AVS 62nd International Symposium & Exhibition
    Tribology Focus Topic Thursday Sessions
       Session TR+AS+NS+SS-ThA

Invited Paper TR+AS+NS+SS-ThA7
Single Molecule Experiments to Explore Friction and Adhesion

Thursday, October 22, 2015, 4:20 pm, Room 230B

Session: Molecular Origins of Friction
Presenter: Rémy Pawlak, University of Basel, Switzerland
Authors: R. Pawlak, University of Basel, Switzerland
S. Kawai, University of Basel, Switzerland
A. Baratoff, University of Basel, Switzerland
T. Meier, University of Basel, Switzerland
W. Ouyang, Tsinghua University, China
T. Glatzel, University of Basel, Switzerland
E. Gnecco, IMDEA-Nanociencia - Universidad Autónoma de Madrid, Spain
A. Filippov, Donetsk Institute of Physics and Engineering, Ukraine
M. Urbakh, Tel Aviv University, Israel
E. Meyer, University of Basel, Switzerland
Correspondent: Click to Email
Controlled manipulation processes of single-molecules with an atomic force microscope (AFM) provide valuable information about their interactions with surfaces, leading to fundamental insights into adhesion and friction properties. To understand such phenomena at such scale, tuning-fork based AFM operated at low temperature is an appropriate tool since complex manipulations of single-molecules can be readily performed and detected via advanced force spectroscopic techniques [1] . With such approach however, the measured frequency shifts are related to normal force gradients, and thus the interpretation of friction phenomena is not fully straightforward. To overcome this issue, we developed analytical models to simulate the experimental AFM data which allow us to determine adhesive energy and nanoscale friction. In this presentation, a first example will be given by the vertical pulling of long polymeric chains on Au(111), where their detachment leads to oscillations of the normal and lateral forces [2] . As in Frenkel-Kontorova (FK) models of friction, the polymer is represented by a chain of units connected by springs of stiffness k , each one interacting with a 2D periodic substrate potential. Force and gradient variations are dominated by the sequential detachment of each molecular units if k i s large enough to cause superlubric sliding. A second example will show vertical and lateral manipulations over a Cu(111) surface of a single porphyrin molecule attached to the AFM tip apex. In the frequency shift traces, atomic sawtooth modulations are systematically observed while sliding over the surface and are related to the internal degree of freedom of the molecular structure [3] .

References:

[1] R. Pawlak, S. Kawai, T. Glatzel, E. Meyer. Single Molecule Force Spectroscopy (ncAFM, vol.3, Springer, Japan 2015).

[2] S. Kawai et al., Quantifying the atomic-level mechanics of single long physisorbed molecular chains, Proc. Nat. Acad. Sci., 111, 3968–3972 (2014)

[3] R. Pawlak et al . Intramolecular response of a single porphyrin molecule during AFM manipulations. Submitted.