晶界处碳含量对超纳米金刚石的结构及电学性质影响的第一性原理计算

Influence of Carbon Content on Grain Boundary on the Electronic and Structural Characteristics in UNCD: The First Principle Calculation

采用MedeA.软件中基于密度泛函理论(DFT)下的平面波赝势方法的VASP软件包进行模拟,计算了不同晶界处碳含量对超纳米金刚石电子特性和结构特性的影响。从对优化后的结构分析来看,晶界处碳含量的增加会增加超纳米金刚石中sp^2-C的含量,并且会使金刚石晶粒最外层的原子产生一定程度的位移或改变其键角。分析不同晶界处碳含量超纳米金刚石的能带发现,晶界碳含量的增加会减小结构的带隙,并且会在带隙里引入悬键能级和与sp^2-C相关的π*能级。对3个结构态密度的分析发现,晶界含量的增加不仅会减小结构的带隙,还会增加带隙里悬键能级和π*能级的能态密度,减小电子从低能级跃迁到高能级所需的能量,从而增加超纳米金刚石的导电性。

In this article, all calculations were carried out within plane - wave density functional theory （DFT） by employing the Vienna ab initio simulation package （VASP） of MedeA. The ultrananocrystal-line diamonds （UNCD） electronic properties and structural characteristics of different carbon content on grain boundaries were calculated. Analysis of structures after geometry optimization found that the content of sp^2 - C in UNCD with increase of the carbon content on grain boundary increases, moreover, the outer-most atoms made a certain degree of displacements or its bond angle changed. Calculations of models, bandstructure noticed that increase of the carbon content on grain boundary will reduce the band gap and will introduce dangling bond level and π＊ level associated with sp^2 - C into band gap. The density of states （DOS） results show that band gap decreases with the increase of the carbon content on grain boundary, but the DOS of dangling bond level and π＊ level increases. This will decrease the upward transition energy of electrons from low to high energy level, thus, increase the conductivity of UNCD.