title: Single-Molecule Tribology: Force Microscopy Manipulation of a Porphyrin Derivative on a Copper Surface.
abstract: The low-temperature mechanical response of a single porphyrin molecule attached to the apex of an atomic force microscope (AFM) tip during vertical and lateral manipulations is studied. We find that approach-retraction cycles as well as surface scanning with the terminated tip result in atomic-scale friction patterns induced by the internal reorientations of the molecule. With a joint experimental and computational effort, we identify the dicyanophenyl side groups of the molecule interacting with the surface as the dominant factor determining the observed frictional behavior. To this end, we developed a generalized Prandtl-Tomlinson model parametrized using density functional theory calculations that includes the internal degrees of freedom of the side group with respect to the core and its interactions with the underlying surface. We demonstrate that the friction pattern results from the variations of the bond length and bond angles between the dicyanophenyl side group and the porphyrin backbone as well as those of the CN group facing the surface during the lateral and vertical motion of the AFM tip.
authors.affiliation: Department of Physics, University of Basel , Klingelbergstrasse 82, Basel 4056, Switzerland.
authors.forename: Rémy
authors.initials: R
authors.lastname: Pawlak
authors.affiliation: Center for Nano and Micro Mechanics, Tsinghua University , Beijing 100084, China.
authors.forename: Wengen
authors.initials: W
authors.lastname: Ouyang
authors.affiliation: Donetsk Institute for Physics and Engineering, National Academy of Sciences of Ukraine , Donetsk 83114, Ukraine.
authors.forename: Alexander E
authors.initials: AE
authors.lastname: Filippov
authors.forename: Lena
authors.initials: L
authors.lastname: Kalikhman-Razvozov
authors.affiliation: Department of Physics, University of Basel , Klingelbergstrasse 82, Basel 4056, Switzerland.
authors.forename: Shigeki
authors.initials: S
authors.lastname: Kawai
authors.affiliation: Department of Physics, University of Basel , Klingelbergstrasse 82, Basel 4056, Switzerland.
authors.forename: Thilo
authors.initials: T
authors.lastname: Glatzel
authors.affiliation: Otto Schott Institute of Materials Research (OSIM), Friedrich Schiller University Jena , Jena 07743, Germany.
authors.forename: Enrico
authors.initials: E
authors.lastname: Gnecco
authors.affiliation: Department of Physics, University of Basel , Klingelbergstrasse 82, Basel 4056, Switzerland.
authors.forename: Alexis
authors.initials: A
authors.lastname: Baratoff
authors.affiliation: Center for Nano and Micro Mechanics, Tsinghua University , Beijing 100084, China.
authors.forename: Quanshui
authors.initials: Q
authors.lastname: Zheng
authors.forename: Oded
authors.initials: O
authors.lastname: Hod
authors.forename: Michael
authors.initials: M
authors.lastname: Urbakh
authors.affiliation: Department of Physics, University of Basel , Klingelbergstrasse 82, Basel 4056, Switzerland.
authors.forename: Ernst
authors.initials: E
authors.lastname: Meyer
keywords: Cu(111); Prandtl−Tomlinson; atomic force microscopy; density functional theory; friction; nanotribology; porphyrin; tip termination