The plasmonic signals of quasi-1D electron systems are a clear and direct measure of their metallic behavior. Due to the finite size of such systems in reality, plasmonic signals from a gold-induced superstructure on Si(5 5 3) can be studied with infrared spectroscopy. The infrared spectroscopic features have turned out to be extremely sensitive to adsorbates. Even without geometrical changes of the surface superstructure, the effects of doping, of the adsorbate induced electronic surface scattering, and of the electronic polarizability changes on top of the substrate surface give rise to measurable changes of the plasmonic signal. Especially strong changes of the plasmonic signal have been observed for gold, oxygen, and hydrogen exposure. The plasmonic resonance gradually disappears under these exposures, indicating the transion to an insulating behavior, which is in accordance with published results obtained from other experimental methods. For C 70 and, as shown here for the first time, TAPP-Br, the plasmonic signal almost retains its original intensity even up to coverages of many monolayers. For C 70 , the changes of the spectral shape, e.g. of electronic damping and of the resonance position, were also found to be marginal. On the other hand, TAPP-Br adsorption shifts the plasmonic resonance to higher frequencies and strongly increases the electronic damping. Given the dispersion relation for plasmonic resonances of 1D electron systems, the findings for TAPP-Br indicate a push-back effect and therefore stronger confinement of the free charge carriers in the quasi-one-dimensonal channel due to the coverage by the flat TAPP-Br molecules. On the gold-doped Si(5 5 3)-Au surface TAPP-Br acts as counter dopant and increases the plasmonic signal.

The behaviour of an organic semiconductor (TAPP-Br) is found to be variable upon condensation on various surfaces and as mixtures with typical dopants.

A detailed infrared spectroscopic characterizationsupported by atomic force microscopyof core brominated tetraazaperopyrene (TAPP-Br) layers in terms of molecular orientation and stability against electron irradiation is presented. The anisotropy and the average molecular orientation of TAPP-Br molecules in optoelectronic device-relevant thin films (with ca. 20 nm thickness), grown by thermal evaporation under ultrahigh vacuum conditions and in a zone-cast sample, were established. To this end, the tensor components of the dielectric function were determined on the basis of spectra of a pellet sample and of a variety of polarization-dependent spectra of layers. Supported by density functional theory, the experimentally derived tensor components were related to dipoles of selected vibrational modes in the anisotropic TAPP-Br molecule and so to the average molecular orientation in the polycrystalline layers. Additionally, electron beam damage for energies ranging from ten to hundreds of electron volts was studied in order to obtain the threshold energy below which scanning electron microscopy can be carried out in a nondestructive way.