Regensburg 2000 – wissenschaftliches Programm

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O: Oberflächenphysik

O 11: Postersession (Eröffnung)

O 11.60: Poster

Montag, 27. März 2000, 19:00–22:00, Bereich C

Stripe-facetting of a vicinal Ag surface induced by chemisorption of a large organic molecule: PTCDA on Ag(775) — •S. Schmitt¹, M. Sokolowski¹, C. Seidel², and E. Umbach¹ — ¹Experimentelle Physik II, Universität Würzburg, Am Hubland, D-97074 Würzburg — ²Physikalisches Institut I, Universität Münster, D-48149 Münster

Facetting of vicinal surfaces is a result of minimisation of the surface free energy and has been found for clean and covered surfaces using mainly small adsorbates. We report in our LEED- and STM-study on strong facetting effects induced by a large organic molecule on a vicinal Ag surface. The idea of the study was to investigate the interaction of perylene-tetracarboxilic-dianhydride (PTCDA) with a stepped surface (Ag(775)) consisting of narrow (111)-terraces, that provide low bonding strength and hinder the formation of multiple as well as large domains, between more reactive single-atomic steps. We found, that PTCDA adsorption induces a reconstruction of the surface on a scale of several to several tens of nanometers by step-bunching thus creating large (111)-facets (empty up to half a ML) and several large new facets with more open structures (always covered). Nearly the same facets were observed for all coverages studied, but annealing (up to 400K) revealed different stability ranges depending on the coverage. Also the differences in lateral size distributions are discussed. In case of half a monolayer of PTCDA, all steps are bunched. In this most interesting case, the covered facets and the empty (111) facets form a regular pattern resembling a grating.