Engineering the band structures of few-layer black phosphorus by adsorbed metal atoms.

• Charge transfer between adsorbed metals and BP builds an internal electric field. • Electronic structures of few-layer BP can be modulated by the Stark effect. • Phase transition of semiconductor-Dirac metal was found in few-layer BP. 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. [ABSTRACT FROM AUTHOR]