What is a nano-crystalline diamond?
By enforced re-nucleation during diamond growth, the diamond grains can be kept very small. This material is called nanocrystalline or ultra-nanocrystalline diamond (UNCD). This material does not have all the unique properties of diamond (e.g. it is not transparent and the thermal conductivity is low). But it exhibits a pretty smooth surface and there are interesting applications in tribology, micro-mechanics, and biochemical sensing.