Dry Friction due to Adsorbed Molecules
  Using an adiabatic approximation method, which searches for Tomlinson model-like instabilities for a simple but still realistic model for two crystalline surfaces in the extremely light contact limit, with mobile molecules present at the interface, sliding relative to each other, we are able to account for the virtually universal occurrence of "dry friction." The model makes important predictions for the dependence of friction on the strength of the interaction of each surface with the mobile molecules. 
C. Daly, J. Zhang and J. B. Sokoloff (Physics Department and Center   for Interdisciplinary Research onComplex Systems, Nort...