Scanning tunneling microscope images of locally modulated structures in layered materials, MoS2(0 0 0 1) and MoSe2(0 0 0 1), induced by impurity atoms

The effect of impurity atoms on the surface electronic structure of semiconducting transition metal dichalcogenides, MoS2 and MoSe2, has been investigated by a scanning tunneling microscope (STM) and by its spectroscopic mode, scanning tunneling spectroscopy. The following impurity atoms have been studied: (1) alkali metal atoms deposited by using alkali dispensers, (2) impurity atoms unintentionally doped during the synthesizing process, and (3) a donor dopant of Re. STM images show locally modulated structures with bright area surrounded by dark area in nm scale at negative sample bias, and their global features depend on the bias polarity. The center region of the structure observed at negative sample bias is flat or caved in regardless of a kind of the impurity atom. It is concluded that the locally modulated STM image arises from the interaction between the electron donated by the impurity and electrons in the d-orbitals of neighboring Mo atoms. This interaction extends by about one Mo–Mo distance, which gives the image of 0.7 nm in diameter.