Single atom adhesion in optimized gold nanojunctions
  We study the interaction between single apex atoms in a metallic contact, using the break junction geometry. By carefully 'training' our samples, we create stable junctions in which no further atomic reorganization takes place. This allows us to study the relation between the so-called jump out of contact (from contact to tunnelling regime) and jump to contact (from tunnelling to contact regime) in detail. Our data can be fully understood within a relatively simple elastic model, where the elasticity k of the electrodes is the only free parameter. We find 5 < k < 32 N/m. Furthermore, the interaction between the two apex atoms on both electrodes, observed as a change of slope in the tunnelling regime, is accounted for by the same model. 
M.L. Trouwborst, E.H. Huisman, F.L. Bakker, S.J. van der Molen, and   B.J. van Wees