Se vacancy modulation of centimeter-scale 2D MoSe2 continuous films via Se evaporating temperature

Vacancy defects, often generated during the in situ CVD synthesis, may lead to the deterioration of the physical and chemical properties of 2D atomically thin layers. Due to the weak chemical reactivity of Se, it is still a great challenge to achieve high-quality selenization of large-area 2D transition metal selenides without Se vacancies. In our work, Se evaporating temperature acts as a facile method for the Se-vacancy modulation of centimeter-scale 2D MoSe2 continuous films. It affects the supply of Se source in vapor phase and hence determines the selenization reaction of 2D MoSe2. Not only the Se-vacancy concentration but also layer-thickness distribution could be effectively controlled by changing Se evaporating temperature. The Se-vacancy concentration of the as-selenided MoSe2 continuous films approximately reduces from 5% at 300 ℃ to 0% at 500 ℃. Correspondingly, their layer thicknesses gradually decrease and tend to become an atomically thin layer with centimeter-scale surface coverage. It demonstrates that the sufficient Se supply is crucial for the complete selenization of 2D MoSe2 via elevating Se evaporating temperature. In addition, 2D MoSe2 continuous films with less Se vacancies exhibit better crystalline quality and higher layer-thickness uniformity. Therefore, Se evaporating temperature provides a feasible strategy for optimizing the selenization reaction and modulating the Se-vacancy concentration of 2D transition metal selenides.