石墨烯以及六方氮化硼在金属表面生长的微观机制研究：基于原子尺度的从成核到生长的动力学模拟

The graphene and the hexagonal boron nitride (h-BN, also called “white graphene”) films are both two-dimensional materials with the iso-structure of the hexagonal honeycomb lattice atomic layers. Due to their increasing complementarity in the application of the electronic devices, the mass production of these two films with high-quality is highly desired. Catalyzed by the transitional metal surfaces, the chemical vapor deposition (CVD) method, a promising method for the mass production of the high-quality films, still faces many challenges, especially in the control of the film quality, morphology and layers. Many problems during the films’ formation, including the small domain size, grain boundaries, defects, etc., severely prohibit these two films from real application. In this project, we propose to study the kinetic formation mechanism of the graphene and h-BN during the CVD growth via the hybrid of molecular dynamics simulation and the Monte Carlo method. The influence of the morphology of the metal surface (e.g., the metal steps, grain boundaries, defects, solid and liquid surfaces, etc.) to the growth of graphene and the h-BN will be investigated specifically. To enlarge the domain size by reducing or removing the the grain boundaries, the formation and motion mechanisms of the grain boundary will be explored. In addition, the kinetic process of the bilayer graphene formed on the metal surface will also be addressed. As for the method, we aim to build new empirical potentials and the corresponding code for the molecular dynamics simulation, which can pave the way not only for the isolated simulation of the graphene and the h-BN CVD growth but also for the simulation of the in-plane hybrid growth of graphene/h-BN heterostructure for the future study.

石墨烯和六方氮化硼(又称"白石墨烯" )薄膜是具有相似六边形蜂巢状结构的二维晶体。随着两者在未来电子器件应用方面的互补性越来越高，规模化制备这两种高质量的薄膜材料显得越发迫切。目前采用的过渡金属表面催化的化学气相沉积法虽然是实现该目标的主要方法，但在实际制备中仍然面临很多问题: 例如制备的薄膜单晶尺寸偏小，缺陷较多，对形貌以及层数的精确控制困难。这些问题严重影响了这两种材料今后的实际应用前景。本项目将结合分子动力学模拟和动力学蒙特卡罗方法从原子尺度对石墨烯以及六方氮化硼在过渡金属表面从成核到生长的连续微观动态过程进行模拟，以期能够获得这两种二维晶体在金属表面生长过程中诸多问题的的关键机制，为实验上实现规模化制备这两种高质量的二维晶体提供更加准确的理论指导。同时，本项目致力于自行开发超越前人工作的经验势和分子动力学程序，为理论模拟这两种二维晶体的其它生长方式(如同层混合生长)打下基础。

从原子尺度深入理解石墨烯及类石墨烯材料（如六方氮化硼）的CVD生长机制是实现其规模化可控制备的关键。为此，本项目结合分子动力学、蒙特卡罗方法、第一型原理计算等多尺度模拟计算，主要进行了以下研究：1)势函数构建及分子动力学程序开发；2)石墨烯CVD生长分子动力学模拟；3)石墨烯生长过程中金属表面结构的变化；4)石墨烯及相关材料缺陷结构形成与演化研究；5) h-BN在金属Cu 表面的成核机制研究。通过以上的研究，我们 a) 获得新一代碳与金属（Ni, Cu）作用经验势函数并成功开发了能够进行大尺寸 （> 300 碳原子）长时间尺度 (> 10 纳秒) 模拟的石墨烯CVD生长分子动力学程序；b) 揭示了石墨烯在Ni、Cu两种金属表面从成核到生长微观动力学机制；c) 发现了生长过程中石墨烯与金属衬底表面互为影响的结构关系； d) 提出了石墨烯及相关材料缺陷形成与演化的物理机制；e）得到了六方氮化硼(h-BN)在金属Cu表面生长过程中，尤其是成核过程中一些关键的构型及能量数据。上述结果为实验上实现这类材料的规模化可控制备提供了有价值的理论参考。