Arrays of Carbon Nanotubes

For a variety of CNT applications, it is desirable to place the growing tubes in parallel on the substrate. There is a number of approaches to this aim that shall be presented in the following. 

Structuring the substrate alone, however, does not suffice if parallel alignment of the carbon nanotubes is desired the orientation must rather be induced by an external effect. The parallel arrangement can be achieved either during or after preparation. 

Different external influences may serve to the alignment of existing nanotubes. 

For instance, the high pressure filtration of an SWNT-colloid under simultaneous application of a magnetic field of 7-25 T yields a membrane of parallel nanotubes. 

The directed preparation of DWNT on a support of sihcon carbide is feasible by selective evaporation of the sihcon atoms in the uppermost layer of the substrate. The carbon atoms released thereby organize themselves in the shape of double-walled nano tubes that grow up vertically on the surface of the substrate. Here the ahgnment is caused by the close proximity of neighboring tubes that does not allow for a deflection in other directions. 

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Fig. 5. Schematic representation of arrays of carbon nanotubes with a common tubule axial direction in the (a) tetragonal, (b) hexagonal I, and (c) hexagonal II arrangements. The reference nanotube is generated using a planar ring of twelve carbon atoms arranged in six pairs with the symmetry [16,17,30].

APPLICATIONS USING NETWORKS AND ARRAYS OF CARBON NANOTUBES... 

Fig. 13.3 Equipotentials around various arrays of carbon nanotubes (a) Field enhancement at an array of widely spaced nanotube emitters, (b) closely spaced emitters, showing the field screening, (c) field screening at a randomly oriented nanotube forest.

Fan. S. Chapline, M. C. Franklin. N. R. Tombier, T. W. Cassei, A. M. Dai, H. Self-oriented regular arrays of carbon nanotubes and their field emission devices. Science 1999 283, 512. 

S. Fan, M.G. Chapline, N.R. Franklin, T.W. Tombler, A.M. Cassell, H. Dai, Self-Oriented Regular Array of Carbon Nanotubes and Their Field Emission Properties , Science, 283,512 (1999)... 

Figure 1. Fabrication of an array of carbon nanotubes in the n-Si/SiOi/Ni nanbporous stfu( ure.

Figure 1. (a) Side-view SEM image of the array of carbon nanotubes grown at Ni/AhCb catalyst. The insets show the close-view of (a) pores in the alumina template (before nickel loading) (b) carbon nanotubes in the array. 

Ordered arrays of carbon nanotubes (CNT) on various substrates [1] seem to be one of the most promising materials of current nanotechnology. Individual tubes in such arrays are bonded by the strong Van der Waals interactions which can be affected significantly by external molecules adsorbed to the inter-nanotubes space. This leads to high value chemomechanical effect of adsorption in CNT array based nanoelectronic structures which can be used in nanosensorics for the development of chemical sensor elements with acoustic pickup [2]. 

Yoon etal)- reported the synthesis of mesoporous carbon using as-synthesised MCM-48 silica/surfactant mesophase as the template, followed by introduction of carbon precursor (divinylbenzene), carbonisation and removal of silica. Hyeon and co-workers " reported the synthesis of mesoporous carbon by the carbonisation of composites containing silica, P123 triblock copolymer and phenol resin, followed by removal of silica. The synthesis was achieved by treating the as-synthesised silica/triblock copolymer nanocomposite with sulfuric acid to crosslink the triblock copolymers followed by carbonisation. " Kim et al. reported the synthesis of carbon nanotubes using PI 23 surfactant inside mesoporous silica, although ordered arrays of carbon nanotubes were not observed.Kawashima et al. synthesised mesoporous carbon via copolymerisation of tetraethoxysilane (TEOS) and furfuryl alcohol. 

Fig. 1.13 SEM images of a quasi-periodic array of carbon nanotubes. Left panel Normal view, with Penrose tile scheme overlaid. Right panel Array tilted by 45. Scale bars 2 pm. CNT heights are 700 nm...

H. Butt, T. Butler, Y. Montelongo, R. Ranjith, G.A.J. Amaratunga, T.D. Wilkinson, Continuous diffraction patterns from circular arrays of carbon nanotubes . Appl. Phys. Lett. 101, 251102 (2012)... 

Hughes M., Shaffer M. S. P., Renouf A. C., Singh C., Chen G. Z., Fray J., and Windle A. H., Electrochemical capacitance of nanocomposite films formed by coating aligned arrays of carbon nanotubes with potypyr-role, Acfv. Mater., 2002,14,382-385. 

Hughes, M., et al. 2002. Electrochemical capacitance of nanocomposite films formed by coating aligned arrays of carbon nanotubes with polypyrrole. Adv Mater 14 (5) 382. 

Huang ZP, Carnahan DL (2003) Growth of large periodic arrays of carbon nanotubes. Appl Phys Lett 82(3) 460... 

Other sensor platforms have also been explored, such as surface plasmon resonance, field-effect transistors, other optical/spectrophotometric methods, for example, Raman spectroscopy and chemiluminescence, and electrochemical techniques. Very recently, Cai et al. have demonstrated that arrays of carbon-nanotube tips with an imprinted nonconducting polymer coating can recognize proteins below the picograms per liter level, using electrochemical impedance spectroscopy. Devices for the specific recognition of human ferritin and human papillomavirus-derived E7 protein were described (Figure 34). 

The primary synthesis methods for single and multi-walled carbon nanotubes include arc-discharge [203, 204], lase ablation [205], gas-phase catalytic growth from carbon monoxide [206], and chemical vapor deposition (CVD) from hydrocarbons [207-209], The scale-up limitation of arc discharge and laser ablation methods would make them cost prohibitive. One unique aspect of CVD technique is its ability to synthesize aligned arrays of carbon nanotubes with controlled diameter and length. The details on these methods go beyond the scope of this chapter. 

Fan, S., 1999. Self-oriented regular arrays of carbon nanotubes and their field emission properties. Science 283, 512—514. 

Sun, G., Huang, Y, Zheng, L. et al. 2011. Ultra-sensitive and wide-dynamic-range sensors based on dense arrays of carbon nanotube tips. Nanoscale 3 4854-4858. 

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