Diamondlike amorphous carbon films prepared by magnetron sputtering of graphite

Abstract

Amorphous carbon films, a-C, were prepared by employing dc magnetron sputtering of a graphite target in an argon plasma. A series of a-C films were deposited as a function of sputtering power. The power was varied in the range 5–500 W and the target effective sputtering area was about 20 cm2. The physical and optical properties of the a-C films show a dependence on the sputtering power. The films, although unhydrogenated, possess diamondlike properties such as high hardness, HV=1200–2400 kgf mm−2, and are transparent in the infrared (IR) region with optical gap Eopt =0.40–0.74 eV. We observe a systematic variation of film properties with increasing sputtering power which suggest a transition from fourfold (diamondlike) to threefold (graphitic) coordination of the carbon atoms. For films prepared at low sputtering power about 3/4 of the carbon atoms have tetrahedral coordination and 1/4 have trigonal coordination. At the highest sputtering power the a-C films consist of equal mixtures of tetrahedrally and trigonally bonded carbon atoms.