Li掺杂少层MoS_2的电荷分布及与石墨和氮化硼片的比较

Charge distribution of Li-doped few-layer MoS_2 and comparison to graphene and BN

基于第一性原理计算,研究了Li掺杂的少层(1—3层)Mo S2的电荷分布,并与石墨片和BN片的电荷分布特征进行了比较.与石墨片和BN片相同的是:电荷转移的大部分只发生在Li与最靠近Li的第一层Mo S2之间.然而,第二层和第三层Mo S2也能获得10%的转移电荷,而石墨片和BN片的第二层和第三层得不到2%的电荷.结合静电能和功函数的分析可知,Mo S2、石墨片和BN片的电荷分布主要由层间的静电相互作用和功函数来决定.这些研究结果对于揭示具有多层结构的电荷分布特征及其电子器件的设计提供了理论支持.

According to first-principles calculation, we study the charge distribution of Li-doped few-layer （1-3 layers） MoS2 and compare it with the results of graphene and BN. It is found that the stable adsorption sites of Li are the top （Mo） site for MoS2 layer, and the hexagonal center for graphene and BN layers. Band structures of pristine MoS~ show that single-layer MoS2 is a direct band gap semiconductor while few-layer MoS2 is an indirect one. As MoS2 is doped, the Fermi level will shift to the conduction band, indicating a charge transfer between Li and MoS2. The charge transfer takes place mostly between Li and the topmost MoS2 layer, which is very similar to that happening between graphene and BN. However, the second and third layer of MoS2, which are far from Li, can acquire about 10% of transferred charges. In contrast, the second and third layer obtain no more than 2% of charges for graphene and BN. Based on the electrostatic theory, we derive for both double and triple layers the formulas of electrostatic energy, which show clearly that only charge transfer between Li and the topmost layer will give the lowest electrostatic energy. Moreover, we calculate the work functions of pristine MoS2, graphene and BN, and find that, despite similar work functions of MoS2 and BN, the larger band gap of BN will make charge transfer between Li and BN harder. The analyses of electrostatic energy and work function show that the charge distribution is dominated by both interlayer electrostatic interaction and work function of material. It is expected that the above results could be helpful for doping layered structures and designing devices.