Time Scales for Cold-Welding and the Origins of Stick-Slip Friction
  Data from an instrument that measures conductance, stiffness and rupture strength of junctions indicates that when two macroscopic metal surfaces are brought into contact a nanometer size junction spontaneously forms over a long time scale (~ 60 s). Furthermore, the parameters of junction rupture match the observed dynamics of stick-slip friction. This suggests that stick-slip friction has its origins in the formation and rupture of junctions that form between surfaces in contact. 
R. Budakian and S.J. Putterman