LIKE the rest of us, carbon nanotubes appreciate a bit of luxury. They turn out to grow prolifically when given a sparkling bed of diamonds.
Nanotubes are generally produced by chemical vapour deposition. A carbon-based gas such as methane is heated to around 700 掳C and passed over a layer of metal nanoparticles 鈥� commonly nickel, cobalt or iron. The nanoparticles act as catalysts, helping the high temperature to break the methane gas apart, creating a cloud of carbon atoms that then congregate on the metal to form nanotubes.
But metal nanoparticles tend to merge in the intense heat and cease to act as catalysts. That means they can鈥檛 be crammed too close together, which limits the number of nanotubes that can grow on them.
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So scientists led by Daisuke Takagi at NTT Basic Research Laboratories in Atsugi, Japan, decided to replace the metal nanoparticles with a densely packed layer of diamonds, each around 5 nanometres across. Passing ethanol gas over these diamonds created a lush forest of nanotubes 1 to 2 nanometres wide (Journal of the American Chemical Society, ). This worked even though diamonds don鈥檛 catalyse the breakdown of ethanol, acting only as seeds for nanotube growth. Diamond鈥檚 high tolerance for heat meant that Tagaki could crank up the temperature to 850 掳C, breaking the ethanol apart without the need for a catalyst.
鈥淧assing ethanol gas over these diamonds created a lush forest of nanotubes 1 to 2 nanometres wide鈥�
