Electrical conductivity nanowires

As discussed above, the exocellular electron transfer mechanisms in MFC systems are rather complex. Different microbes may transfer electrons via quite distinct approaches, and one specific microorganism may have more than one electron transfer paths. For example, Shewanella spp. have outer membrane C5tiochromes for direct electron transfer by contact, but they can also produce electrically conductive nanowires. S. oneidensis also produces flavins that can function as electron shuttles. MFCs are mostly inoculated... 

The diffusive transport phenomena in nanowires can be described by a semiclassical model based on the Boltzmann transport equation. For carriers in a one-dimensional subband, important transport coefficients, such as the electrical conductivity, a, the Seebeck coefficient, S, and the thermal conductivity, Ke, are derived as (Sun et al., 1999b Ashcroft and Mermin, 1976a)... 

Biofuel cells — Figure. Schematic illustration of identified electron transfer mechanisms in microbial fuel cells. Electron transfer via (a) cell membrane-bound cytochromes, (b) electrically conductive pili (nanowires), (c) microbial redox mediators, and (d) via oxidation of reduced secondary metabolites [v]... 

Fig. 1 presents a picture of a path (nanowire) - the constriction in an electrical conductor with dimension W (width), H (thickness) and L (length). The quantization of electric conductance depends neither on the kind of element nor on temperature. For conductors and semiconductors the conductance quantization in units of Go = 2e /h = (12.9 kQ)" was measured in many experiments. In our experiments the quantization of conductance was evident [3]. 

I-V measurements performed on an ensemble of SiNWs with a variety of diameters, growth directions, defect densities etc. are expected to yield only averaged behavior, which is dominated by those wires with the lowest resistivity [as in a parallel configuration of wires (resistors)]. While such ensemble measurements cannot be used to study the electrical conduction properties and mechanisms of nanowires, they can however give rough indications to check a variety of possible applications, one being gas sensing. 

Choi and Park226 have modified surfaces with cyclodextrins to assist in the electroformation of PAn nanowires. Others have utilized the concept of molecular templates to form PAn supramolecular rods with electrical conductivity improved by two orders of magnitude.227... 

Liu, J.S. et al., Tuning the electrical conductivity and self-assembly of regioregular polythiophene by block copolymerization Nanowire morphologies in new di- and triblock copolymers, Angew. Chem. Int. Ed. 41, 329, 2001. 

Even though the nanowire electrical conductance depends exclusively on its geometrical dimensions, and does not depend either on the type of metal or on temperature, the dynamic nanowire formation itself is different for different metals. In particular, the intensity of nanowire formation and the duration of the process are very strongly influenced by the type of metals used. The nanowires forming intensity is measured with statistical calculations of characteristic G =f(t). The result of the calculations is a histogram. 

The conductance quantization has proved to be observable in an experimental setup, giving opportunity to investigate quantum effects in electrical conductivity. The curves of histograms from nanowires with an electrode of cobalt, nickel or tungsten do not contain peaks. In our opinion, a curve of histograms without peaks for some nanowires can be caused by the hardness of magnetie metals [3]. 

The nanowires are formed between two electrodes of the studied material. Measured during the electrode separation, i.e., during the nanowire stretching, the electrical conductance G corresponds to the conductance of the nanowire... 

Figure 1. Electrical conductance in a Co nanowire (a) and the conductance histogram (b).

The second practical challenge in phononic transport rises from heat-to-electricity conversion technology. Here, in order to develop efficient thermoelectric materials, one seeks structures with ultralow heat conductivity in conjunction with high electrical conductivity and a high Seebeck coefficient. Ultralow conductivity was manifested in disordered-layered WSe2 crystals [13], probably due to the localization of lattice vibrations. Si nanowires show enhanced thermoelectric efficiency compared... 

On the other hand, several studies have found out that reduction of the cross-section of nanowires can induce the morphology of the material to change. According to these studies, such effects typically become noticeable as the size of the wire approaches the order of 100-200 nm (Figure 10.42) [68]. However, based on the above analysis, significant alternation of transport physics will not occur until the size of nanowire reaches around 10 nm. Therefore, the increase of conductivity observed is possibly due to more ordered structures within a narrower nanowire, which lead to significant enhancement of the electrical conductivity of the nanowires. 

Y.Z. Long, J.L. Duvail, Z.J. Chen, A.Z. Jin, and C.Z. Gu, Electrical conductivity and current-voltage characteristics of individual conducting polymer PEDOT nanowires. Chin. Phys. Lett., 25, 3474-3477 (2008). 

Interesting data have been obtained for polyamide-HAp composites. The mechanical properties are strongly related to the heterogeneity of the amorphous phase and the localization of HAp in the constrained amorphous phase—a universal behavior. Recent studies have shown promising results for polymer-nanowire composites. Due to their high aspect ratio, these filler particles have a low percolation threshold for electrical conductivity but the enhancement of Young s modulus remains... 

PANI would be typically functionalized with selected dopants via either noncovalent or covalent approaches. In addition, nanostructured PANI materials, such as nanorods, nanowires and nanofibers, offer the possibilities to improve the performance of the PANI-based devices (Huang et al., 2003). PANI has demonstrated its biocompatibility in vivo and sparked great interests in tissue engineering. The biocompatibility of PANI can be further improved by the introduction of biocompatible elements without sacrificing its electric conductivity. 

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