STM investigations of C6Br6 on HOPG and MoS2

Monolayers of the organic molecule hexabromobenzene on HOPG and MoS2 have been imaged with scanning tunneling microscopy. The flat lying molecules form an ordered close-packed array with unit cell parameters corresponding to their van der Waals radii. In both cases the overlayers are incommensurable to the substrate. In the images with submolecular resolution, the molecules appear different on the two substrates. On HOPG the observed STM image contrast shows a detailed submolecular pattern depending on the tunneling voltage, whereas on MoS2 the molecules appear with a less pronounced inner structure. Neither on HOPG nor on MoS2 the observed submolecular contrast depends on the adsorption site.