Dr. Olivier Noel of the Molecular Landscapes and Biophotonic Horizons Group at the University of Maine in France visited the Institute of Physics on Thursday, November 30th. Dr. Noel took part in the SCL seminar of the Center for the Study of Complex Systems.
He held the talk entitled: “The role of adhesion in nano-friction mechanisms” in the library reading room “Dr Dragan Popović” of the Institute of Physics Belgrade.
At the nano-scale, the AFM has proven to be an efficient tool to measure the adhesion force with a high resolution and a mono-asperity contact between the AFM probe and the surface is easily achieved. But, with a commercial AFM, the scanning imposes a back and forth movement of the probe relative to the surface which results in the halt of the displacement when the probe reaches its limit of displacement in one direction and needs to invert its scanning direction. During these rest periods, the contact between the probe and the sample may evolve and no stationary state is achieved. For example, in the case of capillary adhesion, the interval of time of the halt period typically of a few milliseconds is enough to form a water meniscus between the probe and the sample , while, in the case of viscous materials, creep can occur. In order to overcome these limitations, we have developed an innovative AFM mode called the AFM circular mode (or CM-AFM)  generating a circular motion of the AFM probe in the plane of the surface to get a continuous motion with no rest periods and a sliding nano-contact in a stationary state is easily obtained. In the seminar, I will show that the CM-AFM is unavoidable to investigate tribological properties of hydrophilic rigid materials or viscoelastic materials. In particular, I will show that capillary adhesion and viscoelasticity plays an important role in the dynamic friction mechanisms.
 O.Noel et al., Phys. Rev. Lett., 108 (2012) 015503
 H. Nasrallah et al., Rev. Scie. Instrum. 82 (2011) 113703.