Surface modification of nanocrystalline diamond/amorphous carbon composite films

The surfaces of nanocrystalline diamond/amorphous carbon (NCD/a-C) nanocomposite films deposited from a 17% CH4/N-2 mixture have been subjected to a variety of plasma and chemical treatments, namely H-2 and O-2 microwave plasmas, a CHF3 13.56 MHz plasma, and a chemical treatment with aqua regia (HCl:HNO3 3:1). The resulting surfaces have been studied with respect to their chemical nature by X-ray photoelectron spectroscopy (XPS) and time of flight secondary ion mass spectrometry (TOF-SIMS), concerning their morphology with atomic force microscopy, and by contact angle measurements to study their hydrophobicity and their stability. As-grown surfaces are hydrogen terminated, but the number of C-H bonds can slightly be increased by a H-2 microwave plasma, while treatment with aqua regia considerably lowers the number of C-H bonds at the surface. O-2 and CHF3 plasmas, on the other hand, lead to a replacement of the terminating C-H bonds by C-O or C-OH and C-F, groups, respectively. Finally, by contact angle measurements over a period of 150 days it could be shown that the H-terminated surface is very stable whereas the contact angle of the O-treated surface changed considerably with time, probably due to the adsorption of contaminants. (C) 2008 Elsevier B.V. All rights reserved.