Development of the carbon thin films nanostructured by femtosecond laser pulse with a super low friction coefficient and local conductivity

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We report tribological properties of diamond-like carbon (DLC) film of which surface has been nanostructured with femtosecond (fs) laser pulses. A broad area on the DLC surface was nanostructured using a precise target-scan system developed for the fs-laser processing. In the present experiment we have developed two types of laser scan. One is a parallel scan to produce a uniformly nanostructured surface. The other is a crossed scan along a net-like pattern to form a partially nanostructured area on the surface. The results obtained are summarized as follows.1) The nanostructure has been formed uniformly on the DLC surface over the area of 15 x 15 mm^2.2) The structured surface at E=110μJ near the ablation threshold is uniformly modified to the GC layer.3) The friction coefficient of the structured DLC film has shown a small decrease for the steel ball but a small increase for the ceramic WC-Co ball.4) A large improvement of the friction coefficient of the DLC surface has been achieved by coating the MoS2 layer on the nanostructured DLC surface. The measured friction coefficients μ of the surface were 0.07 with the steel ball and 0.02-0.04 with the WC-Co ball.5) The net-like patterning of the ablated zone created by the crossed scan produces an effective method to increase maintaining the initial surface flatness.6) The nano-indentation test and nano-scratch test (100〜2000μN) indicate that the laser-treated surface layer modified to GC becomes soft and its friction coefficient increases as compared with that of the untreated DLC.