金属表面硅烯的形核生长机理与缺陷控制

Epitaxial growth of silicene on the metal surfaces is the main method for silicene preparation, silicene has strong interaction with the metal surface and it was hard to been transferred, moreover, there are numerous vacancies defects and ground boundaries in silicene. The strong interaction with substrates and the existences of defects caused the disappear of the Dirac cone, and hindered the application of silicene in nanoelectronic device. Here, we reveal the nucleation and an atomistic growth mechanism for the silicene by combining crystal growth theory with comprehensive first principles calculations. Based on the investigations of silicene edge structures on metal surface and their formation energies, the equilibrium structures of silicene clusters can be determined. Then the growth kinetics is explored by analyzing the diffusion of silicon atoms at the edges in a step-by-step manner of the nonreactors approach. The nucleation process and nucleation rate of silicene will be calculated according to the crystal growth theory. We should determine the parameters such as temperature and chemical potential that are very important for high quality silicene preparation. The study will enrich the fundamental concept of two-dimensional materials nucleation and growth, and provide some significant details that are important for establishing applications of silicene in electron devices.

目前在金属基底上外延生长是制备硅烯的主要方法，但是制备得到的硅烯与基底作用过强不易转移，并且硅烯中存在大量的空位缺陷和晶界，以上因素严重影响了硅烯的电学性质，制约了硅烯在电子元器件中的应用。本研究课题运用密度泛函理论结合经典形核理论系统地研究硅烯在金属表面的形核生长过程，通过金属基底的表面掺杂和表面修饰调控硅烯电子性质。第一性原理将从原子级别认识硅原子在金属基衬底上的聚集、扩散行为和形核初期硅烯团簇结构的演化过程。结合经典晶体生长理论可以得到硅烯在金属基衬底上的形核尺寸、形核功和形核密度。通过控制形核密度和缺陷形成能降低缺陷密度。此项研究不仅可以为实验上制备高质量硅烯提供优化的温度和化学势等参数，同时深入研究二维材料形核生长的物理机制，建立硅烯结构与性能之间的对应关系，更有助于硅烯及硅烯复合材料在未来器件中的应用。

本课题运用密度泛函理论系统的研究缺陷和镶嵌过渡金属原子对硅烯结构与电子性能的影响。研究了硅原子在Ag(111)表面上的聚集、扩散行为。结合经典的晶体生长理论确定了硅烯在Ag(111)表面上的层状生长机制，并且硅原子个数必须大于10才能够形成硅烯六元环结构。我们发现锰原子掺杂的硅烯体系，表现出稳定的磁矩。并且随着锰原子的距离变化，体系磁矩会发生变化。我们通过压应变实现了Mn@silicene体系中铁磁与反铁磁转变，并通过研究发现其转变机制为RKKY交互作用机制与超交换作用机制的竞争。我们建立硅烯结构与性能之间的对应关系，为硅烯材料在未来器件中的应用提供了理论基础。