Carbon Nanotubes --> Carbon nanotubes synthesis methods


There are three main synthesis methods:
[Obviously there are other tecnniques. Reaserch centers are working hard in order to obtain sustainable (low cost) carbon nanotubes]

Arc-discharge
The carbon nanotubes were produced using an arc discharge evaporation method similar to that used for the fullerene synthesis.
The carbon needles, ranging from 4 to 30 nm in diameter and up to 1 mm in length, were grown on the negative end of the carbon electrode used for the direct current arc-discharge evaporation of carbon in an argon-filled vessel.


Laser ablation [Smalley 1996]
With this method can produced high yields (>70%) of SWNT, laser-vaporization of graphite rods with small amounts of Ni and Co at 1200 C. The Nanotube grows until too many catalyst atoms aggregate on the end of the nanotube. The large particles either detach or become over-coated with sufficient carbon to poison the catalysis. This allows the tube to terminate with a fullerene-like tip or with a catalyst particle.

Chemical Vapour Deposition (CVD)
This method is capable of controlling growth direction on a substrate and synthesising a large quantity of nanotubes. In this process a mixture of hydrocarbon gas, acetylene, methane or ethylene and nitrogen was introduced into the reaction chamber. During the reaction, nanotubes were formed on the substrate by the decomposition of the hydrocarbon at temperatures 700900 C and atmospheric pressure.


Discussion
Both arc-discharge and laser-ablation techniques have the advantage of high (>70%) yields of SWNT and the drawback that they rely on evaporation of carbon atoms from solid targets at temperatures >3000 C makes difficult the purification and application of the samples.

Chemical Vapour Deposition has two main advantages: the nanotubes are obtained at much lower temperature, although this is at the cost of lower quality, and the catalyst can be deposited on a substrate, which allows for the formation of novel structures.

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