THE DEPOSITION MECHANISM OF DIAMOND-LIKE AC AND A-C-H

Diamond-like carbon (DLC) is a dense, partially sp3 bonded metastable phase of non-crystalline carbon or hydrogenated amorphous carbon formed by the deposition from medium energy (50-500 eV) ion beams. The sp3 bonding arises from C ions entering subsurface atomic sites and producing a quenched-in density increase. The process has an optimum ion energy of about 100 eV because the C ions must have sufficient energy to penetrate the surface, but any excess energy could anneal out the density increment. The process is an ion-induced compression of sp2 a-C into the denser sp3 phase. Deposition of a-C: H is more complex, involving a growth step, ion-induced dehydrogenation and ion-induced compression of the C-C skeleton. In the growth step, ions incorporate directly into the film whereas slow neutral species first form an adsorbed layer which then may incorporate into the-bulk. Ion bombardment causes dehydrogenation by the preferential displacement of hydrogen and compresses sp2 sites into sp3 sites, forming extra bonds in the C-C skeleton, as in a-C.