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

类金刚石碳（DLC）薄膜主要由金刚石中的sp^3键合原子和石墨中的sp^2键合原子组成。关于其力学和摩擦学性能的报道很多，但对其变形机理的研究还不够。本研究采用分子动力学方法研究了单轴载荷作用下的键形式变化。从随机漫步法得到的DLC薄膜的单轴张力分析来看，sp^3键合原子的含量率在张力作用下相对于sp^2键合原子的含量率下降。观察到成键的形态变化，这种变化伴随着成键形式的湮灭和生成。通过这些变化，包括背键相互作用在内的局部原子环境得到了能量稳定。在变形过程中，原子间的弯曲和扭转作用比键的拉伸作用更重要。然而，已建立的Tersoff型电势并不能代表其扭转效应。在考虑非晶状非均匀结构的变形时，上述事实可能是致命的缺陷。因此，下一阶段将采用有序(N)紧密结合分子动力学方案（O(N)TB-MD）来阐明这些问题。采用N阶标度的密度矩阵方法，在保持原子间力作为势能的一阶梯度和弹性刚度作为二阶梯度的合理精度的同时，减少了大量的计算时间。通过淬火工艺得到了初始DLC模型中较高的sp^3含量，与实验结果吻合较好。扭转阻力对DLC薄膜的变形起着重要的作用。

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.