Scanning tunneling microscopic investigation of 1T-MoS2

The surface structure of the metastable solid-state compound 1T-MoS2 was investigated by means of scanning tunneling microscopy (STM). In crystalline 1T-MoS2, which is prepared by oxidation from the intercalation compound Kx(H2O)yMoS2 (x ˜ 0.3), every Mo center is octahedrally surrounded by six sulfur ligands, leading to an av3 × av3 surface structure. A similar MoS2-type phase, but with a smaller amount of intercalated potassium (x <0.3) and a different surface structure (2a × a), forms under the same conditions at an earlier stage of the oxidation reaction. Comparison of the surface structures of these compounds revealed that this type of superstructure is determined not only by intrinsic properties, such as the degree of distortion within the [MoS6] octahedra, but also by external factors. The latter lead to stabilization of the structural disorder, as does a film of water on the surface of the compounds. The surface structure of these compounds is, therefore, less characteristic than the bulk structure type as found in a thermodynamically stable solid. Upon heating in inert gas, rearrangement to the stable 2H-MoS2 structure type takes place.