Studies of hexagonal diamond of nano-grain in graphite surface produced byAr+ ion bombardment

Hexagonal diamond nano-grains in irradiated surface of graphite produced by ion bombardment at high doses of 0.6 keV Ar+ have been found,using high-re solution transmission electron microscopy (HRTEM). The average diameter (D) of the grains was varied between similar to 2 and similar to 50 nm,and the grain population decreases almost monotonic ally as grain size increases. It is of interest to note that they exhibit a distinctly bimodal structure. For diameters less than 10 nm,the microstructure of grains are single crys tals,but the polycrystal structure of nano-grains with larger diameter (>10 nm) can be also observed. The characteristics of this bimodal structure ar e on the basis of hexagonal diamond nano-grain nucleation and growth mechan isms,which are restricted by the characteristics of ion bombardment process es.