Nanodots of transition metal dichalcogenides embedded in MoS and MoSe: first-principles calculations.

The energetic stability and the electronic properties of nanodots (NDs) composed of transition metal dichalcogenides, XS and XSe (with X = Mo, W and Nb) embedded in single layer MoS and MoSe hosts, were investigated based on first-principles calculations. We find that through a suitable combination of the ND and host materials it is possible to control the electron-hole localization. For instance, in NDs of WS in the MoS host we find the highest occupied (hole) states localized in the ND region, while the lowest unoccupied (electron) states spread out in the MoS host. On the other hand, by changing the ND and host materials, the electron states become localized in the MoS ND in the WS host. Further electronic structure calculations show that the NDs of NbS and NbSe give rise to a set of spin degenerate empty states within the energy gap of the MoS and MoSe hosts. The spin degeneracy can be removed by negatively charging the ND system. Such n-type doping was examined by considering a van der Waals (vdW) heterostructure composed of a graphene layer lying on the NbS and NbSe NDs. Indeed we found a net magnetic moment localized in the ND region.