The size dependence of the diamond-graphite transition

The transition between nanometre-scaled diamond and graphite as well as the corresponding thermodynamic functions are discussed based on the temperatu re-pressure phase diagram of carbon including the contribution due to surfa ce effects. As a result, the equilibrium transition size between diamond an d graphite as a function of temperature and the thermodynamic function for the transition are obtained. It is found that as the size and temperature d ecrease, diamond becomes more stable than graphite. The obtained result is consistent with the reported experimental results on the chemical vapour sy nthesis of nanometre-sized diamond under ambient pressure.