经典晶体生长理论在石墨烯CVD成核和连续生长中的应用

Application of Crystal Growth Theory in Graphene CVD Nucleation and Growth

石墨烯由于具有奇异的电子性质而成为多个学科研究的热门材料,其在各个领域的潜在应用也逐渐被实现.而石墨烯工业化应用的前提之一是大面积高质量石墨烯的合成.在合成石墨烯的众多方法中,过渡金属表面化学气象沉积法(CVD)作为制备大面积高质量石墨烯的主要方法而被深入研究和广泛使用.作为二维晶体的石墨烯,其生长过程应该遵循经典的晶体生长理论,因此本文从经典的晶体生长理论出发,结合密度泛函理论(DFT)对石墨烯CVD生长过程的具体计算,来介绍石墨烯的微观生长机制.主要从三个方面系统地介绍了石墨烯的CVD生长机理:(1)石墨烯在金属催化剂表面的成核过程,包括二维碳团簇在金属平台和台阶附近的成核过程和成核速率,并据此提出石墨烯在成核生长过程中的种子生长法.(2)经典的Wulff构造理论在石墨烯CVD生长中的应用,通过研究不同石墨烯边界结构在金属表面的稳定性和边界能来获得不同催化剂金属表面石墨烯晶粒的平衡态形状或能量最低结构.(3)动力学Wulff构造理论在石墨烯生长中的应用,通过研究金属原子钝化石墨烯边的稳定结构和不同边界的生长过程来研究石墨烯的生长动力学.金属原子钝化的扶手型(armchair,AC)石墨烯边界的存在大大地降低了碳原子加入到边界形成六元环所需要克服的势垒,导致了AC石墨烯边界的生长速度较快最后消失,而留下生长较慢的锯齿型(zigzag,ZZ)石墨烯边界.以上在原子尺度上对石墨烯CVD生长过程中成核和连续生长过程的微观机制研究对实验上生长大面积高质量的石墨烯材料提供了有价值的理论参考.

Graphene is a star material due to its intriguing electronic, mechanical, thermal and chemical properties and many potential applications. For most of these potential applications, the synthesis of high-quality graphene layers in large scale is highly desired. In the past 10 years, many methods of synthesizing graphene have been developed and explored extensively. Among them, transition metal （TM）-catalyzed chemical vapor deposition （CVD） method stands out for its numerous advantages. As a typical two-dimensional crystal, the growth of graphene must follow the classical crystal growth theory. Here, we introduce three aspects of graphene CVD growth mechanism based on the classical crystal growth theory and the density functional theory （DFT） calculations. （1） The nucleation process and nucleation rate of graphene on metal terrace and near a step edge. On the basis of the predicated very large nucleation barrier, we have proposed a strategy of using the seeded growth method to grow large-area single crystal graphene. （2） Application of Wulff construction in graphene CVD growth. Based on the investigations of graphene edge structures on metal surface and their formation energies, the equilibrium structures of graphene island can be determined by the theory of Wulff construction. （3） The application of kinetic Wulff construction in graphene CVD growth. A detailed investigation on the structural stability and growth kinetics of graphene on the Cu（111） surface have been systematically investigated. According to the kinetic Wulff construction, the armchair edge which growth fast will gradually disappear and the zigzag edges which grows slowly will eventually dominate the circumference of a growing graphene island. The above discussions and conclusions lead to a deep insight into the CVD graphene growth, which are expected to guide the experimental design of growing large-scale graphene with high-quality.