Abstract
The diamond nanowire (DNW) film was deposited by N 2 -enriched microwave plasma-enhanced chemical vapour deposition (MPECVD) process. As-deposited DNW film was treated in O 2 plasma which resulted in chemical and microstructural modification. Sheath of the DNW film is chemically constituted by amorphous carbon (a-C)- and graphite (sp 2 C=C)-like bonding. However, nanowires transformed into ultra-small spherical grains after the O 2 -plasma treatments. In this condition, a-C and sp 2 C=C bonding significantly reduced due to plasma etching caused by oxygen atoms. After the O 2 -plasma treatment, formation of functional groups such as C=O, C-O-C, O-H, O-CH 3 and H 2 O was observed on the surface and inside the wear track as evident from the micro FTIR analysis. H 2 O is hydrogen bonded to oxygen-containing groups such as -OH and -H. The O 2 -plasma-exposed DNW film exhibits surface charging and causes formation of dangling bonds and electron trapping centres. This results in significant decrease in contact angle, hence superhydrophilic behaviour. The friction coefficient of O 2 -plasma-treated film showed super low value ∼0.002 with high wear resistance 2 × 10 -12 mm 3 N -1 m -1 . In the reciprocating ball-on-disc tribology test, only ∼80 nm wear loss was observed after the 1 km of sliding distance at 10 N loads. Such an advance in tribological properties is explained by passivation of covalent carbon bonding and transformation of sliding surfaces by weak van der Waals and hydrogen bondings. High surface energy and the consequent superhydrophilic behaviour of film is attributed to the formation of the above-mentioned functional groups on the surface. This protects against deformation of the wear track leading to extremely high wear resistance. © 2013 IOP Publishing Ltd.