Nanotubes grow up
Aug 14, 1998
Chinese researchers have created the world's largest ever carbon nanotube. They created the 2mm long nanotube using a new technique in which acetylene is passed over a catalyst in a nitrogen atmosphere (Nature 394 631).
The technique uses an iron-silica catalyst created by coating a quartz plate with an iron-silica solution. Once the solution dries it cracks into a film 30-50 microns thick. After the substrate is heated in a vacuum and then in a hydrogen-nitrogen atmosphere to make sure that it becomes chemically unreactive, the film breaks into large quantities of iron-silica nanoparticles. The researchers noticed that the nanotubes became longer if the acetylene was passed over the catalyst for a long period. By increasing the length of time still further, they hope to exceed their new record. Nearly all the nanotubes produced by this method grow in parallel arrays from the catalyst surface, making them easy to remove.
Meanwhile, a team of French and Chinese scientists has constructed nanotubes that can act as'coaxial cables' (Science 281 973). Zhang and his colleagues achieved their breakthrough with nanotubes 50 micrometers long and a few tens of nanometers in diameter. They managed to form a nanotube with three 'jackets' each with different conducting properties. Such behaviour will make nanotubes prime candidates for the developing nanoelectronic components. They found that if they used a selection of boron nitride, carbon, silicon oxide and lithium nitride compounds, the nanotubes form inside each other in a series of 3 layers. A core layer of silicon carbide (semiconducting); an intermediate layer of amorphous silicon oxide (insulating); and a shell of boron nitride and carbon (semiconducting). The authors speculate that by adjusting the quantities of the starting compounds, it may be possible to build self- organising nanocables with different components inside them.