Scanning tunneling microscopy study of PTCDI on Sn/Si(111)-23×23

Perylene tetracarboxylic diimide molecules were evaporated onto a Sn/Si(111)-23×23 surface and studied using scanning tunneling microscopy (STM) and low energy electron diffraction. At low coverages, single molecules are locked into specific adsorption geometries, which are investigated in detail using high resolution STM. The electronic structure of these individual molecules was studied using bias dependent STM images. The molecules form 1D rows that become more common with increasing coverages. Possible intermolecular O⋯H interactions within the rows have been identified. At around half of a monolayer (ML), the rows of molecules interact with each other and form a commensurate 43×23 reconstruction. In a complete monolayer, several structures emerge as molecules fill in the space between the 43×23 stripes. Possible intermolecular interactions within the 1 ML structures have been discussed. At coverages above 1 ML, the growth is characterized by island growth, where the molecules are arranged according to the canted structure within the layers.