From soot to diamond - to microchips

TINY crystals of diamond, consisting of only a few tens of millions of atoms, have been grown in the core of carbon “onions” in a novel process never before observed. The new technique may find application in microchips of the future. Diamond, the hardest naturally occurring material, is formed in nature when carbon is compressed at enormously high temperatures and pressures. Artificial diamonds, usually small and imperfect, are made by trying to imitate these processes.
But scientists at the Max Planck Institute for Metals Research in Stuttgart, Germany, have discovered a new method to produce perfect diamonds, although only in small quantities.
The Stuttgart team, led by Dr Florian Banhart, discovered the new diamond-forming process when they heated specimens containing carbon onions to temperatures of 600-800 degrees Celsius and irradiated them with electrons in an electron microscope. They observed that the shells formed into perfectly regular spheres of carbon atoms.
But they also noticed that the centres of the spheres the shells became more tightly compressed. Atoms had been knocked out of the shells and the shells had shrunk - like a bicycle chain being tightened by having links removed.
The shrinking of the inner shells created enormous pressures - a million times that of the atmosphere at sea level, or about the pressure at the centre of the Earth. The Stuttgart workers observed that the links among the carbon atoms at the centre of the onions changed to yet another structure characteristic of carbon - that of diamond. Diamond owes its strength to its crystal structure, in which the atoms form a network with links in three dimensions, spreading without definite limit.
It may be possible one day to use such techniques to create areas of diamond a few micrometres square, Dr Banhart says. This could be valuable in microchips; some experimental microchips are already helped to keep cool by being mounted on diamond substrates, because diamond is efficient at conducting.
Diamond also has potentially valuable electronic properties that mean it might one day be used for active electronic components in microchips. The new ion-irradiation technique could be the key to fabrication of diamond components on the very small scale.
But for the immediate future the new process offers the promise of understanding crucially important interactions between carbon atoms by observing them as they happen, under the microscope. And it may be possible to squeeze other materials in carbon cages to yield information that cannot be gained in any other way.

MSN NEWS 15.10.1997