Surface energy of amorphous carbon films containing iron

Iron containing diamond-like amorphous carbon (a-C:Fe) films were deposited by filtered cathodic vacuum arc technique. The influences of Fe content an d substrate bias on the surface energy of the films were investigated. The surface energy of a-C:Fe films was determined by the contact angle measurem ent. Atomic force microscopy, Raman spectroscopy, and x-ray induced photoel ectron spectroscopy were employed to analyze the origin of the variation of surface energy with various Fe content and substrate bias. It is found tha t the contact angle for water increases significantly after incorporating F e into the films and the films become hydrophobic. The roughness of these f ilms has no effect on the contact angle. The surface energy is reduced from 42.8 to 25 dyne/cm after incorporating Fe into the a-C film (10% Fe in the target), which is due to the reduction of both dispersive and polar compon ent. The reduction in dispersive component is ascribed to the decrease of a tomic density of the a-C:Fe films due to the increase in sp(2) bonded carbo n. When sp(2) content increases to some extent, the atomic density remains constant and hence dispersive component does not change. The absorption of oxygen on the surface plays an important role in the reduction of the polar component for the a-C:Fe films. It is proposed that such network as (C-n-O -Fe)-O-(Fe-O-C-n) may be formed and responsible for the reduction of polar component. (C) 2001 American Institute of Physics.