Interatomic Description of Clustered Structure for Strength of Diamond-like-carbon Film

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A diamond-like carbon (DLC) film is mainly composed of both sp^3 bonded atoms as in diamond and sp^2 bonded atoms as in graphite. Many reports concerning their mechanical and tribological properties have been published, while there are not enough studies on deformation mechanism yet. In the present research, the change of bonding form under uniaxial loading is investigated using the molecular dynamics. From uniaxial tension analyses of the DLC film obtained by the random walk method, the content rate of sp^3 bonded atom decreases as opposed to the one of sp^2 bonded atom under the tension. The morphological changes of bonding which are accompanied by the annihilation and the generation of the bonding forms are observed. By these changes, local atomic environment which includes the back-bond interaction comes to stabilize energetically. And, it is concluded that bending and torsion effects between atoms are more predominant rather than bond-stretching under the deformation. However, the well-established Tersoff type potential can not represent its torsion effect.The above-mentioned fact may be fatal defect when considering the deformation of the amorphous-like inhomogeneous structure. Therefore, Order (N) tight-binding molecular dynamics scheme (O(N)TB-MD) is applied to elucidate these problems at the next stage. The density matrix method as an Order (N) scaling is adopted to reduce the drastic computational time with keeping the reasonable accuracy of an interatomic force as the first-order gradient of the potential energy and elastic stiffness as the second-order gradient. It is found that the high content of sp^3 in the initial DLC model by quenching process is obtained, which is in good agreement with the experimental results. And the torsional resistance plays an important role in the deformation of the DLC film.