Formation and characterization of coronene monolayers on HOPG(0001) and MoS2(0001):: a combined STM/STS and tight-binding study

Ordered monolayers of the highly symmetric organic molecule coronene (C24H12) have been deposited under ultrahigh vacuum conditions onto several atomically flat surfaces, such as HOPG(0001) and MoS2(0001). The adsorbates have been investigated by scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). We were able to achieve submolecular resolution in the STM images, also while doing STS experiments. Reproducible STS characteristics could also be measured. Monolayer adsorbates of coronene on graphite are found to form a commensurate (root 21 x root 21)R10.9 degrees superlattice, which is in agreement with LEED data from the literature. By applying a density-functional tight-binding method we have calculated the electronic structure of the coronene molecule. These calculations of the spatial distribution of the charge densities and the energetic distribution of the electronic orbitals are compared with our STS measurement data. (C) 1998 Elsevier Science B.V. All rights reserved.