title: Quantifying the atomic-level mechanics of single long physisorbed molecular chains.
abstract: Individual in situ polymerized fluorene chains 10-100 nm long linked by C-C bonds are pulled vertically from an Au(111) substrate by the tip of a low-temperature atomic force microscope. The conformation of the selected chains is imaged before and after manipulation using scanning tunneling microscopy. The measured force gradient shows strong and periodic variations that correspond to the step-by-step detachment of individual fluorene repeat units. These variations persist at constant intensity until the entire polymer is completely removed from the surface. Calculations based on an extended Frenkel-Kontorova model reproduce the periodicity and magnitude of these features and allow us to relate them to the detachment force and desorption energy of the repeat units. The adsorbed part of the polymer slides easily along the surface during the pulling process, leading to only small oscillations as a result of the high stiffness of the fluorenes and of their length mismatch with respect to the substrate surface structure. A significant lateral force also is caused by the sequential detachment of individual units. The gained insight into the molecule-surface interactions during sliding and pulling should aid the design of mechanoresponsive nanosystems and devices.
authors.affiliation: Department of Physics, University of Basel, 4056 Basel, Switzerland.
authors.forename: Shigeki
authors.initials: S
authors.lastname: Kawai
authors.forename: Matthias
authors.initials: M
authors.lastname: Koch
authors.forename: Enrico
authors.initials: E
authors.lastname: Gnecco
authors.forename: Ali
authors.initials: A
authors.lastname: Sadeghi
authors.forename: Rémy
authors.initials: R
authors.lastname: Pawlak
authors.forename: Thilo
authors.initials: T
authors.lastname: Glatzel
authors.forename: Jutta
authors.initials: J
authors.lastname: Schwarz
authors.forename: Stefan
authors.initials: S
authors.lastname: Goedecker
authors.forename: Stefan
authors.initials: S
authors.lastname: Hecht
authors.forename: Alexis
authors.initials: A
authors.lastname: Baratoff
authors.forename: Leonhard
authors.initials: L
authors.lastname: Grill
authors.forename: Ernst
authors.initials: E
authors.lastname: Meyer
mesh_terms: D000268:Adhesiveness; D001696:Biomechanical Phenomena; D001704:Biopolymers / Q000737:chemistry*; D005449:Fluorenes / Q000737:chemistry*; D018625:Microscopy, Atomic Force; D008956:Models, Chemical; D056004:Molecular Dynamics Simulation
chemical_list: D001704:Biopolymers; D005449:Fluorenes; C041509:fluorene
keywords: adhesion; conjugated polymers; force spectroscopy; friction; nanomanipulation