| Pacific Rim Symposium on Surfaces, Coatings and Interfaces (PacSurf 2014) | |
| Thin Films | Wednesday Sessions |
| Session TF-WeP |
| Session: | Thin Films Poster Session |
| Presenter: | Takeshi Tsuruda, Tohoku University, Japan |
| Authors: | T. Tsuruda, Tohoku University, Japan H. Murabayashi, Tohoku University, Japan Y. Wang, Tohoku University, Japan Y. Kobayashi, Tohoku University, Japan T. Kuwahara, Tohoku University, Japan S. Bai, Tohoku University, Japan Y. Higuchi, Tohoku University, Japan N. Ozawa, Tohoku University, Japan K. Adachi, Tohoku University, Japan J.M. Martin, Ecole Centrale de Lyon, France M. Kubo, Tohoku University, Japan |
| Correspondent: | Click to Email |
Diamond-like carbon (DLC) consisting of sp2 carbon (Csp2) and sp3 carbon (Csp3) has low friction property. Therefore, DLC is used as solid lubricant in the sliding parts of machinery to decrease energy loss by friction. It was suggested that the low friction property of DLC is caused by formation of a graphene layer on the surface [1]. Moreover, Si-doped DLC (Si-DLC) films show excellent tribological property because of formation of Csp2 on the surface [2]. Therefore, transformation from Csp3 to Csp2 on the DLC surface is important for the low friction. For further decrease in the friction of the DLC films, we need to clarify the mechanism of the transformation from Csp3 to Csp2 at atomic scale. In this study, to elucidate the transition mechanism from Csp3 to Csp2 on the DLC films by Si-doping, we develop our tight-binding quantum molecular dynamics simulator [3].
First, to reproduce van der Waals interaction and transformation for Csp2 and Csp3, we add Lennard-Jones and trigonometric functional potential to our simulator. Next, to confirm the accuracy of our developed simulator, we perform compression simulation of a-graphite layers under a pressure. Here, the bottom layer is fixed and load pressure is applied to the top layer. From 1 to 15 GPa, the structure change is not observed for 50 ps. At a pressure of 16 GPa, Csp3-Csp3 bonds continuously increase when graphite layers become close. Then, the six-membered rings of diamond structure are generated from graphite layers. This indicates the transformation from Csp2 to Csp3. In the experiment, the structure change from graphene to diamond takes place at 17 GPa [4]. Thus, the simulation result is in good agreement with the experimental result. Thus, our developed program succeeds to reveal the transformation from Csp3 to Csp2.
Next, to investigate how Si-doping influences on the surface structure of the DLC films, we perform relaxation calculation for Si-doped diamond(111) surface with 3.225 % Si content. At 48.9 ps, the chemical bond between the C atom bound with the doped Si atom and C atom of the lower layer is dissociated. Furthermore, we observe generation of the Csp2 atoms after the dissociation. This indicates that the Si-doping induces the transformation from Csp3 to Csp2 and generation of graphene-like structure on the surface. Thus, we propose that Si-DLC films show low friction because Si-doping generates Csp2 on the surface of the DLC films.
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[3] K. Hayashi, M. Kubo et al., J. Phys. Chem. C, 115, 22981 (2011).
[4] L. Wendy, et al., Science, 302, 425 (2003).