Fig. 2: XPS surface chemical analyses for the five self-mated DLC tribopairs inside and outside wear tracks after sliding in PAO+ZDDP. | Nature Communications

Fig. 2: XPS surface chemical analyses for the five self-mated DLC tribopairs inside and outside wear tracks after sliding in PAO+ZDDP.

From: Interplay of mechanics and chemistry governs wear of diamond-like carbon coatings interacting with ZDDP-additivated lubricants

Fig. 2

a Relative chemical compositions of ZDDP-derived chemical elements P, S and Zn inside the wear tracks. b S2p XPS spectra inside (left) and outside (right) the wear tracks. They are fitted using a doublet due to spin-coupling with a separation of 1.2 eV and an intensity ratio of 0.5. Peak coloured in blue correspond to S−Zn or S−P bonds, while red and green peaks correspond to S−C and S−O bonds, respectively. The S2p XPS spectra outside the wear tracks are magnified by a factor of 3 (for the ta-Cs) and a factor 10 (for a-C:H and a-C) to improve visibility. c S2p XPS spectra inside the wear track for a-C:H (left) and ta-C(66) (right) after 5-min sputtering (corresponding to a sputter depth of about 0.5 nm). d Wear volume W as a function of the S−C/S−Zn ratio. For a critical value of the S−C/S−Zn ratio (located somewhere between 1 and 2.5) a transition from negligible to high wear can be observed.

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