Dissipation at Large Separations

Abstract

When two macroscopic bodies slide in contact, energy is dissipated due to friction. Sometimes it is desired, like in case brakes in the bicycle, sometimes unwelcome–when you ask yourself why your automated coffee machine broke for the third time. In nanoscale, a tiny friction force is present when bodies in relative motion are separated by few nanometer gap. This non-contact form of friction might be successfully measured by highly sensitive cantilever oscillating like a tiny pendulum over the surface. The elusive non-contact friction might arise due to vdW interaction, which is mediated by the long-range electromagnetic field or in many cases by fluctuations of static surface charges arising from material inhomogeneities. The huge dissipation might also orginate from hysteretic switching of the studied material under the external action of the oscillating probe. In this chapter several experiments reporting on non-contact friction are discussed. First the Joule dissipation channel is discussed. Next we report on non-contact friction measurement over metal–superconductor transition, which allows to distinguish between phononic and electronic contribution to friction. The non-contact friction due to switching of the charge density wave is discused in the last part of this chapter.