Berlin 2005 – wissenschaftliches Programm

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O: Oberflächenphysik

O 31: Organische Dünnschichten III

O 31.4: Vortrag

Montag, 7. März 2005, 11:30–11:45, TU EB420

The in situ observation of organic growth - a spectro-microscopic study of PTCDA and NTCDA on Ag(111) — •Th. Schmidt¹, U. Groh¹, H. Marchetto², R. Fink³, and E. Umbach¹ — ¹Exp. Physik II, Universität Würzburg, 97074 Würzburg — ²Fritz-Haber-Institut, 14195 Berlin — ³Phys. Chemie II, Univ. Erlangen, 91058 Erlangen

The growth of two similar molecules - PTCDA and NTCDA - on a Ag(111) surface has been studied in situ by the spectroscopic PEEM instrument SMART, using UV-light and polarized monoenergetic synchrotron radiation. Whereas PTCDA grows in a Frank-van der Merwe fashion bellow 300 K, the growth above room temperature is of the Stranski-Krastanov type in both systems: first two closed layers of molecules are formed, followed by three dimensional (3D) growth of islands. Strong differences are observed in the molecular orientations: whereas the PTCDA molecules are always flat-lying on the substrate, the NTCDA behaves differently: the molecules are also flat-lying in the double layer but tilted by about 45^∘ in the islands. We report on surprising observations like reduced sticking coefficient, metastable layers, internal crystal structures, and dynamic changes within the layers. Differences in the growth and the temperature dependence of the two systems are discussed. Funded by BMBF under contract no. 05KS4WWB/4.