 

Electroplated nickel is a relatively soft material with hardness -230 VHN, but coatings with NC stmcture exhibit higher microhardness values of 600 to 640 VHN as-plated (Hui and Richardsort, 2004 Brooman, 2005). NC nickel of about 17 nm size producedby electrodeposition significantly enhances the electrocataly tic activity for hydrogen evolution due to the increased derrsity of active surface sites (Haseeb et al, 1993). Electrochemically prepared Co nanofilms exhibit three to five times greater coercivity (He) than polycrystalline Co (Bartlett et al, 2001). 

Fabrications of arrays of nickel and cobalt nanowires have been reported through electrodeposition at constant potential (Whitney et al, 1993). In order to fabricate 

6 Transmission electron micrograph of NC copper the most frequent grain size is 15 nm (Natter and Hempelmann, 1996). 

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Key words electrodeposition, nanomaterials, pulse and pulse reverse electrodeposition, template-assisted deposition, additives and grain refiners, nanostuctured metals and alloys, nanocomposites, multilayers, biocompatible materials, corrosion resistance of electrodeposited nanostuctured materials. 

Electrodeposition is a versatile technique for the production of nanostructured materials with lower capital investment, higher production rates and few shape and size limitations. Electrodeposited nanomaterials such as nanostractured metals, alloys and metal matrix composites have proven successful in providing superior corrosion resistance of substrate materials compared with the corresponding microstmctured materials. 

Abedin, S. Z. E., Polleth, M., Meiss, S. A., Janek, J. Endres, F. (2007). Ionic Liquids as green electrolytes for the electrodeposition nanomaterials. Green Ghent. 9 549-553. 

Morris, D. G. Munoz-Morris, M. A. Relationships between mechanical properties, grain size, and grain boundary parameters in nanomaterials prepared by severe plastic deformation, by electrodeposition and by powder metallurgy methods. J. Metastable Nanocrystal. Mater. 15-16, 585-590 (2003). 

This critical compaction step is avoided in the case of the electrochemical route of pulsed electrodeposition (PED) [29] which transforms cations, i.e. atomic species, directly into nanomaterials without the detour via nanopartides. In this way densities up to 99% of the theoretical value can be achieved, such that these materials exhibit, for instance, intrinsic mechanical properties and not those dominated by voids. 

Usually there is a lot of effort required to make nanomaterials by electrochemical means. In aqueous solutions the electrodeposition of nanocrystalline metals requires pulsed electrodeposition and the addition of additives whose reaction mechanism hitherto has only been partly understood (see Chapter 8). A further shortcoming is that usually a compact bulk material is obtained instead of isolated particles. The chemical synthesis of metal or metal oxide nanoparticles in aqueous or organic solutions by colloidal chemistry, for example, also requires additives and often the desired product is only obtained under quite limited chemical conditions. Changing one parameter can lead to a different product. 

In ionic liquids the situation seems to be totally different. It was surprising to us that the electrodeposition of metals and semiconductors in 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide delivers nanocrystalline deposits with grain sizes varying from 10 to 200 nm for the different materials, like Si, Al, Cu, Ag and In, investigated to date. It was quite surprising in the case of Al deposition that temperature did not play a tremendous role. Between 25 and 125 °C we always got nanocrystalline Al with similar grain sizes. Similar results were obtained if the deposition was performed in tri-hexyl- tetradecylphos-phonium bis (trifluoromethylsulfonyl) amide. Maybe liquids with saturated nonaromatic cations deliver preferentially nanomaterials this is an aspect which, in our opinion, deserves further fundamental studies. 

Common methods for the fabrication of metallic nanoparticle arrays are electron beam lithography, photolithography, laser ablation, colloidal synthesis, electrodeposition and, in recent time, nanosphere lithography for which a monodisperse nanosphere template acts as deposition mask. A review on advances in preparation of nanomaterials with localized plasmon resonance is given in [15]. 

However, it is only recently that the potential benefits of combining sonochemistry with electrochemistry have increasingly been studied. It should be noted that electrochemical methods, mainly electrodeposition, are well established for the preparation of metals and semiconductor nanomaterials (for a review see Mastai et al. [146]). 

However, the application of cobalt- oxide nanomaterials for immobilization of biomolecelus and biosensor fabrication is rare. Recently we used electrodeposited cobalt-oxide nanoparticles for immobilization of hemoglobin [67], The UV-visible spectrophotometric analysis and voltammetric studied indicates the immobilization of Hb onto cobalt-oxide nanoparticles (Figure 35). 

Abedin SZE, PoUeth M, Meiss SA et al (2007) Ionic liquids as green electrolytes for the electrodeposition of nanomaterials. Green Chem 9 549-553... 

Modes, G. and Rubinstein, I. (2001) Electrodeposition of semiconductor quantum dot films, in Electrochemistry of Nanomaterials (ed. G. Modes), Wiley-VCH Verlag GmbH, Weinheim, pp. 25-65. 

A number of processes are being used for producing nanomaterials for bulk production. The most common techniques used for synthesizing nanostructure materials include inert gas condensation, mechanical alloying, thermal spraying, electrodeposition, jet vapor deposition, vacuum thermal evaporation, and controlled chanical precipitation. 

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