超纳米金刚石薄膜结构相变的第一原理分子动力学研究

Structural transition of super nano-diamond films studied by first principles molecular dynamics

纳米金刚石薄膜的结构相变非常复杂,对稳定性和物理性质又尤为重要.本文用第一性原理分子动力学模拟研究了超纳米金刚石薄膜的结构相变和表面重构.研究发现,纳米金刚石的表面碳团簇通过断开(111)面的σ键,形成具有碳六元环结构的石墨碎片;内部原子sp3杂化向sp2杂化转化的发生是从(111)面上成对C原子向石墨相转化时形成π键的过程中获得了能量,驱动石墨的转变由表层向心部逐渐进行.转变过程中存在一种洋葱状富勒烯和金刚石结构共存的过渡相——Bucky-diamond,表面悬空键的消除和表层的富勒烯外壳最大限度地降低了表面能和系统总能量,Bucky-diamond结构稳定存在.

The structural transitions of nano-diamond films are very complicated and all-important for their stability and physical properties. Using ab initio molecular dynamic methods, we have performed a systematic investigation of the structural transitions and surface reconstructions about diamond films. Through the calculation we observed the graphitization by breaking of highly eorrelatedabonds in diamond（111）surface, and come into being graphite hexahydroxy structures; the carbon atoms in sp3 hybridization state which inside the diamond transform to sp2 hybridization state by obtain energy from π bonds forming of carbon atoms in（111） surface, which take place during graphitization transition, so the graphitization of diamond go along from surface to inside. We also find the transitional structures, bucky-diamond, which keep diamond inside and fullerene-like reconstructions outside. The disappear of hanged bonds and the form of fullerene-like shell on surface lower the surface energy and total energy of system hugely, and the bucky structure stability existence.