Interpretation of STM images: The MoS2 surface

From the elastic scattering quantum chemistry technique, it is shown that the images of the MoS2 surface obtained with an STM depend on the distance between the tip apex and the surface. At large distances, the tip apex and the Mo d-bands are coupled only through the sulphur surface layer. This leads to image the sulphur sites only. At small distances (<4 Angstrom), there is a superposition between this through bond tunnelling and the direct tip apex-Mo d-bands tunnelling. This superposition is destructive and the contrast is inverted; however, the two images remain very similar, which may lead to a difficult experimental interpretation of the STM images when the tip apex-to-surface distance is not well controlled.