Oxygen enhanced atomic chain formation
  We report experimental evidence for atomic chain formation during stretching of atomic-sized contacts for gold and silver, that is strongly enhanced due to oxygen incorporation. While gold has been known for its tendency to form atomic chains, for silver this is only observed in the presence of oxygen. With oxygen the silver chains are as long as those for gold, but the conductance drops with chain length to about 0.1 conductance quantum. A relation is suggested with previous work on surface reconstructions for silver (110) surfaces after chemisorption of oxygen. 
W.H.A. Thijssen, D. Marjenburgh, R.H. Bremmer, and J.M. van Ruitenbeek