Tribological and optical properties of hydrogen-free amorphous carbon films with varying sp(3)/sp(2) composition

Unhydrogenated amorphous carbon films were deposited at different temperatu res on a single silicon wafer by a process known as Filtered Cathodic Vacuu m Are. A transition from diamond-like properties to graphitic properties wa s observed at the substrate temperature of 200 degrees C, This change of pr operties upon transition includes a change in compressive stress, frictiona l coefficient and density. The variation of results is consistent with the subplantation model, which emphasizes the role of carbon atoms trapped in t he subsurface layers in the evolution of a dense sp(3)-rich phase at room t emperature, At higher temperature (>200 degrees C) diffusion of carbon atom s to the surface of the evolving film releases internal stress and leads to the formation of a graphitic sp(2) phase. Based on x-ray reflectivity meas urements, it was found that a thin interlayer formed between the tetrahedra l amorphous carbon film and the silicon substrate contributes greatly to th e good fitting of the spectra, The thickness of this interlayer is independ ent of the temperature. The optical properties were found to undergo a more gradual transition with the deposition temperature. Copyright (C) 1999 Joh n Wiley & Sons, Ltd.