Chemical vapor deposition carbon nanotube arrays

The field emission properties of carbon nanotube forests and single nanotubes are described. Controlled emission is possible for aligned CNT arrays where the spacing is twice the CNT height, as grown by plasma enhanced chemical vapor deposition. This leads to the maximum field enhancement factor. For random forests, the field enhancement obeys an exponential distribution, leading to a lower emission site density and imperfect current sharing. Ballast resistors can help alleviate this problem. Random nanocarbons perform less well than CNTs. Some applications are covered. Elec-... 

Figure 3.16 Different steps in the fabrication of MWNT nanoelectrode arrays, (a) metal film deposition, (b) catalyst deposition, (c) plasma-enhanced chemical vapor deposition for CNT growth, (d) dielectric encapsulation with Si02, (e) planarization with a chemical mechanical polishing to expose the ends of the carbon nanotubes, (f) electrochemical characterization. Readapted from Ref [6].

Figure 1.6. Carbon nanotube structures obtained by chemical vapor deposition synthesis, (a) SEM image of self-oriented MWNT arrays. Each tower-like structure is formed by many closely packed multiwalled nanotubes, (b) SEM top view of a hexagonal network of SWNTs (line-like structures) suspended on top of silicon posts (bright dots), (c) SEM top view of a square network of suspended SWNTs, (d) Side view of a suspended SWNT power line on silicon posts (bright) and (e) SWNTs suspended by silicon structures (bright regions). Reproduced from reference 3 with permission from American Chemical Society.

Cobalt complexes among other metals such as iron and nickel are known to catalyze the growth of carbon nanotube (CNT) by chemical vapor deposition (CVD) [79-81]. Thanks to the thermal stability of the hyperbranched polyyne backbone, spin-coated films of the organometalhc polymer were successfully probed to function as catalyst and arrays of CNT bundles could be prepared (Figure 2.4). This preliminary result already suggests potential application in the field of paUemable tailor-made catalysts. 

Puretzky AA, Geohegan DB, Jesse S, Ivanov IN, Eres G. In situ measurements and modeling of carbon nanotube array growth kinetics during chemical vapor deposition. Appl Phys A 2005 81 223-40. 

Yun, Y.H., Shanov, V., Tu, Y., et al. Growth mechanism of long aligned multiwall carbon nanotube arrays by water-assisted chemical vapor deposition. J. Phys. Chem. B 1KK47),... 

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. 

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