Few-layer black phosphorus (BP) is an important member in a family of two-dimensional materials because of its unique physical properties. But, for future applications, further tuning its electronic structure is necessary. Here we investigate, using ab initio density-function theory, the band structures of few-layer BP after the adsorption of the alkali metal atoms. It is shown that such adsorption can modify the band structures of few-layer BP in terms of the Stark effect. The charge transfer between the adsorbed atoms and few-layer BP is responsible for the internal electric field. Both the effects of the layer thickness and the concentration of adsorbed atoms on the band structures of few-layer BP are also quantitatively studied. The calculated results show that the band gap decreases with increasing the concentration of the adsorbed atoms. Further increasing the thickness of few-layer BP will close its band gap and induce the phase transition of semiconductor - Dirac metal. These findings imply that the electronic properties of few-layer BP can be modulated by adsorbing the alkali metal atoms.

几层黑磷（BP）由于其独特的物理特性而成为二维材料家族中的重要成员。但是，对于将来的应用，有必要进一步调整其电子结构。在这里，我们使用从头算起进行调查密度泛函理论，碱金属原子吸附后的几层BP的能带结构。结果表明，这种吸附可以根据斯塔克效应改变几层BP的能带结构。吸附的原子和多层BP之间的电荷转移是内部电场的原因。还定量研究了层厚度和吸附原子浓度对多层BP的能带结构的影响。计算结果表明，带隙随吸附原子浓度的增加而减小。进一步增加几层BP的厚度将缩小其带隙，并引起半导体-Dirac金属的相变。这些发现暗示，可以通过吸附碱金属原子来调节薄层BP的电子性质。