title: Coupling between diffusion and orientation of pentacene molecules on an organic surface.
abstract: The realization of efficient organic electronic devices requires the controlled preparation of molecular thin films and heterostructures. As top-down structuring methods such as lithography cannot be applied to van der Waals bound materials, surface diffusion becomes a structure-determining factor that requires microscopic understanding. Scanning probe techniques provide atomic resolution, but are limited to observations of slow movements, and therefore constrained to low temperatures. In contrast, the helium-3 spin-echo (HeSE) technique achieves spatial and time resolution on the nm and ps scale, respectively, thus enabling measurements at elevated temperatures. Here we use HeSE to unveil the intricate motion of pentacene admolecules diffusing on a chemisorbed monolayer of pentacene on Cu(110) that serves as a stable, well-ordered organic model surface. We find that pentacene moves along rails parallel and perpendicular to the surface molecules. The experimental data are explained by admolecule rotation that enables a switching between diffusion directions, which extends our molecular level understanding of diffusion in complex organic systems.
authors.affiliation: Fachbereich Physik, Philipps-Universität Marburg, 35032 Marburg, Germany.
authors.forename: Paul
authors.initials: P
authors.lastname: Rotter
authors.affiliation: Cavendish Laboratory, University of Cambridge, JJ Thomson Avenue, Cambridge CB3 0HE, UK.
authors.forename: Barbara A J
authors.initials: BA
authors.lastname: Lechner
authors.affiliation: Fachbereich Physik, Philipps-Universität Marburg, 35032 Marburg, Germany.
authors.forename: Antonia
authors.initials: A
authors.lastname: Morherr
authors.affiliation: Cavendish Laboratory, University of Cambridge, JJ Thomson Avenue, Cambridge CB3 0HE, UK.
authors.forename: David M
authors.initials: DM
authors.lastname: Chisnall
authors.affiliation: Cavendish Laboratory, University of Cambridge, JJ Thomson Avenue, Cambridge CB3 0HE, UK.
authors.forename: David J
authors.identifier: http://orcid.org/0000-0002-1587-7011
authors.initials: DJ
authors.lastname: Ward
authors.affiliation: Cavendish Laboratory, University of Cambridge, JJ Thomson Avenue, Cambridge CB3 0HE, UK.
authors.forename: Andrew P
authors.initials: AP
authors.lastname: Jardine
authors.affiliation: Cavendish Laboratory, University of Cambridge, JJ Thomson Avenue, Cambridge CB3 0HE, UK.
authors.forename: John
authors.initials: J
authors.lastname: Ellis
authors.affiliation: Cavendish Laboratory, University of Cambridge, JJ Thomson Avenue, Cambridge CB3 0HE, UK.
authors.forename: William
authors.initials: W
authors.lastname: Allison
authors.affiliation: Fachbereich Physik, Philipps-Universität Marburg, 35032 Marburg, Germany.
authors.forename: Bruno
authors.initials: B
authors.lastname: Eckhardt
authors.affiliation: Fachbereich Physik, Philipps-Universität Marburg, 35032 Marburg, Germany.
authors.forename: Gregor
authors.initials: G
authors.lastname: Witte