Fluoreszenz-Spektroskopie an dünnen im UHV aufgedampften Coronen-Schichten
Abstract Fluorescence Spectroscopy on UHV-Deposited Thin Films of CoroneneThin films of coronene, UHV-deposited on different inorganic substrates (Si(111), Si(100), Si/Si02, graphite(0001) and MoS2(0001)) have been investigated via laser induced fluorescence and fluorescence excitation spectra at various coronene coverages (from submonolayers to 1000 Å) and temperatures (4.2 K - 300 K). Independent of the substrate the films reveal a characteristic absorption which is red-shifted with respect to that of the coronene crystal and is attributed to a new film-specific structural modification (in accord with X-ray data). At film thicknesses d > 50 Å this absorption is increasingly superimposed by crystal-type absorption. The fluorescence spectra at low coverages and low temperatures strongly depend on the substrate. On Si/Si02, graphite and MoS2 the fluorescence is similar to that of the coronene crystal. Thin films on Si(100) and Si(111), on the other hand, show monomer-like narrowband fluorescence originating, presumably, in substrate-induced trap states