New method for mass producing CNTs

A method for producing a specific single-walled carbon nanotube type with a predefined structure has been developed by scientists.

While carbon nanotubes (CNTs) have uses in a variety of applications, ranging from solar cells to light detectors and sensors, the inability to mass produce single-walled carbon nanotubes that are all nearly exactly alike has hindered their widespread use.

Now, researchers have developed a way to produce a ‘batch’ of nanotubes that all have the same characteristics.

To make that happen, the team began with predefined ‘seeds’– organic molecules that were specifically created for the purpose – and used a multistep process. The seeds were placed on a platinum surface, and then the whole works were heated to 500°c – ethanol was used as the source for the carbon atoms. The arrangement of the atoms in seeds determines the species of the nanotubes that grow, and in their experiments, they grew carbon nanotubes with a (6, 6) chirality index (the numbers of which describe tube diameter and the angle of the walls relative to the base when the tube has been rolled up, respectively).

The researchers have proved that, by using made-to-measure molecular ‘germs’, it is possible to clearly predefine the growth (and thus the structure) of long SWCNTs. The SWCNTs synthesised in this study are mirror-image symmetrical entities. However, depending on the manner in which the honeycombed atomic lattice is derived from the starting molecule (‘straight’ or ‘oblique’ in relation to the CNT axis), it would also be possible to produce helically-wound nanotubes, i.e. nanotubes twisting to the right or left that are not mirror-image symmetrical.

This very structure also determines the electronic, thermoelectric and optical properties of the material. Therefore, in principle, the researchers can produce materials with different properties in a targeted manner, by selecting the starting molecule.

As their next step, Fasel and his colleagues intend to gain an even better understanding of the way in which SWCNTs populate a surface. Although well over 100 million nanotubes per square centimetre are already grown on the platinum surface, actual ‘fully-grown’ nanotubes only grow from a comparatively small proportion of the germs. This raises the questions: which processes are responsible for this, and how can the yield be increased?

The research has been published in the journal Nature.