Molecular interactions of PTCDA on Si(1 0 0)

The interactions of PTCDA molecules with the Si(1 0 0) surface have been investigated by means of X-ray photoelectron spectroscopy (XPS) and scanning tunnelling microscopy (STM). Among the large distribution of the adsorbates observed by STM for submonolayer coverages, around 20% show a distinct feature, which is interpreted as the product of the covalently linkage between PTCDA and Si atoms. The formation of this product through the anhydride groups is further supported by the XPS measurements. The occurrence of different adsorption states results eventually in the formation of a disordered initial layer, which nevertheless acts as a passivation layer and leads to the formation of islands for coverage above 1 ML. These islands have a common layer structure, similar to the molecular arrangement found in the (1 0 2) plane of PTCDA bulk phase.