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October 16th, 2009

Nanotube properties manipulated by catalyst composition

Published on October 16th, 2009 | By: pwray@ceramics.org

Researchers know that single‐walled carbon nanotubes have a lot of potential in the world of electronics. Besides being cheap to produce, it’s been show that SWNTs can be produced that have an enormous variety of functions and behaviors (chirality).

Nanotubes can be formed by “rolling” sheets of graphene. The actual process can involve using a hot reactor vessel such as a DC microplasm reactor, in which two gasses, acetylene and hydrogen are introduced in the presence of a metallic catalyst, such as nickel.

Researchers have already figured out that there is a link between angle in which the sheets are rolled or formed, and the different characteristics that appear in the SWNTs. But, engineering the SWNTs with a particular chirality has not been so easy.

A group of researchers at Case Western Reserve University, however, think they are on to something that may provide a breakthrough. They say that by manipulated the mix of metals used in a catalyst to produce the SWNTs, they can also manipulate nanotube chirality.

In a letter in Nature Materials, R. Mohan Sankaran, a CWRU professor, and postdoc Wei-Hung Chiang, wrote:

“We have established a link between the structure of a catalyst and the chirality of carbon nanotubes. Change the catalyst structure by varying its composition, and you can begin to control the chirality of the nanotubes and their electrical and optical properties.”

The duo notes that when SWNTs are grown using a typical nickel catalyst, the result is a mix of metallic (about one-third) and semiconducting nanotubes (about two-thirds). Separation of the two types, however, so far has proven difficult. Instead, the ideal situation would be to be able to create a pure batch of SWNTs.

Chiang and Sankaran experimented with various ratios of nickel and iron in the catalyst, and eventually found that a 27:73 ratio of nickel to iron produced a product that was almost entirely semiconducting SWNT.

The two say they are hoping to use their semiconducting nanotubes to form thin film transistors. They also see they are experimenting with other catalytic ingredients and ratios to see if they can fine-tune their process.


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