Nanotubes transport properties

Fischer, J. E., Zhou, W., Vavro, J., Llaguno, M. C., Guthy, C HaggenmueDer, R., Casavant, M. J., Walters, D. E. and Smalley R. E. (2003) Magnetically aligned single wall carbon nanotube films Preferred orientation and anisotropic transport properties./. Appl. Phys., 93, 2157-2163. 

To date, the transport properties of inorganic nanotubes have not been reported. A wealth of information exists on the transport properties of the bulk 2D layered materials, which is summarized in a few review articles [see, e.g., (72 and 89)]. 

J. Chen, L. Yang, H. Yang, J. Dong, Electronic and transport properties of a carbon-atom chain in the core of semiconducting carbon nanotubes, Phys. Lett. A, vol. 316, pp. 101-106, 2003. 

For applications where only mechanical properties are relevant, it is often sufficient to use resins for the filling and we end up with carbon-reinforced polymer structures. Such materials [23] can be soft, like the family of poly-butadiene materials leading to rubber or tires. The transport properties of the carbon fibers lead to some limited improvement of the transport properties of the polymer. If carbon nanotubes with their extensive propensity of percolation are used [24], then a compromise between mechanical reinforcement and improvement of electrical and thermal stability is possible provided one solves the severe challenge of homogeneous mixing of binder and filler phases. For the macroscopic carbon fibers this is less of a problem, in particular when advanced techniques of vacuum infiltration of the fluid resin precursor and suitable chemical functionalization of the carbon fiber are applied. 

The nanotechnology report issued in February 2004 by the UK Royal Society makes the general observation that Electrical transport properties across interfaces remain poorly understood in terms of science/predictive capability. This affects all nanomaterials . This observation most keenly summarizes the present state of play for Gbit level random access memories (RAMs), and it is our view that the electrode interface issues may dominate the device physics. Within the nanotech roadmap , high-dielectric ( high-K ) materials are strongly emphasized, as are nanotubes and new interconnects. 

Another direction of investigation is to extend the nanotube array architecture to other metal oxides, most noticeably a-Fc203 and mixed FeTi oxides, to develop materials capable of efficiently responding to the visible light spectrum, while maintaining the outstanding charge transport properties demonstrated by the HO2 nanotube arrays. 

Generally, a carbon nanotube FET device is constructed by a substrate (gate), two microelectrodes (source and drain), and bridging material between the electrodes, which is typically an individual SWNT or a SWNT network. A SWNT FET is usually fabricated by casting a dispersion of bulk SWNTs or directly growing nanotubes on the substrate by chemical vapor deposition (C VD) either before or after the electrodes are patterned.64 Due to the diffusive electron transport properties of semiconducting SWNTs, the current flow in SWNT FET is extremely sensitive to the substance adsorption or other related events on which the sensing is based. 

Nanocarbon material (NCM), containing both the ordered carbon structures (carbon nanotubes (CNT), the particles of nanographite) and the particles of the disordered carbon phase, is known to be promising for using as elements of the nanodimensional devices and as fillers, for example, of lithium batteries. Structure and phase composition of NCM depend essentially on the methods of their obtaining and the regimes of the subsequent temperature and chemical treatment. Therefore, finding the correlation between the structural and phase composition and transport properties of NCM as well the description of the mechanisms of their conductivity are the important problems. 

As far as the nanotube conductivity is concerned, it obviously depends on the nanotube structure (MWNT or SWNT) and also on its helicity (in the case of SWNTs). TEM has also permitted to relate the helicity to the transport properties of nanotubes (52), the helicity being determined from electron diffraction patterns and the transport properties being probed with a dedicated TEM specimen holder. 

Interest in carbon nanotubes has grown at a very rapid rate because of their many exceptional properties, which span the spectrum from mechanical and chemical robustness to novel electronic transport properties. The field is reviewed and several of the important directions, including their chemical structure, electronic structure, transport properties, electronic, elastic and field emission properties are summarized. 

Recently, it has been predicted for armchair SWNTs that the electron mean free path should increase with increasing nanotube diameter, leading to exceptional ballistic transport properties and localization lengths of 10 pm or more [149]. The effect arises because the conductance is independent of the tube diameter (i.e. 2Go) and the electrons experience an effective disorder which is the real disorder averaged over the circumference of the tube [144,149]. The effective disorder then reduces as the tube diameter increases so that scattering becomes less effective. 

Issi, J.P. Charlier, J.C. Electrical transport properties in carbon nanotubes. In The Science and Technology of Carbon Nanotubes, Tanaka, K., Yamabe, T., Fukui, T., Eds. Elsevier New York, 1999 Chapter 10, 107-127. 

Rafli-Tabar, H. (2004). Computational modeling of thermo-mechanical and transport properties of carbon nanotubes. Phys. Rep., 390, 235-452. 

These characteristics make CP-AFM ideal for studying electrical transport of nanotubes, nanoparticle assemblies, micro- or nanofabricated semiconductor devices, and individual molecules. Detailed appraisal of these characterizations can be obtained by comparing CP-AFM and STM. Although CP-AFM and STM share high spatial resolution imaging capability (STM 0.1 mn CP-AFM -10 nm, due to larger tip apex) that is critical in linking nanoscale structure to transport properties, an important distinction is the position of the tip with respect to the sample. In the case of CP-AFM, a metal-coated tip is directly contacted to the sample under a controlled load. This means that the measured I V relationship is mainly affected by the electrical properties of the tip-sample contact. 

High-field transport properties of single wall carbon nanotubes (SWCNT) are analyzed on the basis of phonon-assisted tunneling (PhAT) model. This model enables to explain not only temperature-dependent current-voltage characteristics of SWCNT, but also the crossover from a semiconducting-like temperature dependence conductivity to a metallic-like one as temperature is increased. 

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