无定形碳膜原子尺度超滑机理研究

Study on superlubricity has great value in application areas in energy, environment and micro- and nano- manufacture, which is also one of the most challenging scientific issues now. The intrinsic mechanism of superlubricity must be learned at atomic, molecular and even electronic scales. On the basis of Youth Science Foundation, this project aims at further discover the atomic-scale mechanism of superlubricity of amorphous carbon film in depth. The screened bond-order potential and reactive force-field based molecular dynamics simulations together with first-principles calculations are adopted to conduct the atomistic simulations of superlubricity. By introducing the shear-induced tribochemical interactions, and combining with surface passivation and shear-induced graphitization mechanisms, a systematic superlubricity model for amorphous carbon film is established, which will provide theoretical guide to achieve superlubricity in actual working conditions (especially for high-speed high-load conditions and ambient environment). An in-situ observation and characterization method with atomic-scale resolution is conducted to verify the proposed theoretical models and to reveal the atomic-scale superlubricity mechanisms of amorphous carbon film. Based on the superlubricity model, the relationship between superlubricity and microstructures/doping at the nanoscale is elucidated. Based on the studies on growth mechanisms of amorphous carbon films, the relationship between preparation and structure/composition is revealed, which will contribute to experimentally preparation of superlubricious amorphous carbon film with more excellent performance.

超滑研究对能源、环境、微纳制造等领域具有重要的应用价值，也是当今最具挑战性的科学问题之一，有必要从原子、分子甚至电子层面上揭示其内在形成机制。本项目拟在青年基金基础上进一步深入探索无定形碳膜原子尺度超滑机理。采用基于屏蔽键序势函数和反应力场的分子动力学模拟、第一性原理等方法开展超滑的原子尺度模拟。引入剪切诱导摩擦化学作用，结合表面钝化机制与剪切诱导石墨化机制，建立较为完备的无定形碳膜超滑模型，为实际工况下（特别是高速重载、大气环境）超滑提供理论指导。采用原子级分辨在线观测和表征方法验证所提理论模型，揭示无定形碳膜原子尺度超滑机理。在该超滑模型的基础上，探索无定形碳膜超滑与薄膜纳米尺度微观结构及元素掺杂的关系，并基于无定形碳膜生长机理研究，揭示薄膜制备与结构/化学组分的关系，从而指导实验中制备出性能更为优异的超滑无定形碳膜。

本项目主要围绕无定形碳膜原子尺度超滑机理开展研究，取得了如下创新性成果：.（1）采用分子动力学模拟了无定形碳膜微观尺度摩擦过程，发现了剪切诱导的界面共价键沿滑动方向定向排列、原子结构有序化以及薄层剪切带的形成对无定形碳膜自润滑的决定作用；提出了基于剪切局域化的无定形碳膜超滑机理，即在较高的压力作用下，会自发形成双层不公度类石墨烯的滑动界面，具有原子级光滑、层间无局域共价键作用等特征，可实现近零摩擦。.（2）揭示了含氢无定形碳膜sp3结构形成机理，以及不同入射粒子类型，入射能量和入射基团特性对薄膜微观结构的影响。分析了结构相变及氢钝化效应对含氢无定形碳膜摩擦行为的协同作用机理：低含氢量碳膜在较高载荷下，摩擦会形成局部类石墨层状结构，导致摩擦系数降低；而高含氢量碳膜在较低载荷下，摩擦会导致氢原子表面聚集，及在对偶面上形成富氢的转移层，体现出显著的钝化效果，可获得较低的摩擦系数。在干燥氩气环境下实验实现了摩擦系数0.003的超低摩擦，发现光滑连续的界面膜对超滑具有关键作用。.（3）基于类石墨界面膜对于超滑具有重要作用这一发现，采用石墨烯薄膜实现了微观尺度超滑，发现石墨烯薄膜超滑具有较好的环境不敏感性和耐磨性，有望成为下一代自润滑材料。.在Nature Communications (IF: 12.124)、Scientific Reports (IF: 4.259)、ACS Applied Materials & Interfaces (IF: 7.504)、Journal of Physical Chemistry C (IF: 4.536)等主流学术期刊发表论文17篇，全部为SCI检索。申请发明专利3项。做国际会议特邀报告4次，国内重要会议大会特邀报告2次。项目负责人获得2017年度教育部青年科学奖（全国8人获奖），入选2017年度青年长江学者。项目参与人获清华大学优秀博士学位论文（二等奖）和清华大学优秀硕士学位论文，获International Conference on Planarization/CMP Technology（比利时）最佳学生论文奖。