Stability of single-atom promoted MoS2 quantum dots: diffusion and incorporation of noble metals by first principles.

In this work, we describe -at the atomic level- the adsorption, diffusion, and incorporation mechanisms of single atom noble metals: Ru, Rh, and Pd to form promoted MoS2 triangular structures. The presented models are consistent with the experimentally observed morphologies -Mo(10-10) and S(-1010) terminations- in which the MoS2 system stabilizes under sulfiding conditions. Our results show that for both terminations, the adatoms adsorb on a hollow site over the basal plane; however, a lateral four-fold configuration with the S atoms over the edge has the lowest energy configuration. Two diffusion trajectories showing the energy barriers are presented for each termination, starting from the basal plane toward the lateral site. We have employed the surface formation energy (SFE) formalism to analyze the stability of the incorporations considering exchanges between adatoms and one Mo atom at the center, lateral edge, and tip against the lateral adsorption. For all the models, the lateral adsorption corresponds with the model with lower SFE. Upon varying the chemical potential limits, the analysis unveils that for Mo poor conditions, the incorporation is favored only in the lateral site but depends on the adatom's size.