Metal nanowires

Di Francia et al. (2009) believe that the use of metal nanowires can contribute to improvement in operating characteristics of gas sensors, because metal nanowires have features such as ductility and chemical stability. Furthermore, when the diameter of these structures is in the nanorange, they could represent interesting transducers since the surface/volume ratio increases with the inverse of the wire 

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A wide range of novel low bandgap polymers with bandgaps ranging from 

ITO/PEDOT/PBDTT ScDPP PC7iBM/ Ti02/AgNW 7.2% 4.5% AVT = 58% — — 54 

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Pena DJ, Mbindyo JKN, Carado AJ, Mallouk TE, Keating CD, Razavi B, Mayer TS (2002) Template growth of photoconductive metal-CdSe-metal nanowires. J Phys Chem B 106 7458-7462... 

Walter EC, Murray BJ, Favier F, Kaltenpoth G, Giunze M, Penner RM (2002) Noble and coinage metal nanowires by electrochemical step edge decoration. J Phys Chem B 106 11407-11411... 

The above syntheses of metal nanowires are based on the thermal hydrogen reduction. However, we found that the reproducible synthesis is difficult by this method, because the hydrogen reduction needs careful control of the reaction conditions. For the reproducible and selective synthesis of wires and particles, we need to clarify the factors controlling the sintering of metals. The key factors are the concentration of residual solvent and the relative rate of reduction and migration of metal ions. The details are shown in the next section. 

Figure 3. Schematic representation of the selective synthesis of metal nanowires and nanoparticles by the Sintering Controlled Synthesis approach, (a) Mesoporous silica, (b) impregnation of mesoporous silica with metal ions, (c) addition of water/alcohol vapors and UV-irradiation, or wet H2-reduction, (d) formation of metal nanowires, (e) dry H2-reduction, (f) formation of metal nanoparticles.

Reches, M., and Gazit, E. (2003). Casting metal nanowires within discrete self-assembled peptide nanotubes. Science 300, 625-627. 

Mbindyo, J.K.N., Template synthesis of metal nanowires containing monolayer molecular junctions, J. Am. Chem. Soc., 124, 4020,2002. 

There has been extensive recent use of track-etched membranes as templates. As will be discussed in detail below, these membranes are ideal for producing parallel arrays of metal nanowires or nanotubules. This is usually done via electroless metal deposition [25], but many metals have also been deposited electrochemically [26]. For example, several groups have used track-etched templates for deposition of nanowires and segmented nanowires, which they then examined for giant magnetoresistance [27-29]. Other materials templated in the pores of track etch membranes include conducting polymers [30] and polymer-metal composites [31]. 

Et-HMM (HMM-1) and Ph-HMM (or HMM-p), respectively, have a highly ordered 2D-hexagonal structure that exhibits more hydrophobic properties than the sihca FSM-16. They may work as attractive templates for metal nanowires and nanopar-tides by the hydrophobic surface-mediated reaction. 

XRD patterns of Pt/FSM-16 [25] (and HMM-1 [32]) show no significant change at 26 = 1-10° before and after the incorporation of metal nanowires and nanoparticles (Figure 15.7). This indicates that the pore structures and mesoporous channels of FSM-16 (and HMM-1) remained unchanged in the synthesis of the Pt wires and Pt particles [18-20, 23, 24] by wet photo-irradiation with methanol -i- water vapor and dry H2 reduction, respectively. Furthermore, in the high 26 region, typical peaks assigned to Pt fee crystalline are observed for both samples of Pt nanowire/FSM-16 and Pt nanoparticles/FSM-16 [25]. 

Other Surface-Mediated Synthesis of Metal Nanowires 623... 

Alumina nanotubes have been prepared by the anodic oxidation of aluminum [41] the resulting tubes have one-dimensional channels with uniform diameters of 5nm and lengths of 50-100 nm. An alumina membrane with a highly ordered nanohole array in 50-100 nm diameter has also been synthesized by long-period anodization thus these local alumina nanotubes have been tried as a template for metal nanowire formation. 

Reches M, GazitE. Casting metal nanowires within discrete self-assembled peptide nanotubes. 

Lee JY, Connor ST, Cui Y, Penmans P (2008) Solution-processed metal nanowire mesh transparent electrodes. Nano Lett 8 689... 

Govindaraj A, Satishkumar BC, Nath M, Rao CNR (2000) Metal Nanowires and Intercalated Metal Layers in Single-Walled Carbon Nanotube Bundles. Chem Mater 12 202-205... 

Enzymes functionalized with metallic NPs were used as biocatalytic hybrids for the growth of metallic nanowires. The catalytic enlargement of metal nanoparticles by products generated by different enzymes was used to develop different optical sensors that follow the activities of enzymes and analyze their substrates.57 For example, hydrogen peroxide generated by the biocatalyzed oxidation of glucose by O2 in the... 

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... 

The bottom-up synthesis of metallic nanowires was further applied to construct a nanotransistor device.93 The sequence-specific winding of the homologous nucleic acid carried by the RecA-protein into the duplex DNA was used to address the nucleic acid/protein complex on the DNA scaffold (Fig. 12.27). The subsequent association of the anti-RecA antibody to the protein DNA complex, followed by the association of the biotinylated antiantibody, and the linkage of streptavidin-modified carbon nanotube deposited the tubes in the specific domain of the DNA scaffold. The further... 

Other important experimental techniques utilized in the molecular transport studies include the mercury-drop junctions52,53 which have been used to study the transport through alkanethiols, and nanorods (a metallic nanowire-S AM-metallic nanowire junction)54 which have been used to measure 16-mercaptohexadecanoic acid. 

Single-walled carbon nanotubes (SWNTs) had been considered for the crossbar components of the defect-tolerant molecular computers but they have been found to be too difficult to handle due to their insolubility and their tendency to form bundles or ropes. Instead, metallic nanowires have become the materials of choice used in the construction of the crossbar devices, with ultrahigh-density lattices and circuits being built, having groups of nanowires 8 nm in diameter and 16 nm apart in layers perpendicular to each other to create nanowire junction densities of 1011 per cm2.52 The process does not depend on self-assembly but rather on molecular beam epitaxy. 

Mbindyo Jeremiah, K. N., Mallouk Thomas, E., Mattzela James, B., Kratochvilova, I., Razavi, B., Jackson Thomas, N. Mayer Theresa, S. Template synthesis of metal nanowires containing monolayer molecular junctions. J. Am. Chem. Soc. 124, 4020-6 (2002). 

Sordan, R., M. Burghard, and K. Kern. 2001. Removable template route to metallic nanowires and nanogaps. Appl. Phys. Lett. 79 2073-2075. 

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