Hydrothermal growth of diamond in metal–C–H₂O systems

Abstract

The first report of synthetic diamond involved a high-pressure high-temperature (HPHT) process in which diamond was the thermodynamically stable phase¹. Subsequent attempts to make diamond at less extreme conditions culminated in the rapid growth of diamond films by chemical vapour deposition^2,3. But the question of whether diamond might be grown in hydrothermal conditions mimicking those under which it is formed in the Earth has been long debated^4–6. It seems reasonable to suppose that metals might play a catalytic or solubilizing role in this context, given their role in the HPHT method¹, in a recent low-pressure solid-state synthetic approach⁷ and in the recrystallization of diamond in the Ni–NaOH–C system⁸. Hydrothermal synthesis of diamond has been explored at some length^9–13, but with equivocal results. Here we report evidence from spectro-scopic, diffraction and microscopic techniques which suggest that aggregates, tens of micrometres in size, of small diamond crystals can be grown in a hydrothermal environment from a mixture of carbon, water and metal (usually pure nickel). Crucially, we have been able to distinguish new diamond from the diamond seeds added to nucleate new growth.