Nature of Point Defects in Single-Layer MoS2 Supported on Au(111)

The interaction between molybdenum disulphide monolayers and gold is studied by combining scanning tunnelling microscopy (STM) measurements on extended MoS2 films grown by pulsed laser deposition and density functional theory (DFT) calculations. The lattice mismatch between MoS2 and Au leads to the growth of extended monolayer films displaying a non-commensurate lattice with the metal substrate. STM images are also characterized by a high concentration of features related to two kinds of point defects. DFT calculations highlight the role of the local MoS2/Au registry in driving the film-substrate interaction, showing that in the regions of the moiré superlattice where a top-coincidence is found, Au atoms are lifted up to some extent as a result of the interaction with the MoS2 film, reducing remarkably the interfacial distance. The combination of ab initio thermodynamics and Tersoff-Hamann simulated images permits to assign the most commonly observed defect features to single-sulphur vacancies located either on the outer surface or at the interface with gold. This fact has important implications on the conductivity and catalytic properties of this material