Tribochemistry of Diamond-like Carbon: Interplay between Hydrogen Content in the Film and Oxidative Gas in the Environment

S Jang and M Rabbani and AL Ogrinc and MT Wetherington and A Martini and SH Kim, ACS APPLIED MATERIALS & INTERFACES, 15, 37997-38007 (2023).

DOI: 10.1021/acsami.3c05316

The lubricity of hydrogenated diamond-like carbon (HDLC)filmsis highly sensitive to the hydrogen (H) content in the film and theoxidizing gas in the environment. The tribochemical knowledge ofHDLC films with two different H-contents (mildly hydrogenated vs highlyhydrogenated) was deduced from the analysis of the transfer layersformed on the counter- surface during friction tests in O-2 and H2O using Raman spectroscopic imaging and X-ray photoelectronspectroscopy (XPS). The results showed that, regardless of H-contentin the film, shear-induced graphitization and oxidation take placereadily. By analyzing the O-2 and H2O partialpressure dependence of friction of HDLC with a Langmuir-type reactionkinetics model, the oxidation probability of the HDLC surface exposedby friction as well as the removal probability of the oxidized speciesby friction were determined. The HDLC film with more H-content exhibiteda lower oxidation probability than the film with less H-content. Theatomistic origin of this H-content dependence was investigated usingreactive molecular dynamics simulations, which showed that the fractionof undercoordinated carbon species decreased as the H-content in thefilm increased, corroborating the lower oxidation probability of thehighly-hydrogenated film. The H-content in the HDLC film influencedthe probabilities of oxidation and material removal, both of whichvary with the environmental condition.

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