Nb and Re substitutional doping in MoSe₂ monolayer: shallow dopants, defect creation and heterointerfaces

Intentional doping offers an effective way to manipulate the physical properties and functionalities of two-dimensional materials. Charge transfer by gating, surface modifications and substitutional doping are three primary doping strategies. Among them, the substitutional doping directly modifies the sample structure and thus produces stable doping effect.

Here, we report substitutional doping of Nb and Re in MoSe₂ monolayer during molecular beam epitaxy (MBE) and the structural properties of heterointerfaces of MoSe₂-NbSe₂ and MoSe₂-ReSe₂. Scanning tunneling microscopy and spectroscopy (STM/S) measurements reveal Nb and Re are both shallow energy level dopants, and the Fermi level of the sample can be effectively tuned by controlling doping concentrations. The as-grown n-type pristine MoSe₂ deposited on graphene can be doped into p-type by Nb, whereas it becomes more heavily electron-doped by Re. Besides substituting Mo, Nb and Re dopants would introduce mirror twin boundaries (MTBs) of varying character in MoSe₂. At the heterointerfaces between MoSe₂ and Nb(Re)Se₂, dense MTBs are always found when MoSe₂ is grown after NbSe₂. Sharp interfaces are obtained when MoSe­₂ growth proceeds NbSe₂ deposition. At the interfaces between ReSe₂ and MoSe₂, mixing of atoms is observed.