Oxygen plasma modification of submicron vapor grown carbon fibers as studied by scanning tunneling microscopy

Scanning tunneling microscopy (STM) has been employed to monitor the changes in surface structure induced by oxygen plasma treatments of submicron vapor grown carbon fibers (VGCFs). It is shown that the fibers preserve their general smoothness upon plasma oxidation and that the structural changes brought about by this treatment essentially take place only at the atomic scale, where the relatively ordered domains typical of the untreated material are replaced by atomically rough and disordered structures. These atomic-scale changes imply the modification of some physico-chemical properties of the fiber surface, such as concentration of oxygen functionalities. The STM results, together with those obtained from nitrogen physical adsorption measurements, suggest that the potential improvement of plasma treatment in VGCF-matrix adhesion for application in composite materials should proceed mainly from chemical bonding due to the addition of functional groups rather than from increased mechanical interlocking.