Regensburg 2000 – scientific programme

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O: Oberflächenphysik

O 22: Adsorption an Oberflächen (IV)

O 22.3: Talk

Wednesday, March 29, 2000, 15:00–15:15, H36

Vibrational signature of the precursor state of PTCDA on Ag(111) — •F.S. Tautz¹, S. Sloboshanin¹, J.A. Schaefer¹, V. Shklover², L. Kilian², M. Sokolowski², and E. Umbach² — ¹Institut für Physik, Technische Universität Ilmenau, PF 100565, 98684 Ilmenau — ²Experimentelle Physik II, Universität Würzburg, Am Hubland, 97074 Würzburg

We have carried out UHV adsorption experiments of the molecular semiconductor PTCDA on Ag(111), Ag(775) and Ag(110) surfaces. While the substrate orientation has no influence on the vibrational HREELS spectra of multilayers ( > 3-4 ML), the spectra in the submonolayer regime differ greatly, thus reflecting the different bonding situations of the PTCDA molecule on these surfaces. Specifically, on Ag(111) submonolayer spectra show strong scattering intensity of in-plane modes. It turns out that this anomalous intensity is due to interfacial dynamical charge transfer (IDCT) occurring at the PTCDA-covered Ag(111) surface. This IDCT is connected to the formation of hybrid-states between PTCDA orbitals and Ag wave-functions which strongly couple vibronic and electronic degrees of freedom. If PTCDA is evaporated onto Ag(111) at 100 K, it adsorbs into a precursor state also visible in UPS which morever does not show IDTC. Annealing these surfaces leads to an irreversible change of molecular bonding with the formation of the above-mentioned hybrid orbitals. The connection between the precursor state and low-temperature growth behaviour is discussed. (Supported by DFG So 407/2).