Cultured diamonds

One of the best ways of purifying a chemical substance is by crystallization. A growing crystal accepts molecules that fit its lattice, and rejects those that do not, so a pure product will crystallize from even quite an impure solution. Indeed, even thermodyamically unstable crystals will grow from a solution, if a few ‘seed crystals’ are added to give them a start.

The most valuable of all thermodynamically unstable crystals is, of course, diamond. So Daedalus wants to use the crystallization principle to grow big, pure diamonds. His first idea was to dissolve buckminsterfullerene (the only soluble form of carbon) in benzene or liquid xenon, add a few seed crystals of diamond, and let the solution evaporate. But it seems unlikely that a complete C₆₀molecule would rearrange to a diamond lattice merely by colliding with a diamond surface. A smaller carbon unit is required.

The smallest stable carbon unit is the C₂radical. It is most easily generated by heating carbon in a vacuum. The hot surface slowly evaporates by emission of these radicals — which is why the old carbon-filament lamps had such a limited life. A C₂radical hitting a diamond surface should combine with it to extend the diamond lattice. So a steady rain of such radicals should, by the crystallization principle, grow a diamond of any size from a small initial seed.

Daedalus's diamond-growing apparatus has a source of C₂radicals (a carbon filament or arc) surrounded by a heated precious-metal nozzle to direct them as a beam towards an array of seed diamonds on a cooled platform. The whole thing is in a vacuum chamber. The seed diamonds are first cleaned by argon-ion bombardment, to remove surface contamination and expose their pristine lattice surfaces; the C₂beam is then turned on to grow them to the required size. By narrowing and steering the beam, and orienting the diamonds under it, they can be shaped as well.

Cheap diamond-growing will transform the industry. Diamond jewellery will lose chic and value, while industrial and scientific diamonds will proliferate in the form of cutting tools, optical windows, heat-sinks and so on. But Daedalus muses that nature may have got there first. Many ‘carbon stars’ shower carbon vapour out into the interstellar vacuum. If a few seed diamonds happen to be orbiting in the vicinity, they might over millions of years grow into diamond planets.