The search for manganese incorporation in MoSe 2 monolayer epitaxially grown on graphene

The introduction of magnetism in two-dimensional (2D) materials represents an intense field of research nowadays and the quest to reach above-room-temperature ordering temperatures is still underway. Intrinsic ferromagnetism was discovered in 2017 in CrI 3 and Cr 2 Ge 2 Te 6 in the monolayer form with low Curie temperatures. An alternative method to introduce magnetism into conventional 2D materials is substitutional doping with magnetic impurities similarly to three-dimensional diluted magnetic semiconductors. The case of Mn-doped transition metal dichalcogenide (MoS 2 , MoSe 2 , WS 2 , WSe 2 ) monolayers is very interesting because combining out-of-plane ferromagnetism and valley contrast leads to ferrovalley materials. In this work, we focus on the incorporation of Mn in MoSe 2 by molecular beam epitaxy on graphene which has been rarely addressed up to now. By using a multiscale characterization approach, we demonstrate that Mn atoms are incorporated into the MoSe 2 monolayer up to 5 atomic percent. However, when incorporated into the film, Mn atoms tend to diffuse to the grain edges forming undefined Mo x Mn y Se z phase at grain boundaries after completion of the MoSe 2 monolayer. This segregation leaves the crystalline and electronic structure of MoSe 2 unmodified. Above 5%, the saturation of Mn content in MoSe 2 leads to the formation of epitaxial MnSe clusters.