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Quantifying the atomic-level mechanics of single long physisorbed molecular chains

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Koch,  Matthias
Physical Chemistry, Fritz Haber Institute, Max Planck Society;

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Grill,  Leonhard
Physical Chemistry, Fritz Haber Institute, Max Planck Society;
Department of Physical Chemistry, University of Graz;

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Citation

Kawai, S., Koch, M., Gnecco, E., Sadeghi, A., Pawlak, R., Glatzel, T., et al. (2014). Quantifying the atomic-level mechanics of single long physisorbed molecular chains. Proceedings of the National Academy of Sciences of the USA, 111(11), 3968-3972. doi:10.1073/pnas.1319938111.


Cite as: http://hdl.handle.net/11858/00-001M-0000-0018-C634-8
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.