空位缺陷对金属基外延石墨烯态密度和电导率的影响

考虑到空位缺陷的存在和原子非简谐振动，以铜、镍基外延石墨烯为例， 研究了金属基外延石墨烯空位缺陷浓度和态密度以及电导率随温度的变化规律，探讨了空位缺陷的影响。结果表明：(1) 空位缺陷浓度随温度升高而非线性增大，外延石墨烯的空位缺陷浓度及其随温度的变化率均大于石墨烯； (2) 与石墨烯相同，金属基外延石墨烯的态密度变化曲线对电子能量为0为对称，但空位缺陷的存在使态密度在电子能量为零时的值不为零，空位缺陷对导带态密度的影响大于价带；态密度随空位缺陷浓度的增大而线性减小，但减小幅度不大，而温度对石墨烯态密度几乎无影响；（3）金属基外延石墨烯的电导率近似等于电子声子相互作用贡献的电导率，并随温度升高而非线性减小；空位缺陷的存在使电导率有所减小，但只在较高温度下才明显。原子非简谐振动情况的电导率稍大于简谐近似的电导率，温度愈高，两者电导率的差愈大，即非简谐效应愈显著。

Effect of vacancy defects on the density of state and the electrical conductivity of metal-based epitaxial graphene

Considering the vacancy defects and atomic anharmonic motion, taking copper and nickel-based epitaxial graphene as examples, we investigated the variation of vacancy defects concentration, the density of state and the electrical conductivity of metal-based epitaxial graphene change with temperature. Moreover, we discussed the effect of vacancy defects concentration on metal-based epitaxial graphene. The results show that vacancy defects concentration increases nonlinearly with increasing temperature, and so does its changing rate. Both the changing rate and the vacancy defects concentration of metal-based epitaxial graphene are larger than those of graphene. We also obtained the density of state of metal-based epitaxial graphene with electron energy is symmetrical about the electron energy as that of graphene. But unlike graphene, the density of state of metal-based epitaxial graphene is not zero because of the existence of vacancy defects. And the effect of vacancy defects on the density of state of conduction band is much greater than that of valence band. Furthermore, the density of state of epitaxial graphene nonlinearly decreases with increasing temperature, but the change is minimal, which can be ignored in graphene.. In addition, the electrical conductivity of metal-based epitaxial graphene approximately equals to which contributed by the interaction between electrons and phonons, and decreases nonlinearly with increasing temperature. Vacancy defects reduce the electrical conductivity, but just at higher temperatures. When the anharmonicity of atomic motion is taken into account, the electrical conductivity is greater than that under the harmonic approximation, and the higher the temperature, the greater the difference between the anharmonic and harmonic approximation.