Structural modification of ion-implanted and postannealed polycrystalline diamond studied by transmission electron microscopy

We have presented a convenient and effective method to ex situ study ion-implanted and postannealed polycrystalline diamond by transmission electron microscopy (TEM) without thinning the specimens. Chemical-vapor-deposited (CVD) diamond used for transmission electron microscopy study was directly deposited onto Mo TEM grids, and then implanted and postannealed. TEM images clearly reveal that there exists an ion-induced amorphous layer on the as-implanted CVD diamond surface, in which graphitelike structure is embedded. The amorphization processes depend on the irradiation conditions. Hydrogen plasma treatment was employed to anneal the as-implanted CVD diamond. High resolution electron microscopy images indicate that hydrogen plasma treatment can effectively remove the ion-induced surface amorphous layer without graphitizing the diamond. After treatment, high density ball-like diamond blisters appear on the surface, of which the average diameter is only about 2.5 nm, implying the critical size for the stable existence of CVD diamond crystallites may be on the order of a few atomic layers.