A method for fabricating nanodiamond particles in a nanodiamond fabrication reactor, which method entails: a) forming a composite of a plurality of diamond monolayers interspersed with a plurality of non-monolayer dihydrobenzvalene (DHB), one over the other, by reacting kinetically energized carbyne radicals with a supported layer of DHB, thus sealing off any subtended, unreacted DHB from further reaction with the kinetically energized carbyne radicals. b) subjecting the diamond monolayers to an anvil having a nanomachined strike face, with sufficient force to fracture the diamond monolayers, to thereby produce nanodiamond having a shape in the X-Y plane matching that of the nanomachined strike face and a Z-axis dimension (thickness) which is that of a diamond monolayer.