Research ArticleMATERIALS SCIENCE

Triboemission of hydrocarbon molecules from diamond-like carbon friction interface induces atomic-scale wear

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Science Advances  15 Nov 2019:
Vol. 5, no. 11, eaax9301
DOI: 10.1126/sciadv.aax9301
  • Fig. 1 Operando QMS analysis results during the friction experiment of DLC.

    (A) Operando QMS detection results for the fragment ions of methane (CH3+; m/z = 15), ethylene (C2H3+; m/z = 27), ethane (C2H5+; m/z = 29), propane (C3H7+; m/z = 43), and butane (C4H9+; m/z = 57) during the friction experiment of DLC. The experiment is conducted from 1 to 6 min. Blue dashed lines indicate the background intensities of each fragment ion in the experiment chamber. (B) Molecular weight distribution of hydrocarbon molecules emitted after friction test.

  • Fig. 2 Snapshots of the friction simulation of DLC-D.

    (A) Initial configuration of sliding asperities. (B) Deformation of DLC asperities during the collision. (C) Deformation disappears during the separation of asperities, and hydrocarbon molecules are emitted from the DLC surfaces. (D to F) Continuous triboemission of hydrocarbon molecules with repeated collision and separation of sliding asperities. During the 500-ps simulation, the two DLC asperities collide five times because of the periodic boundary condition.

  • Fig. 3 Hydrocarbon emission from DLC friction interface.

    Molecular weight distribution of the hydrocarbon molecules generated after friction for (A) DLC-A, (B) DLC-D, and (C) DLC-E, in the range of 10 to 60 g/mol. Insets in (A) to (C) show the molecular weight distributions in the range of 200 to 1000 g/mol. The inset in (C) shows snapshots of two large hydrocarbon molecules. (D) Schematics of the generation of a hydrocarbon molecule (CxHy). Hydrocarbon CxHy is originally connected to the DLC substrate by several C─C bonds and subsequently desorbed by the dissociation of the connective C─C bonds.

  • Fig. 4 Time evolution of the number of interfacial CC bonds.

    ─ Blue solid circles, brown squares, green triangles, pink diamonds, orange crosses, and red open circles indicate the results for DLC-A, DLC-B, DLC-C, DLC-D, DLC-E, and DLC-F, respectively. The error bar for each sample indicates that the SE is calculated from four individual simulations with different initial structures.

  • Fig. 5 Uplift of DLC-D upper asperity.

    (A) Snapshot of DLC-D after 500-ps friction. (B) Upper asperity being uplifted. (C) Two asperities are completely separated. Chemical and mechanical wear indicated in (C) correspond to hydrocarbon emission and carbon transfer, respectively.

  • Fig. 6 Wear amount versus hydrogen concentration.

    Blue and red bars indicate the amount of chemical wear and mechanical wear, respectively. Black triangles indicate the total wear amount as the sum of the chemical and mechanical wear. The error bar for each sample indicates that the SE is calculated from four individual simulations with different initial structures.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/11/eaax9301/DC1

    Text S1. Evaluation of the emission rates.

    Text S2. Hydrogen diffusion.

    Text S3. Effect of sliding velocity on the wear.

    Text S4. Wear amount as a function of sliding distance.

    Text S5. Mechanism of hydrocarbon emission.

    Text S6. Effect of rigid layer on the wear.

    Text S7. Optimization details of ReaxFF parameters.

    Fig. S1. Example of evaluating the evolution rate of fragment ion of CH3+.

    Fig. S2. Friction simulation model of DLC asperities.

    Fig. S3. Molecular weight distribution of the emitted hydrocarbon molecules.

    Fig. S4. Mean squared displacement of hydrogen atoms along z direction.

    Fig. S5. Effect of sliding velocity on the wear.

    Fig. S6. Wear amount as a function of sliding distance.

    Fig. S7. Effect of rigid layer on the wear.

    Fig. S8. Friction simulation of DLC-A in the hydrogen gas environment.

    Fig. S9. Fitting results with the first-principle calculations.

    Table S1. Structural information for DLC samples.

  • Supplementary Materials

    This PDF file includes:

    • Text S1. Evaluation of the emission rates.
    • Text S2. Hydrogen diffusion.
    • Text S3. Effect of sliding velocity on the wear.
    • Text S4. Wear amount as a function of sliding distance.
    • Text S5. Mechanism of hydrocarbon emission.
    • Text S6. Effect of rigid layer on the wear.
    • Text S7. Optimization details of ReaxFF parameters.
    • Fig. S1. Example of evaluating the evolution rate of fragment ion of CH3+.
    • Fig. S2. Friction simulation model of DLC asperities.
    • Fig. S3. Molecular weight distribution of the emitted hydrocarbon molecules.
    • Fig. S4. Mean squared displacement of hydrogen atoms along z direction.
    • Fig. S5. Effect of sliding velocity on the wear.
    • Fig. S6. Wear amount as a function of sliding distance.
    • Fig. S7. Effect of rigid layer on the wear.
    • Fig. S8. Friction simulation of DLC-A in the hydrogen gas environment.
    • Fig. S9. Fitting results with the first-principle calculations.
    • Table S1. Structural information for DLC samples.

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