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采用密度泛函理论对Li以不同覆盖度吸附在石墨烯表面上时系统的结构稳定性和场发射性能进行了计算.计算结果表明:Li吸附在石墨烯表面的碳六元环的中心位置时系统的能量最低,随着Li的覆盖度增加,碱金属与石墨烯之间的吸附作用逐渐减弱.在(4×4)R0°结构中,由于碱金属Li的修饰作用,Li/石墨烯体系的功函由原来的4.625eV降至3.156eV,但是随Li的覆盖度增大,系统的功函反而上升.电荷分布和态密度结果表明:随Li覆盖度增大,碱金属Li—Li之间的排斥作用逐渐增强,这不仅导致金属向石墨烯转移电子数逐渐减少,同时还使得Li层的功函较纯Li金属表面功函明显增加,这是Li/石墨烯的功函不会因Li覆盖度增加而单调递减的原因.
The structure stability and field emission properties of Li system with different coverage on graphene were calculated by using density functional theory. The calculated results show that when Li is adsorbed on the center of carbon six-membered ring on graphene surface The energy of the system is the lowest, with the coverage of Li increasing, the adsorption between alkali metal and graphene gradually diminishes.In the (4 × 4) R0 ° structure, due to the modification of alkali metal Li, Li / graphene system The work function drops from 4.625eV to 3.156eV, but as the coverage of Li increases, the work function of the system increases instead.The charge distribution and density of states show that with the increase of Li coverage, The repulsive effect between Li and graphene increases gradually, which not only leads to the decrease of electron transfer number from graphene, but also increases the work function of Li layer more than that of pure Li metal surface. This is because the work function of Li / Li coverage increases monotonically decreasing reasons.