The deposition mechanism of diamond-like a-C and a-C: H

Abstract

Diamond-like carbon (DLC) is a dense, partially sp 3 bonded metastable phase of non-crystalline carbon or hydrogenated amorphous carbon formed by the deposition from medium energy (50–500 eV) ion beams. The sp 3 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 sp 2 a-C into the denser sp 3 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 films 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 sp 2 sites into sp 3 sites, forming extra bonds in the C-C skeleton, as in a-C.