Dresden 2003 – scientific programme
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O: Oberflächenphysik
O 27: Organische Dünnschichten I
O 27.8: Talk
Thursday, March 27, 2003, 13:00–13:15, HSZ/02
Vibronic and electronic excitations for an order-disorder phase transition in organic monolayers — •Dominique Hübner1, A. Schöll1, L. Kilian1, R. Fink2, and E. Umbach1 — 1Experimentelle Physik II Unversität Würzburg, Germany — 2Physikalische Chemie II, Unversität Erlangen, Germany
The properties of organic monolayers largely depend on their interaction with the underlying substrate. For organic molecules adsorbed on metals in many cases a covalent bond is formed resulting in substrate-induced superstructures. For NTCDA on Ag(111) the bonding is regarded as weak chemisorption as revealed by photoemission and other techniques, and as observed by desorption of intact molecules upon thermal treatment. Recently an unusual phase transition upon cooling of NTCDA submonolayers on Ag(111) has been observed in electron diffraction experiments (LEED). Reducing the temperature to about 150 K, the diffraction pattern (i.e. long-range order within the film) disappears. This order-disorder phase transition can be considered as inverse melting. HREELS investigations (high-resolution electron energy loss spectroscopy) of the phase transition demonstrate huge modifications for the vibronic and electronic excitations, which will be discussed in direct comparison to other spectroscopic techniques (SPA-LEED, photoemission, NEXAFS). This project in financed by the BMBF (contract 05 KS1WWA-5).