Diamondoid

Diamondoid is a thus-far hypothetical allotrope of carbon that has been proposed as a building material for nanotechnology components. Its structure is similar to diamond, but in most proposed applications it would be formed in pieces containing several thousand down to only a few dozen carbon atoms, making it significantly different in physical properties from the bulk crystalline material.

Carbon nanotubes could, analogously, be considered a sort of "graphitoid" as it is structurally similar to a sheet of graphite molecule rolled into a tube. It is not itself diamondoid, however, lacking the three-dimensional interatomic bonds of diamond.