CNT bundles

It is important to construct aligned CNT arrays in order to measure properties of individual tubes and to advance the development of electrical and/or electronic devices. From this viewpoint recent developments concerning CNT preparations involve the creation of aligned CNT bundles. 

FIGURE 12.18 Schematic illustration for lithium insertion in CNT bundles. The state of lithium-inserted CNT bundles can be classified into two schemes (1) lithium simply dispersed on the CNT surface and (2) lithium existing in the space between tubes, which might be clusters induced by Li-Li interactions. 

Atomic force microscopy [6, 7] is one of the most suitable methods for research carbon nanotubes. AFM allows to receive not only a relief of the studied sample, but also distribution of mechanical characteristics, electric, magnetic and other properties on its surface. With the help of AFM, controllable manipulation of individual CNTs and CNTs bundles became possible. In this paper we report our approach to manipulating SWCNTs bundles with lateral force microscopy. LFM gives possibility to study lateral forces that probe acts upon bundles. In spite of good visualization of LFM, its lack is absence of reliable techniques of quantitative interpretation of results. The new way of calibration developed ourselves has allowed to pass from qualitative estimations to quantitative investigations [8], The given calibration technique is much more exact, than others known till now [9, 10], and does not assume simplification. With the help of new technique we may study adhesion of bundles to substrate and adhesion of CNTs in bundle qualitatively in real time more easy way. This result will provide new possibilities for nanotube application. 

The other interesting material for electronics is carbon nanotubes. We have shown the application of individual single-walled carbon nanotubes for field effect transistors (FETs) [3]. Carbon nanotubes (CNT) or CNT bundles can be placed between two carbon electrodes playing the role of source and drain. The gate electrode can be made of thin metal stripe under the dielectric film in the region between source and drain. 

Photocurrent response in the near-infrared region up to 1600 nm, related to absorption features of semiconducting SWNTs in blends with MEH-PPV and P30T, offers principally the operation of infrared sensitive photodetectors with these materials [318]. To enable the photon harvesting in this spectral region, the SWNTs needed to be finely dispersed within the polymer matrices, thereby switching off the excitation quenching observed within CNT bundles. 

Taking into account the electromagnetic coupling of carbon nanotubes (CNTs), the low-frequency surface wave of the finite CNT bundle is analyzed. Geometric resonances of surface wave emerge and can be used for the qualitative interpretation of experimentally observed features in the optical response of CNT bundle-based composite mediums. 

The surface wave can propagate also in the CNT bundle, which is usually considered as an infinite 2D array of parallel nanotubes [5]. A bundle consists of 2-800 CNTs and has the finite diameter (1-50 nm), which is much less than the bundle length L and the free-space wavelength A. The most part of the electromagnetic field of the low-frequency surface wave extents outside the CNT bundle. 

Let a CNT bundle contains N infinitely long metallic CNTs, closely packed together, with surface conductivity aQ. The bundle radius Rb is much less than the wavelength A. Since the incident field is almost homogeneous over the bundle cross-section, a symmetrical surface wave is excited in the bundle. In order to take into account the symmetrical local field distribution inside and outside the bundle we model one as a system of n coaxial thin-walled cylinders with the radii R, (l = l,2.,.n, Rb = Rn> Rn x> > Rx) and the surface conductivity cr, /(2 R,), where cr, is equal to the sum of linear conductivities of CNTs placed between the surfaces of cylinders with radii R, and R,, . Boundary conditions for electric Hertz potential on the surface of I -th cylinder in the cylindrical coordinate system (p, q>, z) is as follows [2] ... 

M = K0(tdil)-ico/[4ziRl(7lie2I0(KRl)],al=a0N I R2b, a, =a0N R2-R2 x)IR2b, l,m = l,2,3...Nc. The minimal root of this equation gives the wave number of the surface wave. For comparing, we also developed many-body technique for calculation of the dispersion properties of CNT bundle with N <73. The results obtained by different methods are in a good agreement with the variance less... 

Thus, varying the CNT bundle radius and length one can obtain resonance response of the CNT bundle-based antenna and, consequently, similar features of... 

Figure 2. Frequency dependence of imaginary part of CNT bundle polarisability.

We have proposed a simple electromagnetic model of the CNT bundle, in which the bundle is considered as a system of coaxial thin-walled cylinders with effective conductivities. The bundle surface wave phase velocity was found increasing with the bundle radius. This shifts the frequency of geometric resonances into infrared range as compared with a single-wall CNT. 

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