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O: Fachverband Oberflächenphysik
O 100: Surface Dynamics II
O 100.6: Talk
Friday, April 4, 2014, 11:45–12:00, PHY C 213
Rotation and translation in surface diffusion of pentacene on pentacene: Extracting different processes from Helium-3 spin echo measurements. — •Paul Rotter1, Antonia Morherr1, Barbara Lechner2, David Chisnall2, Andrew Jardine2, John Ellis2, William Allison2, Bruno Eckhardt1, and Gregor Witte1 — 1Fachbereich Physik, Philipps-Universität Marburg, 35032 Marburg, Germany — 2Cavendish Laboratory, Cambridge, CB3 0HE, UK
We advance surface diffusion investigation to comparatively large organic adsorbates on organic surfaces. In this study a coplanar monolayer of pentacene chemisorped on Cu(110) was used as a well characterized organic surface on which isolated pentacene molecules diffuse. Helium-3 spin echo measurements provide a complete statistical description of the adsorbate motion at adequate length scales (nm) and time scales (ps). The potential energy landscape is explored via molecular mechanics and is used for molecular dynamics simulations to compare to experimental results for different azimutal surface directions. An analytical model is derived, which links our observations to known diffusion characteristics and explains key features of the measurements. It turns out that a diffusing molecule lies flatly on the surface but rotates its long axis between two preferred orientations. Thereby the anisotropy of a pentacene molecule considerably impacts its movement across the surface.