Friction Measured A Few Atoms At A Time

Frictional forces between surfaces sliding across each other are behind the wear and tear on things such as car engines, computer hard drives, and shoe soles. The study of these forces, called tribology, helps scientists and engineers develop longer-lasting products that require less energy to operate. Physicist A. Jay Weymouth of the University of Regensburg, in Germany, and colleagues have now pushed tribology to the atomic level for the first time. The team prepared a silicon crystal in which the orientation of silicon surface dimers in one region is perpendicular to that of an adjacent region. By using a specially equipped atomic force microscope, the team measured the drag caused by sliding the AFM tip across the different regions. They found that friction depends strongly on the orientation of the dimer bonds with respect to the sliding direction (Phys. Rev. Lett. 2013, DOI: 10.1103/physrevlett.111.126103). The technique provides an opportunity to compare quantum mechanical friction simulations, which are currently limited by computing power to a few atoms, with laboratory measurements that could not be made at the atomic scale until now.