Electronic structure of ultrathin heteromolecular organic-metal interfaces: SnPc/PTCDA/Ag(111) and SnPc/Ag(111)

The SnPc/PTCDA/Ag(111) heteromolecular interface and the SnPc/Ag(111) interface are studied by photoelectron spectroscopy of the core-level and the valence regime as well as by work-function measurements. Accordingly, the interaction between the first and the second adsorbate monolayer is comparatively weak and noncovalent in contrast to what is found for the interaction between the substrate and the first adsorbate layer. Furthermore, a rigid level shift is observed for the SnPc spectra of the heteromolecular film, which decreases with increasing SnPc coverage, similar to what is known for Schottky contacts. It will be demonstrated that the built-in electric field at the interface can be explained by the formation of an interface dipole, which extends over several adsorbate monolayers. Moreover, the comparison with the SnPc/Ag(111) film suggests that the interface dipole can be altered by the interlayer.