Investigation of Surface Charge Doping for Monolayer WSe₂ Based on Simple Liquid-phase Treatment

In this paper, we report a very facile and easy method to achieve electronic doping monolayer WSe₂ efficiently. A mass fraction of 40% (NH₄)₂SO₄ solution at a relatively low temperature can realize the n-type doping of WSe₂, while, the 98% H₂SO₄ gives rise to the p-type doping of WSe₂. It is found that the monolayer WSe₂ can keep its crystal structure stable up to as high as 140 ℃ in (NH₄)₂SO₄ solution to approach the maximum doping effect. Both n-type and p-type doping of monolayer WSe₂ are reversible by putting the samples in vacuum and followed by cleaning in ultrapure water. And the samples p-doping effects can be significantly enhanced by two-step reaction, which is n-doping in (NH₄)₂SO₄ solution firstly and then followed by p-doping in H₂SO₄. Therefore, modulate the electronic doping of monolayer WSe₂ effectively not only demonstrates a simple way to tune its photoluminescence properties, but also of great importance to guide the design of WSe₂-based flexible electronic device.