Our research interest is focussed on large pi-conjgated molecules which can form thin semiconducting films. Such films have been investigated over the last years in the context of optoelectronic devices, for instance, organic light emitting diodes (OLEDs) or organic field effect transistors (OFETs). We fabricate these films by sublimation of the organic molecules onto surfaces of single crystals under vacuum. The sublimation technique allows us to prepare films with very well defined thicknesses which can range from the submonolayer range up to thicknesses of several hundred nanometers.

The role of the substrate surface turns out to be very important. This surface is usually that of an inorganic single crystal, for example an Ag(111) or Au(111) surface.  Its properties (geometry and chemical composition) are decisive for the chemical bonding of the deposited molecules, and consequently their spectroscopic and structural properties at the interface. Hence our investigations usually start with surface sensitive experiments which give information on the adsorption and bonding of the large molecules to the substrate surface. Starting from the monolayer, we are then interested in the growth of multilayer films and their resulting optical and charge transport properties. Based on these results we try to develop new concepts for the optimization of devices based on organic semiconductor layers, e.g. OFETs.