Conductive metallic nanowires, synthesis

The synthesis of conductive metallic nanowires that bridged two microelectrodes separated by a gap of 12-16 im was demonstrated by the growth of a silver nanowire on a DNA template that bridged the gap (Fig. 12.26).92 Short thiolated nucleic acids (12 bases long) were attached to the microelectrodes, and these acted as sticky ends for the hybridization of /.-DNA that bridged the gap. The association of Ag+ to the phosphate groups of the template, followed by their reduction with hydroquinone under basic conditions, resulted in the formation of Ag° nanoclusters on the DNA template. The subsequent enlargement of the Ag° seeds by the catalytic reduction of Ag+ by hydroquinone, under acidic conditions, yielded continuous Ag nanowires with a width of ca. lOOnm. The nanowires revealed nonlinear I—V... 

Another method of template-assisted synthesis, mainly used for the growth of metal nanowires, involves the deposition of metal into the cyUndrical pores or channels of an inert, non-conductive nanoporous electrode material. Track etch membranes, porous alumina, nanoporous conductive rubber polymers, metals, semiconductors, carbons and other solid materials have been used as templates to prepare nanometer-sized particles, fibrils, rods and tubules. The experimental set... 

The synthesis of Pt metal nanowires and nanotubes electrochemically deposited through nanoporous membranes was reported by Ichikawa (2000). Palladium deposits with high specific surface areas, up to 50 m g", have been synthesized by Tsirlina et al. (2002) from palladium chloride solutions with additions of polyethylene glycol and polyvinyl pyrrolidone. Details of the globular structine of the deposits depend on the polymer additives. A comparison with electrochemically determined true surface areas demonstrates the coalescence of nanoparticles. Wang et al. (2003) electrochemically synthesized thin films composed of ordered arrays of palladium nanowires using silica mesoporous channels. Mesoporous channels were deposited on a conductive glass substrate. In this method, nanowires with face-centered cubic crystal structure are continuously deposited from the conductive substrate upward until the mesoporous channels are filled. 

The formation of elemental gold layer at the surface of conductive polymers has been reported in the literature 92,93 Synthesis of nanostructures and self-assembled palladium nanowires from Pd(II) complexed solutions using hydrazine as a reducing agent were reported by Shi et al.94,95 The process was carried out for 120s at 60°C. Electroless deposition of nanowires of other metals is also possible and quite realistic. However, no particular engineering applications are yet known. 

H. Chang, Y. Chunhe, and L. Yongfang, Chemical synthesis of coral-like nanowires and nanowire networks of conducting polypytrole. Synthetic Metals, 139, 539-545 (2003). 

Metal and/or metal alloy nanowires/nanofibers have attracted considerable attention due to their potential applications in relation to transparent electrodes and metal catalysts with a ID structure. In this regard, metallic nanofibers such as Au, Cu, and Ni with high electrical conductivity have been prepared by electrospinning (Figure 13.3). Gries et al. suggested a new fabrication process for the synthesis of Au nanofibers. Au nanoparticles (NPs) were embedded within a matrix polymer of PVA (M = 195 000 g mol ) by electrospinning followed by the pyrolysis of PVA and a subsequent calcination step. The sintered Au NPs... 

As mentioned earlier in situ approach has also been used for the synthesis of conducting polymer-metal hybrid nanocomposites. Xu et al. [35] have reported the decoration of PPy nanotubes with gold nanoparticles by an in situ reduction process. They prepared PPy nanotubes by MO-FeCl3 self-degrade template method and then reduced HAuCLi within PPy nanotubes in the presence of different surfactants such as sodium dodecyl sulfate (SDS), cetyltrimethylammonium bromide (CTAB) and Tween-80. Nanowires of silver PAni nanocomposites have been reported via in situ polymerization method [36]. In this method aniline is oxidized by ammonium persulfate (APS) in the presence of dodecylbenzene sulfonic acid (DBSA) and silver nitrate (AgN03). In another approach gold-PAni core-shell... 

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